Ideal Compression ratio
Thread Starter
!Dial-up Director
Joined: Nov 2001
Posts: 3,100
Likes: 1
From: Louisiana
Ideal Compression ratio Say someone were to have the following setup, what would be the ideal compression ratio given these conditions..
Stock Block and Crank
Ported Heads / Mild cam
Forged rods / pistons
More then adequate fuel system ( adjustable fuel pressure )
Cold plugs ( .030 range ) / stock coils / taylor wires
Turbo / air-air Intercooled
10psi on 93 Octane
15+ psi on 104+
Where does the CR become to low that it will perform poorly down low, and when does it become to high that the risk of detonation. What factors play in to this?
Is it more efficient to lower comprsseion by using an inverted dome piston or using larger chamber heads?
Justin
<small>[ December 05, 2002, 07:33 PM: Message edited by: Jsears8 ]</small>
Stock Block and Crank
Ported Heads / Mild cam
Forged rods / pistons
More then adequate fuel system ( adjustable fuel pressure )
Cold plugs ( .030 range ) / stock coils / taylor wires
Turbo / air-air Intercooled
10psi on 93 Octane
15+ psi on 104+
Where does the CR become to low that it will perform poorly down low, and when does it become to high that the risk of detonation. What factors play in to this?
Is it more efficient to lower comprsseion by using an inverted dome piston or using larger chamber heads?
Justin
<small>[ December 05, 2002, 07:33 PM: Message edited by: Jsears8 ]</small>
Re: Ideal Compression ratio the only larger chambere'd heads we have (6.0's) dont move the compression much..
the popular compression ratio for a street/strip car is around 9.0
i'm planning on about 15psi on 93 octane with 8.75:1 but thats with the smaller of the 2 turbos.
the popular compression ratio for a street/strip car is around 9.0
i'm planning on about 15psi on 93 octane with 8.75:1 but thats with the smaller of the 2 turbos.
Thread Starter
!Dial-up Director
Joined: Nov 2001
Posts: 3,100
Likes: 1
From: Louisiana
Re: Ideal Compression ratio Thanks Mike, so let me ask you this..
I have 5.3L heads milled .015 for a 11.3:1 compression ratio with stock pistons. Would you keep these and just use an inverted dome piston to drop the compression down to 9.5:1 or switch to the 6.0L heads and an inverted dome piston?
Justin
I have 5.3L heads milled .015 for a 11.3:1 compression ratio with stock pistons. Would you keep these and just use an inverted dome piston to drop the compression down to 9.5:1 or switch to the 6.0L heads and an inverted dome piston?
Justin
TECH Apprentice
Joined: Jan 2002
Posts: 320
Likes: 5
From: Nottingham, Notts, England, UK
Re: Ideal Compression ratio Hi Justin. The main reason as I see it for lowering the static compression ratio is so that when you are 'on boost' the cylinder pressures don't become so high as to damage the engine. I can't comment on your set up but plenty of people run 10 psi safely on stock engines with stock pistons (I'm not talking specifically about the LS1). I saw something interesting on the Haltech site about an LS6 engine which was boosted with stock pistons. I think they failed at 14 psi but check it out for yourself. I found it quite interesting. I found on my own stuff that 8-9:1 is really good. You want to have at least 5 psi reliablt to have fun. I have gone to 7:1 on V6's with tight squish bands and they have still been really responsive to the throttle. If you stick with stock bottom and modest/low boost it should be ok or you could lower comp with 6.0 heads. If you decide to spend money on forged pistons then you can pick your own compression ratio and not change the heads. If your not after mega power then the lower comp heads might do it for you. You may find that once you do this you become addicted and want more. You could aim for 8.5:1 with the forged pistons and stock heads. This gives you the option of 5.3 or 6.0 heads later on depending on if you like the engine. Mike.
