[The Camaro Guy]

454 30 over with 2broken pistons due to detonation. Going to replace all of them. Current is Hypertech H581P. 600 lift cam stock heads, GM 427 intake, HEI, Holley 750 VA, headers in a 69, 4 SPD, 3:42 Posi. Should I replace the same ones with new, or any other suggestions. Engine has about 5k miles before the racket. Street car driven very little. Had very good power. Built by PO.

 

[LeoP]

If he doesn't see this, message BillK as he owns an Automotive Machine Shop and good luck!!

 

[Ericnova72]

I'd be going forged.....you dodged a bullet that those hypers didn't take the block and more with them when they broke.

 

[Malibu ss 64]

Maybe lower the comp ratio some? Do you know the ratio? Or head cc?
Icon seems like a decent forged budget piston.

 

[BillK]

The Sealed Power piston you have now should be just fine as long as you know what was causing the detonation and fix it first.
What heads are on it ? If they are cast iron heads you are probably pushing the limit for pump gas even if they are open chamber. If they are aluminum heads you should be OK.

You could go with the H118CP and lower the compression some.

The main problem you will have in switching to a different piston is you will probably have to rebalance the crankshaft.

More details on the heads will help making a decision.

 

[pannetron]

If it's a street car that you plan on putting a lot of miles on, I recommend forged pistons made from 4032 alloy. That alloy has higher fatigue strength and doesn't expand as much as the stronger 2618 alloy so you can run a tighter cold clearance. I'm partial to CP pistons.

 

[The Camaro Guy]

Stock oval port heads, 346236, intake 3866948

 

[Malibu ss 64]

Stock oval port heads, 346236, intake 3866948

Depending on exact chamber size and if block is zero decked, gasket thickness and so. Probably 10.2-10.5 in comp. With that comp ratio, iron heads and pumpgas the tune needs to be pretty good. H693CP or some forged pistons like icon 9919 both will put you closed to 9.5:1 but like mentioned you will probably need to rebalance.

 

[68Chevele]

What oct. fuel and how much timing were you running? I just built a 468 with those same pistons but if I run it the engine will have no more than 36° and 110 oct fuel. Any detonation will kill hypers quick.

 

[Tom Mobley]

what the others said. You need to be thinking 9.5:1 max with iron heads. if you're going to run on the edge of detonation you should think carefully about forged pistons even if it involves re-balancing the engine. if the piston weight is close to what you have now you may not need to re-balance.

 

[The Camaro Guy]

Detonation can occur if the builder or parts are in question, like the PO. The cam was not degreed properly as well. Before the "noise" I replaced the carb and distributer, wire and plugs 3 times with hardly any miles, carbon was terrible, my mechanic said I was lucky and probably would not have lasted another 50 miles. Anyway, I cannot ID the cam on the Crane web sight. I have had the car 15 years with a whopping 1000 miles put on it in that time! Here is the number on the cam HIT 292-2 NC 17 40 86, the 7 could be half a 3. The block appears to be fine, rod bearings showing copper wear. My thinking is have the heads gone through, clean up the block, new pistons, same or forged, new bearings and re-balance. Replace the intake, it is a Holley made for GM, 3866948 05 6 date and chrome plated, with an Air Gap. The cam seemed pretty radical so that is still in the discussion. could be the way it was degreed or wrong with the pkg. Thoughts? What is the difference when the piston part # has a P or a CP after the number like H581P VS H581CP

 

[Malibu ss 64]

Detonation can occur if the builder or parts are in question, like the PO. The cam was not degreed properly as well. Before the "noise" I replaced the carb and distributer, wire and plugs 3 times with hardly any miles, carbon was terrible, my mechanic said I was lucky and probably would not have lasted another 50 miles. Anyway, I cannot ID the cam on the Crane web sight. I have had the car 15 years with a whopping 1000 miles put on it in that time! Here is the number on the cam HIT 292-2 NC 17 40 86, the 7 could be half a 3. The block appears to be fine, rod bearings showing copper wear. My thinking is have the heads gone through, clean up the block, new pistons, same or forged, new bearings and re-balance. Replace the intake, it is a Holley made for GM, 3866948 05 6 date and chrome plated, with an Air Gap. The cam seemed pretty radical so that is still in the discussion. could be the way it was degreed or wrong with the pkg. Thoughts? What is the difference when the piston part # has a P or a CP after the number like H581P VS H581CP

Probably a very old crane grind? Somebody might have an old catalog with the spec?
If you dont lower the comp I think you will have problem again.
P vs CP is probably just new part nr basically same piston but the weight can have changed over the years since they moved manufacturing to India. More mordern pistons like the icon I mentioned are lighter. I used SRP 212135 in a 454 I built last year.

But before you buy pistons make sure the bores are ok.