cylinder head selection, cross-section and other stuff

hi,
there seems to be a lot of questions about how to select a cylinder head for a given application. I'll give you an idea of how/why i choose a given head for a given application. One thing to keep in mind is that nothing is ever perfect. People who have dedicated there entire lives to cylinder head developement still change there mind daily about what is best and most important. The information presented is mostly gathered from peers in the industry and can be used as a general guideline. As a whole these numbers are generally agreed upon, but these are not rules written in stone.
First things i want to know are these-
budget
cubic inch
budget
rpm
budget
intended application
and did i mention how much you have to spend?
It will never cease to amaze me how many people want an 8000 rpm small block and have an old set of "camel humps" and $250 to spend. Some things just aren't doable.
When i have that information there are some formula's that i use to help me determine where i want to start. I have a pretty good data base that allows me to choose a head based on the cross sectional area available. This minimum cross section will determine when the head will "shut off" or fail to make decent power past a certain rpm level. I'll use a typical engine for an example. We'll build a hypothetical 500hp 350 engine. We'll use 7200 rpm as our target rpm. We will also use a standard 4.00x3.48 bore/stroke. Using this rpm level and bore/stroke this is the formula i would use to get a baseline minimum cross section needed-

(bore x bore x stroke x rpm x .00353)/614

Using this formula and our numbers we can determine that we need a min. cross-sec of about 2.30 square inches. This will allow our motor to turn 7200 rpm without exceding 614fps or .55 mach (the same thing). That number is generally considered to be the point at which most "conventional" type cylinder heads will reach a point of choke. A modern pro-stock style head moves that number up a bit, because of port efficency. A flat head wouldn't even come close to that number. If you put numbers in for a typical 400" small block you would see that it would take about 2.64"sq to make power to the same rpm level.Quite a bit larger. If you go the other direction, that same head with 2.3" on a 302" engine would put your rpm level up around 8300 rpm! Makes it easy to see why a smaller motor will "rpm", huh? On a conventional aftermarket small block chev head, the pushrod pinch area represents the smallest cross section. Normally 1.050" is about all you will safely get at the width of the port. This means we need about 2.2" of height in the same spot. This would probably put you into the 210-220cc volume for a typical head. Now it starts to get a bit tougher. When you are porting a cylinder head localized velocities are what will make or break a head. When i say localized velocities, i mean the actual measured air speeds when flowing it on a bench. These are not to be confused with the air speeds generated by rpm/cubic inch/cross-sec. that we just talked about. These are numbers that can be figured using a formula with measured airflow and cross-sec or by using a pitot. A pitot is a steel tube with a small hole in it that will measure pressure differential when put into the airstream. They look like this-
http://www.superflow.com/flowbenches/index_1017.cfm
We use these to figure out how fast the air is moving through various parts of the port. I'll take and stick the pitot in the port and measure speed at the top of the short turn, across it in three or four different spots and three or four different levels. I'll take other measurements in the same manner at different spots including the pushrod pinch, and opening of the port. I prefer to use this method of measurement to the "calculated" method because it is hard to get an accurate measurement of the cross section at the short turn, and in other spots, without making a port mold, cutting it and measuring it. Even then using the calculated method you will only get an average, not the true localized velocities. In most conventional heads, you don't want these velocities to excede 350fps, as measured. So if i probe the port and find that at .500 lift my short turn has speeds that are 450fps, i need to do something to that port to change that. Anything that is over my 350fps limit is going to create turbulence and separation of the air in the port. This is going to limit my ability to fill the cylinder as well as i can. This is where the time and energy spent by a good head porter separates themselves from the fluff and buff crowd. Knowing what to do in these instances is what makes a good head. The formula used to figure out flow bench air speed based on flow in cfm @ 28"h2o and cross sec. is this-

(cfm/cross sec) x 2.4
this will give you air speed at that point. If we use our example of 2.3" at our minimum cross sec you'll see that we would require about 335cfm @ 28"h20 before our head would have a flow problem at that point, at least based on our numbers anyway. This is why going in there and wacking that area larger isn't always the best thing to do and why having a huge opening at the gasket doesn't do anything but slow that air speed down. We want to approach that 350fps as best we can, to get maximum filling, without stepping over it.
I just "fixed" a set of heads on an engine. It had a problem with short turn airspeeds. The head flow well for what it was, but the short turn needed some work. I spent about 10 minutes in each port fixing the area. The head gained about 2 cfm of airflow. On the dyno it picked up 27hp and extended the usable power range of the head by about 400rpm. All with 1 1/2 hours worth of work. Pretty good gain for just paying attention to one small thing, huh?
If you pay attention to air speeds, localized velocities, and cross sectional areas you will end up with a head that is driveable and makes good power. I don't even flow a head for a "curve" until i have satisfied these needs. You need to be realistic with power expectations and rpm levels when you set out on your project. An 8000 rpm n/a 327" motor probably isn't going to be very streetable. Almost allways error to the side of small and you normally won't go wrong.
shawn

Shawn, I want to use my combo as an example to see if I am calculating this correctly.

It's a 383, 4.030 bore, 3.75 stroke, opperates at 7000 RPM.

4.030 x 4.030 x 3.75 x 7000 x .00353/614 = 2.45 minimum cross section.

Correct so far?

Now, how do I find the cross section my AFR Race Ready 210cc heads? Do I have to measure the port, is it advertised in the specifications?

I'm trying to piece this information together, so bear with me.

It looks like your math is correct. Your 210's are probably around 2.2". The thing to keep in mind is that most engines are only going to have a "usable" rpm band of about 1500 rpm. This means if you build an engine that you want your peeks in the 7000 rpm area you are going to put your torque peek around 5500 rpm. In a drag race application this would need a 5500 converter and cam/intake/compression/gear to go along with this combo. Depending on how tight the converter is, you would probably shift this combo around 7500 rpm. A good ported set of 210's on your 383, some compression a cam in the 270 @ ..050 area, good intake, should get you about 620-630hp. Just make sure you have plenty of converter.
Shawn

Shawn is the RPM you mention above in the formula is that the MAX RPM you wanna spin the motor at or where you want peak power? Sorry if this is a stupid question:o :p

This is a estimation of where the head will go into a choke situation. At this point it gets difficult to move more are through the engine. If you don't have the ability to effectively fill the cylinders at a higher rpm level, you stop making power. You can move that mark around a bit with intake/exhaust/cam tuning but in a n/a engine your curve will fall pretty fast after that point.
Shawn

Shawn, here is my current combination: http://www.stevesnovasite.com/forums/showthread.php?t=31922

According to the calculation, the heads I have appear to be a bit smaller than what I should have gone with...yes or no?

Thanks for your insight Shawn!

It looks pretty good to me. I skimmed through there and it looks like you have a converter in the 4500 rpm area? With one that tight putting larger head on the engine might make better dyno numbers but with the weight of the car and the conveter/gear it would probably be slower at the track. The head is allowing you to recover from the gear change better. If you want to go faster I would call a good converter company like A-1,Coan, or the like and have them spec you out one. It will be expensive, but I wouldn't be surprised if you picked up .40 or so.
Shawn

I'm currently running a TCI group 2 competition converter and the stall range is 4400-4800 RPM.

Thanks for all of the great info Shawn!

We'll use 7200 rpm as our target rpm. We will also use a standard 4.00x3.48 bore/stroke. Using this rpm level and bore/stroke this is the formula i would use to get a baseline minimum cross section needed-

(bore x bore x stroke x rpm x .00353)/614

Using this formula and our numbers we can determine that we need a min. cross-sec of about 2.30 square inches. This will allow our motor to turn 7200 rpm without exceding 614fps or .55 mach (the same thing).

Shawn, Can you tell me where you got this formula and how it works?

The bore x bore x stroke is part of the equation for CID but what's the .00353 number?

The 614 number your 614 fps max?

How do you convert cubic inches into square inches and how is revolutions per minute resolved with feet per second?

I'm just curious. I played around with it and say a 283 at 5,000 rpm needs 1 square inch of cross section? That's pretty small. Even at 6,000 rpm it results 1.22 square inches. I think an unported 283 head has 1.5 square inches?

That means by your logic that the cross section makes it rev happy, then a 283 with a stock 1.5" cross section port, stock 1.72" intake valves, would or could make power (under load) to 7375 rpm.



Again, can you explain the formula?

Paul, My experience says it will, with the right cam.

a 283 with a stock 1.5" cross section port would or could rev to 7375.

Paul, My experience says it will, with the right cam.

Crap...that would be one high reving 283:eek:

I can attest to 6900 with stock power packs and a big cam in a 283.

Kev

I can attest to 6900 with stock power packs and a big cam in a 283.

Kev

is that the rpm the rods let loose at:rolleyes: :D

OK, back in the late 60's I was given a Duntov cam that was lifted from the GM tech center in Warren. I used this in a stock 283, powerpac heads, solid lifters, and 2 barrel carb. I used to shift at 6500, 3.55 gear, go thru the lights at 6500 in second gear(three speed) ran 16 flat and 85 mph. Full size biscayne.
Frank(the terror of PP/S):D

Shawn, Can you tell me where you got this formula and how it works?

The bore x bore x stroke is part of the equation for CID but what's the .00353 number?

The 614 number your 614 fps max?

How do you convert cubic inches into square inches and how is revolutions per minute resolved with feet per second?

I'm just curious. I played around with it and say a 283 at 5,000 rpm needs 1 square inch of cross section? That's pretty small. Even at 6,000 rpm it results 1.22 square inches. I think an unported 283 head has 1.5 square inches?

That means by your logic that the cross section makes it rev happy, then a 283 with a stock 1.5" cross section port, stock 1.72" intake valves, would or could make power (under load) to 7375 rpm.



Again, can you explain the formula?

Hi,
you sure you want know? Just kidding.

(Pi/4) = (3.141592654 / 4) = .785398163

360 * .785398163 = 282.7433388 or .003536777


the .00353 is just the 1/x reciprocal of 283.286119

its a combination of conversion constants into 1 constant = 282.286119
it converts inches into area and inches into feet
The 614 is the limiting port velocity for most applications. The number is actually 613.9758744, but that creates just a bit more math than I want to do, and 614 will get you close enough.
Yes, i would start there with a cross section of that size, for that application. For years the corps built cylinder heads that were waaaaaayyy to big for the application. GM wasn't as big a culprit as Ford. Have you ever seen a 302 BOSS head? Perfect example. Chev did have some like it too, though. The 283's were a bit oversized for their application, like you noted. The worst ones were the square port 396 engine. We fill those intake runners in any motor smaller than 500" and 7500rpm. Way to big.Like i said above, we unfortunatley don't work in a world of perfects. There will always be exceptions to the rule. I'm not certain that this works with some 4-valve engines or formula 1 type stuff. I don't have experience with them. But i would use it to start, if i did.
There are TONS of other things that i take into consideration when doing a cylinder head. These are some other ones-
Curtain area
Curtain area cfm/in2
valve cfm/in2
throat velocity
primary choke velocity
runner opening velocity
curtain area velocity
discharge coefficient
While i truthfully wouldn't spend a lot of time figuring these things out for a 600hp small block, it does show some of the things that are considered when doing an unlimited type engine.
shawn

That's a pretty neat math trick, at least to the outside observer:)

The rods let loose in my 283 going down the highway at 2500 rpm lol. Sometimes you wear em down instead of going out revved to the moon.

Kev

Hi,

Very cool info.. I really do not know anything about the math. If it wasn't for the mention of the 283 port vs rpm under power I would just be quiet and read.

I have seen many "stock" port 283 (really 292-294) cid super stock engines that exceed the 9000 rpm level. The ports are generally modified but the basic port is still generally the same. Years ago there were no mods on the ports at all and the rpms were comparable but the power was not equivalent to today's standards. This is usually with a 4gc carb, an aftermarket intake and a "huge" camshaft, high dollar valve train etc., but a very small port- 1.72 valve.

These cars really do amaze me in how quick they are. The same with the stockers.

I don't really have any opinion here, I guess I am just commenting.



Thanks
Jeff

Thanks

Jeff

I have seen many "stock" port 283 (really 292-294) cid super stock engines that exceed the 9000 rpm level. The ports are generally modified but the basic port is still generally the same. Years ago there were no mods on the ports at all and the rpms were comparable but the power was not equivalent to today's standards. This is usually with a 4gc carb, an aftermarket intake and a "huge" camshaft, high dollar valve train etc., but a very small port- 1.72 valve.


Stock and Superstock heads are interesting creatures. A true "stock" eliminator head doesn't allow you to change the port at all, other than the valve job. A superstock head you can port all you want, as long as the finished runner volume meets the NHRA standard. I'll give you an example. An '041x chev head in superstock is limited to 165cc's. You can do just about anything you want in that port, as long as it is 165cc's when finished. A good '041x head will allow a 350ci engine to make peek power around 7200rpm. Here's the specs on a good running superstock, 041x engine-
280-286 @.050,.726-.726 on 106 installed 103
victor e intake
these engines have to maintain the "stock" compression ratio of about 11-1
1.94-1.50 valves
this engine would produce around 575hp and will run low 10's in a superstock car. It utilizes a 5500+ converter and is shifted at 8000+rpm. What we are doing is using cam and horsepower to accelerate the car. If we could find a way to move the torque peek higher, we would. The biggest single thing holding back the combo is the intake port. It simply cannot be made large enough to do what we are trying to accomplish. A smaller engine would allow you to do this, with the same cylinder head. This motor does quit making power at 7200rpm and coincides fairly well with the math format layed out before. The reason it's turned higher is to get it to accelerate off of the bottom of the gear change. With the cam, the torque curve is moved high, so in order to hit that point on the gear change, the engine is reved high, but it doesn't really make power up there. It just makes the car faster.
shawn

Hi Shawn,

I basically agree with you. My only observation is that you still have a 165cc runner 1.94 valve on 360-362 cid engine. The compression at "only" 10.5-11.0 may or may not help the limited port application- I dont really know.

The 520t head on the 283 is really, I think a better example of what I was getting at. Its a very small port, small valve, and generally a very high rpm application. (super stock applications)

Most of the 520t head stockers I have been involved with dont see many Rpms (about 7000-7500 I guess) but they have only about .380-420 valve lift (the 67 has .390-.410).

The 302s and 350s with 041 style head (with 2.02 -1.6-ususally a 186-492 casting) and 455 lift cams will usually run in 8000-8500 rpm range with a stick- and thats a "non modified port" of 165 cc.

I guess thats my observation, a pretty small port can still produce an amazing amount of power at a pretty high rpm. Maybe a very narrow power band and very specific tuning, but still an amazing amount of power.

I dont doubt that the motor you were referring to was not making peak power at the max rpm but for a "low" compression engine its still pretty impressive to me. The 7200 figure seems pretty low to me, but Im not sure. When the porting first became legal most of the improvements I noticed were not in "size", but location. Raising the runners showed great gains, but the porting was very expensive and usually involved serious welding or furnace brazing.

This is very interesting. I enjoy the discussions here.
Thanks Shawn

Jeff

They are pretty neat motors. A good friend of mine holds the A/SA national record, so I still get my fingers in some stock/superstock stuff on occasion, but I don't do much of that stuff anymore. I'm amazed that we are making 600+ with our non-ported vortec head circle track motors. Seems like just yesterday a good one was about 530hp, now that would get you lapped.
shawn

Shawn,
Tell us more about 600 HP out of a stock Vortec head.
I like those stories!
Dan

Shawn,
Tell us more about 600 HP out of a stock Vortec head.
I like those stories!
Dan

I'm with this guy....I want a vortec headed motor...

Originally Posted by Dan_Lebherz
Shawn,
Tell us more about 600 HP out of a stock Vortec head.
I like those stories!
Dan


I'm with this guy....I want a vortec headed motor...

What would you like to know about them?
shawn

What would you like to know about them?
shawn

How do you get that kind of power from a vortec head? Compression? Cam Type? RPM?

Would the motor work well in a 3300-3500lb car?

What would you like to know about them?
shawn

EVERYTHING!! EDUMICATE US?

What's the cost per HP for 600hp out of iron Vortecs :eek:

Now you guys don't really think i'm just going to give up all the details on how to build such a thing do ya?
:)
shawn

:D I do. :D

Shawn, Im impressed that you can get that kind of power and not crack the Vortecs on a circle track engine.

Jeff

Shawn, Im impressed that you can get that kind of power and not crack the Vortecs on a circle track engine.

Jeff

Maybe they only last one lap :eek: ;) :D

I do.

Ha! your right! :)

The motors start with a dart block, if rules allow which most tracks do now. You can subtract about 10-15hp if you have to use a stock block. The bore finish is extremely important with the rings that we use. More on that later. The blocks are completely machined from one end to the other as well as lightened. The lifters bores are bored and bushed to either .874 or .903 depending on what the track will allow. In some cases the blocks are decked to 8.800.
Cranks are ultra light weight pieces. With the vortec headed motors we usually run a 3.5 stroke motor, 6.125 rod. Not that the rod length makes any difference, but it does let us put a shorter, lighter piston in the motor. The pistons are custom pieces that are skirt coated,box in box style, with a dome profile that is digitized off of the final, angle milled head. The compression ratio usually ends up around 14.5-1 Rings are ultra thin back cut pieces from a custom ring manufactorer that are also coated.
Oiling systems usually consist of a 4-6 stage dry sump pump. Bearings are small diameter, usually 283 small journal on the mains and small journal or honda on the rods.
Rockers are all shaft assemblies with anywhere from 1.7 to 1.9 ratio.Camshafts will vary a little bit.They are all flat tappets, by rules. Last motor was 258-264 @.050 around .660-.680 lift. These are all custom grinds. It always makes me giggle when people talk about a "secret" cam. What a bunch of b.s.. I would be happy to tell anyone what cams we have. It's all the combonation. Nothing else. My cam in someone else's motor may make it a dog. I have 5 cams sitting here that are all within about 2 degree's duration and .020 lift. There is 40+ hp difference in them. The lobe profile, intake centerlines and lobe seperation make big differences. Also, the cam that makes the best power doesn't always go around the track the fastest. I could easily add about 25hp to the engine, but it would be undrivable. A little off track, sort of, we changed lobe separtion on one of my late model motors earlier this year. Not a single other change. The engine lost about 12hp. It also went around the track .30 quicker and he lapped the ENTIRE FIELD twice. So much for racing dyno's.
Now the heads. You'll probably be disappointed. The are angle milled GM vortecs. We put a 2.00 custom built to my spec titanium intake valve in them with a 1.55 titanium exhaust. The valve job is very, very specific and takes multiple cutters and a lot of time to do. End product flows about 245cfm on the intake and 170 or so on the exhaust. No hand port work is allowed to the heads at all. Back to the bore/stroke. We run a 4.030 bore because we can't alter the chamber on the heads. A larger bore just creates a "step" between the bore and chamber that we don't want there. Valve springs are quite heavy by most peoples standards. We run about 170lbs on the seat with 460-480 open. Yes, this is with a flat tappet cam. The lifters are special flat tappets that we get from Ferrea or PPPC. The cam cores we use are call PRO-55 cores. This lifter/core combo along with correct break in procedures and cam profiles allows you to run these types of pressures. The springs are critical to the engines combonation, along with everything else.
Intake manifolds are "elite" cores. Lately it seems we have been using the super victors. I have a manifold company that i work with that buys lots (read pallets) of intakes. The ones that flow best, because they are not all the same, they sell us and use the others for ported applications because after grinding on them, it doesn't really matter which one you start with. Carbs are limited to 1 11/16 throttle bore (this is normal 750). Add a good dry sump pan and oiler valve covers, along with a good step, over the top, two into one header and your ready to go racing.
Every single piece of this is required to make the kind of power we do. These engines make from 585hp to 600+. If you take away cam, you lose power. If you don't use the correct lobe profiles, you lose power. Less compression, lose, non select intake,lose. ALL of the things are required pieces. Not a single one of them would i consider "cheap" either. Maintenance is also high. Depending on the cam profile, we change valve springs anywhere from 2-6 races. These are $550-600 a set. The engine is freshened about every 10 races. A good "legal" carb will set you back $1500-2000. So there you go. Let me know if you have anymore questions. Or how many you want. :D
shawn

Shawn, out of curiosity what material are the lifters made out of? and the cam lobe material?

Thanks
Jeff

Let me know if you have anymore questions. :D
shawn



i'm modest at times but will proudly say... i'm good with a broom... can i sweep yer shop ??? :D :D :D

I read an article (last year in CHP I think) about using Chrysler lifters in Chevy blocks. Is that what you guys are doing Shawn?

I read an article (last year in CHP I think) about using Chrysler lifters in Chevy blocks. Is that what you guys are doing Shawn?

the .903" he mentioned is the chrysler lifter dia. the other dia. he mentioned(.874") is for ford lifters I believe.....both are larger in dia. then a chevy lifter and I believe they allow you to run a cam with a more aggressive lobe profile without the lifter edging itself into the lobe and destroying both the lifter and the lobe

Chevy used to offer(maybe still do) mushroom lifters and cam profiles designed specificly for the mushroom lifters...its the same theory...it allows a more aggressive cam to be ran without premature lobe/lifter failure

is this being done to bring the lifter centerline or running area closer to exactly where YOU want it ta run... or is it because of the mass difference in lifters ??? i've heard of this procedure (swapping lifters/bushing) years ago... but never knew the "whys"


Thanks Shawn... EXCELLENT reading... i appreciate the style in which ya 'splain thangs :D

Thanks Shawn... EXCELLENT reading... i appreciate the style in which ya 'splain thangs :D

Ditto...:)

between Shawn and Jeff I'll soon be edgimacated:rolleyes: :D

I agree its very interesting reading.

I have run close to those spring pressures (i should say rates- I don't run that much lift- but seat pressure is about the same) but its with a ceramic lifter and sometimes a billet cam (stock lifter diameter). I have seen some circle track lobes that were welded in stellite.

Jeff

Shawn, do you work at Britco?

. Also, the cam that makes the best power doesn't always go around the track the fastest. I could easily add about 25hp to the engine, but it would be undrivable. A little off track, sort of, we changed lobe separtion on one of my late model motors earlier this year. Not a single other change. The engine lost about 12hp. It also went around the track .30 quicker and he lapped the ENTIRE FIELD twice. So much for racing dyno's.

shawn

This sentence bears highlighting and repeating.

If peak HP was all there was to going fast then all racers would have to do to win would be to submit dyno slips! don't get so focused on numbers and forget that the objective of racing is winning.

That other part about the importance of all the parts working in combination witrh each other is also very true. Too many guys say I have exactly the same combo...except.... why am I slower?

It ain't the same combo if it's different!

Shawn, you left out the all important part of a good combo: The 12:30 am dyno pull. "one pull then turn off the lights!":D

Shawn, out of curiosity what material are the lifters made out of? and the cam lobe material?


The lifters are what they call "super clean Tool Steel alloy" that have a special heat treat. The rockwell, if i remember, is about 65? We started out using the edm hole lifters but we have gone away from them and are just using the normal ones now without the holes. I have a friend in N.C. that does a lot of late model engines and he told me that some of the company's were putting the hole in them after the heat treat and creating a "soft" spot right where they poked it through. Last thing i need is a cam failure filling the engine full of metal. The normal ones haven't had any negative results, that i can see. The Ferrea lifters aren't made this way, for what it's worth. I wouldn't mind using thier EDM lifter. The cam cores are cast pieces, like a normal flat tappet, but have a higher density and a treatment of some sort. The combo works out pretty well. The next step is "cup" type stuff with steel cores and higher maintenance.

I read an article (last year in CHP I think) about using Chrysler lifters in Chevy blocks. Is that what you guys are doing Shawn?

Sort of. They are the Chrysler diameter lifter, but built for a chev block. The oil groove in the lifter is different from chev to mopar to ford. So while the
.874 and .903 lifter diameters are ford and mopar, the lifters themselves are built for a chev application. They larger diameters are used like 69novass says, to be able to run a camshaft with a faster profile. This let's you put more area under the curve, much like going from a flat tappet to a roller profile, but not as drastic. The side by product is lifter alignment also. On a stock block, the lifter bores on some cores are so bad that even going from stock .842 diameter to .874 the bores won't clean up because they are so far out of alignment. Those engines we have to bore them to 1.00 and put a bushing in them, if the .903 lifter isn't legal.

Shawn, do you work at Britco?

Ah, another local. lol. I did at one time. The "Shawn" that is there now isn't me. We do get confused quite a bit though. Except in the looks department. He's the tall skinny one with the hot girlfriends. I'm, well, not.

Shawn, you left out the all important part of a good combo: The 12:30 am dyno pull. "one pull then turn off the lights!"

Now Dave, we don't want to alert the Po Lice to things like this do we? :D

shawn

Im thinking they may be able to hear it.:eek: BWAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Shawn, do you know Mark Craig in Walla Walla? He builds mostly NASCAR engines so I thought you might know him or of him. Also, do you build any of the sprint car guys engines? (410's)

Im thinking they may be able to hear it. BWAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Ya think? lol

Shawn, do you know Mark Craig in Walla Walla? He builds mostly NASCAR engines so I thought you might know him or of him. Also, do you build any of the sprint car guys engines? (410's)

Yes, i do know him. Good builder. I thought he moved/quit though? I don't do any sprint stuff right now. I've done some heads for them, but that's about it. It's a pretty specialized market and I really don't have the time to invest in learning the tricks to them.
shawn

This is a good example of spending astronomical amounts of money to produce power/TQ, etc. and stay within the rules. If there weren't rules dictating what pieces you had to use, I imagine you could build something that would surpass this and at 1/4 the cost using aftermarket parts.

It's always very interesting to learn how inovative people can be. Kinda like stock elim guys putting aftermarket steel body panels on the car because they are lighter than the originals...simple, but effective lol

Hi,

David in my opinion most of these rules have been developed to try and (in a vain attempt) to keep the cost down. Its just someone with resources (generally money) always raises the stakes. I imagine the use of flat tappets and the Vortec head along with the non ported intake (among)other things Shawn mentioned were all attempts to keep costs down.


The only things I have ever seen that did actually make a dent in the cost were "claimer " engines where someone could actually buy a competitors engine for (usually) a very small amount and a sealed spec engine that the sanctioning body supplied, that you were not allowed to open.\

The claim deal is kinda neet if peer pressure is not allowed to apply, but generally if a competitor does "buy" an engine it leads to all kinds of threats and disputes. So generally it seems to be not to favorable.

Oh, I agree Jeff. I'm sure the rules are in place to keep costs down. It doesn't seem to work well though. It just causes people to spend more money to figure out how to get around the rules. It drives me nuts. At least in drag racing (bracket) you still have to dial a number and cut a light to win.

Anyway, back to the subject at hand (it's amazing at where a thread can go lol).

Still a bit off track. Trying to cut costs in racing is impossible. I had a real smart guy tell me once that the only way to make a small fortune in racing is to start with a large one. People will spend what they have in the budget to spend. Period. If you can spend $30,000 on the latest engine you will. If you only have $15,000 to spend, you spend that. Putting a limit on it does nothing. People will only spend what they have to spend. The "have's" will always have a better chance than the "have not's".
The horsepower thing cracks me up too. Everyone wants to know what the other guy has. Makes me laugh when a guy comes up and wants to know what kind of power the last engine made that I did. I always ask them if they want one. Almost always it's "well, I can't buy one now, but...". To which I always respond "then it doesn't really matter, does it?". If your not going to buy one, then it doesn't really matter if they have 500hp more than you. It won't change a thing. If you limit what you can do to the engine, people will spend more to work around it, or just spend that money on some other part of the car. Which in reality is probably where they should be spending it in the first place. :D Always brings strange looks from people when I tell them to spend the extra $1000 on good shocks instead of a billet crank. I don't argue with them, but i always let me know that money is better spent on the car/chassis then to make an extra 20hp. Always.
shawn

Shawn, thanks...Mark built my big block...I really thought he was a great guy and seemed to be pretty meticulous when building...that's why I selected him to do it. I've been meaning to give him a call...I hadn't heard that he moved or got out of the biz...I hope not. I'll have to check it out.

Good to have you on the board! I may be needing your services in the future, especially if Mark is out of the picture...you might pass along your contact info in an E-mail if you want. Thanks

Hi,
you sure you want know? Just kidding.

(Pi/4) = (3.141592654 / 4) = .785398163

360 * .785398163 = 282.7433388 or .003536777


the .00353 is just the 1/x reciprocal of 283.286119

its a combination of conversion constants into 1 constant = 282.286119
it converts inches into area and inches into feet
The 614 is the limiting port velocity for most applications. The number is actually 613.9758744, but that creates just a bit more math than I want to do, and 614 will get you close enough.
shawn

Ok, I've read through stacks of text books and SAE papers but I still don't know how this was derived.
As near as I can find the earliest reference to your equation is in Dave Vizard's 1991 book " How to Build and Modify Chevrolet small block V-8 Cylinder heads'.
He doesn't explain where the formula came from or the magic constant.
I'm guessing he came up with it or maybe he got it from someone else but didn't give credit. He does mention Charles Fayette Taylor and his most excellent book 'The Internal Combustion Engine' but none of Vizard's math is directly tracable to Taylor's equations since they all use valve dimensions. I found information published in an SAE paper (790484)
by Itaru Fukutani and Eiichi Watanabe of the Japanese Institute for Vocational Training
That references the all important intake valve closing point in their equations.
Dave talks about intake closing and the "inertial block" because the air in the port has to start and stop as the valve opens and closes. This is something that is not part of flowbench testing and why just CFM alone is not the whole story.

Your Pi/4 * 360 is part of basic trigonometry and circular functions, but I can't connect the dots on how it translates to square inches and feet per second.
The only thing I can guess is it's an inverse slope function or something in radians?
Please explain the math. This is driving me crazy.

I'm not really an advanced math literate. I do know that the conversion constant, it just that. It is a mathematical constant that converts the inches into area and inches into feet. Maybe if i give you another example of how to use the constant it may help?
You can use this constant along with Air Velocity FPS to solve for what is the required Intake Valve diameter needed for a certain "Peak HP RPM"

Intake_Valve = (( RPM * CID ) / ( Cylinders * 314.5 * 282.7433388 )) ^.5

where;
RPM = the point you want Peak HP to occur
CID = total engine size in Cubic Inches
Cylinders= the number of engine cylinders
314.5 = Air velocity in Feet per Second
282.7433388 = Units Constant
^ .5 = Square Root of a Number
This would be using current ProStock stuff.

2.515 = (( 9000 * 500 ) / ( 8 * 314.5 * 282.7433388 )) ^ .5

Another using our earlier superstock example-

4.065 Bore X 3.493 Stroke = 362.661 CID with a 1.940" OD Intake Valve

1.940 = (( 7200 * 362.661 ) / ( 8 * 306.7 * 282.7433388 )) ^ .5

7200 RPM for NHRA SS 350 with 041x heads 1.940/1.500 valves
is very close to the Norm average

The 306.7 and 314.5 are variables in these equations. Why? The ProStock port can handle higher air velocity more efficient because of
less port centerline axis -to- valve axis ..and a better overall shaped port
with more constant cross-sectional area.
Lets say your ProStock head design is as inefficient as a SuperStock Head
then the required Intake Valve diameter would be larger -

2.547" Int OD = (( 9000 * 500 ) / ( 8 * 306.7 * 282.7433388 )) ^ .5

Of course these valve size recomendations are just one piece of the puzzle, and are not designed to be used as an "exclusive" tool.

shawn

If you didn't invent it, where did this math come from? Vizard or somewhere else? What's your source, book or reference? Based on comparisons to engineering textbook equations, I think it may be in error.
In Charles Fayette Taylor's book, 'The Internal Combustion Engine', the basic Mach Index formula is Piston Area x S divided by Inlet Valve area. S is not stroke but Piston velocity.

In Vizard's equation for example, Pi times Bore x bore is Pi times Bore^2 or essentially PI times Diameter squared. Area of a circle is Pi times Radius squared.

maybe it's one of those "trade secrets" :D :D :D

If you didn't invent it, where did math this come from? What's your source, book or reference? Based on comparisons to engineering textbook equations, I think it may be in error.

I origianally got it from Richard Maskin, but it's the same equation that is used by most top engine builders/head porters I know. I guess I'm not sure what your asking? The .003536777 is not a variable. It's a simple conversion. While I supose that we could all be doing it wrong, but i know the math is correct, and the conversion is the correct one, so I'm not sure what could be in error? The only thing in the equation that is a potential variable is the 614fps. This could move around based on the effiency of the port/induction system. I'll ask some friends of mine to see if they know where the original equation came from.
shawn

Here's the basic formula for 'Z' (Mach Index or the Inertial supercharging index)

Piston area x Mean Piston Speed / Inlet valve area.

Vizard's equation you used had me puzzled until I finally found what I was looking for.
There are two ways of figuring the area of a circle:

The area of a circle equals
1. Pi times radius squared
2. Pi times diameter squared divided by 4,
or 0.78539 times diameter squared.

Since the "Bore" is the diameter, Bore x Bore = Bore^2
Pi * Bore^2 / 4 = Bore^2 x .78539
This part is the Piston area in square inches.

Vizard's equation overlooks something that Taylor noted experimentally:
If you just take the piston area and speed and divide by the inlet area, the results don't correlate.
He has a chart that shows a wide range of experimental data based on this equation.
He then goes on to say that the flow coefficient derived from the lift/diameter ratio plotted vs crank angle in degrees was important to taming the data.
Once the flow coefficient is considered the data curve is more reliable.
Z = (Bore/ Valve diameter)^2 * MPS/Flow Coefficient * Sonic velocity (@ pressure & temp)

The SAE paper I mentioned adds more on the subject. Judging from all the Japanese work on the subject, I really think these preliminary studies lead to the success of Honda's VTEC system. My Integra has a really flat torque curve after the VTEC kicks in. The inlet valve closing adjusts with increasing rpm, maintaining the inertial ram effect all the way to peak power.

I think what Vizard has done is substitute port cross section area for valve area and fix or ignore several variables to come up with a rough estimate of velocity.

Because of that I'm just not sure about is how reliable it is, but like a lot of formula's it's better than nothing or guessing.

It's a good discussion and shows once again how important math is to hot rodding.

Hi Paul,

I was just wondering how you found piston speed?


Thanks
Jeff

Hi Paul,

I was just wondering how you found piston speed?


Thanks
Jeff

Here's what I use in my calculator:

Mean Piston Speed

MPS = stroke x rpm x .167

Somewhere I have a formula for instantaneous piston speed that takes into account rod length...I just can't find it right now.

What is .167 in that equation?

What is .167 in that equation?

Ha! I just knew someone would ask that.

There are two verticle (1 up & 1 down) piston strokes per crank revolution.
So for example, with a 3" stroke the piston travels 6" per revolution.
Multiply by the number of revolutions per minute and you get the total inches of linear travel per minute:

RPM * stroke * 2

The stroke is in inches so we divide by 12 to get feet:

RPM * stroke * 2/12

Fraction is reduced to
2/12 = .167

RPM * Stroke * .167 = MPS in Ft/Min

dividing the result by 60 will give it to you in feet per second.
Air Velocity is often in Ft/Sec so keep the MPS in Ft/sec if using both in an equation.
It's important to keep track of the units or it can get away from you.

This equation is for Mean Piston Speed. It's the average speed. Instantaneous speeds can be much higher or lower all the way to zero at TDC and BDC.
The instantaneous speed at any crank position can be calculated with a much more complicated formula that utilizes trigonometry and the rod length variable.

Expert engine designers consider true piston speed plotted vs cam timing events since it influences port velocity. The VTEC system exploits this relationship very effectively.
If a 505Hp Corvette Z06 could produce 125hp per liter like an Integra Vtec Type R, it would make 875Hp!

Hi,

This interesting stuff.

Im not trying to be picky but, I really hope the piston speed is "0" at TDC and BDC. I have had a few that were not, and it wasn't pretty.

I think the instantaneous speed statement is a little different than I generally configure things in my mind (remember feeble kinda mind). To me rod length and created piston acceleration rate is very important to creating the the start of cyl filling. Have seen it have such a change in flow (and flame propagation) that it took some work to get the desired results.

I know the valve angles here are very important as well.
I dont really know how to address this mathematically.

Im really tied up today, and I got to run, but Paul and Shawn, you guys are doing a great job and this is very interesting.


Jeff

I wrote a program in MS Excel in College that would calculate piston position (inches below TDC) as a function of crankshaft angle (degrees past TDC). The user could input rod length and stroke and evaluate how these variables affected piston position.

With some help from my peers we took it a few steps further. We had MathCad calculate the derivative of the position formula. This gave an equation for piston velocity. The input variables were those listed above plus RPM. The instantaneous piston velocity was calculated as a function of crank angle in feet per minute.

Next, we calculated piston acceleration. The formula would output instantaneous acceleration as a function of crank angle, in feet per minute per minute.

I recall inputing several different rod lengths for a given stroke. The piston position as a function of crank angle does not change much. The instantaneous velocity changes is a bit less in a long rod motor compared to a short rod motor. The instantaneous acceleration was a bit less in a long rod motor compared to a short rod motor. The difference in velocity was greater than the difference in position, and the difference in acceleration was greater than the difference in velocity when rod length was varied.

Now the bad news is that I lost that program prior to graduation. I have since rewritten the position formula. Unfortunately, I am not smart enough to calculate the derivatives by hand, and don't have access to MathCad.

I've seen others that have done similar and this apparently has lead to the current internet buzz that rod length "doesn't matter". What they don't take into account is the interaction of cam timing and inlet velocity relative to piston speed.

Flow bench data is taken with the valve opening fixed and often without the intake manifold or carb attached so even that doesn't closely simulate the dynamics of a running engine where the air in the port has to stop when the valve is closed and accelerate when it opens.

We've already shown that bore diameter changes piston area which influences inlet air velocity for any minimum cross section. We've seen that the stroke variable influences MPS which impacts air velocity and inertial supercharging. You've confirmed that instaneous piston speed is effected by rod length. Maybe not as much as big stroke changes but it has to be considered.

A change of only 2-4 crank degrees can have a measureable effect on engine output. A typical multi position cam sprocket has only +4, 0 and -4 crank degrees of adjustment but the cam is turning half as fast as the crank.

Anybody that's changed a stock cam for an aftermarket cam knows that inlet valve opening and closing relative to crank degrees has a big influence on VE, torque and HP. Air velocity relates to VE which translates into torque combined with rpm, hp is derived from.

It can get very complicated and some variables may have an effect on operating parameters other than HP so the consequences may get overlooked
Fuel economy, width of torque curve, exhaust temps, driveability never seem to come up in discussions but an engine builder may notice these come out less than ideal after changes.

If you compare the modern Z06 7 liter and an L-88 7 liter engine and you can easily see the operating characteristics are very much different (and improved) thanks to engineering progress.

You can't point to any one thing that makes the whole difference. It's the combination of everything and the optimization of variables that some think "don't matter".

I have asked a few of my engine/cylinder head friends and none can seem to come up with the source. One of them that does prostock heads told me "huh, guess i don't know, just know it works", which has kind of always been my take on it. Whether or not the thing came from some deep reasoning by a SAE engineer type or that someone said, wow, look here, this fits well, doesn't really matter to me. I just know that if i need something to get me in the ballpark, it comes very,very close. That being said, nothing is perfect. Here's another example of using it in practice that one of my sources shared, thought you might find it interesting-

Dart Pro-1 215CC Dyno Test + Flow Numbers
Pushrod Area Choke Testing

i just finished a series of Dyno Tests using Dart Pro-1 aluminum SBC
215 CC Heads

SF-600 FlowBench Data (Ported but unwelded, 1st series of Tests)
Manley Valves= 2.125" Int +.100 Long 1.600" Exh +.100 Long
4.125 Flow Fixture No-Pipe on Exhaust Port
Lift---Intake--Exhaust
.200--146.6--111.0
.300--215.5--161.3
.400--260.0--203.8
.450--279.0
.500--293.5--228.4
.550--300.8
.600--304.0--239.7
.650--307.0
.700--310.6--243.7
.750--315.8
.800--318.8--243.3
.850--320.8
Comments=> Speed FPS too high at pushrods



Engine Specs=> 4.165 Bore x 3.875 Stroke = 422.4 CID
GM "Bowtie" Intake Manifold max-ported + reworked plenum
with Moroso #65000 2 inch Dominator adapter
Dart Pro-1 215CC 2.125/1.600 max-ported but unwelded @ pushrods
HP-1250 Carb
C-16 Race Gas
MSD Distributor
Diamond Pistons 14:1 CR 224 Cranking psi
Cam Motion solid roller .776"/.743" Lift 284/300 Duration @.050"
112 Centers on 108 CL .025" lash across hot
Cam Motion Red Rockers 1.65/1.65 Ratios

RPM--Torque---HP--SF-901 Dyno Data @ 600 RPM/SEC
5500--551.0---577.1
5600--553.2---589.8
5700--556.5---603.9
5800--557.6---615.7
5900--558.8---627.7
6000--562.1---642.1
6100--560.6---651.1
6200--560.2---661.3
6300--558.1---669.4
6400--555.7---677.2
6500--550.4---681.2
6600--549.3---690.3
6700--547.7---698.7
6800--543.3---703.4
6900--531.6---698.4
7000--524.5---699.1
7100--509.9---689.3
7200--509.0---697.8
7300--500.5---695.6
7400--492.6---694.1
7500--481.5---687.6
7600--475.3---687.8

Avg=> TQ=535.9 HP=665.4 Fuel=260.2 Lbs from 5500-7600 RPM

Note Fuel= 260.2 Lbs. avg from 5500-7600


************************************************** ******


2nd Test Series Results
with Welded Heads at Pushrod area + slight more Short Turn rework
with widened Port's pushrod area
Pushrod area outside wall thickness = .040"
with Offset Lifters + Crane 1.65 Offset Rockers


SF-600 FlowBench Data
Manley Valves= 2.125" Int +.100 Long 1.600" Exh +.100 Long
4.125 Flow Fixture No-Pipe on Exhaust Port
Lift---Intake--Exhaust
.200--146.6--111.0
.300--215.5--161.3
.400--262.0--203.8
.450--278.0
.500--293.5--228.4
.550--302.0
.600--314.0--239.7
.650--317.5
.700--319.1--243.7
.750--321.4
.800--323.4--243.3
.850--325.4

Slowed down Speed FPS @ pushrod area to more acceptable level


RPM--Torque---HP--SF-901 Dyno Data @ 600 RPM/SEC
5500--555.0---581.2
5600--555.4---592.2
5700--560.2---607.9
5800--561.3---619.9
5900--565.6---635.3
6000--566.4---647.1
6100--570.6---662.7
6200--568.7---671.3
6300--567.3---680.5
6400--567.8---691.9
6500--563.1---696.8
6600--555.2---697.7
6700--554.1---707.3
6800--551.3---713.7
6900--538.8---707.9
7000--540.8---720.8
7100--527.9---713.7
7200--518.3---710.6
7300--517.3---719.0
7400--511.5---720.6
7500--503.8---719.4
7600--492.9---713.3

7700--489.9---717.5
7800--480.7---713.8

Avg=> TQ=546.1 HP=678.7 Fuel=258.5 Lbs from 5500-7600 RPM

Note Fuel= 258.5 Lbs. avg from 5500-7600



With AirSpeed @ Pushrod area slowed down to more acceptable level,
Engine has a better Torque + HP Curve..especially after RPM point
of Peak HP
and using about the same amount of Fuel


Note= my Dyno is on conservative side,
so 720 HP on my Dyno at 600 rpm/sec
could be 740 to as much as 770 Hp on other Dynos
especially at slower test rates.

likewise FlowBench is about 10-15+ CFM numbers on conservative side

shawn

Hi,
you sure you want know? Just kidding.

(Pi/4) = (3.141592654 / 4) = .785398163

360 * .785398163 = 282.7433388 or .003536777


the .00353 is just the 1/x reciprocal of 283.286119

its a combination of conversion constants into 1 constant = 282.286119
it converts inches into area and inches into feet
It seems that the minimum cross section area is tough information to come by if a person is cylinder head shopping.
I called both CFE and Air Flow Research; neither one could tell me the minimum CSA of their heads.
I have a set of CFE 350cc BMF heads on my 548 Chevy, and wanted to run the numbers through the formulas given.

Also, not to nit pick, but in the above quote there is three different numbers
282.7433388
283.286119
282.286119
I assume that the first two are different due to rounding and the third is a typo. Just wanting to confirm that they are basically the same number.
Brian

I know Carl knows the min. cross of the BMF heads. I'm sure AFR could give you there's too. You probably just didn't talk to the right person, or they just didn't want to do the work to find out. The BMF head is cnc'd so all you need is the CAD of the port and you can find out in a few minutes. I'm not sure if you were talking about the cnc version of the AFR head or not. That 350 head on a 548 should run good, if you have enough compression and cam. Those are a very good cylinder head. I know at 14.5-1 , a healthy roller, and a ported single 4 with dom. you should be able to make 925hp+ on our dyno. That engine will spin nicely to about 8000. You'll need at least a 5500rpm converter to maximize the potential of the combo. Yes, the third shoud be 283., not 282.
shawn

I ran a 283 with stock bore and arias 12:1 piston my engine would twist 7000 all day long with stock rods and bolt. I would not recommend everyone try this but it worked for me my cam was a extrem 274 comp which was .501/.510 soild lift I was running a seat late model camel humps and a torker intake and 600dp.

2 equal engines in power, the one that accelerates to its powerband the fastest will always win.

If I can stress one thing is that an engine is a give and take receipe. If you are going to give it a lot of head then take camshaft away. If you don't have a lot of head then add camshaft.

2 equal engines in power, the one that accelerates to its powerband the fastest will always win.



hi chris,
good to see you here. statement is very true. figuring out how to do it is the hard part.
shawn

hi chris,
good to see you here. statement is very true. figuring out how to do it is the hard part.
shawn

Combination, Combination, Combination......A well thought out combo will save you tons of ****$'s down the road.

I figured it was you Shawn.