View Poll Results: what CR?
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what CR would YOU run?
Thread Starter
TECH Enthusiast
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From: Gettysburg, PA
what CR would YOU run? I know, I know. Overthinking a little but I cant seem to decide with all the info out their. It WILL be a low comp. engine though.
Basic setup will be:
Forged LQ9
billet caps
GM #317 heads
Intercooled ST80R
Meth Inj.
Running up to 15lbs max, untill new pcm.
Basic setup will be:
Forged LQ9
billet caps
GM #317 heads
Intercooled ST80R
Meth Inj.
Running up to 15lbs max, untill new pcm.
Thread Starter
TECH Enthusiast
iTrader: (42)
Joined: Mar 2006
Posts: 725
Likes: 0
From: Gettysburg, PA
yeah i put them close 8.5-9 is what im thinking, it will have -15cc pistons but i can tailor the CR regardless, I want to get the quench as close to .050 as possible and be able to mill just a little off the heads to be sure they are tru.
Pump gas (93 octane), or race gas? If 15#'s of boost is your max, and you'll be intercooled and meth injected on pump gas, you should be fine in the 9.0-9.5:1 range. If on race gas only, I would say 10:1
FWIW, I am running a setup that would take 22-24#'s of boost on pump gas, and I am at 8.8:1.
FWIW, I am running a setup that would take 22-24#'s of boost on pump gas, and I am at 8.8:1.
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Verdad Gallardo If thats the case, then you'll be fine with up to about 9.5:1 on the safe side, but if you plan up to say 18-20#'s of boost, you might want to lean towards the 9.0:1 if you are going to stay on the pump gas.
9.5:1 is what I ended up going to. Only because I had flat tops with -2cc valve reliefs already in the motor and just put a set of stock 317s on with some good springs to bring it down from 10.3 to 9.5:1. Had I known I'd be rebuilding the entire motor I probably would've gone back with some 8.7:1 pistons.
Intresting thread. I'd be intrested to know what all the 7 second lsx cars are running for compression. I have a funny feeling that they are running more then you think, to help with spooling the big turbo's, and they can make the same power with less boost pressure, probably less boost fluctuation between shifts this way as well.
Put this another way, if fuel isn't an issue, what would make more power, 8-1 compression with x amount of boost, or 12 -1 compression with less boost, knowing that no matter which way you go about it, you can only get away with so much cylinder pressure before the head gaskets, studs and pistons will fail?
Put this another way, if fuel isn't an issue, what would make more power, 8-1 compression with x amount of boost, or 12 -1 compression with less boost, knowing that no matter which way you go about it, you can only get away with so much cylinder pressure before the head gaskets, studs and pistons will fail?
not really the discussion here as this has been talked about frequently but for the oposition the happy medium seems to be around 9:1 however I chose 8.5 for max boost on pump gas. Eaqch to his own and every setup is different. If you plan to push it hard and run race gas, go to the track allot, etc than go witht he higher CR. If you are happy with lower boost and max power, again higher Cr but if you want to go all out on the street/track whever and have a better piece of mind on your expensive build than its a no brainer. Gio with a lower CR hands down. Up to about 9:1 I believe you will be ok, meth for the added security too but some believe to think its a bandaid. I have a kit, if I need it and will set it up to mist a bit in for the added effect of cooling and octane/boost, etc.
I'm not really talking about anything that would be on the street, more a max effort race build, track only car. Intresting though, I just wonder what the ratio of boost for what compression is the allowable amount for pump gas, compared to what the ratio is for an all out race setup.
Better yet, if there is a definite # for cylinder pressure for a given fuel, does it really matter how you get to that, wether it be at 5 psi and 12 to 1 compression or 12 psi and 8 to 1
Better yet, if there is a definite # for cylinder pressure for a given fuel, does it really matter how you get to that, wether it be at 5 psi and 12 to 1 compression or 12 psi and 8 to 1
I'm not really talking about anything that would be on the street, more a max effort race build, track only car. Intresting though, I just wonder what the ratio of boost for what compression is the allowable amount for pump gas, compared to what the ratio is for an all out race setup.
Better yet, if there is a definite # for cylinder pressure for a given fuel, does it really matter how you get to that, wether it be at 5 psi and 12 to 1 compression or 12 psi and 8 to 1
Better yet, if there is a definite # for cylinder pressure for a given fuel, does it really matter how you get to that, wether it be at 5 psi and 12 to 1 compression or 12 psi and 8 to 1