How to lower compression on my 2004 z06?
10-04-2009, 06:18 PM
#1
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How to lower compression on my 2004 z06? I have a 2004 z06 right now that is procharged (p1sc1), and putting down 509/441 at the tire. Completely stock exhaust incl manifolds. I am running 6psi of boost and have 42lb/hr green tops with a boost a pump and racetronix harness. I want to run more boost, and I want to do so safely because this is a new motor. I read that I could lower the compression into the 9's by changing the heads. My question is what heads do I use in the LS6?
I also understand that while not in boost I will be losing power with the different heads Ill need, but how much power will I sacrifice for this deduction in compression?
Furthermore, how much more boost could one run with compression in the 9'2 vs the stock 10.5:1?
what else would need to be changed with the heads? Would I need different length pushrods?
I also understand that while not in boost I will be losing power with the different heads Ill need, but how much power will I sacrifice for this deduction in compression?
Furthermore, how much more boost could one run with compression in the 9'2 vs the stock 10.5:1?
what else would need to be changed with the heads? Would I need different length pushrods?
10-04-2009, 06:33 PM
#2
the heads most people use to lower compression is 317 truck heads off of a LQ4 truck engine. you can get them from the junk yard or ported from tea of some other sponsors.
10-04-2009, 06:39 PM
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yea, ive been using the search button and figured out I can use the 317 heads. but what will they lower my 10.5:1 compression to? What head gaskets to I need to get? What head bolts should I use, and will there be any need for changed to pushrod length or is the stock 7.4 still right?
am I even on the right track? Will doin this permit me to run above 10psi without the major fear of blowing stuff up as we have running the high compression these things have ?
am I even on the right track? Will doin this permit me to run above 10psi without the major fear of blowing stuff up as we have running the high compression these things have ?
10-04-2009, 06:58 PM
#4
i'm not positive on what you compression will be but your rods and everything else will be fine as they have the exact same design as LS6 heads just with bigger cc combustion chamber.
You could also use GM head bolts for the LS6 but just don't reuse yours because I believe they are torque to yeild (one time use) design. I would either get the ARP's bolts or studs.
Lowering the compression will let you run a little more boost but most will reccomend not using stock pistons and rods past 600 rwhp and your already getting pretty close to that. You should consider saving up and forging the shortblock and using some dished piston. That way you wouldnt have to worry about you shortblock at all, you could then reuse your heads, and if you plan to upgrade blowers in the future you would be fine.
You could also use GM head bolts for the LS6 but just don't reuse yours because I believe they are torque to yeild (one time use) design. I would either get the ARP's bolts or studs.
Lowering the compression will let you run a little more boost but most will reccomend not using stock pistons and rods past 600 rwhp and your already getting pretty close to that. You should consider saving up and forging the shortblock and using some dished piston. That way you wouldnt have to worry about you shortblock at all, you could then reuse your heads, and if you plan to upgrade blowers in the future you would be fine.
10-04-2009, 07:17 PM
#7
Honestly you should be able to make 550 with what you have now, it all depends on a good tuner. Lowering the compression will help by making it easier to add boost on pump gas without detination, so you would benifit. But at the same time if you add to much boost the cylinder pressure will get to high and cause problems.
You ever consider using meth? That would add some hp and allow you to run a little more boost but I wouldn't reccomend going crazy with it because if you ever run out while driving you could have problems.
This is all a cautionary tale, because there are people all over this board that have sprayed 250hp shots of nitrous and run turbos and blower up in teens without problems. Its really up to you if your willing to take the risk and try it. If you dont mind replacing the shortblock or forging it than boost away, but if its daily I would keep things conservative until you get your parts together.
You ever consider using meth? That would add some hp and allow you to run a little more boost but I wouldn't reccomend going crazy with it because if you ever run out while driving you could have problems.
This is all a cautionary tale, because there are people all over this board that have sprayed 250hp shots of nitrous and run turbos and blower up in teens without problems. Its really up to you if your willing to take the risk and try it. If you dont mind replacing the shortblock or forging it than boost away, but if its daily I would keep things conservative until you get your parts together.
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10-04-2009, 07:22 PM
#8
heres the perfect thing for you to check out:https://ls1tech.com/forums/forced-in...lity-list.html
It lists what people have gotten away with on a stock shortblock. some of them switched to 317's so the combo would be basically what your asking about.
It lists what people have gotten away with on a stock shortblock. some of them switched to 317's so the combo would be basically what your asking about.
10-04-2009, 07:22 PM
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hmm, I think I would rather lower the compression if im goin to try it on stock internals. That way in addition to meth (yes im considering meth) I could be running safer.
The question is how much power will I sacrifice by putting these heads on in order to run the additional boost? Will I be able to flow 600RWHP out of the stock 317 heads? Or do they need to be ported? I know that ill want to upgrade pushrods, and valve springs on them as well as use 6.0 head gaskets, and Im prepared to buy arp head bolts.
The question is how much power will I sacrifice by putting these heads on in order to run the additional boost? Will I be able to flow 600RWHP out of the stock 317 heads? Or do they need to be ported? I know that ill want to upgrade pushrods, and valve springs on them as well as use 6.0 head gaskets, and Im prepared to buy arp head bolts.
10-04-2009, 09:33 PM
#12
the 317s are damn near the same as 243s i thought? just a bigger combustion chamber right? and iirc the compression ratio should be around what a lq4 is right? roughly 9.2 to 1?
10-05-2009, 07:47 AM
#16
yea, ive been using the search button and figured out I can use the 317 heads. but what will they lower my 10.5:1 compression to? What head gaskets to I need to get? What head bolts should I use, and will there be any need for changed to pushrod length or is the stock 7.4 still right?
am I even on the right track? Will doin this permit me to run above 10psi without the major fear of blowing stuff up as we have running the high compression these things have ?
am I even on the right track? Will doin this permit me to run above 10psi without the major fear of blowing stuff up as we have running the high compression these things have ?
317's will put you right around 9.5- 9.7:1 depending on your head gastket and final camber volume (lets just say 71cc after resurfacing). Use a GM MLS head gasket and ARP head studs. Pushrods can be the same.
You can run more boost safely and add more timing but you will be on borrowed time if you are on stock pistons. You may need to address your fuel system also.
You may notice a tiny loss in low end power @ 9.5:1 off boost if you are on the stock cam but nothing dramatic. Your best bet is to pm Bob @ EPP and get his recommendations. GL!
10-05-2009, 10:25 AM
#17
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yea, im still on stock pistons, but arent I on even more borrowed time with the stock high compression? I just dont have the cash right now to pull the motor and have the pistons and rods forged. I just paid for a new rpm tranny, and a new clutch, not to mention the s/c kit.
So i got to do what I can do to be safe with the money I currently have. Id love to add methonal, and maybe run 10-12 psi, which I think would be alright with the lower compression, upgraded to 317 heads, and some nice valve springs.
So i got to do what I can do to be safe with the money I currently have. Id love to add methonal, and maybe run 10-12 psi, which I think would be alright with the lower compression, upgraded to 317 heads, and some nice valve springs.
10-05-2009, 04:10 PM
#18
10+ psi on the stock pistons and it won't last. Even if you eliminate all detonation with meth, the pressure will most likely break a ring land. I wouldn't run more than 8-9 lbs max on stock bottom end especially if you don't have the money to build a new short block. You need a intercooler and 60lb injectors too.
10-05-2009, 04:35 PM
#19
not to jack the thread, but I got a set of 40k mile stock heads for 250 shipped. One header bolt is broken off, so it will need to be extracted. PM me if you're interested
10-05-2009, 04:38 PM
#20
10+ psi on the stock pistons and it won't last. Even if you eliminate all detonation with meth, the pressure will most likely break a ring land. I wouldn't run more than 8-9 lbs max on stock bottom end especially if you don't have the money to build a new short block. You need a intercooler and 60lb injectors too.