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Re: Best compression for max power on methanol?
[Re: gregsdart]
#2763115
04/12/20 04:17 PM
04/12/20 04:17 PM
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Joined: May 2016
Posts: 630
Ct
Wirenut
mopar
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mopar
Joined: May 2016
Posts: 630
Ct
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Title says it. What would you or do you run? I use meth and am at 12.5 . I would think or from what I have read this is almost as low as you want to be. I don’t know that there is a max / perfect compression. I would think it is a combo as with any set up.
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Re: Best compression for max power on methanol?
[Re: gregsdart]
#2763164
04/12/20 07:18 PM
04/12/20 07:18 PM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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There is a point where more compression needs a very complex dome shape with big valve reliefs which masks the valves during overlap. Torque goes up, but peak power doesn't because high RPM VE is down.
This is worst with a "real" hemi like the Gen-2 426, and somewhat in BBC, Ford 385, Cleveland because of the valve angles. A wedge with nearly vertical valves and long stroke can run CR than these.
It also varies with bore/stroke ratio: longer strokes have more compact chambers for the same displacement and static CR.
You won't get the same benefit with lower CR, but I assure you that sidevalve engines with 6:1 CR and huge cams like methanol a lot.
Boffin Emeritus
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Re: Best compression for max power on methanol?
[Re: polyspheric]
#2763197
04/12/20 08:48 PM
04/12/20 08:48 PM
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Joined: Jan 2003
Posts: 9,997
Frostbitefalls MN (Rocky&Bullw...
gregsdart
OP
master
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OP
master
Joined: Jan 2003
Posts: 9,997
Frostbitefalls MN (Rocky&Bullw...
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There is a point where more compression needs a very complex dome shape with big valve reliefs which masks the valves during overlap. Torque goes up, but peak power doesn't because high RPM VE is down.
This is worst with a "real" hemi like the Gen-2 426, and somewhat in BBC, Ford 385, Cleveland because of the valve angles. A wedge with nearly vertical valves and long stroke can run CR than these.
It also varies with bore/stroke ratio: longer strokes have more compact chambers for the same displacement and static CR.
You won't get the same benefit with lower CR, but I assure you that sidevalve engines with 6:1 CR and huge cams like methanol a lot. I follow on the dome issue. Mine is .078 high and flat so no problem there. I was told a long time ago (2002) that 15.25 to 15.5 was about max due to more compression wanting a tuneup that negated any gains, plus it got harder on parts. I am curious if that has proven to be the case with 440-1 strokers. Since 2002 I would expect there have been a number of big motors built with 15+ compression.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Best compression for max power on methanol?
[Re: Mopar_Rich]
#2770487
05/02/20 04:09 PM
05/02/20 04:09 PM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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15:1 if NA. 12:1 if boosted. That greatly depends on how much boost. We use less than 12:1.
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Re: Best compression for max power on methanol?
[Re: BobR]
#2770578
05/02/20 10:24 PM
05/02/20 10:24 PM
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Joined: Jan 2004
Posts: 903
Saskatchewan, Canada
cudabin
super stock
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super stock
Joined: Jan 2004
Posts: 903
Saskatchewan, Canada
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I went to 15.5 to 1 compression using custom Diamond pistons with a dome shape to match the Indy 440-1 heads. Makes good HP at 976hp...
67 Cuda 8.48@ 158.7 mph 1.18 60' 2,600 DA(so far...)
70 Super Bee 440 Six Pack 4-speed. 13.2 @ 104 Stock exhaust/Street tires.
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Re: Best compression for max power on methanol?
[Re: Biginchmopar]
#2770661
05/03/20 08:36 AM
05/03/20 08:36 AM
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Joined: Feb 2005
Posts: 20,174
PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,174
PA.
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Works great at 11:1 too and I know guys running far less with great results.
1970 Duster
Edelbrock headed 408
5.984@112.52
422 Indy headed small block
5.982@112.56 mph
9.42@138.27
Livin and lovin life one day at a time
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Re: Best compression for max power on methanol?
[Re: pittsburghracer]
#2770666
05/03/20 09:00 AM
05/03/20 09:00 AM
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Joined: Aug 2011
Posts: 250
Saskatchewan (SK)
79410aspenrt
enthusiast
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enthusiast
Joined: Aug 2011
Posts: 250
Saskatchewan (SK)
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Works great at 11:1 too and I know guys running far less with great results. i'm going to give it a try at 11:1 on my 360''. a few racers around here have had awesome results with 10.5-11:1 compression.
Last edited by 79410aspenrt; 05/03/20 09:00 AM.
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