This is a similar problem to the one I am contemplating on. I definately want to go with the LE2 kit but eventually I am going to want to spray the car as well. I don't wan't to have to run race fuel with the N2O nor do I want the car to run like a dog off the spray. What would be the ideal compression ratio for this situation?? And for what its worth, I have seen personally several 12:0+ LT1's that run on pump gas all day long. I don't mean to put anyone downbut I believe a lot of these local shops with "experienced" engine builders are thinking of how the old carbed setups run on high compression instead of modern day fuel injection systems and tuning. With as many guys as there are on this site using Lloyds products I would tend to believe him more than local guys who deal with one maybe two LT1's each year.

 

Ever LE setup has a compression ratio range that it will run well in.... the more compression you have the bigger the cam and higher the RPM range it will run.

LE2 = 10.8-11.2
LE3 = 11.2-11.7

This goes for both 350's and 383's

The difference in a LT1 and a SBC is the small chambers and the reverse cool.... those two things allow more compression ratios to be run with pump gas.

Bret

 

alright looks like i'll be going 11.5:1. Email me back when you get time bret

 

Reverse cooling runs the cold water to the heads first then the block, this is the key for high CR with pump gas. Before I changed out my thermostat and chip for lower fan temp turn on, my LT1 would hit 220/230+ degrees in traffic. Those temps with 12/1 compression would surely ping, but at 190* you'll be OK.
Alot of very good (but old school) engine builders don't know this and stick with the old "10-1 compression for street" rule.

 

i have a 160 thermo too so that shoud help

 

Not to fault anyone but... most of these guys recommending "~10:1 max" just don't understand what's going on. I won't narrow it down to "old timers" cause that just aint fair. The "old timers" who are in the know... know that the static compression don't mean a helluva lot in the scheme of things.

Sure, the LT1's reverse cooling is a factor but it's not anything you can't achieve with a 1st generation block. A big factor in the overall picture is the dynamic compression (DC). If you don't want to do a little study on what DC is then be prepared to leave hp and tq on the table.

You want to be somewhere in the neighborhood of 8.5:1. Mine is actually right on 9.0:1 and I have seen absolutely no signs of detonation.... logged or audible. If you will start worrying more about your final DC then your static build compression, you'll be miles ahead of the 'game....... well, maybe not this one.

Let's hear a big HOORAH for concentrating on the stuff that matters and putting the old wives tales to rest.

-Mindgame

 

BTW,

Welcome to the forum 69.

Don't forget to leave feedback on your other threads. I can tell you from experience... having been around here a little while, that you want to keep the milk cows happy.

-Mindgame

 

How do i leave feedback? Everyone here has been sooo much help to me. i appreciate all the time you all have taken to explain the difference in the dynamic and static compression ratios.

 

Hey, just ribbing you a bit.

I was referring to this thread...

http://web.camaross.com/forums/showthread.php?t=354427

Did you make a decision yet? If you're working with a smaller budget, you definitely want to put that money where it counts. Just trying to send you in the right direction.

Good luck.

-Mindgame

 

Me and bret are working on what combo i should go with so when we figure it out, i'll post up.

 

Thanks for the post Mindgame.....

Guys if you don't take it from me and my experience take it from this guy.... He has more time with motors than most people I know and has had some extremely quick cars and cool things such as 500+ cube SBC motors, not to mention one of the coolest LT1 NA motors made.

Bret

 

Umm, not all us "old guys" are ignorant.

I didn't read this whole thread, but FWIW, relatively "small" nitrous shots don't require any lower compression ratio than an NA setup.They do require the timing be retarded a few degrees. As far as the mechanical components go, a "good" NA piston should stand up to 100-200hp of N2O just fine. Paradoxically, a really premium NA piston may not be what you want for nitrous use. A piston optimized for NA use is going to be designed to minimize mass. It will be strong enough for NA use, but should not have any more mass than it needs to be as strong as it has to be. Of course, that is true for any good design. But the location of a premium NA slug on the mass v. strength curve will be different from a "nitrous" piston or even a "good" vs. a "great" NA piston. The crown will be thinner, the pin thinner, the pin boss area less beefy, etc. To some extent, premium materials will make up for this, but maybe not entirely.

Bottom line: discuss your intended use with the piston manufacturer or a knowledgable engine builder before selecting parts. Don't adjust your CR for small nitrous shots, adjust your timing. Avoid lightweight pistons for nitrous use. Listen to Bret and Mindgame. We are lucky to have them post here, they know their stuff.

Rich (old guy)

 

I guess I'll put my 2 cents in.
The SRS Probe pistons are nice, 2618 alloy, -12.8cc dish, and 412 grams.
Around the same price as the SRP's I think. Mine sit .005 in the hole with a .029 gasket and 53.8 chambers to give me 11.6 static and 8.3 dynamic.
I tried to get all the compression I could without having to swap pistons and this was the highest I could get it. I was shooting for 11.8 but fell short.

BTW, Jeff Creech told me he is running 12.6 cr with a 240 duration cam on 93 octane. Not recommended for the faint of heart.

Dean

 

Good addition Rich,

Also it's good to look at the top ring land depth on pistons to determine what they are good for. I'm using a flat top piston in a turbo motor now.... with the top ring land being .250" down from the top of the piston its in the right spot for turbo/blower and big shots of N2O. I was able to get the CR to where I wanted it with the chambers and still have a good burn, so this will give me a thicker piston than a big dish with a decrease in mass in the piston.... nothing wrong with that.

BTW guys Rich has one hell of a nice blown LT1 motor, it's good to have both these guys around here.

Bret