Im building a motor up for two stages of nitrious. One will be a plate TPI setup good for a 150 shot and then the second stage will be for a wet fogger setup, good for 300 shot.

I currenty have a 355 4 bolt block
- h beam forged rods
- scat crank
- Sealed Power forged dished pistons -21.1 d shaped cup
- cast iron heads 64cc

This is on a tpi setup with a superram and cam has not been ordered yet. I plan on buying a progressive nitrious controller among other things.

My question is would i be okay with my low compression, somewhere around 8.5 ? Or would you go higher ?

The reason im running these pistons is because i already have them balanced, they are suppose to handle spray and i like the idea of running cheap gas since gas prices are so high.

 

I don't think low compression is needed to run nitrous, although it won't hurt either. A "wet" system "cools" the combustion by going a bit rich with the fuel, and this is what's making it work without detonation.

Sounds nice the setup you have on your motor, stock L98 heads?

 

Althou running a lower static compression ratio will allow you to get away with a larger shot of NOS with a larger margin of safetey, I'd recomend that if you're going to hit it with a 300hp shot or hit both stages at once that you run 110+ high octane race gas. Even at 8.5:1

 

I have ported L98 heads, but i might buy some sportman II's before i drop it in.

 

I think the going rule is not to add more than 50% additional HP, or the engne will have problems digesting it, making devastating backfiring a possibility.

If you keep it at that youll be fine. But dont add 300 hp to a 280 hp motor..

 

I talked to summit today and they told me that i should use different pistons. They told me to go for around 10:1 and they would swap pistons with me and only charge me a small restocking fee.

 

What happened to the twin turbo setup?

 

Don;t even think about spraying your motor, even a small shot using 87 octane gasoline. Not even once.
Reguardless of the engines compression ratio.
This is a sure quick path to a broken piston.

Use the highest available octane pump gas you can buy if you want to run the juice. At least 92 octane.

87 octane is only good for cruising and commuteing back and forth to work.
If you want your motor to live using Nitrous don't be cheap with the gasoline octane you buy. You won't save your self any $$$. rebuilds ae expensive.

I've seen motors with cheap stock cast pistons live a long life using large shots of juice without a problem.

Its all a matter of having the right tune ( AFR, timing, fuel pressure and fuel octane nessessary)( race gas) . Cast pistons can tolerate the extra power that nitrous creates but cannot tolerate tuning mistakes (detonation, low octane gas, lean mixtures, exessive over heat etc etc)
A forged piston is stronger than a cast piston. Especially in the critical top ring land area.
But if the rings butt hard enough from excessive run away combustion heat and shock ( detonation, preignition) either type piston will loose the top ring land instantly.

A forged piston will just tolerate a little more abuse for a little longer before it too self distructs. If you make a dumb a** tuning mistake, like using 87 octane gas while spraying a motor,
the $$$end result$$$ is going to be the same.

If you plan on giving 'er a big shot, open up the top ring gaps big(er)

 

Thats the kind of input I needed. thanks F-BIRD'88!