dwyer125
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What compression ratio should I run?
I have just assembled my block with forged ross pistons and eagle rods. I have measured the volume of the head and the volume above the piston at TDC with a sheet of perspex and syringing oil in. So I have made a quick compression ratio calculator to help determine the head gasket I should get. It uses volume at BDC/ Volume at TDC. I have attached a pic of the excel sheet if you'd like to see. So my question is basically, what Compression Ratio should I be aiming for? Block is 1mm oversize, gen3 head, ported, 1mm oversize valves, GT3076R with 0.82 A/R, Haltec ECU and W2A intercooler. Thanks
post edited by dwyer125 - 2013/06/07 14:32:48
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MR2QIK
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Re: What compression ratio should I run?
2013/06/07 16:24:30
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What fuel are you planning to run?
For higher boost strategy on pump fuel - 8.5:1
For better response & E85 I'd go with 9:1
MR2QIK - "The Little Car That Could"  320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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just_ace
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Re: What compression ratio should I run?
2013/06/07 17:14:29
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1mm OS in a 3s block? Id go 9:1 and keep boost lower.
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MR2QIK
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Re: What compression ratio should I run?
2013/06/07 17:21:30
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With that turbo on pump, I'd rather 8.5 & more boost so the tarby's in its efficiency range. One thing myself & Hitman noticed with my motors over the years is they respond better to more timing, boost & lower comp when on pump 98.
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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dwyer125
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Re: What compression ratio should I run?
2013/06/07 18:04:25
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BP ultimate will be what's used, E85 isn't around where I am. Yes 3S block
A 1.676mm will get me 8.63:1
A 1.778mm will get me 8.57:1
A 1.905mm will get me 8.48:1
This are all based off my volume measurements being exact, which they wont be but should be close enough.
Thanks again
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MR2QIK
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Re: What compression ratio should I run?
2013/06/08 12:57:59
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Either of the first 2. Too small a difference between em.
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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-Totenkopf-
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Re: What compression ratio should I run?
2013/06/08 18:07:40
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As above. Obviously something to note is that compression ratio given on pistons is with standard headgasket thickness (~1.4mm?). You've done it the right way and measured everything up, but for others your compression ratio may actually be higher then what your pistons are designated at if you are running a 1 or 1.1mm gasket. I had planned on running E85 and was going to run around 9.5:1 CR. BTW, I have found a few things off my car that you may want or need. I have the front plastic trim from above the radiator, I have some wheel arch plastic liner here as well, not sure if it was from my car or another wreck I have had? Umm, what else was there, I think one of the plastic cups from in the door trims. I've been throwing everything I think may have come off to the car to one side. Let me know what you want me to do with it.
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kameleon
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Re: What compression ratio should I run?
2013/06/08 18:13:23
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Agree also. Mines even lower than that, but i don't think you should go as low these days with the slightly better fuel quality we now have in Australia.
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dwyer125
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Re: What compression ratio should I run?
2013/06/16 10:43:23
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Dylmrt is going to set me up with a Cometic for a good price.
My other option for the thickness I need is Apexi, at about double the price.
Is Apexi HG worth the extra $?
Totenkopf, if you have room just leave them to the side if you can and we can work some way of getting them if I need them. I never let you know, the car came off the truck fine, a little scrape when going down as i was sitting in it. I haven't done any work on the car yet, just been building this engine for it while studying for exams.
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MIDN1T3
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Re: What compression ratio should I run?
2013/06/16 10:59:58
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Dywer, I'm guessing that you bought James mr2? If you did, good work mate - good to see its gone to another mr2 enthusiast.. I was thinking about it but just didnt have the time or money at the time.
1990 SW20 MR2 N/A with 1994 Gen 3 GTS 3S-GTE swap.
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dwyer125
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Re: What compression ratio should I run?
2013/06/16 11:30:15
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Thanks Mate, yeah I can't wait to get the time to put it together. But need to sell my Yellow one now.
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kameleon
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Re: What compression ratio should I run?
2013/06/16 19:00:57
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The APEXI race gasket? if so i have that. It is nice but i am sure the Cometic works just as well.
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dwyer125
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Re: What compression ratio should I run?
2013/08/23 15:18:36
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I received my HG today.
I ordered the 1.8mm to get the 8.5:1 CR, as I can only get 98 pump and would like to put the boost up a bit.
But I got sent the wrong one. With this my CR would be just over 8.8:1
Is this going to be an issue or should I ask to get the correct one sent to me? I dont mind waiting, just a bit of a hassle.
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beagle_senior
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Re: What compression ratio should I run?
2013/08/23 16:51:10
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bit of a side note for you mate, in reference to the plastics from james, I am driving up to bris in Oct and again over xmas, if you want I can bring them back down with me, as early next year, round feb-april, i will be in vic for a course for work if you want me to bring them over to you, if you are in no rush for them?
Up to you...
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dwyer125
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Re: What compression ratio should I run?
2013/08/23 23:34:57
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beagle, thanks for that, that sounds like a good plan, gets them a long way closer either way. I'll PM you my contact details
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