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Too much compression for pump gas?
#617545
02/18/10 11:57 PM
02/18/10 11:57 PM
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Joined: Jan 2006
Posts: 735
Spokane,WA
Genuinejed
OP
super stock
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OP
super stock
Joined: Jan 2006
Posts: 735
Spokane,WA
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I'm swapping a set of Pro Comp victor knock offs on my 426 Wedge and I'm wondering if I'm going to have to run into problems with detonation. The motor is .070 over and has kb237s .025 in the hole. The heads are 72ccs and the cam is a Voodoo 60304. The compression calculator I used said 12.2 to one! Anyone have ideas or experience with a combo like this on pump? With the old 452s I never had any problems, but I'm a little concerned I might hurt the pistons.
1968 Plymouth road runner
1968 Dodge Coronet 500
64 D200
Good, Fast, Cheap. Pick Two.
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Re: Too much compression for pump gas?
[Re: Genuinejed]
#617546
02/19/10 12:29 AM
02/19/10 12:29 AM
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Joined: Aug 2003
Posts: 43,157
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,157
Bend,OR USA
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What altitude is it where you drive it? What compression was the motor with the 452 heads and is it the same cam still?
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Too much compression for pump gas?
[Re: topbrent]
#617549
02/19/10 08:45 AM
02/19/10 08:45 AM
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Joined: Jan 2006
Posts: 735
Spokane,WA
Genuinejed
OP
super stock
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OP
super stock
Joined: Jan 2006
Posts: 735
Spokane,WA
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Thanks for the link. When I enter the 72cc chamber KBs website says 11.5 to 1, the more accurate calculator says 12 to 1. I'm at 2120 feet above sea level. With the old heads and the same cam it was 10.47 to 1 using the calculator. I'm hoping the cam will lower the dynamic compression. I'll probably add some race gas when I go to the strip, I'm just hoping I don't have to run it all the time. Thanks for the help! 
Last edited by Genuinejed; 02/19/10 09:14 AM.
1968 Plymouth road runner
1968 Dodge Coronet 500
64 D200
Good, Fast, Cheap. Pick Two.
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Re: Too much compression for pump gas?
[Re: BradH]
#617552
02/19/10 02:29 PM
02/19/10 02:29 PM
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Joined: Feb 2007
Posts: 6,295
U.S.
moparniac
master
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master
Joined: Feb 2007
Posts: 6,295
U.S.
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67wedge runs a 268/272 at 11.4 to 1 on pump gas and i was 11.12 and ran pump 93 with a 248/254 and made my passes on pump 93 ......the higher the Intake closing ABDC cam timing event helps with this...
I checked my cranking pressure on one of those calcs(engine not done yet) and its saying 180psi and im gonna be right at 11 to 1 with a 269/269 bullet roller .... I was torn between the 11.5 /11.0 deal also...... I also had my heads milled back to the correct 75 cc rating after the cnc porting was done...
Mopar Performance
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Re: Too much compression for pump gas?
[Re: moparniac]
#617553
02/19/10 02:55 PM
02/19/10 02:55 PM
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Joined: Jul 2004
Posts: 19,317
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,317
State of confusion
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My 12.11 comp. heap cranks at around 170 w/275-280 dur.@.050 and runs fine on 91 but, I ALWAYS mix in 110 when racing........do I need it? Not sure but gas is cheap and pistons/rings arent.
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Too much compression for pump gas?
[Re: moparniac]
#617556
02/20/10 12:41 PM
02/20/10 12:41 PM
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Joined: Jan 2005
Posts: 866
Winnipeg ,Mb. CA.
chryco
super stock
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super stock
Joined: Jan 2005
Posts: 866
Winnipeg ,Mb. CA.
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I have a question . My 557"KB/RBRE Hemi is a 11.5 : 1 motor (static) and won`t run with 91 oct pump gas . Can the dynamic comp be higher than the static comp ????
Chryco
Gas is fer washin' parts ....Alky`s fer drinkin' ...Nitro`s fer Racin'!
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Re: Too much compression for pump gas?
[Re: moparniac]
#617559
02/20/10 02:58 PM
02/20/10 02:58 PM
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Joined: Jul 2004
Posts: 19,317
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,317
State of confusion
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Unless I`m doing something wrong,it says my dynamic comp. is 7.59........damn that seems low. 
Last edited by Thumperdart; 02/20/10 02:59 PM.
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Too much compression for pump gas?
[Re: chryco]
#617560
02/20/10 05:50 PM
02/20/10 05:50 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Quote:
I have a question . My 557"KB/RBRE Hemi is a 11.5 : 1 motor (static) and won`t run with 91 oct pump gas . Can the dynamic comp be higher than the static comp ????
Chryco
Static will always be higher than dynamic , unless of course the intake valve shut @ BDC.
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Re: Too much compression for pump gas?
[Re: Thumperdart]
#617561
02/20/10 05:58 PM
02/20/10 05:58 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Quote:
My 12.11 comp. heap cranks at around 170 w/275-280 [Email]dur.@.050[/Email] and runs fine on 91 but, I ALWAYS mix in 110 when racing........do I need it? Not sure but gas is cheap and pistons/rings arent.
I lost a good 3/10ths down track using 116 race gas , the motor is 9.5:1 & i was using the 116 for nitrous , ran the motor NA on the 116.
If the motor does'nt warrant high octane fuel it will always slow down , you can add advance to the motor to compensate but the more advance you give the motor the more it will slow the piston down.
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Re: Too much compression for pump gas?
[Re: 602heavy]
#617562
02/20/10 07:18 PM
02/20/10 07:18 PM
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Joined: Jul 2004
Posts: 19,317
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,317
State of confusion
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Are you saying your static or dynamic was 9.5:1?
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Too much compression for pump gas?
[Re: Thumperdart]
#617564
02/20/10 08:54 PM
02/20/10 08:54 PM
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Joined: Dec 2008
Posts: 1,200
UK
602heavy
pro stock
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pro stock
Joined: Dec 2008
Posts: 1,200
UK
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Quote:
Are you saying your static or dynamic was 9.5:1?
Static was 9.5:1 , i gave this as an example , obviously the motor does'nt need race gas @ that CR , but some guys use race gas for belt & braces...........higher octane requires the spark to be fired off earlier , as the mixture expands it trys to push the piston down the hole , the less spark lead to get optimum leverage ATDC the better , spark lead on my motor was around 40*  , since raised the CR for this reason.
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Re: Too much compression for pump gas?
[Re: Maximus_Wedges]
#617567
02/21/10 02:02 PM
02/21/10 02:02 PM
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Joined: Jul 2007
Posts: 653
Fort Worth, TX
Dago Red
mopar
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mopar
Joined: Jul 2007
Posts: 653
Fort Worth, TX
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My biggest problem with pump gas has never been detonation, but inconsistancy. My buggy only has around 8.5 but every so often it tosses out a really off pace run or picks up. I went to the 100 unleaded gas and it stopped. All fillin' station fuel is not created equal.
If You Can't Be Good, At Least Be Colorful
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Re: Too much compression for pump gas?
[Re: Dago Red]
#617568
02/22/10 08:57 AM
02/22/10 08:57 AM
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Joined: Jan 2006
Posts: 735
Spokane,WA
Genuinejed
OP
super stock
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OP
super stock
Joined: Jan 2006
Posts: 735
Spokane,WA
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Thanks for the input. The motor is stock 440 bore and I checked valve clearance on a 440 and it looks fine. The pistons have some pretty decent reliefs, and I plan on checking clearance there. The heads are off right now waitting on parts. I think quench is gonna be a strech at .025 in the hole, and a .039 head gasket. I was thinking about putting on a thick head gasket to drop the compression a tad since now would be the time. dynamic calculator says my CR should be 10.7 to one.
1968 Plymouth road runner
1968 Dodge Coronet 500
64 D200
Good, Fast, Cheap. Pick Two.
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