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02-24-2007, 03:36 PM | #1 |
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Location: Woodberry, IN
Vehicle:... ripper's sister. |
Big boost, big cams, high compression?
I'm looking for some insight from those running similar setups.
Essentially I'm doing 272i/e w/ +1mm valve train. I am debating on what route to go compression-wise. I like my high-compression insta-spool, but I'm worried I will have a too low of a threshold for detonation on 93oct if I run another STi HG. Traditionally, I don't trust changing comp ratios by using a different sized gasket, but I am still concerned OEM won't be sufficient. I'd like to run about 23-24ish psi on pump. Anyone have any experience with this?
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02-24-2007, 05:07 PM | #2 |
Scooby Specialist
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Chapter/Region:
Tri-State
Location: '04WRX-Axis ej257, IPT 4eat.
Vehicle:CNC 'd heads, cams DB18g/EWG - F/S $8K |
No experience, but you can have material removed from the combustion chamber to increase volume.
BUT - with better flowing heads and cams, can't you safely run higher compression? I thought it had something to do with better volumetric efficiency or something which makes detonation less likely. |
02-24-2007, 05:12 PM | #3 | |
Scooby Newbie
Member#: 102682
Join Date: Dec 2005
Location: Woodberry, IN
Vehicle:... ripper's sister. |
Quote:
I know the chamber can be shaved down, I was wondering if that could be avoided though. |
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02-25-2007, 09:06 PM | #4 |
Scooby Newbie
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anyone?
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02-25-2007, 09:12 PM | #5 |
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Location: Lou. ky
Vehicle:08 OBP Sti |
Interesting........
I may have to rethink my motor options since the motor i had built for some reason the guy keeps stalling on shipping it. Im still thinking of a jdm v7-8 shortblock + cosmetic gasket though instead of a 2.5l. |
02-25-2007, 10:41 PM | #6 |
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Vehicle:2004 Mitsubishi Evo 701whp 9.91@146 |
DrinkAV8, define "high compression"
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02-25-2007, 10:50 PM | #7 |
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NESIC
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Not sure if your looking to have a motor built for you or whatnot, but if I were you I'd definitely talk to Howard at AR Fab, he does a lot of work with high compression motors and may be able to give you some good insight. His stroked motor had a 10.5:1 compression ratio and he does build a stroked wrx motor with a 9.8:1 compression ratio.
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02-25-2007, 11:14 PM | #8 |
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I am looking to run 9.2-9.5 on my motor...still working out my last bit on the decision before getting the pistons made.
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02-26-2007, 12:45 AM | #9 |
Scooby Newbie
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02-26-2007, 05:40 AM | #10 |
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02-26-2007, 08:06 AM | #11 |
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MWSOC
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Are you using 2.0 or 2.5 heads? When you had the heads machined for the valves, did you have the chamber volume measured? Also, at that time, were the combustion chambers polished?
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02-26-2007, 08:53 AM | #12 |
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Vehicle:2004 Mitsubishi Evo 701whp 9.91@146 |
8.7:1 is not high compression. You will be fine with your setup.
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02-26-2007, 09:20 AM | #13 |
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8.7 is plenty fine so long as you have a good quench pad....
my buddy's evo was seeing 32 psi with meth injection on 93 pump...this was on the factory 16g |
02-26-2007, 12:53 PM | #14 |
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Vehicle:2002 WRX |
Yeah, the cams bleed off some of the pressure due to the overlap so you can run higher compression, i believe that's what you're referring to.
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02-26-2007, 03:16 PM | #15 |
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Vehicle:04 Improved STI Dirty White |
9.2 custom pistons on the EJ257. I will likely go with Cosworth cams, which will effectively lower the dynamic compression somewhat. Cams at 8.2 are a dog at low RPM even with AVCS.
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03-09-2007, 04:56 PM | #16 |
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Vehicle:02 WRX BLAZE YELLOW |
I am debating on which cr to go with on my build. I like running pump gas but there is a gas station 1 mile away with 110.??? Ill either go 8.7:1 or 9.0:1.Leaning towards 8.7 though.
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03-09-2007, 05:39 PM | #17 |
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We are currently running 10.5:1 static compression on our L-time attack car (clock car) This engine always sees race gas.
On a car that sees pump gas I would stay with 9.5:1 static compression or lower.. higher compression can be done depending on application and tune. |
03-10-2007, 08:06 AM | #18 |
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Jeremy what about a 83 mm stroked block. is a 8.7 static CR or higher usable with cams on 91 Calif. pis gas with a smaller turbo.
I'm looking at 102mm bore and 83mm stroke. I want long rods but my BASIC math says problems with keeping the piston below the deck and with a reasonable CR even if I go with smaller pins raised in the piston. Jeremy we need to talk about a stroker block. I have shot your company e-mails but I have had little luck. I'm going for gobs of low end on a small turbo (deadbolt sz55 or bigger) but need a street-able Cr to decide on................... Need to know if the 83 mm crank will work or should I go 81? All depends on the rod angle right? |
03-13-2007, 06:02 PM | #19 |
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RMIC
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Vehicle:1995 95 Impreza red |
I was wondering about this as well. I live in Wyoming and we get 91 octane at best. I am building a 2.2 block with 25 heads from a 98 legacy. I am using a vf 22 and lloking for better response off the bottom. What compression could i safely go with and still push 15-19psi (should be the sweet spot for this turbo correct)? Car will be run off a 95 Sti-ra ecu for a short time with a move to an autronic later.
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