[livewire516]

At what horsepower level would you recommend switching from stock L67/L32 pistons to forged pistons? What I'm really asking is how much boost would you run comfortably as a DD?

 

[jakesq]

From my personal experience of breaking/chipping pistons I think stock pistons would be pretty decent for whatever you could through at them on a stock SC with pulleys that fit without modifying(approx3.0 to 3.2). When I trashed my stock pistons, I looked for the cause. Turned out the stock ring "end gap" was too tight even as checked on used stock rings. When the rings get hot under heavy use, they expand. In my case to the point of closing the gap from expansion. When this happens a lot of drag occurs against the cylinder wall. This drag then is also pressure in the ring grove of the piston. Stock pistons are short on the deminsion from top ring grove to the top of piston. This is the part that most frequently breaks/chips as the rings drag on them. You would have to install new rings and gap them at .020 to .023" to stop this end gap lock up. But, if you are going this far, it would be silly to not use a god set of forged pistons.

All this said and done, however you go, the tune must be "ON" an fuel delivery correct or disaster will still strike. I lost a set of 9.5 diamonds when my fuel pump took a crap at the track.

 

[livewire516]

Thanks for your response,
To clarify, I will be building a turbocharged, intercooled motor (a2a or chem. intercooling i haven't yet decided) from the ground up. But with what you described, that's roughly 9-12 non-intercooled psi?

FWIW: Even though I will be building/machining/blue-printing the motor, I'm not getting forged pistons simply out of principal; I want to make the most of parts I find in swap meets/ salvage yards. Save quick-wear items, I want to pride myself in using a catalog as little as possible. I have no horsepower/ e.t. goals; this is going to be the motor to replace my DD's LT1 in some 50k miles (no rush). If the L67/L32 stock pistons can't take a mild beating, I'll simply build an LM7 or LR4-or for the money difference of the forged pistons, I'll pick up an LLT and deal with the tuning/wiring nightmare. Honestly, I want to build a turbo-buick because the sound of a 90* V6 coupled with a turbo whine is just mean.

 

[1bad6]

Blueprinting and machining really wont save your pistons if your making concernable boost. Your objective sounds like, aside from your principle, is to build on a budget. Jake is giving you reasonably well advice that I believe you could take into consideration. I would invest in forged pistons for strength at this point. Heck, I hate to plan for failure, but if you dont, failure will plan you. Your call here. Building on a buget is not bad, just put the money where it needs to go.

 

[livewire516]

My mistake, I'm not being clear. I was just saying that since I would be building and blueprinting this motor, that I would have no problem choosing different piston rings-I'm well aware what blueprinting/machining does and does not do. The budget is self imposed; like I said, I'd spend that money on a more expensive motor before I buy diamond forged pistons...it's just not as fun! From my hasty research: am I correct in believing that the pistons are the weakest link in terms of an L32's major parts?

I'm still curious if someone could hazard a guess on tolerable horsepower levels for a turbo-intercooled set up while keeping my stock pistons. I will keep the hp down before I go buying aftermarket pistons

 

[chrisb]

well the zzp drag car, ran 8.6 on a completly stock bottom end. l67, it was making 730whp. i know they made over 40 passes on that block and never broke it. They switched to forged pistons because there lighter so they could make more hp as they hit the wall with the stockers. but they never broke. theres a thread where Matt sprayed nitrous and it went lean, blew the stainless gasket out and melted the aluminum head but the stock pistons were still ok. its all in the tune no knock!!

 

[chrisb]

ClubGP Message Forum troubleshooting

 

[livewire516]

40 passes isn't really much but that's somewhat reassuring. Thanks for making me aware of it.

 

[chrisb]

well they had it in for 3 years, and its the one they used for the dyno runs and what not

 

[1bad6]

Stock pistons on the L67, made 730 horses with over 40 runs. Dont know at what boost, but that sounds pretty reasonable. Tolerance levels of the L32's should easily match it.

 

[livewire516]

I know the L32's rods are improved from the L67's but iirc the pistons are identical-are they not?