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How much comp. with pump gas?

  #1  
Old 09-08-2009, 01:13 PM
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Default How much comp. with pump gas?

I have a B20 w/ LS head, it has 12.2 to 1 pistons. The heads have 53.5cc chambers(opened them up, cut the eye-brow's out etc.) The pistons are +7cc dome. I have heard two differnt stoies with this, 1. it will be fine,2. thats alittle high?......
I can see where this might be ok, assuming we can get rid-of cylinder pressure with the cams? (stage 2 BC cams)Open the exhaust early and let some of the pressure out? Is this outta line here or what is your experience with this?
Thanks for your replies.

Thanks, T-flow cylinder heads
 
  #2  
Old 09-08-2009, 01:32 PM
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12.2:1 seems a little high for pump gas, but with the right tune it's not impossible. You're definitely looking at 93+ octane though (anything over 10.5:1 should definitely be running premium). As far as the cams, it won't make a difference. Cams will absolutely do nothing for the CR. The valve timing and overlap are at specific times for three reasons: getting air in, getting air out, and to create a slight scavenging effect in the combustion chamber to aid in both getting air in and out. If you want to lower compression slightly, look into a thicker head gasket.

I also hope you knew what you were doing (or whoever did it did) when you ported the head. Contrary to popular belief, a large smooth area isn't always best. OEMs put small bumps and things like that in the ports to aid in air flow, and shaving them tends to actually reduce flow in the head. It's all fluid dynamics, really.
 
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Old 09-08-2009, 02:21 PM
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I am T-flow cylinder heads, I've been doing cylinder heads for over 10years. Yes, the head is fine.This is my first Honda build, I don't claim to know everthing and have no problem asking ?'s if im not sure. We build alot of Toyota's and have some of the fastest around. But these are all turbo car's and This is my little project so I like to do most of the work. But thanks for your replie, I need all the help I can get.
I am using a .060" head gasket(it mic'[email protected]")
How many cc's per a piont of compression w/ 84mm bore? 5.5cc's ?
 
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Old 09-08-2009, 02:29 PM
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Yes, we have a Flow bench w/ port Analyzer,chassis dyno. We can make 1000+whp w/ 4cylinders, no problem.
 
  #5  
Old 09-08-2009, 02:34 PM
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I'm not questioning your abilities; I'm just pointing out that a lot of people assume because something's smooth, it must flow better than something with a bump or crest in it

Regarding your last question, I honestly can't answer it. I know enough about calculating CR's to get by, but I'm by no means an expert on it.
 
  #6  
Old 09-08-2009, 02:46 PM
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Hey, thank's. That is what I've come up with, I have some spread sheet's for this but it is all done based on sbc,bbc,sbf ect. I can measure it all out, but was wondering if the tune and such was right. Would this be OK, 11.8 ish. comp.? Thanks,
T-flow cylinder heads
 
  #7  
Old 09-08-2009, 03:01 PM
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It's still high, but like I said before, if a tuner knows what he's doing, he should be able to make it work with the right AFR and timing curve.
 
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Old 09-08-2009, 04:19 PM
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Omg. A question Reaper couldnt answer. What has this world come too?!??!? Seems someone tore a page out of this information book.
 
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Old 09-08-2009, 05:03 PM
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Haha, yeah. Actually, I probably could answer it, but I don't know any shortcuts, so I'd end up doing a lot of math to answer a simple question that might not even have a simple answer. I'm talking I'd probably end up pulling my hair out trying to figure it out... there's a lot of variables to deal with, and once I got the number, I'd have to go back and throw it into a CR formula a few times with different bores/strokes to make sure it actually works.
 

Last edited by reaper2022; 09-08-2009 at 05:08 PM.
  #10  
Old 09-08-2009, 05:31 PM
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I have 11.68:1 with my spread sheet. But this just based on manuf. specs, .010 in the hole, +7cc piston, 53.5cc chamber, .060" head gasket,8.350" deck height,84mm bore=3.307",89mm strock=3.63" , so - 7cc from 53.5cc and thats what I came up with.
But I guess I'll have to measure the piston in the bore to get exact(cc's). I guess it seem's more reallistic now. T-flow cylinder heads
 
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