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Old 08-26-2008, 19:56   #1 (permalink)
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Horsepower nosedive!

I'm running the following:

72 Mustang with a 351 Cleveland
Weiand single plane intake (up to 7000 rpm)
Holley 750 double pumper
Malory Comp 9000 unilite distributor (vacuum advance)
Mallory Promaster coil
Mallory 6A (not 6AL) Hyfilre box (no rev limiter)
Comp cams cam - 2,500-6,500 rpm

I put it on the dyno (chassis) and it takes a nosedive at around 5400 rpm! It drops about 50 horsepower for some reason as soon as it hits 5400 rpm. I noticed that it has a fuel starvation issue, so I put a new fuel pump on it today (with a pressure regulator) and that gained me another 22 horsepower, but again, it still dropped off 50 horsepower at around 5400 rpm! I'm thinking that it may have something to do with the timing (distributor), but wondered if anyone else might have any ideas. Right now, I have it at 10 degrees BTDC and noticed that 12 BTDC only hurts total HP, so 10 appears to be the magic number. The distributor gives off about 26 degrees of timing (mechanically), so that'd give me 36 total. Any ideas?
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Old 09-07-2008, 02:16   #2 (permalink)
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Re: Horsepower nosedive!

If it's nosediving at such a low rpm then two things i would look at are lifter pump up and valve springs too weak. . More likely valve springs though.
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Old 09-17-2008, 18:42   #3 (permalink)
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Re: Horsepower nosedive!

Nope, neither of those are the culprit - checked them both and they are fine (plus both are brand new). We did some dyno tuning today and it's plain and simply not going to get any more horsepower (or torque) as everything I have is working together as best it can. I did 19 runs on the dyno today changing all kinds of things and not one thing did any better than my original runs (I only got 55 one hundreths improvement). It looks like there's a "Parker Funnelweb" intake out there that outperforms the Weiand single plane intake that I currently have. I've noticed that in their performance testing against the Weiand Xcelerator intake, the Weiand didn't perform that well out past 5500 RPMs either, so maybe it's the intake that's causing the problem. Gonna take a look at that intake and see if 1) it'll fit under my hood, and 2) if it will perform any better if it will. It's very frustrating to have gone through so much and have all the parts that are advertised to 6500 or better RPM's, yet something is not performing as advertised!
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Old 10-20-2008, 15:42   #4 (permalink)
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Re: Horsepower nosedive!

Hey mate,

I found that my car does the same thing as well but at 5000rpm. Iv got a 393 clevo with the weiand manifold as well and all the goodies and it doesnt make power past 5000rpm which is doing my head in. Iv also been told that it could be the valve springs or cam degrees. I you've checked your valve springs then check your cam degrees. Im still to get around and take it past the workshop to get it all checked up.
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Old 12-06-2008, 02:48   #5 (permalink)
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Re: Horsepower nosedive!

I have a similar set up on a brand new engine weiand 2v brand new 750dp holley 562/588 hyd cam with double valve springs and 4v vales in 2v closed chamber heads with roller rockers ive reved it to 5000 quite easy but it needs sorting out the carby is dumping so much fuel at idle and the dizzy needs to be re-graphed to the cam specs its only a standard xe eletronic model /also do the c/chamber 2v need some more work they have the 58cc chamber and it has mega comp.Should u get them opened up a bit to around 65cc.
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