Best compression ratio for N/A ls7
12-22-2015, 10:26 AM
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Best compression ratio for N/A ls7 i have purchased all the parts for my H/C/I and making sure everything is how i want it before i tear the car down. ive heard different people tell me what compression ratio is best. so heres what ive got. its a 2007 with 17k miles. i have bought PRC 285 LS7 heads milled to 68cc chambers. if i run those with stock gm gaskets ill have close to a 11.2:1 CR. if i run a cometic .40 head gasket ill be close to 11.47:1. ive heard some say 12.0:1 would be fine too. other mods include fast 102 ported to match heads, morel 5290 lifters, nw 102, callaway honker, BTR stage 4 cam ( cam motion 8620 core), ATI 10% super damper, katech red ported oil pump, katech c5-R chain, kooks long tubes, kooks o/r mid pipe, borla atak acle back, 160 therm, all arp hardwear, etc. im wanting to break 600 rwhp so i really want to make sure i dont miss any details. what CR's are all the N/A 600+ rwhp c6 z06's running?? anything else im missing that i should do while doing install?
12-22-2015, 01:33 PM
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68 cc heads with a stock short block and GM .051 MLS gaskets is a touch more than 11.2:1. Also, the Cometic .040 gaskets may get your quench a bit tight, depending on piston-deck clearance. The pistons can be up to .005 out of the hole. That would put your quench at .035...That's absolutely as tight as I'd go, and that is not leaving much margin for error. You don't want the pistons hitting the head. You will also have to verify PTV clearance. Measure your piston-deck clearance, and then you'll know for sure, where you stand.
I put 25k on my 600rwhp setup, running around 11.7:1. I only ever ran it on 93 octane. My new setup is going to be crowding 12:1 now, due to different pistons. Its going to be on the edge for pump fuel I feel. Some say 11.5:1 is too much for pump fuel, but I know quite a few who are doing it, without much change to the timing tables.
I put 25k on my 600rwhp setup, running around 11.7:1. I only ever ran it on 93 octane. My new setup is going to be crowding 12:1 now, due to different pistons. Its going to be on the edge for pump fuel I feel. Some say 11.5:1 is too much for pump fuel, but I know quite a few who are doing it, without much change to the timing tables.
12-22-2015, 01:54 PM
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68 cc heads with a stock short block and GM .051 MLS gaskets is a touch more than 11.2:1. Also, the Cometic .040 gaskets may get your quench a bit tight, depending on piston-deck clearance. The pistons can be up to .005 out of the hole. That would put your quench at .035...That's absolutely as tight as I'd go, and that is not leaving much margin for error. You don't want the pistons hitting the head. You will also have to verify PTV clearance. Measure your piston-deck clearance, and then you'll know for sure, where you stand.
I put 25k on my 600rwhp setup, running around 11.7:1. I only ever ran it on 93 octane. My new setup is going to be crowding 12:1 now, due to different pistons. Its going to be on the edge for pump fuel I feel. Some say 11.5:1 is too much for pump fuel, but I know quite a few who are doing it, without much change to the timing tables.
I put 25k on my 600rwhp setup, running around 11.7:1. I only ever ran it on 93 octane. My new setup is going to be crowding 12:1 now, due to different pistons. Its going to be on the edge for pump fuel I feel. Some say 11.5:1 is too much for pump fuel, but I know quite a few who are doing it, without much change to the timing tables.
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12-22-2015, 04:33 PM
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As far as 12:1 on stock bottom ends...a .030" cut from stock heads (65cc chambers) and a .040 head gasket would get you there. Would just have to make sure there is no PTV clearance issues, as you just moved the valves .070" closer to the pistons.
Last edited by MyLS1Hauls; 12-22-2015 at 04:37 PM. Reason: Updated gasket info
12-22-2015, 05:12 PM
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If you check how far the pistons stick out (ideally check cylinders 1,7,2,8, as they may not all be the same), and it is less than .005", then I'd possibly try the .040 Cometics. Some claim that Permatex copper spray on both sides is required, to lessen the chance of coolant leaks. May want to look into that. I haven't personally used them. Have you talked to Tooley about it, since you're running his cam? Know that running quench distance that tight is pushing the envelope...will help resist detonation, but there is less margin for error with piston/valve/head contact. EDIT:Cometic does make a .045 gasket as well, so that would buy you a bit more piston to head clearance, if you felt it was required.
As far as 12:1 on stock bottom ends...a .030" cut from stock heads (65cc chambers) and a .040 head gasket would get you there. Would just have to make sure there is no PTV clearance issues, as you just moved the valves .070" closer to the pistons.
As far as 12:1 on stock bottom ends...a .030" cut from stock heads (65cc chambers) and a .040 head gasket would get you there. Would just have to make sure there is no PTV clearance issues, as you just moved the valves .070" closer to the pistons.
!
12-23-2015, 10:36 AM
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Going .035" is an ideal goal for a daily driven, high performance street build. At least, that's what every Hi-Po engine builder I've asked have said......
KW
Last edited by KW Baraka; 12-23-2015 at 10:41 AM.
12-23-2015, 02:35 PM
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The OP can do as he chooses, but for an engine such as this, I choose to err on the side of caution. I'm not going to tell someone across the internet to run tight quench, and act like he can do it without thinking twice about it. Last thing I want is for someone to pinch the ring lands, because of advice they received from me. He runs it a little on the wider side and he'll be fine, but a little too tight, and he'll be tearing the short block apart.
TN-If you're serious about being ok with mixing in some MS109, then I'd cut the heads to 65cc, and run a .040-.045 gasket. That should get you to just over 12:1. If you don't want to worry about race fuel, then leave the heads where they are, and run a 40-45 gasket. Good luck with your decision.
12-23-2015, 08:18 PM
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yes we do. they just built a station 1/2 mile from my office that has 4 different selections of e85. however, intake occasional trips out of town and not sure if it would be available there. also, i would have to upgrade fuel system to run E85 right?
12-24-2015, 02:10 PM
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I have a Walbro 255 in tank with a hot wire kit and 85lb injectors. I'm at 14:1 on E85 and log 65% duty cycle. I log fuel pressure too and it stays strong all the time. I have the stock C5 filter/regulator along with the stock main feed line to my fuel rails.
But, I certainly understand the concern about availability when taking a road trip.