[Scooter]

How does one know which pistons are light? I've always heard that spending the money to get light pistons is very worthwhile, but I've looked in many cataloges and such and they never seem to list the piston wieght. It just says "light weight" or something like that but no hard facts or actual weight measurements.

Also what is generally considered a lightweight piston? There must be a range of weight that is considerably lighter than stock yet heavy enough not to break too easily. Right now someone could tell me any weight is "lightweight" and I'd believe them simply becuase I have no idea what a performance piston should weigh.

-Aaron

 

[Mike Goble]

Here's a site with various pistons for sale that lists the weight of the pistons:

http://www.flatlanderracing.com/pistons.html

 

[bowtie0069]

JE/SRP lists all the weights on their site. The flyweights start at 300 grams; then you have the 490 gram slugs I run, which is still a fairly light piece. Some are a lot heavier!!

 

[Real McCoy]

You may want to consider what the motor is going to be used for then consider weight next. GM didn't use those heavy TRW forged pistons in all their muscle motors for nothing. They hold up to alot of street driving and abuse. They are still a great piston for the average fast street car. Average street driving is very tough on a motor. That's why Wisco makes flat top pistons for a SBC in so many different styles. The super ultra lites are not street pistons for the average guy. RM

 

[Scooter]

The engine will go into my nova which is my daily driver. It will only see track use for fun runs a couple times a year. I just want a fun powerful streetable engine that I don't have to worry about blowing up. I'm aiming for a 383 with 400-450 HP and Torque.

The main reason I was thinking light pistons were good was becuase they won't put as much stress on the crank and rods. So instead of having to buy stronger crank and rods for the heavy pistons, I'd just buy lighter pistons and use more affordable crank and rods.

 

[sproosemoose]

remember piston speed can change the effective weight of a piston. force is speed times mass. longer stroke=higher speed=more force on the crank and rods.

 

[Paul Wright]

Piston weight is very important. Here's a previous thread on the subject and pix of a comparison of some 327 pistons

 

[69NovaSS]

I guess my question on this subject is what is considered a good weight piston for a street/strip kinda car....400g, 500g, 600g, etc???? I understand that in an all out race car the lightest piston you can get is likely a very good thing and is well worth the money. But for a street car that might see the track 10x a year just for the fun of it the cost of the flyweight pistons may not be worth it...so then you have to compromise...light weight VS cost...what would you consider a good weight for a piston in this type of environment?

BTW for those who may not know 454g is equal to 1 pound...when you think of it that way you can see how having 600+ gram pistons flying around inside your motor might not be the best thing for an all out race car..

 

[Scooter]

69novass you said the question perfectly. That is exactly what I was wanting to know. So now we just need an answer.......

-Aaron

 

[Paul Wright]

Well, in my picture you can see stock 327 pistons weigh about 750 gms and the 350 forged are about the same.
Any engine will fair better with lightweight pistons provided they are durable....but you'll pay for light.
I think you'll notice a difference in the engine with a 250 gram reduction x 8 or a whopping 4.4 lbs.
It won't make much difference in steady state HP but it will make a difference in net acceleration.

Piston acceleration: a=
(3.14 x RPM /30)^2 x (stroke/2) x COS(Crank Angle) + (stroke / (2 x rod_length)) x (COS(2 x Crank_Angle))

Inertia Force: F = reciprocating mass (Piston +rings+wrist pin+small end of conn rod) x a

The maximum strain is at TDC on the exhaust stroke.

 

[69NovaSS]

so if I could find forged pistons in the 500g range that would be pretty good for a street/strip combo?

the following are examples of forged pistons:

TRW L2490F(10.0cr) are 495g for 40 bucks a pop...not too bad IMO...
Federal Mogul LW2256F (9.7cr) are 499g for 33.95 per..again not too bad
SRP Pistons SRP138081 (10.3cr) are 494g for about 50 bucks a pop...still pretty good

How about hypereutecic are they, in general, any good?

Keith Black KB119(11.2cr) are 553g for 30 bucks each..really a good price
Keith Black KB193(9.6cr) are 528g for just over 31 bucks each...again very good price...

 

[Real McCoy]

You'll get alot of opinions from a question like that. If I was building a motor for a street cruiser that I would take to the track a couple times a year I'd use a TRW forged piston and spend some money on a good set of lighter wrist pins. The lighter pins will help with the weight and the TRWs and light pins will still be cheaper than the set of Wisco or JE pistons and you still want the light pins even if you go that way. You decide to spray it down the road those TRWs will live even if you toast it a little. Just my humble opinion. RM

 

[69NovaSS]

piston ring width

This sorta goes with the piston weight thread but I didnt want to highjack the thread with a somewhat related question. (They are related so I combined them anyway~ Paul W.)

So again were talking about a street/strip car (way more street than strip) what is the better choice for ring width? I have read that the 5/64, 5/64, 3/16 ring sets are a better choice for the street than the 1/16, 1/16, 3/16 rings sets. Wadda ya think?

They say(the books I have read) that the 5/64, 5/64, 3/16 will last longer, and have lower oil consumption. While the 1/16, 1/16, 3/16 ring sets will have better high rpm ring seal and will generally consume more oil than the wider rings, along with a reduced ring life span. My understanding is if your motor doesnt see the high end of the RPM range very often then the increased ring seal of the narrow rings is more than offset by their reduced life span and the wider rings would be a better choice.

 

[Mike Goble]

Piston Design, An Evolutionary Tale

http://www.aa1car.com/library/2003/eb40354.htm

Advancements in Piston Technology

http://www.stockcarracing.com/techarticles/3023/

 

[Paul Wright]

Along time ago pistons required 3 or 4 fat rings and two oil rings just to seal the bore due to precision(or lack of it) in those days.
Now a lot of Japanese engines are using narrow 4mm( .157), 3mm (.118) or even 1.2mm(.047") rings. It's all about efficiency, friction reduction AND advances in ring design and machining technology. The Buick 3800 v-6 is one of the lowest friction engines because of these advances and it has very narrow rings. The Chevy V-8 can benefit from narrow rings but piston to bore clearance, ring gap, cylinder concentricity and many other factors I can't tthink of tright now will determine if it works or leaks.
If you are worried about costs and longevity then stay with conventional 5/64" rings and the common Federal Mogul/TRW/Sealed Power forged piston. I think they have them now in weight matched sets with skirt coating and rings.

The only thing to watch out for on some cheaper pistons to check pin fit. Some PN's need pin fitting. If you just hang them on the rods they will seize.

 

[69NovaSS]

Along time ago pistons required 3 or 4 fat rings and two oil rings just to seal the bore due to precision(or lack of it) in those days.
Now a lot of Japanese engines are using narrow 4mm( .157), 3mm (.118) or even 1.2mm(.047") rings. It's all about efficiency, friction reduction AND advances in ring design and machining technology.

So if a bore is properly machined then using the thinner rings should be no problem and might free up a few ponies to boot?

 

[Paul Wright]

Yes...BUT...it requires extraordinary atttention to detail. IMO 8 out of 10 machine shops couldn't pull this off. You could be dissappointed if it doesn't work out. If it does you could be dissapointed with the few HP vs the many extra bucks. If the difference in price between a set of JE's and a set of TRW's causes grief then it's not for you.
A "few ponies" can be gotten cheaper in other ways. I think I'd rather have a set of Total Seal gapless rings rather than 1/16" rings on a street car.

 

[69NovaSS]

Yes...BUT...it requires extraordinary atttention to detail. IMO 8 out of 10 machine shops couldn't pull this off. You could be dissappointed if it doesn't work out. If it does you could be dissapointed with the few HP vs the many extra bucks. If the difference in price between a set of JE's and a set of TRW's causes grief then it's not for you.
A "few ponies" can be gotten cheaper in other ways. I think I'd rather have a set of Total Seal gapless rings rather than 1/16" rings on a street car.

Paul I hear ya on the cost issue....I'm just not sure the more than doubling of piston costs can really be justified in a car that MIGHT see 10 miles worth of track time in a year...on the street those few ponies will really make no difference in the enjoyment of the car...and if I have to compromise in the build somewhere so that I can make it possible I guess I would rather compromise in the all out performance aspect of the car and make it somewhat more affordable and in the end more doable (not that it will be cheap..nothing about these cars is cheap)

If this was a race car and that was its only purpose inlife I would fuly agree with you...and in that instance you either do it right or stay at home (sorta the "If you cant run with the big dogs stay on the porch" kinda thing) BUT in the end it will be a long ways from a race car of any sort

So you would rather use the gapless type ring...what are the advantages of that? What precautions must be understood to run them?

 

[YFH8SIT]

http://www.probeindustries.com/Pistons/Pistons_SRS/Chevrolet/Chev_400_dish.htm

Have you checked out Probe Pistons, there a very reasonable priced piston.

I'll be running the 1/16" comp - 1/8" oil ring by total seal (not the gapless) I was told I wouldn't have any problems using them on the street, I guess I'll find out when I finish the engine some day.

 

[Paul Wright]

So you would rather use the gapless type ring...what are the advantages of that? What precautions must be understood to run them?

If you recall, I made Kev spring for the Total Seal Gapless on his claimer 350.

One advantage with the gapless is there is no gap* (leak path) to grow as the engine wears. The "Claimer" rings were only about $30 more than typical file fit Moly. They do have pricier rings. With gapless you should get lower initial leak down numbers and they should stay lower as the engine wears.

What to look out for is to be sure to hone the cylinder to proper cross hatch with a block plate, makes sure it's straight and round (something that should be done for any ring).

*keep in mind that gapless rings actually do have gaps that have to be filed. It's tedious process so take your time. You'll have your few more ponies but better life expectancy.

I can't emphasis enough that basic foundation for reliable street power is not in exotic tricky tricky stuff that racers use and hope it lasts 500 miles but in careful machine fitting of components to get the best seal and fit.
You'll have more confidence in the short block when you change cams or experiment with manifolds in the future.

You'll see more on the basic techniques as Kev's engine comes together.