compression equals power, sooo

[tontot77]

so my engine is a 4.6 4v with a GT40 turbo at 8 psi... I used to be making 470 hp and 490 lbs of tq... but that was at stock compression. I had Tim lower the compression to right around 9.0:1 so do any of you engine Guru's that lurk around stangnet have any guess as to how much power I will lose with a lower compression at the same psi?

 

[White360RFnSwee]

what is stock cobra compression?

That means you can turn the boost up..

 

[Aaron 4.6]

I expect you might lose 15-20 hp. Compression makes power, but low compression and high boost makes a lot more power than low boost and high compression...

 

[Route666]

with the same boost I would estimate

new power = (original comp ratio / new comp ratio) * old power.

 

[Route666]

make that new / old lol DOH!

 

[98superstangGT]

make that new / old lol DOH!

there is no way that can be right????? Thats saying its dropping hime down to around 430 or so hp. Isnt the cobra's compression like 9.8:1?? If it is and your dropping down to 9.0 then you might lose about 15 or so at most. Not 40 or so hp like that equation was giving you.

 

[mogs01gt]

same timing? or is that the trick question part you are going for .

 

[tontot77]

I do plan on turning the boost back up so that I run back around 500 hp, but... not until I can get a new dyno tune and chip burned... I'll post more after I get home tonight... like the current a/f ratios

 

[mogs01gt]

what about timing

 

[Aaron 4.6]

with the same boost I would estimate

new power = (original comp ratio / new comp ratio) * old power.

I'm not saying this to be insulting, but that is a blatant guess and wrong to boot. There are some pretty fundamental physical laws that can be expressed as ratios, but this is a much more complicated system than that. Desktop Dyno would not be a very powerful tool if we could use systems like the one above and a simple calculator.

 

[Route666]

there is no way that can be right????? Thats saying its dropping hime down to around 430 or so hp. Isnt the cobra's compression like 9.8:1?? If it is and your dropping down to 9.0 then you might lose about 15 or so at most. Not 40 or so hp like that equation was giving you.

Yeh, it works for na more, with a turbo the cylinder would fill easier, so you would get a little more in, so it wouldn't drop quite so much, I agree. It was just a roughstimate.

 

[tontot77]

same timing, and whats the compression ratio in the new 03 cobra's?

 

[twidge]

same timing, and whats the compression ratio in the new 03 cobra's?

8.5:1

I vote you lose 8 RWHP all across the board @ same timing, same boost, etc.

 

[tontot77]

8? wow, thats an optimistic guess, I hope your right on the money... Whats the stock 03 cobra run as far as psi? I'm trying to figure out how much boost I can run in the future...