11.3:1 compression and boost?
Thread Starter
Teching In
Joined: Sep 2004
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From: Olive branch, Miss
11.3:1 compression and boost? So I'm looking at a car thats setup for a 200 shot but I'm not a huge nitrous fan. The car is built exactly like I want other than that though. 12 bolt, 4l80, forged 408, all the good stuff. The only fuel I can really run around here is 93 and meth for boost. Could I make this work with a pro charger or single turbo setup? Or should I just stick with nitrous until I can lower compression with a different set of heads? Car makes close to 500 on motor.
Ehhhh, I think you are maxed out on cylinder pressure before you even start, but it depends a lot on your cam timing. If your running a big nasty cam that bleeds off a lot of cylinder pressure and you pour the water/meth to it, you could run a little bit of boost on 93. What are your cam specs ?
Thread Starter
Teching In
Joined: Sep 2004
Posts: 32
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From: Olive branch, Miss
The cam is decent size and has some overlap. I forgot the exact specs but I think it was high 230's low 240's on duration and I can't remember lsa. I guess I could get rid of the trick flow 220's and go with some 317's or something.
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Thread Starter
Teching In
Joined: Sep 2004
Posts: 32
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From: Olive branch, Miss
which a/c retaining kit would you go with and what turbo for a 408? On3 thinks the 84 with their kit will be good but thompson motorsports didn't like any of the a/c retaining kits for a 408 because of back pressure.
Run 2.5 inch collectors for the 408 and it wont matter if there are a couple extra small bends to make AC work. The back pressure will come from your turbo selection more than the off the shelf plumbing kits.
Thread Starter
Teching In
Joined: Sep 2004
Posts: 32
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From: Olive branch, Miss
Anybody else running a decent amount of boost with compression around 11:1 or a touch higher? Another car I'm looking at has a 408 with flat tops and ls3 heads. I calculate somewhere around 11.25:1. I know my brothers ls3 is 10.7:1 and he's running around 14lbs on 93 and meth. How much would the extra compression hurt me?
I don't know why all the hate is here with high compression and boost. All the Class racing guys that are limited by turbo size run high compression. If you're running meth you can run decent boost and keep it alive if the timing is conservative, and run a lot more than 5 psi. Swapping the heads to a 317 or 70-72cc head is reasonable if you decide you want more cushion, but a goal should be mentioned first before capping on the high CR and turbo.
Thread Starter
Teching In
Joined: Sep 2004
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From: Olive branch, Miss
I was hoping to be able to run 12 to 14 lbs and make 700whp on 93 and meth. I know plenty of ls2 and ls3 guys that are doing this but they are 10.7 and 10.9 compression ratios. I'm wondering how much the little extra compression is gonna hurt me.
a properly sized turbo so backpressure isn't an issue, the right cam, and meth and you'll make 700rwhp no problem at that boost.
even better....more linear power with a blower than with a turbo. I'm about 700fwhp through a stock short block and heads, d1sc with an f13 cam. Stock at with yank 360 stall, stock 10 bolt. That cam you specd has a crap ton of overlap so you'll bleed off a bunch of boost. Which will help keep it together but also sacrifice power. A better cam, a smaller cam, will drive better and make more power.
I like the compression cause you don't need to run crazy high amounts of timing or boost to achieve your goals. Still on the stock bottom end LS3 currently. Ran it to 780 on pump 93 on 12psi and as it sits now with the switch to ethanol it makes 932 on 16psi. New setup is underway and we are shooting for 11.3:1 minimum.