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CC Advertisers
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01-02-2007, 02:30 PM
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CC Member
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Join Date: Feb 2006
Location: Columbus,
OH
Cobra Make, Engine: Shell Valley- 390 FE, 4 speed toploader, 3.50's
Posts: 249
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Not Ranked
Whats your compression ratio?
Just interested in what compression ratios some of you are running in your engine. I have been calling a few places, looking for pistons, and was told by someone that 9.5:1 is about MAX for a street engine- which just happened to be the only thing he had available for my particular application.
So, what compression ratio are you running, and what is your opinion on the highest compression ratio for a street engine with todays fuel?
Greg
*edit* FWIW- I plan on going with the Edelbrock aluminum heads (72cc)
Last edited by blueovalfanatic; 01-02-2007 at 03:07 PM..
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01-02-2007, 02:59 PM
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CC Member
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Join Date: Apr 2006
Location: Los Angeles,
ca
Cobra Make, Engine: Hurricane Motorsports, 427w
Posts: 439
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Not Ranked
I'm running 10.25 to 1 with aluminum heads. 9.5 to 1 with iron heads or 10.25 to 1 with aluminum is about as high you can go and still run pump gas.
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01-02-2007, 03:22 PM
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CC Member
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Join Date: Feb 2004
Cobra Make, Engine: shellvalley 428 ford
Posts: 397
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Not Ranked
Hi Greg,
I am going to have right at 10.0 to 1 with my FE and Ededl heads. I know I could push it but I don't need the max. I want to be able to run on pump gas. I agree that 9.5 is just about max with iron heads.
Later,
Byron
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01-02-2007, 03:28 PM
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CC Member
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Join Date: Aug 2006
Location: Charlotte,
NC
Cobra Make, Engine:
Posts: 288
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Not Ranked
I am running 10.5 (I think its more like 10.8 based on what I have been told - not really a gear head) on 93 octane. Is 93 what you are calling pump gas or do you guys mean that because I am over 10.25 that I need to run race fuel?
James
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Charlotte, NC
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01-02-2007, 03:31 PM
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Senior Club Cobra Member
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Join Date: Jun 2005
Location: Scottsdale,
az
Cobra Make, Engine: Bought an Exact carbon car in TX. Bought a 427 sideoiler with 630 HP
Posts: 1,714
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Not Ranked
It all depends on how hard you want to run. I have 10.5:1 with iron heads and get by with 91 octane. If I was going to run hard 93 octane or higher would be in the car. Having said that, a guy I really respect because of his knowledge and background said 9.5:1 is the max he could recommend for 91 octane.
John
__________________
double ugly
The average fighter pilot, despite the sometimes swaggering exterior, is very much capable of such feelings as love, affection, intimacy and caring. These feelings just don't involve anybody else.
Last edited by double ugly; 01-02-2007 at 03:34 PM..
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01-02-2007, 03:34 PM
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CC Member
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Join Date: Feb 2004
Cobra Make, Engine: shellvalley 428 ford
Posts: 397
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Not Ranked
All we can get here seems to be 91. There are a couple of stations around the metropolitan area that has 93 but they are not at all convenient. By the way, here is Indep Mo.
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01-02-2007, 03:35 PM
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Senior Club Cobra Member
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Join Date: Jul 2002
Cobra Make, Engine:
Posts: 15,712
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Not Ranked
Was 12.5 to 1, iron heads, NIGHTMARE on the street, loved it on the track with race gas! Rebuilt, went with 9.6, iron heads, NICE, and STILL darn near as fast as it was before!
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01-02-2007, 03:35 PM
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CC Member
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Join Date: Feb 2005
Location: Truckee and Kailua,
Ca
Cobra Make, Engine: B&B 351/402 Fi roller everything
Posts: 527
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Not Ranked
10.1 to 1 with aluminum heads ,351 stoked to 402. I live at high alttitude 6000 ft. so 91 octane works great for me. It ran at sea level but complained a little(lumpy idle and such)probably needed some timing taken out. go big or ?10 to 1 is fine with alu heads.
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the older i get the faster i was.
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01-02-2007, 04:10 PM
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Senior Club Cobra Member
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Join Date: Aug 2005
Location: Toronto, Canada,
Ont
Cobra Make, Engine: Shelby CSX 4995, Keith Craft built 427 SO
Posts: 1,168
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Not Ranked
I'll be running 10.1 to 1 in the 427, KC is building for me. Aluminum heads, HR cam. I told Keith that I wanted it to run on pump gas, and that was what he recommended. We have 94 Octane here, so it should run just fine!  Used to run 12.5 to 1 in my old Corvette. I had to run Vortex Octane Booster, though for that!
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"The 427 Cobra is easily the highest performance car ever sold for street use. A decent 427 - not the worst, not the best, will go from zero to 100 mph and back down again to zero in less than 14 seconds. All thing considered, you can put together a pretty good argument that the 427 Cobra is the ultimate performance car, judged on any basis you want to name." Taken from; Corvette, The Sensuous American 
Last edited by 427SnakeSC; 01-02-2007 at 04:14 PM..
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01-02-2007, 04:43 PM
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Beam Me Up Scottie
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Join Date: Aug 2004
Location: Squantum (part of Quincy),
MA
Cobra Make, Engine: SPF1049 Titanium w/black stripes, 351W with Trick Flow Heads, Tremec 3550
Posts: 7,592
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Not Ranked
Mild 351 with aluminum heads and 10.2:1 compression ratio.
With about 35 degrees total advance, it runs great on 89 octane (mid-grade).
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Warren
'Liberals are maggots upon the life of this planet and need to get off at the next rotation.' (Jamo 2008)
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01-02-2007, 05:11 PM
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Senior Club Cobra Member
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Join Date: Mar 2005
Location: Meriden,
CT
Cobra Make, Engine: ERA 427 SC s/n 718, 428 FE
Posts: 1,731
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Not Ranked
I'm running 10.0:1 on 93 octane with my 428 FE w/iron heads...should be fine with the Edelbrock Performer RPM intake manifold.
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01-02-2007, 05:46 PM
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CC Member
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Join Date: Jun 2001
Location: taxmehard,
Ca
Cobra Make, Engine: Compomotive. 351w, close ratio four speed, live axle, 4wdb.
Posts: 226
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Not Ranked
I am at 10.5 and run either 105 or 112 race gas mixed with 91 pump gas. The cobra snarles like a rabid dog. I luv it!!
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Tinman
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01-02-2007, 05:50 PM
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CC Member
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Join Date: Dec 2003
Location: Lehigh Valley, PA,
PA
Cobra Make, Engine: Look-a-like cobra POS
Posts: 955
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Not Ranked
10.5, alum heads, all in @ 38deg timing. 93 octane / use 2 gal of av (100LL) gas per 10 of ultra. Runs fine.
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B. Ewing
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01-02-2007, 05:50 PM
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Senior Club Cobra Member
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Join Date: May 2001
Location: Florence,
AL
Cobra Make, Engine: RCR GT 40 & 1966 Fairlane 390 5 speed
Posts: 4,511
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Not Ranked
5.0 EFI 10.9:1 with aluminum heads and 93 oct gas. I made about 18 pulls on dyno's in three years. And a thousand 6000 plus rpm shifts, no problems.
Dwight
And about 18 runs down the Main Street of London. 
__________________
''Life's tough.....it's even tougher if you're stupid.'' ~ John Wayne
"Happiness Is A Belt-Fed Weapon"
life's goal should be; "to be smarter than inanimate objects"
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01-02-2007, 05:53 PM
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CC Member
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Join Date: Mar 1999
Location: TACOMA,
WA
Cobra Make, Engine: Everett Morrision FE 427 so 2-4s
Posts: 2,025
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Not Ranked
I'm runninig 11.5 to 1 with Dove alluminum heads. I buy the best pump gas available (ussually 91 sometimes 92 rarely 93) and add Octane Booster & Fuel Stabilizer concentrate additative by Manhattan Oil . A 4 fluid oz. bottle treats 60 gallons of gas at 1 increment per 5 gallons. It was recamended by the previous owner. If I could buy 93 it would be great but. I had more a problem with cam and lifters going flat. 14° of initial advance and 20° in the distributor.
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Mike H
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01-02-2007, 05:58 PM
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CC Member
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Join Date: Mar 2005
Location: Orange County,
CA
Cobra Make, Engine: SPF Brock Coupe #88, Keith Craft 427w
Posts: 707
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Not Ranked
I am running a Keith Craft 427 Windsor. Dart iron block with aluminum heads. 10.5 to 1 compression and does just fine on Kalifornia krappy 91 octane.
Doug, SPC088
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Now back to my midlife crisis...
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01-02-2007, 06:21 PM
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CC Member
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Join Date: Aug 2006
Location: Charlotte,
NC
Cobra Make, Engine:
Posts: 288
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Not Ranked
So it sounds like there is no hard and fast rule then. As I said, I am somewhere between the 10.5 and 10.8 numbers I have been told. Its an all aluminum Dart block 351W bored and stroked to 427 with aluminum (AFR 205) heads and I run 93 octane only. The 93 is at almost every station around here and alot have 100 race fuel, but I didn't think I needed it... so do I? What if I plan on running a dyno? If I run a road race I would put race fuel in for sure, as thats what its for... but just cruising with the occasional squirt of the loud pedal???
James
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Charlotte, NC
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01-02-2007, 06:33 PM
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CC Member
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Join Date: Mar 2004
Location: Sunnyvale,
CA
Cobra Make, Engine: Factory Five Racing MKIII Roadster 347
Posts: 1,053
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Not Ranked
On my 347 w/aluminum Edelbrock heads, I have a "static" compression of approx. 10.3:1 and on 91 Octane here in California. So far, it's been running great. I am going to see what happens when we start hitting 100deg. weather this summer; all the driving so far has been in moderate to cold temperatures since early October.
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01-02-2007, 06:39 PM
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Senior Club Cobra Member
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Join Date: Jul 2001
Location: Carrollton,
TX
Cobra Make, Engine: JBL now SOLD
Posts: 1,735
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Not Ranked
I am running 10.8 with Aluminum heads. I use 93 octane, but in cool weather I can run 89 ok if I need to.
I also have very tight piston quench clearance which supposedly helps.
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6th generation Texan....
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01-02-2007, 07:17 PM
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Senior Club Cobra Member
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Join Date: Feb 2006
Location: Syracuse,
NY
Cobra Make, Engine: BDR 228, Roush 342R, 457HP/428TQ, modified AOD
Posts: 1,378
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Not Ranked
10:1 and aluminum heads.
Have only run 93 octane in it, and no problems at 6,500 miles.
Cheers!
Dave
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Dave
Nolite id cogere, cape malleum majorem - Don't force it, get a bigger hammer.
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