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 7Likes
08-21-2015, 05:51 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
what air cleaner is on the motor?
what is your rear end ratio? Rear tire size?
What trannie?
Dwight
__________________
''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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08-21-2015, 07:07 PM
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CC Member
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Join Date: Sep 2013
Location: Memphis,
TN
Cobra Make, Engine: SPF#1867 , KC427
Posts: 431
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Not Ranked
Quote:
Originally Posted by Dwight
what air cleaner is on the motor?
what is your rear end ratio? Rear tire size?
What trannie?
Dwight
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Just one of those slim oval cobra setups. It's a paper filter and on the dyno the car made 4hp more with the filter removed. The rear end ratio is 3:23 with a TKO-600. Tires are Goodyear Eagle 315s in rear. In 3rd gear at 6000rpm Pman blew me off the road |
08-21-2015, 07:18 PM
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Senior CC Premier Member
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Join Date: Nov 2004
Location: SoCal,
CA
Cobra Make, Engine: CSX #4xxx with CSX 482; David Kee Toploader
Posts: 3,574
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Not Ranked
Seems that I would agree with above comments...
Compression
Leak-down
Pull valve covers and check everything in valve train
Fuel pressure?
Timing set up right when cam was installed? (Did they maybe index it wrong?)
Just trying to think of anything I can.
You have tall gearing, but that shouldn't do what you describe. I run 3:31 and have no problem. But then..I am running a big block 482.
__________________
All that's stopping you now Son, is blind-raging fear.......
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08-21-2015, 08:03 PM
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CC Member
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Join Date: Aug 2008
Location: Memphis,
TN
Cobra Make, Engine: Superformance SP02423 KCR 445W 611hp 599ft lbs
Posts: 321
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Not Ranked
Fuel pressure is on my list to check at idle and under acceleration on Ace's Cobra. My brothers hot rod truck had a fuel pump issue and experienced similar problems.
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08-22-2015, 04:45 AM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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Not Ranked
252/262 @ .050"?
If that's duration at .050", that's a very large camshaft for a 427. My engines that are around this displacement and use hydraulic rollers have about 12-14 degrees less duration and peak at around 6000-6200.
My guess is that the cam has been changed sometime in the car's life and that cam does not match the rest of the engine/car/goals. Your compression test shows low because the cam is so large and the numbers actually jive for a cam that large.
I'm thinking that if these are .050" duration numbers, the cam is so big that you have no bottom end and you can't run high enough in the rpm range where the cam wants to be efficient.
If those numbers are advertised duration numbers, then that would be a tow truck cam....
I'd change the cam....
Last edited by blykins; 08-22-2015 at 04:49 AM..
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08-22-2015, 08:24 AM
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Senior Club Cobra Member
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Join Date: Jan 1999
Location: MARKSVILLE,LA.,,
Posts: 3,235
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Not Ranked
Quote:
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My guess is that the cam has been changed sometime in the car's life and that cam does not match the rest of the engine/car/goals. Your compression test shows low because the cam is so large and the numbers actually jive for a cam that large
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and the engine originally came with a dual plane intake and Davinci 950 carb.....now it has a Victor Jr. intake and another carb.....
Makes one wonder what else has been changed on the engine from the time it left the engine builder till now????????
David
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DAVID GAGNARD
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08-22-2015, 10:22 AM
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Senior CC Premier Member
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Join Date: Nov 2004
Location: SoCal,
CA
Cobra Make, Engine: CSX #4xxx with CSX 482; David Kee Toploader
Posts: 3,574
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Not Ranked
Quote:
Originally Posted by DAVID GAGNARD
and the engine originally came with a dual plane intake and Davinci 950 carb.....now it has a Victor Jr. intake and another carb.....
Makes one wonder what else has been changed on the engine from the time it left the engine builder till now????????
David
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If that current manifold is a single plane it will explain a lot of things as well, especially street performance. I'm with the folks comments above. Starting to suspect cam and intake... 
__________________
All that's stopping you now Son, is blind-raging fear.......
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08-22-2015, 03:12 PM
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CC Member
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Join Date: May 2008
Location: Brisbane,
QLD
Cobra Make, Engine:
Posts: 2,797
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Not Ranked
Quote:
Originally Posted by blykins
252/262 @ .050"?
If that's duration at .050", that's a very large camshaft for a 427. My engines that are around this displacement and use hydraulic rollers have about 12-14 degrees less duration and peak at around 6000-6200.
My guess is that the cam has been changed sometime in the car's life and that cam does not match the rest of the engine/car/goals. Your compression test shows low because the cam is so large and the numbers actually jive for a cam that large.
I'm thinking that if these are .050" duration numbers, the cam is so big that you have no bottom end and you can't run high enough in the rpm range where the cam wants to be efficient.
If those numbers are advertised duration numbers, then that would be a tow truck cam....
I'd change the cam....
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Yes, I agree also.
Either the specs the OP has quoted are incorrect, or the cam is way too big or way too small for the expected outcome.
__________________
Gary
Gold Certified Holden Technician
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08-26-2015, 10:08 PM
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CC Member
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Join Date: Sep 2013
Location: Memphis,
TN
Cobra Make, Engine: SPF#1867 , KC427
Posts: 431
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Not Ranked
Quote:
Originally Posted by blykins
252/262 @ .050"?
If that's duration at .050", that's a very large camshaft for a 427. My engines that are around this displacement and use hydraulic rollers have about 12-14 degrees less duration and peak at around 6000-6200.
My guess is that the cam has been changed sometime in the car's life and that cam does not match the rest of the engine/car/goals. Your compression test shows low because the cam is so large and the numbers actually jive for a cam that large.
I'm thinking that if these are .050" duration numbers, the cam is so big that you have no bottom end and you can't run high enough in the rpm range where the cam wants to be efficient.
If those numbers are advertised duration numbers, then that would be a tow truck cam....
I'd change the cam....
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Following up on this. Per the Comp Cam Slip that is part of the motor build sheet the info below is listed. If this information makes since to you it makes you wonder why a camshaft such as this was used.
*Gross Valve Lift .576 Intake / .576 Exhaust
*Duration at .006 Valve Lift 314 Intake / 329 Exhaust
*At 112 Intake Center Line / Duration at .050 252 Intake / 262 Exhaust
Last edited by Ace23; 08-27-2015 at 05:41 PM..
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08-27-2015, 03:51 AM
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CC Member
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Join Date: Dec 2001
Location: Louisville,
KY
Cobra Make, Engine: I'm Cobra-less!
Posts: 9,417
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Not Ranked
Quote:
Originally Posted by Ace23
Following up on this. Per the Comp Cam Slip that is part of the motor build sheet the info below is listed. If this information makes since to you it makes you wonder why a camshaft such as this was used.
*Gross Valve Lift .576 Intake / .576 Exhaust
*Duration at .006 Valve Lift 314 Intake / 329 Exhaust
*At 112 Intake Center Line / Duration at .050 252 Intake / 262 Exhaust
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I'm not sure why it was used. Poor choice. That much duration in a hydraulic roller with a 427 inch engine will kill the bottom end and kill the top end too. As I said before, this is what all the fingers are pointing at, IMO.
Nothing wrong with the 112 LSA, BTW, it helps with vacuum and with making the curve broader, but that duration is just out of the ballpark. When you see advertised durations near 320-330 degrees, that's why your cranking compression is very low.....TONS of overlap and the intake valve is not closing until very late.
I have custom hydraulic rollers that I like to use for my 427's and as I mentioned before, you're about 12-14 degrees too high... |
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