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Re: 440 Compression Curiosity
[Re: Exit1965]
#1950419
11/13/15 11:23 AM
11/13/15 11:23 AM
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Joined: Jun 2008
Posts: 3,916
usa
lewtot184
master
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master
Joined: Jun 2008
Posts: 3,916
usa
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currently i have my 3rd open chamber head pump gas big block on the engine stand. i know from experience 10:1 or greater won't work with pump gas; good quench or not. stay between 9:1-9.5:1 with a good tune-up and quench between .040"-.050" to be safe. There are people running 11:1 with pump gas. they must be throwing an extra $20 bill in the plate on sunday morning.
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Re: 440 Compression Curiosity
[Re: elmor353]
#1950433
11/13/15 11:58 AM
11/13/15 11:58 AM
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Joined: Jan 2003
Posts: 75,043
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,043
U.S.S.A.
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Sitting here contemplating my winter engine build and I thought I would try to get some input. I have a set of 915 heads and was wondering about how much compression I could run on pump gas? What I have gleaned from reading about quench, is that it reduces the tendency to detonate with higher compression ratios and that somewhere around .039 to .049 is the ideal range. If I use a flat top piston at zero deck and my closed chambered heads with a .040 head gasket, I end up with approximately 11.28:1 for my compression number. Will this work with 92 octane pump gas or will I need to run an additive or racing gas? I'm hoping to be able to use my heads since they have been mildly ported and completely gone through. Am I just wishful thinking? Do I need to save my money and buy a set of Stealths? You can do it but not with a flat top, get a piston with a D shaped Dish to lower the compression but still give you quench/squish , and personally you don't want more than .045 , try to keep it as close to .040 as possible. 10.0 would be good with iron heads.
running up my post count some more .
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Re: 440 Compression Curiosity
[Re: dvw]
#1950569
11/13/15 04:06 PM
11/13/15 04:06 PM
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Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,419
Kalispell Mt.
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currently i have my 3rd open chamber head pump gas big block on the engine stand. i know from experience 10:1 or greater won't work with pump gas; good quench or not. stay between 9:1-9.5:1 with a good tune-up and quench between .040"-.050" to be safe. There are people running 11:1 with pump gas. Not with factory 440 Mopar OPEN CHAMBER heads. Doug Fixed it. You can not do it with open chamber heads, they suck and no reason to run them unless you have to for a certain class you choose to run.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: 440 Compression Curiosity
[Re: lewtot184]
#1950591
11/13/15 04:50 PM
11/13/15 04:50 PM
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Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
64Post
master
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master
Joined: Aug 2003
Posts: 8,716
Baltimore/Denver
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I'm more of a cylinder pressure kind of guy.
Being in Denver, I try to plan the build around known fuel quality, purpose, gearing, trans, and especially altitude.
If I can get 93 octane at sea level, I generally try to target no more than 180 psi with iron heads. Without running the specific numbers, I'd say 10:1 mechanical compression is about it, then juggle some cam timing numbers to get close to target. Cams are a lot easier to change than pistons. i live at 750ft elevation and have found 180psi can be touchy. i would treat 180psi as the upper limit. Yes, 180 would be the limit and even that would depend on variables previously mentioned. I hate leaving power on the table.
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Re: 440 Compression Curiosity
[Re: 64Post]
#1950653
11/13/15 07:08 PM
11/13/15 07:08 PM
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Joined: Jan 2003
Posts: 27,421
Balt. Md
383man
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 27,421
Balt. Md
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My old 440 I built that I used to have in my 63 had 10.0 comp with 906 heads and I ran 92 pump all the time in it and it ran fine with no ping and 38 total timing. I used the KB quench pad pistons and built a nice .045 quench in it. But it was a real pain to use open chamber heads and quench pad pistons as you have to measure all the head cyl chamber depths and do alot of work getting them all right. As all the cyl head chambers are not the total same depth and it takes alot of work. I wont ever run them again as I had them so I used them. But to use 915 closed chamber heads and a flattop piston is the way to go. You can run 10.0 comp with the iron 915 heads if you build it with good quench and use the right cam to keep cyl pressure at no more then about 180. I did it and it worked great but I dont reccomend going higher then 10.0 with iron heads and pump gas. Ron
Last edited by 383man; 11/13/15 07:09 PM.
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