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some of the.. uh.. er.. older / more experienced members here will disagree. they seem to remember the 302 stock not a hot as the rumors and fairy tales
have made them to be.
 

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Really? I wonder why?....Yes I sure wasnt born in that time frame so I dont have experience with them. But there is a lil 67 302 Camaro floating around my neck of the woods(Orange with White Strips) and its a very strong runner for what it is. Onlything I think the owner did was nice intake, nice cam, and some carb work, nice wheels and did some rearend work on it with some better gears. Other then that its still in stock form, but does it like to rap up and has ran since I was in high school ! :eek: Super clean car I need some pictures of it so I can share !! :(
 

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Those 302's in the Camaros had to be used with a 4.10 gear to get anything out of them. And the M22's only had a 2.20 1st gear ratio in them. I seem to recall Paul Wright trying to council a would-be 302 builder that if the 302 was such a wonderful engine more poeple would be building them instead of the ever popular 383 stroker.
 

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Necro said:
some of the.. uh.. er.. older / more experienced members here will disagree. they seem to remember the 302 stock not a hot as the rumors and fairy tales
have made them to be.
I qualify for "one of the.. uh.. er..older / more experienced members " and I still like the way a 302 winds out. They are not super high hp motors but back in the day they ran well for their limited cubic inch size. Sure the 350s of today make them look weak by comparison but I still like them. When we built them they were 301 but Chevy called them 302. Go figure!
 

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Onlything I think the owner did was nice intake, nice cam, and some carb work, nice wheels and did some rearend work on it with some better gears
not to be a jerk but a cam carb and intake can make a big difference. the stock designs are going on 40 years old, a new grind (like an XE or roller cam) will make more power hands down. the reason a 302 gives the impression of being a beast of an engine because you can wrap the pi$$ out of it without blowing it up (short stroke=low piston speed) and because they came in fairly light cars with a decent suspension package (i.e. z-28). i'm not going to say that it wouldn't be a blast to drive, or that anyone is a fool for building one, but IN IDENTICAL VEHICLES: cubes win. always. period. end of story. obviously a 73 impala with a stock 200,000 mi 400 will not beat a lightened 67 camaro with a 302 set up to drag, but that's apples to oranges.

but back to the question at hand...i remember hot rod doing a bore vs. stroke comparison and the power numbers were pretty much neck and neck. the short stroke big bore made slightly more power. as in very slightly. less than 10hp and it had a couple more cubes. same heads, carb, intake, cam, and as close as they could get with compression. the simple fact is that within limits (in other words, no 4" stroke-2" bore or 2" stroke 6" bore) bore-stroke ratio doesn't mean much. i.e. you don't gain enough from a 302 to beat a 383. nor do you gain enough with a 377 to beat a 406. again, i'm not saying that you can't build a fast one, or that it's foolish to do so. do your own thing. have fun. but if the 283 had made more power than anyone could ever use, chevy wouldn't have invested money in the 327. If that had been enough, we'd have no 350, etc. food for thought.
 

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This question keeps coming up so I've merged them together.

As far as the question about the 305 it's not as complicated as you might think. The Arab oil embargo's of the seventies (73 and 78 you probably don't remember that) caught the american car companies off guard. Plus they had EPA rules to contend with. It was cheap and easy to reduce the bore on a 350 to get better fuel economy and still have enough torque to move a car around. GM didn't spend a lot of money on the 305 compared to other more expensive solutions that came later (OD trans, EFI, GEN III engines).

Chevy played around with other combo's (262, 267) to wring better economy out of the SBC but NONE of these engines have performance potential.

Ford used the 5.0 which has a 4" bore and 3" stroke during the same years and it had shorter rods. Early versions of the 302/5.0 were real turds. Later with the HO 5.0L and an OD T5 trans they got pretty good economy from a performance engine. EFI and roller cams improved it even better. I'm pretty sure they got at least 21 mpg.
That's old hat now.
A GenIII 350 has 3.9" bore x 3.62" stroke and gets 21 mpg. A Modern Vortec 5.3L (326) has a shorter stroke and gets even better mpg.

I doubt a Gen I SBC can duplicate the MPG even if the bore and stroke are the same. There's much more to it than that.
 

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Plus they had EPA rules to contend with.
I recall reading that the 305 design was driven by something to do with flamefront travel across the small bore. Seems like they found it easier to reduce a certain type of emmision by shrinking bore size.

FWIW, GM still builds small bore long stroke motors. Colorado I-5 (and I-4 and trailblazer I-6) motors use a 3.6x bore and a 4.00" stroke. What is intersting, is that my little 3.5L Colorado w/ 4" stroke is set-up to shift at 6000 rpm. They must be using some light pistons, or the PM rods must be pretty dang tough (probably both true).
 

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Yes, you'll see that a lot especially with 4 valve heads. You can get good breathing area in a small bore when you have 4 smaller valves than you could with 2 valves like the 305. The longer stroke gives good driveability and burn time. The ZR1 Covette Lotus/Mercury Marine 350 4 valve engine had small 3.9" or so bore also, I think.

I have a valve size equation somewhere. I think that's where you start. If it's a 2 valve or 4 valve there's a minimum valve area required to get enough air to feed a desired HP level. Bore size is often a valve "packaging" restraint.
That's why you see 18 degree and 12 degree heads. It helps fit the valves in the bore and straightens the intake tract.
 

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Guys IMO your right (no sounding like jerks here ;) ), there is no replacement for displacement (I get all tiggley and giggley inside when I hear Big and Block in one sentence) :D ;) After the 302 was mentioned, I just remember what a small underdog it was for its time. Surely it wasnt or not a beast to today's standards, but IMO I still think its above a 302 Ford :D for as old as they are just wishful someone still produced them :(

IMO the bore vs stroke has alot to do with the weight and balance of the interals (ie rods, crank, pistons )and how efficient they work together.

This is why when you have a 377 vs a 406, The 406 will make more Torque due to the cubes of the A/F, but the 377 has a better response due to the more efficient of the weight and how much better its balanced with the shorter stroke and the rod length playing a key. Would that be a correct statement? For the lack of piston slap and the weight difference of the crank ?

Another example : 377 with light weight standard stroke and 5.7 alumi rods
vs a 406 with 3.75 standard stroke light weight and 6.0 alumi rods. From what Ive gathered over the years in the famous SBs the 6.0 rods is what helps the 406 being more efficient. But to match the 377 in response, you have to match the weight of the internals of the 377 with a longer rod in the 406 for it to be just as efficient to reduce the piston slap. From what I understand thats how to really match a 406 vs a 377 in comparison for horsepower. Does that make sense or am I off ?
 

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Ok guys, I know the more cubes the more HP. I have a couple 400's in the shop now. I don't need 500hp to get to work or cruise the freeways, but I want to go with a V8, so I was thinking about the difference in fuel economy between the 302 vs 305 IF everything else was the same. You can't compare the 302 that GM built with the 305 because the 302 had big heads, valves, intake etc. The 305 had small ports, valves and was not a performance engine. The 302 would make more power because the 4" bore allows bigger valves. I think if you compare a 383 with a 302 using the same heads cam etc. the 383 would make more power down low in the RPM's, but because of cubes not stroke length.

If you were to put 305 heads, cam and intake on a 302, would the torque and horsepower be the same and would it take the same amount of fuel to make the same power #'s ? :confused: Would the 305 be more efficient at 1800-2300 rpm due to piston speed?

KenDog
 

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Why didnt GM just stick with 307s instead of 305s? Seems like a waste of money on re-tooling when 307s were never built as performance engines either.
 

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you're looking for a daily driven combination with good MPG. (On the dyno) you need to look at the VE(volumetric efficiency) and BSFC throughout the power curve.
Obviously you want to be as efficient as possible with it using as little as fuel as possible but not being too lean(A/F over 13.0 at WOT)
Try not to overthink this and not reinvent the wheel. Engineers and engine builders have figured it all out for you. Take a look at the Engine masters challenge. They had to build an engine with tight rules and restrictions, one in particular was a small block with max cubes of 365. Go to www.enginemasters.com and read up, or go back thru your old popular hotrodding mags. Joe Sherman built a 365(4.040x3.562) and made incredible HP and Tq, and conversely John Beck built a small bore long stroke combo(cant remember the numbers) and made killer power as well. His idea was to really try to make alot of TQ down low. So you do have alot of choices, but the bottom line comes down to what you can afford.
Simply you cannot beat cubic inches. My theory is the bigger the motor, the less you have to push the gas to get a given vehicle to move.
Bottom line, TORQUE is where its at as far as what your doing. My nova had a stock 350 with a comp 268 cam, 8.5 to comp, stock heads, small headers, performer intake, 750 vac sec, and HEI and that thing made excellent power and got decent mileage considering my foot was in it 80% of the time. Stepping to a 383 from here, longer stroke means more leverage from that crank, thus more TQ. As a matter of fact, Im building 2 383's right now, one is to replace the 305 in my wifes 89 camaro, and the other is going in my 76 GMC stepside.
There are some die hards out there that truely love small inch motors, 327's are a great motor. you could easily make 330 hp and decent tq with a 327.
As far as the 302 is considered, them things don't make tq and you'd have to put in some steep gears to get that little motor to work right. I had a friend with a real DZ 302 69 Z/28 with 3.73's and a 4 spd and that thing had no power till 4500 then weeeeee......revved to 8500. But I would whoop his *** in my nova!!! with that 350 and a th350, stock ten bolt with 3.08's .

So, bottom line, TQ and effciency are what you need to aim toward. As far as budget goes, you can easily build a good 350-383 or 400 and make plenty of power. You can tailor your RPM with cam and head design, exhaust and gear ratio.
 

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Stroke

I am prolly going to get blasted for this but...
in the previous posts, a person eluded to a 4 inch stroke in a 4cly and 6 cly.

long stroke and low rpm go hand in hand, short stroke and high rpm the reverse

Swept volume is where your trades off occure. to promote good hp and tq you need stroke, but in doing so you gain weight. the short you gain friction from the higher cycles. If I were able to play with Bore vs stroke I would go with the longest stroke and smallest bore for economy. With the thinking of a lower rpm to get the car moving by using the kinetic energy or the long stroke, and a medium weight flywheel to store it. With the long stroke able to do more work at a lower rpm, heads I would strive for high velocity ports and a static comp. of 9.0 to 9.5 with a cam with fast opening ramps and quick closing on the intake and fast opening on exhaust and slow closing. but its just MY .02



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Paul Wright said:
EFI and roller cams improved it even better. I'm pretty sure they got at least 21 mpg. That's old hat now.
A GenIII 350 has 3.9" bore x 3.62" stroke and gets 21 mpg. A Modern Vortec 5.3L (326) has a shorter stroke and gets even better mpg.

I doubt a Gen I SBC can duplicate the MPG even if the bore and stroke are the same. There's much more to it than that.
I'm sure that the physical design of the motor has a lot to do with the potential MPG it will be able to achive but IMO I think the biggest single factor that increased MPG was adding a CPU to the car that controled spark, timing curve, air fuel mixture, etc, etc. The CPU can make 1000's of small changes every second the A/F mixture, timing, etc, in an effort to keep the motor running at its peak efficency which is something that was largely impossible to do before the advent of CPU's in cars.

I'm sure I am going out on a limb here but if you took a 1st gen SBC and added a CPU to control everything that the CPU on a modern car does I suspect, JMO, that its MPG would be way higher than anything the 1st gen SBC got when it was new.

Yes of course I am not discounting the OD tranny they are important too. And if you added that along with the CPU I would think the MPG would be fairly compariable to anything today. Just pure speculation on my part here :)
 

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I was working one day and overhead two guy debating as to why the F**d 302 ran stronger than the Chevy 305. I don't remember their specifics but they were kind of out there. Anyway, not being actually in the conversation made me think of something I never had considered before. I went to school on hydraulics and pneumatics years ago. As part of the training, we would have to work formulas on what weight a given size piston in a cylinder will lift with a given psi applied. As piston diameter was increased, more weight could be lifted with the same psi. This would give the 302 an advantage. Past experience also tells me that the smaller bore of the 305 makes it more proned to detonation. Curve kits and extra ignition timing do not give the great returns you see with a 350.
As far as the bore vs stroke controversy goes. I think it gets over analyzed. I think displacement is displacement and bore and stroke have to be dramatically different to seperate the performance by a noticable margin. I am not going to build a small engine for gas mileage. I don't think that is the answer. Experience makes me prefer a 4" or larger bore on a two valve cylinder head. That marks the 305 off my list and I have built 307's and don't see the point in traveling that road again.
Ten years ago, I installed a stock 305 TPI engine and 700R4 in my Nova. The 60 ft times were great but it ran out of grunt by 4500 rpms. We played around with all the traditional hop-ups and for that engine, I think stock is about the best all around you can get with that particular engine. The car got 22 mpg with the 305. We swapped in two 350 and added the TPI to each. I expected to take a hit in fuel economy. The car still got 22 mpg with a 350. I decided to build a dedicated 350 TPI engine and that is what is in the car now. It has Edelbrock heads, larger intake, and a Lunati hydraulic roller cam. This one pulls strong to 6000 rpms. The new 350 has manage 24 mpg and it has more go fast parts than any of the past engines.

It is my belief that gearing and driving habits are a much bigger factor for fuel economy than displacement. (Until you buy a big block.) I believe my overdrive transmission helps my fuel economy more than the EFI. I firmly believe that if you are going to build a hot rod, you should build a strong enough engine to justify all the hard work and money invested. Even if it cost a little more at the pump. You only live once. Would you rather tell you grandkids about the Nova you puttered around in for twenty years or the car that pinned you in the seat everytime you hit the go pedal? Buy an econobox for everyday driving but if you are going to build a hot rod, build a real hot rod.
 

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I like the old 283. They are good work horse engines. Once I get my 63 impala SS convertable powered by a 283 backed with a power glide tranny here from Nevada it will be a nice cruiser. No I'm not going to set any land speed records in it, but it is smooth and fun to just cruise in. The Car is a numbers matching car and I intend to keep it that way. It is sometimes fun to drive something that is just comfortable to drive. On the other hand my 72 Nova will start its second life with a 350 and when I get to the point that getting more out of the engine becomes to costly I'll step up to something with more cubes and keep that process up as long as the car has life left in her. She'll be for the summer days when I want to fill the rumble of power and feel of banging gears and smoking tires. As far as the Bore vs. Stroke question I've read alot about it and as far as I have seen for the Basic Hot Rodder who builds an engine to put in his car with the intention of driving it the stroke and Bore is not going to make enough difference. Your time will be better spent making sure there is nothing in the passenger seat that could cause a run in your girlfriends or wifes panty hose. Now if your going into the world of "Massive power Adders" like huge blowers and turbos that look like they would work on a jet engine then you might be able to notice a big enough difference to worry about it. My bet is anybody on this site working with those engines arn't asking the question since they know alot more about engines then most professional mechanics. As far as fuel efficency concerns, there might me a 1-2% advantage of one over the other. Your better off looking into gears, transmissions, tires, air intake system, and even the various lubricants through out your drive terrain before I'd worry about the Bore to Stroke possible savings.
 

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Rod/Stroke Ratio - 400 SBC

With the stock 400 con rod length being 5.565 vs the standard small block rod of 5.7 my understanding is that running the 5.7 rods obviously will increase the rod to stroke ratio. In fact it increases from 1.48 stock to 1.52 using the longer rods. With a 350 cid ratio being 1.64, is this slight increase in the 400 ratio worth changing to the 5.7? And why exactly are we trying to increase this ratio. How about the piston compression heght? Are there issuse created here with the 5.7 rods? I'm assuming that the higher the ratio, the less sidewall loading on the cylinder bores. Are there other advantages to running the longer rods? Preliminary plans here are for a large cube small block with a factory 400 block - torquey street motor with a max rpm of approx 5500.
 

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Are you buying new parts? It's probably easier and cheaper to buy 5.7" rods and pistons to match if you do. Here's some numbers:

Connecting Rod Length Comparison
By Rick Draganowski
[email protected]

Piston movement was computed by simulating the crankshaft/connecting rod/piston assembly in several precise engineering drawings (DesignCad) and then determining the exact amount of piston movement for each of 256 divisions of one rotation.

The piston movement data was then used as an input vector in a MathCad program to calculate velocity, acceleration, and dynamic forces.

The simulation of an infinitely long connecting rod, which imparts true harmonic motion to the piston, is the starting point.

The motion generated by a finite length connecting rod is quite distorted by comparison. It has much more velocity and acceleration at the top of the stroke compared to the bottom. A graph of the movement is peaked at the top of each cycle and rounded and flattened at the bottom. This is caused by the rod angle increasing and pulling the piston down and adding to the motion caused by the crankshaft rotating down from top dead center. At the bottom as the rod journal slows the angle decreases. This retards the movement of the piston by subtracting the rod angle component that was added at the top of the stroke from the crankshaft movement component at the bottom of the stroke.

Compression and combustion pressures are in opposition to the inertial forces so the top of exhaust and intake strokes generate the largest forces on the rod.

1) Maximum Piston Acceleration

This table is for a 3.75" stroke used in a 400 0r 383 small block Chevy engine.

------infinite rod--------6.0" rod---5.7" rod---5.565" rod

5000rpm 1332G 1749G 1776G 1790G

6000rpm 1933G 2525G 2558G 2578G

7000rpm 2631G 3437G 3482G 3509G

Percent difference due to rod length in above table.

Difference between 6" rod and 5.565" rod 2.34%

Difference between 6" rod and 5.7" rod 1.54%

Difference between 5.7" rod and 5.565" rod 0.79%

This table is for a 3.48" stroke used in a 350 or 305 small block Chevy engine.

------infinite rod---------6.0" rod---5.7" rod

5000rpm 1240G 1600G 1623G

6000rpm 1786G 2305G 2338G

7000rpm 2432G 3138G 3182G



2) Maximum Connecting Rod Dynamic Load (Tension)

This table is for a 3.75" stroke used in a 400 or 383 small block Chevy engine. The forces are based on the weight of the piston and pin assembly and do not include the percentage of force generated by the acceleration of the end of the connecting rod. The reference piston is the stock replacement Silv-O-Lite piston for a 400 engine.

------infinite rod-----------6.0" rod-----5.7" rod----5.565" rod

5000rpm 2249LBS 2938LBS 2976LBS 3000LBS

6000rpm 3239LBS 4232LBS 4287LBS 4320LBS

7000rpm 4409LBS 5769LBS 5834LBS 5849LBS

Percent difference due to rod length in above table.

Difference between 6" rod and 5.565" rod 2.34%

Difference between 6" rod and 5.7" rod 1.54%

Difference between 5.7" rod and 5.565" rod 0.79%



3) Maximum Rod Angularity

This is the angle the connecting rod makes with the axis of the cylinder bore at 90 degrees after top dead center (maximum excursion from bore axis. This measurement is for the 3.75" stroke of the 400 and 383 only.

6.0" rod-----18.21 degrees

5.7" rod-----19.20 degrees

5.565" rod-19.69 degrees



4) Cylinder Wall Load

Percentage of compression and combustion force against the top of piston transmitted to the major thrust face of the piston and then to the cylinder wall.

This table is for the 3.75" stroke.

6.0" rod----32.89%

5.7" rod----34.83%

5.565" rod-35.64%

This table is for the 3.48" stroke.

6.0" rod---30.31%

5.7" rod---32.05%



5) Piston Speed

Maximum piston speed for the 3.75" stroke at 5000 rpm.

Infinite rod---81.68 feet per second, 55.69 MPH

6.0" rod------85.64 feet per second, 58.4 MPH

5.7" rod------86.01 feet per second, 58.6 MPH

5.565" rod---86.20 feet per second, 58.8 MPH



6) Effective Stroke

Because of the mechanical advantage provide by the toggling effect of the rod the shorter rods act as if they were in a longer stroke engine at the top of the stroke. This effect would make the short rod engine rev faster from 2000 to 4000 rpm and the circle track people claim that acceleration out of the turns is significantly improved with the shorter rod. In all other factors the longer rod comes out superior...

Effective stroke as compared to the infinite rod model for the 3.75" stroke.

infinite rod-=- 3.75"

6.0" rod------- 4.20"

5.7" rod------- 4.23"

5.565" rod---- 4.25"

Note that the differences are subtle...



7) Dwell Time

This measurement is of the number of crankshaft degrees the piston is within 0.250 inches of top dead center. It is the subject of much conjecture and controversy in the automotive literature.

This table is for a 3.75" stroke used in a 400 0r 383 small block Chevy engine.

Infinite rod---59.853 degrees

6.0" rod------52.397 degrees

5.7" rod------52.071 degrees

5.565" rod---51.915 degrees

Percentage difference in dwell time between the 6.0" rod and the 5.7" rod is 0.626%.

Percentage difference in dwell time between the 5.7" rod and the 5.565" rod is 0.3%.

Percentage difference in dwell time between the 6.0" rod and the 5.565" rod is 0.928%. (Still less than 1 percent)



This table is for a 3.48" stroke used in a 350 or 305 small block Chevy engine.

Infinite rod---62.188 degrees

6.0" rod------54.929 degrees

5.7" rod------54.605 degrees

Percentage difference in dwell time between the 6.0" rod and the 5.7" rod is 0.593% at the 3.48" stroke.



8) Author’s comments:

The data in this report seems to indicate that the differences between the rod lengths are exaggerated in the literature. In many (most) cases claims are anecdotal and represent the vested interests of the suppliers. I have seen no objective dyno testing of rod lengths but keep hoping for one.

There are real gains to be had by going to longer rods but they are small, usually a lot less than 2 percent. However, the hard-core racers are grasping at every tiny bit of performance and can justify the expense. For the more average rodder I would suggest staying with the rod length specified by the factory. Money would be far better spent on improving the heads, cam, and induction and exhaust systems. (and perhaps a supercharger..)

http://www.rustpuppy.org/rodstudy.htm
 
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