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Re: What's the latest on your CR vs street octane requirement?
[Re: jwb123]
#2689460
08/19/19 03:34 PM
08/19/19 03:34 PM
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Joined: Oct 2007
Posts: 4,219
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,219
New York
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I'm curious.
How do you know the RPM where reversion stops and the cylinder volume captured approaches 100%? It would be different in 2 engines with the same cam, same head, and same CR if the rod ratio were different.
The hot spot that is frequently the cause of knocking is the closest to the plug and/or exhaust valve. How do you know how hot that is since it follows load as well as water jacket temperature?
I'm certain that these are relevant factor, but do their ranges contribute so little to the calculation that the results are still useful?
Boffin Emeritus
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Re: What's the latest on your CR vs street octane requirement?
[Re: polyspheric]
#2689567
08/19/19 08:54 PM
08/19/19 08:54 PM
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Joined: Dec 2013
Posts: 4,841
Wichita
GY3
master
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master
Joined: Dec 2013
Posts: 4,841
Wichita
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I'm at 10.63:1 and my software tells me 89 octane is safe. I usually run 91.
'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
9.92 @ 135mph with a 350 shot of nitrous and 93 octane pump. 1.43 60 ft. 3,750 lbs.
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Re: What's the latest on your CR vs street octane requirement?
[Re: GY3]
#2689573
08/19/19 09:08 PM
08/19/19 09:08 PM
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Joined: Aug 2003
Posts: 43,897
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,897
Bend,OR USA
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I wouldn't, and don't ,trust any software formulas on predicting detonation on any Hi Po pump gas motor  To many variables like fuel quality, current air density, spark plug heat range and so on  I do start off on the safe side on total ignition timing and spark plug heat range, colder is far better than a tad to hot on the spark plug heat ranges IMO. I'll drive and tune the carb. on the light part throttle cruise and idle mixtures first and then step up to the higher RPM on the primary only cruise to get it where I like it (I like lean, 14.8+ AFR)  and then tune for WOT throttle last. I will find out where the edge of detonation is on both the AFR, timing, gasoline and spark plug heat range and record the weather and all the tune up information   
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: What's the latest on your CR vs street octane requirement?
[Re: MR_P_BODY]
#2689647
08/20/19 07:34 AM
08/20/19 07:34 AM
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Joined: Jan 2007
Posts: 8,121
Mt Morris Michigan
mopar dave
master
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master
Joined: Jan 2007
Posts: 8,121
Mt Morris Michigan
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My 511 has 11.3:1 static. I use Kroger 93 octane fuel. No sign of any detonation on the plugs yet. Just this year a have been mixing in a gallon or 2 of 110 race fuel to a tank of 15gal just for the smell. 3 or more gallons and it will run richer and I see it on the wide band. Exhaust note changes from crisp to a dull note and the car feels slower and less responsive.
Last edited by mopar dave; 08/20/19 07:35 AM.
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Re: What's the latest on your CR vs street octane requirement?
[Re: mopar dave]
#2689652
08/20/19 07:40 AM
08/20/19 07:40 AM
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Joined: Jan 2003
Posts: 13,530
Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,530
Marion, South Carolina [><]
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My 11:1 hemi loses about a tenth and about 1.5 mph on straight VP 110 versus pump 93.
Not very scientific. I ran low on fuel at the track one day and all they had was race fuel, so I threw some 110 in it. Didn't change timing or jetting.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 4 speed, Dana 60
'71 Demon 340, no drivetrain, on blocks behind the barn
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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Re: CR on the street and your octane requirement...
[Re: BradH]
#2689738
08/20/19 12:40 PM
08/20/19 12:40 PM
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Joined: Oct 2007
Posts: 4,219
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,219
New York
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There may be significant differences between A and B besides octane that color power and mileage: how well does it atomize (minimum droplet size), what's the vapor pressure.
Chemists: more?
Boffin Emeritus
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Re: CR on the street and your octane requirement...
[Re: 440Jim]
#2690574
08/23/19 08:49 AM
08/23/19 08:49 AM
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Joined: Jan 2003
Posts: 8,101
Tulsa OK
Bad340fish
master
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master
Joined: Jan 2003
Posts: 8,101
Tulsa OK
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Can cranking compression give any indicator as to what you can get away with? My motor is a 10:1 W2 headed 416. The pistons have a nice smooth dish and no quench. Solid roller, 270ish @.050 off the top of my head, last cranking compression was 165. I just got it running again after a fresh valve job and replacing an incredibly worn timing chain so I need to check it again. It makes about 575-600HP now and has no trouble on 91 octane with 40* of timing WOT.
I had a 340 that was 10:1, quench motor, 243@.050 hydraulic flat tappet with rhoads clickety clack lifters. It cranked like 210psi and ran on 93 octane.
I would like to bump the compression up on the 416 on the next refresh but I do not have the budget or desire to run race gas since It is a street car. I do have E70 available in town and the fuel system to support it but I get mixed reviews about ethanol and limited use street cars(I don't drive it near as much as would like to).
68 Barracuda Formula S 340
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Re: CR on the street and your octane requirement...
[Re: BradH]
#2690594
08/23/19 10:08 AM
08/23/19 10:08 AM
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Joined: Dec 2006
Posts: 1,178
Indy
FlyFish
super stock
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super stock
Joined: Dec 2006
Posts: 1,178
Indy
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My previous motor was 10.8:1 compression (410 small block), ported eddys, small solid street roller (248/254 @0.05 with about 0.575 lift), Victor, 750dp, 727, 4:10 gear, 8" converter in my 3250# Barracuda. This ran fine on 93 octane (34° timing, locked out). It ran 10.8's...then I switched to e85 and it ran 10.7's. Blew that one up about 4 years back....
Fast forward to now...current motor is a 408, 13:1 compression, same heads/carb/transmission/ same everything except a larger solid cam (264/268 @ 0.05 with about 0.620 lift). Running e85 in the heat of summer it runs low 10.4's to high 10.3's...should really boogie in the cool fall temps (hoping for 10.1's) AND I can drive it all over town.
67 Barracuda street car, 408, e85, 1.38 60', 6.44 @105.9 in the 1/8 mile, 10.19 @130.5 in the 1/4...so far....
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Re: CR on the street and your octane requirement...
[Re: Bad340fish]
#2691462
08/26/19 07:27 AM
08/26/19 07:27 AM
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Joined: Jan 2003
Posts: 13,530
Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,530
Marion, South Carolina [><]
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Can cranking compression give any indicator as to what you can get away with? My motor is a 10:1 W2 headed 416. The pistons have a nice smooth dish and no quench. Solid roller, 270ish @.050 off the top of my head, last cranking compression was 165. I just got it running again after a fresh valve job and replacing an incredibly worn timing chain so I need to check it again. It makes about 575-600HP now and has no trouble on 91 octane with 40* of timing WOT.
I had a 340 that was 10:1, quench motor, 243@.050 hydraulic flat tappet with rhoads clickety clack lifters. It cranked like 210psi and ran on 93 octane.
I would like to bump the compression up on the 416 on the next refresh but I do not have the budget or desire to run race gas since It is a street car. I do have E70 available in town and the fuel system to support it but I get mixed reviews about ethanol and limited use street cars(I don't drive it near as much as would like to). My old 446" motor w/ Indy heads is over 14:1 compression (Ross domes and the heads have been shaved a lot). The old roller cam in it was around 262/268 at fifty on a 106 LSA and it cranked at 275 psi. Changed to a custom roller from Dwayne Porter w/ 274 at fifty duration on a 108 LSA and it cranks 185 psi now. I don't think I'll be trying pump gas in it, lol. My hemi at 11:1 w/ 275/284 at fifty on a 112 LSA also cranks 185 psi.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 4 speed, Dana 60
'71 Demon 340, no drivetrain, on blocks behind the barn
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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