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Old 01-15-2012, 10:39 PM
JTL JTL is offline
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Pontiac 400 falls flat at 4500 rpm

I have a 72 pontiac GTO with a 400 in it 750 carb edelbrok big cam etc. Sounds cool and starts strong but usually falls flat around 4500 rpm

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Old 01-15-2012, 10:58 PM
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This could be several things so I'll list the most common. First, do the valve springs match the cam? If not it's to be expected it won't rev far as stock springs aren't designed to the pressures a high performance cam produces.
If the springs are up to snuff then that leaves ignition timing low, ignition spark weak, or the carb is not getting enough fuel to support high RPM operation. Lastly what exhaust system is on the vehicle?
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Old 01-16-2012, 01:22 PM
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Quote:
Originally Posted by DoubleVision
This could be several things so I'll list the most common. First, do the valve springs match the cam? If not it's to be expected it won't rev far as stock springs aren't designed to the pressures a high performance cam produces.
If the springs are up to snuff then that leaves ignition timing low, ignition spark weak, or the carb is not getting enough fuel to support high RPM operation. Lastly what exhaust system is on the vehicle?
I frankly don't know what the builder did but I believe the cam springs and lifters were done together from a set. Ignition is a DUI summit knock off. Exhaust hooker headers and 3 inch dual flow masters. It dawns on me that I have never changed the fuel pump. It could be original or at least old.
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