Compression ratio too low?
12-04-2005, 02:15 PM
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Compression ratio too low? I am in the process of rebuilding my motor for a Turbo set up that I have. I have a set of 6.0L heads, -9cc Mahle pistons, and forged connecting rods. I am using some online calculators and coming up with around 8.7 CR, is that too low for FI and a stock 346 block. The piston are going to make the bore go to 3.905. My tunner told me to try to keep the CR around 8.8-9.0 I dont want to be to low and I dont know what kind of boost I can push with these CR.
Please some of you that have done this let me know what you think.
thanks
Please some of you that have done this let me know what you think.
thanks
12-04-2005, 02:23 PM
#2
I think 8.7 is pretty good... a lot of people go as low as 8.5:1 and maintain good driveability. The only thing I would watch on that Mahle piston is whether or not it is a full dish or an inverted dome... the full dish pistons don't have a quench deck and I'm not sure if that is good or not for the chamber design on the LS1 heads.
12-04-2005, 02:25 PM
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If you're using methanol then I'm not sure why you're trying to keep the CR low.
If you have a good tuner then you may be better off discussing this with your tuner.
If you have a good tuner then you may be better off discussing this with your tuner.
12-04-2005, 02:51 PM
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The pistons are dished a little with a flycut to get the -9cc.
As for the Meth I am running that just to give me lower intake temps and more fuel. I dont know if I will need it after I do this motor overhaul
As for the Meth I am running that just to give me lower intake temps and more fuel. I dont know if I will need it after I do this motor overhaul
12-04-2005, 02:55 PM
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Originally Posted by white2001s10
If you're using methanol then I'm not sure why you're trying to keep the CR low.
If you have a good tuner then you may be better off discussing this with your tuner.
If you have a good tuner then you may be better off discussing this with your tuner.
12-04-2005, 04:07 PM
#7
i have almost the same setup...diamond -8.6cc pistons and 6.0 heads and my c/r is around 8.7-8 on a 346. It is fine as far as driveability when not under boost. I could run 15 psi with no meth on 93 octane with about 15 deg total timing. I now run meth and have even run 16 psi..15 deg of timing with NO intercoolers while the leaks were being repaired on 93 octane
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12-04-2005, 07:07 PM
#9
as far as meth failing...my Dynojet wideband commander has a bright led that the software let me configure to tell me if the a/f gets leaner than 12.0 if i'm over 4000 rpms...when my hobbs switch for my 2nd pump failed...the red led immediately made me get off the gas
12-04-2005, 09:46 PM
#12
Wow... 15psi non-intercooled AND no meth?! How'd you manage that?? Also, did it run any different without the intercoolers??
Also, do you run a stock MLS gasket to get that CR? I think I am going to go with those same Diamond pistons, and I already have the 317 heads.
Also, do you run a stock MLS gasket to get that CR? I think I am going to go with those same Diamond pistons, and I already have the 317 heads.
Originally Posted by cablebandit
i have almost the same setup...diamond -8.6cc pistons and 6.0 heads and my c/r is around 8.7-8 on a 346. It is fine as far as driveability when not under boost. I could run 15 psi with no meth on 93 octane with about 15 deg total timing. I now run meth and have even run 16 psi..15 deg of timing with NO intercoolers while the leaks were being repaired on 93 octane
12-05-2005, 06:40 AM
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Originally Posted by FastKat
Wow... 15psi non-intercooled AND no meth?! How'd you manage that?? Also, did it run any different without the intercoolers??
12-05-2005, 11:27 AM
#16
Okay, my bad... I get it now. Still pretty impressive though!
Where do you hit peak torque? and are you using a stock GM MLS head gasket?
Where do you hit peak torque? and are you using a stock GM MLS head gasket?
Originally Posted by cablebandit
correct...15 psi with either meth and no intercoolers or
intercoolers and no meth.
Of course with both you can run more..just posting what i have done. Now i have the intercoolers back on and even more meth
intercoolers and no meth.
Of course with both you can run more..just posting what i have done. Now i have the intercoolers back on and even more meth
12-09-2005, 04:38 PM
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I talked to Duttwieler himself. He was actually in the process of dynoing a tt ls1! He sai no lower the 8:1 is recommended.
I run 8.1:1 and the car is insanely fast. From a light, a roll, it does'nt have any lag. Keep in mind when you take a motor that already has 400 hp to start with, you are not going to have turbo lag. I make about 900 hp right now and I have not even really tuned on it yet. And that is on pumpgas!
I run 8.1:1 and the car is insanely fast. From a light, a roll, it does'nt have any lag. Keep in mind when you take a motor that already has 400 hp to start with, you are not going to have turbo lag. I make about 900 hp right now and I have not even really tuned on it yet. And that is on pumpgas!