FueledSoul

iTrader: (18)

I have read theres a rule of thumb, That cast pistons are good for 1 horsepower per cubic inch in a performance oriented motor (I.E road racing, drags etc) if thats the case given that a 400ci engines bore is 4.125" and if the rule of thumb applies a 400 piston can take 400 horsepower loads but a 305 with 3.735" bore and if the rule of thumb a applies 305 horsepower obesvsly this is a genreal gide line or thumb rule. but how could a 400 pison take that much over a 305 psiton of same material? There is less surface area on the 305 piston wouldn't the 305 cast piston take more in terms of loads? I know theres different variables. im not sure what this rule of thumb means - (consistent abuse without failure?). I have seen and heard of stock pistons regardless of motor size take 150 shoots of nitrous or used with a forced induction system with 8psi in the 9.5:1 compression area. detonation is one of the leading failures to cast pistons. does anyone know the braking points of the cast pistons as in how much PSI it could take or the max compraion level , stress levels, tensile strength, impact strength, low - max temperatures etc. . .

Sonix

iTrader: (1)

Good lord you're overthinking a rule of thumb.
A 400cid piston can "accept" more HP (theoretically, according to the rule of thumb) due to the fact that a piston will typically fail simply due to over-revving it. That's the hardest thing on a piston (or rod, or crank)... RPM is higher stress than compression pressure. That's why a turbo charged 500HP 305 will live, but a 500HP 7500RPM 305 will not. (exaggerated example).

So, in order to get 400HP, a 400cid motor will rev lower than a 305 engine. Hence it'll make the power at a less destructive RPM.

Remember - rule of thumb. It's pretty vague though, don't bet money on it.

AlkyIROC

I never heard of a cast piston rule of thumb.

Back when I had a cheap 383 with cast pistons, I was pumping out about 500-550hp with it. It already had a lot of street miles and after racing it for 2 years and 200 1/4 mile passes, something finally failed. I don't know if it was the cast pistons or the stock 400 rod bolts but spinning it to 7000 took its toll and the engine self destructed. Pulled the heads and intake and threw the rest in the scrap metal.

FueledSoul

iTrader: (18)

hmmm

http://www.popularhotrodding.com/eng...cks/index.html

So if for an example a 305 making 305hp which is 38hp per cylinder if you increase the output to 65more hp = 370hp thats increase of about 8hp per cylinder as a whole that seems like a lot but each individual cylinder making around 8 hp per cylinder over that general rule limit that doesnt seem like a lot? how long would a piston last under lets say an endurance race like road racing or auto cross scenario
iv heard that later stock blocks like mid 80s have hypretec pistons or smiler do to more added silicone? or are they the same casting as older pistons? and just thinking about something else the olds diesel 350 motors had 22.5:1 compression on stock cast pistons. . . so would it be safe to say high RPM (what would be considered high rpm for cast?) and detonation would lead to there failure?

five7kid

iTrader: (14)

"Hypereutectic" pistons are cast using an aluminum with higher silicon content for higher strength, using a modified casting process to keep the material molten throughout the pour. They typically haven't been used in production engines.

A local racer and engine builder uses cast pistons in his blown 400 SBC '37 Chevy pickup racer. His blower uses more power than a stock 305 makes.

Cast pistons can take more power than usually advertised. They just don't like detonation or lean, which you should try to avoid, anyway.

Apeiron

Pistons aren't much of a weak point in a stock rotating assembly.

Sonix

iTrader: (1)

As mentioned with the diesel example, combustion pressure is not the strongest factor on a piston - it's RPM. (or detonation, but that's a different example...)
Pistons are very strong when compressing a gas, or when the gas is pushing it down, but when the rod is yanking it down, that's where it's weak.

FueledSoul

iTrader: (18)

Thats another thing iv heard and also read - rods even recondition rods im not sure if they where
(X, pink, or powdered- kind) as far as i know just the everyday gm rod cant deal with much stress or the longevity of of an endurance race or high rpm drag race and failure is larking around the conner

Apeiron

Stock rod bolts are still going to give out at high RPM long before the pistons will.

FueledSoul

iTrader: (18)

iv read even stock GM reconditioned rods with APR bolts are likely to fail at around 375hp in a road race application not the apr stuff but the rod(s) bend, brake, crack etc etc

FueledSoul

iTrader: (18)

how beneficial would something like this be?

http://www.techlinecoatings.com/arti...ns_Article.htm

BASSETT IROC 85

iTrader: (2)

GM uses cast pistons and powdered metal rods in there crate racing engines for round track. They hold up ok but I would rather have forged pistons anyday.