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In a nutshell: you have a good engine built by a pro. Tuned by a pro, it made good power. Now, some time later, it was tuned by another pro, and it did not make good power.
So, the question is: What changed? Something broken? Something failed? PO changed something, like the cam? Time for some serious investigation to find the answer to that question. I would start with these things: - basic tune up: plugs, wires, cap, rotor. - pull the valve covers, and check all the valves and springs. - adjust the rocker arms, again. - compression check, wet and dry - leak down test - coolant system test, rule out a bad head gasket. Careful diagnosis now will save time, money, and frustration later. |
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Good luck! |
ACE
look at Classic Cobra Pack mufflers 3" with the louvers turned to the engine. Measure your old muffler and see if you can install longer Cobra Packs. When you install longer mufflers, they are quieter but allow more exhaust out. My 354 / 302 stroker put made over 400 rwh - tq and I think a lot of it was my exhaust system. Classic Chambered Exhaust Inc. - Cobra |
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I agree with you 100%,I was referring to a small block stroker making 585 hp.....A big block stroker making the same hp will be a lot "tamer" and streetable engine than the 427 small block stroker....... David |
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Spark, timing, fuel and exhaust. Really, if you have good hard parts what else is there? |
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I agree a leakdown test should be done. Also the numbers for compression look to be low closer to 190.
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Figured I would follow up with some information from my records that came with the car. The superflo dyno sheets shows a max hp of 585 at 6100rpm and a max tq of 568 at 5000rpm.....the AFR ratio's are at 13:0 and climb to 14:3 at max rpm which was 7000. The only variances from the build sheet are that it listed a Davinci 950 carb and Performer RPM intake. The carb on the car now is a 750QF and intake is a victor jr. The camshaft that is listed is a Comp Cam .576 intake and exhaust gross lift with 252 exhaust and 262 intake with 112 lobe separation. I hope the camshaft isn't anything proprietary....this is from 10 years back and its stamped all over the build information so it doesn't appear top secret. I was aware the car did have a Davinci carb on it but that it was removed....I'm wondering if the intake manifold listed on the build sheet is a typo as I undertand it to have always had a victor jr on it. This is purely to provide information based on peoples questions about the motor....not to debate someone's dyno numbers and if they are accurate. With work being as busy as it is there has not been any time to start going down the checklist of to do items.
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Okay, I'm here to confirm Ace's concerns. We took our cars out yesterday evening and did a third gear roll-on and my car just pulled away. I then drove his car and in his words and I agree is a slug. No wonder he is talking big blocks and Coyote motors. His motor builds rpms slowly with no shock value. Not impressed at all! Our motors are similar builds with mine using a 4.1" stroke crank and his obviously a 4.0". We should have been neck and neck on our roll-on. When he gets back in town and he can drop the Cobra off I'm going to dive into this matter.......
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Ace, you can struggle with where the horsepower you have lost may have gone and you might even get your mileage up into the low teens. You will spend considerable time and monies to get fuel injection in the car and properly tuned. When you are done you might get to 450 RWHP
Imagine for a moment how your 03 Cobra would have felt if you could have taken 1500 lbs out of it. You had a Blown 4.6 w/a KB on it, right? Pretty impressive, right? Well you can do that with this car that is 3/4 ton lighter! You already said you don't care about the under hood originality so put in a blown 03/04 Cobra engine (it does have the right DNA). As you already know from personal experience you will go from 300/350 RWHP to 600+ with lightening fast throttle response and 20+ mpg, but again this is not new ground for you — you have already been there. Remember that broad flat torque curve the engine had and the bottom end blast? I bet you miss that! Now put that in a 2300 lb car! BTW if/when you do it, polish the valve covers. When you open the hood it will be wall to wall blown and injected Cobra — with the blower front and center! The visual is stunningly similar to the 427 SOHC powered cobras except this engine is way lighter and easily as powerful if not more so. Ed |
what air cleaner is on the motor?
what is your rear end ratio? Rear tire size? What trannie? Dwight |
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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. |
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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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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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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On a big inch motor the single plane intake isn't an issue, but that cam is the root of all evil here....
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