which compression is better?

[migsk8]

ok so whats the difference in buying 8:5:1 and 9:0:1 in a boosted car? im not quite sure, all i know is lower is better for boost and helps the tuner. but i also see alot of high HP cars with a slightly higher compression like 9:0:1. someone clear this up for me please .

p.s. i plan on going with boost and fully built engine. and my goals are 400whp, also i want 400 on less than 20 psi.

[Taylor008]

Let's say this first. The higher compression, the bigger the boom. Same way with bombs, if you just light a bit of gunpowder you will see a little sparking, if you compress it and seal it, you will get an explosion. Tighter you pack it, the bigger the boom.

Higher compression is just that. Higher compression. If your running +-20lbs of boost and higher compressrion you will need forged rods and 95+ octane with that set-up. I'm not sure if you can make 400 on less than 20. Unless you mean 19. Lol.

Think about it. Your pushing 19psi into a enclosed area, say a metal box, 5"x5"x5" Which would represent 8:5:1. Then your pushing the same 19psi into a box 4"x4"x4". Which would represent 9:0:1. As you can imagine, the strain on the walls will be greater because of the decreased volume. Now think about this in engine terms. It will be harder on the rods to compress all that into a smaller place, than the stock stroke. Which will in time lead to bent connecting rods and poor compression.

Higher compression engines like the LS1 which is I think 10:1, they don't have to push all that boost in there, so they can have higher compression without sacrificing their engines.

Correct me if I'm wrong.

Hope this helps.

[redtop91]

Correct me if I'm wrong.

The general idea is right except:

If your running +-20lbs of boost and higher compressrion you will need forged rods and 95+ octane with that set-up. I'm not sure if you can make 400 on less than 20. Unless you mean 19. Lol.

This is entirely generic. There is no reason why you would need forged rods running a high compression setup versus stock compression at 400hp. The strain on the pin journals, rod, and rod bolts will be the same. Also how much horsepower you make at a specific boost level has much more to it than just being able to attach a number to a boost pressure. Different turbos flow different amounts of air. If you have a GT6041 you could make 400 south of 20 PSI like cake. Ben (Idahotuner on this board) made 416rwhp on a .64 GT2871R at 20 PSI. Most engines around 8.5:1 make 7 or so hp per PSI so at 19 he'd have still been over 400. It's all relative.

[Hijacker]

9:1 isn't high...even for a turbo setup.

It really comes down to fuel management and tuning.

[DrifterProdigy85]

Its tuning. Theres quite a few people that are able to do near 21psi on 93 octane and 9.0 Compression. Alot relates to how effecient your cylinder head is. I personally run 18-19psi on 93 octane with 9.0 CR. I did this with my 2871R and im doing it now with my T67. A nicely tuned 2871R setup will do around 400whp @ 19-20psi.

[migsk8]

ok so heres whats gonna end up happening, im buying this car with an SR, it has a built bottom end, the compression ratio is 9:0:1. and im prob gonna buy apexi power fc for tuning. hopefully i get a good tuner

[Taylor008]

ok so heres whats gonna end up happening, im buying this car with an SR, it has a built bottom end, the compression ratio is 9:0:1. and im prob gonna buy apexi power fc for tuning. hopefully i get a good tuner

Is the built bottom end the only thing done? Or is there an upgraded turbo or what?

[CSUPUEBLOTIM]

I also am kinda going through the cr debate. I was considering Enthalpy for a tune, but I have access to other stuff as well in my state. We only get 91 octane here with our elevation and I was shooting for at least 350 on up to 400 whp daily driven. I plan to go with CP pistons and head should have all brian crower stage 2 cams and springs and retainers.

[migsk8]

Is the built bottom end the only thing done? Or is there an upgraded turbo or what?

for now the bottom end is like that everything else is stock, i have the rest of the parts sitting around because i dont have the inkectors or the turbo manifold to put it on yet