[c81zxt]

I am rebuilding a turbo motor and am replacing the stock pistons with cast pistons (forged are just too expensive!) I was wondering what kind of boost I can run. I won't have my intercooler installed when I first get the car running but I do have a '90 supra intercooler that will be installed eventually. I heard that cast pistons can only handle a max of 8psi for short periods of time or they crack. Let's exclude detonation/pinging/running lean from this question. Pretend the engine is running normally.

So... What kind of boost can I run with and without an intercooler that will be safe for cast pistons.

Thanks for the input,
C.Wade

 

[yo2001]

about 6psi. may be more if you coat the piston with ceramic coat.

 

[T4240Z]

The stock pistons are cast and you can still break a forged piston they'll just take a little more abuse. Detonation will be your limiting factor as far as how much boost you can run, especialy without an intercooler as would be the case even with forged. If you're running cast use the turbo pistons, they have a thicker top ring land compared to the non turbos. I'm running 20 psi on them. Just don't let it detonate and you'll be ok. Rattle it once at high boost and it'll be all over with.

 

[ghostkilla2179]

c81zxt said:
"Pretend the engine is running normally. "


hahahahahaha like that ever happens with a z car. lol jk

david karey
socalz prez

 

[Tony D]

If you don't mess with it it will!

If you change for the sake of change, you will ALWAYS be chasing your tail with problems creeping up continually!

Stock? Running Normally? "Detonation not a factor?" Well, you have a contradiction in terms there, c81zxt...

Detonation IS the prevailing cause of failure. Stock pistons or not. Fact is, you will not be able to use the power long enough on hte street to get into stress limits of the pistons UNLESS you detonate. Think about it: how many times have you kept your foot in it, ON FULL BOOST for more than a minute? 30seconds?
In top gear, under full boost, at the 30 second mark, you will be doing 130+. Under high0cruise, the PSI will back off anyway.

I mean, what are your goals? How much can you turn up the wick on a stock bottom end before it blows? Probably 450HP given proper fuel management. You should get (in my mind) an acceptable lifetime out of the engine. By that I expect I could live through a summer before having to tear down the engine and replace the rings and pistons. Doing that every six months will add up to the cost of a forged ste in a year, given the cost of Nissan Ringsets and Pistons new. $600 for a set of thick-dome forged turbo pistons is really the way to go. My plan is to setup the FI system on the cast pistons, and if they go boom, then I replace them with another set. Until I get my fuel maps set up and right, I don't want to risk my forged pistons. Once it's right, and I know more about the FI Tuning, THEN I'll install the forged slugs, and can be reasonably assured of a decent lifespan...