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spark plugs
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As the above link points out: Shut off the engine at the end of a drag strip run, after a full throttle blast at high load and high rpm. Then tow the car back to the pitts to read the plugs. That would eliminate the problem with the Multiple Spark Discharge changing the plug coloring.
That would sure be tough to do with a typical Cobra though. How are you going to tow it, or get it back to the pitts after a 1/4 mile run? :) |
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I had a situation very similar to yours. Mine is an EFI motor, but the popping is what is similar.
Everyone who listened to the car told me it was an exhaust leak. I even moved the Oxygen sensor forward of the slip fit headers in an effort to zero in on the air leak issue since the wide band was giving me bad numbers (rich to lean and vice versa). Finally took out the injectors and found one on the bank that was popping with some trash in it. Changed the injector...no more popping. It fooled everyone. Now, my thought is that you may have a fuel problem in addition to a possible exhaust leak. The stumbling upon acceleration after you have let off suggests to me that it is fuel. Anyway, this is what happened to me. Believe me, some VERY knowledgeable people swore my problem was an exhaust leak. Hope you can fix this problem...mine drove me crazy. |
If your interested in buying a highly polished stainless steel side pipe system that will be very less restrictive than most, send me an email.
3.5" muffler with no glass to stuff up TQ & HP. I even gained 6 HP at idle. |
I want everyone for their comments. As usual, the knowledge here has been priceless!
Thanks!! Mike |
Russ, your onto something about a rich fuel condition. That extra potentially unburnt fuel would more easily re-ignite with the introduction of fresh air via an exhaust leak in the system. End result, "popping" on decelleration which MIGHT go away by simply adjusting the fuel/air ratio. If it's rich enough, it might self ignite even if you didn't have a significant exhaust leak allowing extra fresh air into the system.
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After reading this, i have to ask what an original 427fe with iron heads, flat tappet cam, steel rockers, and low profile intake actually would or did make at the rear wheels.
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Sounds like a very stock build, like would be typical in a station wagon or big Ford. The answer of course is: Not Much! :) 300 at best, likely in the 200 range would be my guess.
Side oilers excluded because they were almost always the high performance application. |
Here's an interesting article on a side oiler at only 433 cid. Near stock stroke (actually short throw), larger bore. We hear so much about "mega cube" motors these days it was refreshing to see what a near stock bore/stroke FE with some "good stuff" could do.
670 flywheel horse, not bad... My original side oiler was very much like these specs, except high compression (12.5 to 1) and race gas. It made 667 horse. "Plan B", a high-riser FE made with leftovers, shelf parts and running pump gas. Plan A was a SOHC that didn't work out. :) http://www.popularhotrodding.com/tec...ine/index.html |
Excal...that is exactly what was happening to me. I was dumping fuel into hot pipes and even without added air, unburnt fuel and hot pipes resulted in popping on decel.
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Good advice and info so far. I have all the same problems you've explained but the solutions have involved multiple changes...Unfortunately, its usually not just one thing...its the whole combination. I might suggest port and polish on those aluminum heads and for a couple hundred bucks, get a single 4V intake and a Holley 750 cfm carb. Port match the new intake and slap it all back together. Buy some good header gaskets and consider having a new set of bigger headers fabricated. Dyno it again and see what you get? This, to me, is what makes it so damn fun owning a Cobra...
jw |
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There is a WIDE variety of build specs for 427's, they were also used in dump trucks (boats, industrial motors for pump's, etc.)! :)
Seems to me most of the originals ran a 2X4 carb, could well have been a low riser in many or most cases. Comp cars and SC's were different. Of course plenty originals had a 428 as well. 12 second 1/4 mile was pretty common, nothing special really (VERY fast for that era though). H.P. has been widely debated for a long time. I suspect many originals had relatively low h.p. Ford advertised 425 for their "big dog" 427 but for the most part I believe the side oilers easily exceeded that. The Ford Thunderbolt factory drag race cars were more like 500 right out of the box (high riser, 2X4, high compression, wild cam). The T-Bolts didn't stay "stock" for long though, you can be sure they were torn down and built up even more before hitting the 1/4 mile. Some say there were more 428 Cobras than 427's, I don't know, it's hard to get an accurate number on that, maybe, maybe not. |
I wasnt trying to get off topic, was just curious. My apologies to the original poster. I just thought a 427FE with aluminum heads, roller cam, etc would make at least one hp per cubic inch. I guess i was wrong.
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Resto, I think your comments are right on target, not a thread drift at all.
Assuming Rawkkrawler has lost about 25% h.p. from flywheel to rear wheels he is right at one h.p. per cube. 25% loss maybe be a bit high, but within reason considering we don't know a lot about the specifics of sidepipe loss, drive train loss and accuracy of the dyno. Dyno numbers can sure be miss leading and are fraught with variables difficult to nail down. Could be as simple as what gear did you use to get the dyno reading in the first place? Some say third is better than 4th. Or, should you use 5th? Theres actually a math equation that arrives at the best gear selection for a particular setup, so there in no one single correct answer there. |
where did you get the engine???? Maybe it is only a 390?????
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Of course a carb could cause the same symptoms, as well as EFI, if either one is running well on the rich side for whatever reason. Slightly ruptured or leaking power valve in a carb comes to mind. Or simply jetting that is way to rich. Certainly a stuck injector in the case of EFI. But running rich is only one possible cause of a backfire, there are others.
In the case of the old "air injecting" via a "smog pump" it was more common to have a backfire condition. The smog pump, pumps, fresh air into the exhaust system on purpose! |
Most chassis dyno manufacturers recommend testing with the car in the whatever gear is 1:1. With my Doug Nash 5-spd, that is 5th, yet with a Tremec, it would 4th.
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