ArcticWhite

I've been slowly collecting parts for my LT1. I plan to do ported blower, ported LT1 heads, cam, upgraded heat exchanger, and meth kit. The car will be run 90% of the time on 91 octane fuel. I am putting an aux fuel system and LT4 HPFP and injectors on it for the odd time I will run E85. I have to order E85 in by the barrel, so it won't be that often.

I'm going to be doing rods and pistons as well.

I'm hoping for 700+rwhp.

I'm curious if I should be dropping the CR to 10.5:1 like the lt4 due to my access to only 91 octane, or has 11.5:1 still worked well with this type of setup at those power levels?

Joshinator99

If you’re doing pistons anyway, then just go to 10.5 compression now. With only 91 to work with, you’ll hit the octane wall very quickly with higher boost levels and 11.5 compression. So, just go for 10.5 now.

blue_bomber697

If you are ordering in custom pistons, I was recommended to go to 10.5:1 and thats what I'm at. I'm far from an expert in the subject, but I was told its better for boost if you have the option. Haven't run into any negatives from it.

0Billy@MTI

Higher static is never a bad thing. Less boost, lower IATs.
Billy

robert miller

I agree with you here Billy if you looking at a race car only & 25 to 35 lbs of boost & 1300 plus rwhp I would say yes then go with the lower comp on the motor. But for a street car 650 to 850 rwhp on just LT4 inj & pump & a cam fuel increase. I am in this here & went with the 11:5 :1 on my set up...with meth..Robert

0Billy@MTI

That last C7 we did made 923hp on 12psi..... High static is the reason why it makes so much power, on so little boost. Btw the IATs only went up 8 degrees for the start to finish of the pulls and weren't over 100 degrees without the meth hitting the air temp sensor.
Billy

Joshinator99

I suspect that was not 91 octane at 11.5 compression when you made that run... likely E85 or meth?

ArcticWhite

He posted a thread that says 93 + meth for that setup to hit 923hp. This was on a D1X blower.

Joshinator99

So, if your original post was regarding 91 octane with infrequent E85, then that’s not a very relevant example IMO...

0Billy@MTI

93 and meth, but I don't turn up the timing on any of our meth injected cars. I tune them just like it only is running 93.
Billy

Joshinator99

Which is perfectly fine. I agree with that approach wholeheartedly. That way you don’t have major problems if the meth system goes down. But the meth is definitely having a cooling and anti-knock effect on your build, to be sure. My point was, the thread was regarding a guy stuck with 91 octane only with occasional E85. I just didn’t think your D1X build with high compression using 93+meth is a great comparison in this particular situation. Not saying it’s not a great build though!