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I gained nearly 20 horsepower when I changed the exhaust pipes on my old cobra. Also you haven't taken into account any of the parasitic loss in the movement of engine parts and I don't know if you have air conditioning or not, but the water pump alone takes some power as does anything attached to the engine. Remember, when they run them on an engine dyno, it is with open headers, no water pimps or anything else and the only loss is what is in the engine itself. On mine my flywheel horsepower was 530 and the RWHP was 390.
Ron |
what size are the header tubes?
a motor is a air pump, cubic feet of air in and same cubic feet of air out. When you try to make max hp/tq you need to look at your carb, air cleaner, intake, heads, headers and sidepipes. All must work together. Everything could be matched but the air cleaner and you will lose hp/tq. Take a look at Classic Chamber Classic Chambered Exhaust Inc. - Cobra I bought a pair of 3" i.s. pipes that were 4" longer than the ones I have. More hp and quieter. I have a 354 c.i. motor in my Cobra with 401 rwhp / 416 rwtq. A 155 hp lost is a lot. Keith Craft told me that he typical saw a 20% lost in a Cobra from engine dyno to chassis dyno for the same motor. Part of the fun is looking for 10 more hp.:) Dwight when they dyno motor they use air horns, largest headers, no mufflers, no alternator, electrican water pumps and other tricks to make max hp for the motors they sell. the chassis dyno is the real story. |
Cobra Muffler Retrofit
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Great replies so far. looking into exhaust options.
Basically, I'll start with exhaust, move to air cleaner (any suggestions?),and finish off with the carb if needed. Hopefully I'll get her up to full potential. I'll document along the way |
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If it was breaking up you likely have something else going on.
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That was a small concern which I have addressed. Like I said earlier, it was running very Rich in some parts, and very lean in others, so I have been adjusting. Since it was on the dyno, I just wanted to get an idea of real whp... And frankly I was disappointed. So now, I am seeing what I can do to make more power
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ssqpolo I would suggest since you are in Fl that you select a carb body without the choke horn. I found with my car the air cleaner was practically resting on top of the choke horn causing an air flow restriction. Also as others have said certain muffflers can be restrictive, I picked up 80 hp by switching mine out to Classic Chambered 2 1/2" bore and also a better intake manifold.
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I really don't know why the Street Avengers are turds...possibly because they are just smaller, vacuum secondary carbs, with minor adjustability.
The Q-series Quick Fuel carbs are mechanical secondary carbs, with no chokes or choke horns, and are pretty much infinitely adjustable. |
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hammer hitting the nail squarely on the head........... David |
Check to make sure the throttle is opening all the way. Some backdrafts had a problem with the gas pedal bracket bending and there was no amount of adjustment that would make the carb go WOT. My car dynoed 383rwhp before fixing the pedal assembly so that it wouldn't bend when you push the pedal, and it now makes 482rwhp. It was running rich and the a/f was very bumpy.
Also, was this with or without an air filter, and which air filter? My little K&N ate up something like 30rwhp (EDIT: It was 21rwhp). |
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http://www.clubcobra.com/forums/fe-t...alculator.html David |
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Wow. Very interesting information. Had no idea such massive gains could be made from intake and exhaust.
I will probably leave the carb for last, exhaust and intake first. I have been searching, but which air filters do you recommend? I have the stock one that comes with the Roush 427r crate motor. Sorry for all the questions, this is my first old style carb motor |
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use the largest diameter and tallest air filter you can fit under the hood and flow thru top will certainly help small air filters...... I'm using a 14 inch diameter x 3 inch tall air filter with a 1.5 inch drop base,but it is in a 65 Mustang and not a Cobra..... most Cobra's don't have the room/hood clearance for an air filter that size.. David |
I have the 14" oval. I'll have to check exact specs. Per backdraft website it's a 14" with k&n filter
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You should be fine with that filter.
I would definitely make sure your carb is going wot. It's the easiest thing to check and is a proven problem on the backdrafts. |
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