Compression
Compression Now I know this subject has been touched on many times. But I cannot seem to get a straight answer. I was just reading reading the Turbo FAQ section in FI and I quote "if you lower the compression ratio in your engine by larger combustion chamber heads, thicker gaskets or dished pistions, this will also allow you to run more boost on the given octane.".
Okay, so my situation is that my CR is currently 10:6 (yes I know its high) with a .045 HG to preserve quench. Now would getting a thicker HG be the wrong way of lowering compression? (I asked in the LT1 forum but not many speculated on it) Or just because its FI should I be ok and be able to turn up the boost. Im thinking no more than .60 HG....
I will be running E85 and meth injection (the meth is only for running 10+lbs of boost on track days)
Any thoughts would be appreciate. Build info in my sig.
Okay, so my situation is that my CR is currently 10:6 (yes I know its high) with a .045 HG to preserve quench. Now would getting a thicker HG be the wrong way of lowering compression? (I asked in the LT1 forum but not many speculated on it) Or just because its FI should I be ok and be able to turn up the boost. Im thinking no more than .60 HG....
I will be running E85 and meth injection (the meth is only for running 10+lbs of boost on track days)
Any thoughts would be appreciate. Build info in my sig.
TECH Fanatic
Joined: Oct 2011
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Personally if you are running E85 I think your compression ratio is perfect. This isn't the old days where everyone wants a low compression engine. I have run 11.0 on E85 with No intercooler, and 25lbs of boost. It only lasted 7 months, but shoot it had 180,000 miles on it and I did nothing to the engine.
I would run a Ls9 Gasket, keep your timing conservative. Meaning around 14-16 at full boost, and run a good 8 range plug. That is a starting point. Most people run 10 something compression now when they build a turbo set up. I think anything under 11 is fine with E85.
I would run a Ls9 Gasket, keep your timing conservative. Meaning around 14-16 at full boost, and run a good 8 range plug. That is a starting point. Most people run 10 something compression now when they build a turbo set up. I think anything under 11 is fine with E85.
Keith at PCM forless told me all his turbo LT1 he builds he runs them at no lower 10:1 CR. I mean Im not trying to run 25lbs of boost. But I thought with a little higher CR and maybe 8lbs I figured that would be a nice medium for the car, since the bottom end is all forged.
TECH Fanatic
Joined: Oct 2011
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I regress. I did not know you were a LT1 engine. When you said you asked on the LT1 Forums I figured they didn't answer you because you were a LS. lol I know nothing about the LT1 and don't want to get you on the wrong track.
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I figured you didnt know that LOL. But either way it goes I think CR is CR. I brought the question over to FI section because their is only a few guys in LT1 who actually understand (ShowNoMercy). I just thought you guys would know a little more about compression and understand my setup
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I would say shoot conservatively, sacrifice your quench with a thicker HG to get your SCR down a bit towards 9.5-10 area and have LE spec you a cam accordingly.
Redoing HG later on is a lot easier than pulling out melted pistons. You also have to worry about someone getting a spot on tune which sad to say is gonna be tough working with an LT1 PCM. Even with E85 I would guess you will have an interesting time on hot summer days if you try to get on it.
I assume you are going to run head studs?
Redoing HG later on is a lot easier than pulling out melted pistons. You also have to worry about someone getting a spot on tune which sad to say is gonna be tough working with an LT1 PCM. Even with E85 I would guess you will have an interesting time on hot summer days if you try to get on it.
I assume you are going to run head studs?
I wish we could cruise someday
. You a long way from me LOL
I just did some calculations. My CR is 10:68 with a .060 MLS HG my CR will be 10:30. Is this cool? Or gasket too thick? I could not find a .055 HG with 4.110 bore. I think 4.40 bore is cutting it to close.........
. You a long way from me LOLI just did some calculations. My CR is 10:68 with a .060 MLS HG my CR will be 10:30. Is this cool? Or gasket too thick? I could not find a .055 HG with 4.110 bore. I think 4.40 bore is cutting it to close.........
I would leave it alone and run the meth all the time on a progressive controller like Alky Control that starts spraying at 3-4psi. Heck, my stock bottom end LS3 is holding together with 13.5psi and 91+meth. I run way less timing than when I ran it on E85+meth, but it's doable. E85+meth I was running 18* of timing for 754rwhp at 11.5psi. On 91 with 11.5psi I ran 14* of timing. Since I just swapped pulleys and went to 13.5psi I'm sneaking back up on it and only have 9* up top right now.
So your advice is to run the 10:6 compression? Or should I just lower it just a tad to around 10:5/10:4 to make things a tad easier. What is the stock CR on a LS3? With a stock bottom end I would be nervous but you made work. So I should be fine.........
10.7 is my stock compression. I just did a 4th gear pull to 6800rpm at 11* of timing and my meth controller maxed out at 8 on the dial. 10.4:1 AFR and no appreciable knock. I'm on 91 octane crap gas too. I'm going to try 12* tomorrow.
On The Tree
Joined: May 2012
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I'm a hair over 10.5 on a gen1 355. 88mm t6, e85, forged pistons, stock rods/crank, eBay A2A. Dynoed 720whp at 15lbs, 18lbs for over a year now. Idle 29°, cruise 34°, wot no boost 32°, full load/boost 17°. Tuning that stock PCM will be your biggest issue probably.
On The Tree
Joined: Nov 2013
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From: Waterford, MI
I have asked this question before, got some good input, I've got a Gen1 332 which is just under 10.5:1 but has a dome top piston so quench is kinda high, BUT I have a pretty big camshaft for the engine and the intake valve closes pretty late, hence the actual cylinder pressures are low.. so I would say depending on your actual camshaft specs if it closes real early your cylinder pressures are going to be much higher, but E85 will handle quite some abuse from what ive read. tuning is key, but all these 5.3's running around most are at least 10:1 and they take 20+ lbs of boost.
Ok cool. I feel better now. I just dropped my CR down to 10:52. And my cam specs are 226/226 with a 114 LSA. So I think I should be on the right path! Ive been reading a lot that LS1 stock bottom end are taking 18lbs and over 800hp to the crank with out blowing up! So even with my 10:5 and forged bottom end I hope to at least get 650rwhp.......
I have asked this question before, got some good input, I've got a Gen1 332 which is just under 10.5:1 but has a dome top piston so quench is kinda high, BUT I have a pretty big camshaft for the engine and the intake valve closes pretty late, hence the actual cylinder pressures are low.. so I would say depending on your actual camshaft specs if it closes real early your cylinder pressures are going to be much higher, but E85 will handle quite some abuse from what ive read. tuning is key, but all these 5.3's running around most are at least 10:1 and they take 20+ lbs of boost.