What would cause engine break-up at 5200 RPM?

spirockp said:

Wow, this thread received a lot of play...

Ok this is what I got from all the responses..

1. Check Fuel pressure at 5000+ RPM

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this must be done under load. you can tape the fuel pressure gauge to the windshield to run the test.

2. Test Coil / try another one perhaps. Currently using a 10 year old Mallary.

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coils are cheap enough these days that you can just replace the old one.

3. No Rev Limiter, running an MSD Ready To Run Distributor. (no Box)

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check the ignition module

4. Spark plugs, running what was installed at the time I received the motor, new of course, once a year.

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try one heat range colder plug

5. Fuel Pump voltage should be OK, using the correct feed from Ron Frances

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check to be sure. never assume

6. Motor Temp, I usually run between 185 and 190, not an issue.

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good temps, hopefully there is no hot spot in the head.

7. Octane, I usually only run 89 because I again usually only just cruise around, but I can try 93 or 94 and see if that makes a difference.

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when running at the track, always bump the octane rating. you always want to avoid detonation.

8. Spark plugs look good, I will heck the gap.
9 Wires are new, 2 years old, MSD.

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check the resistance of the plug wires as well. also check that the insulation isnt starting to breakdown. run the engine at night and look under the hood. if you see any electrical activity, replace the wires.

10. Alternator charging at 14 volts.

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full voltage is nice, but what amp output? if you have a 55amp alternator, even though it is putting out properly, it still may not be enough. rememer that the fuel pump and the ignition systems are power hungry, and if you have an electric fan...............

As far as how the motor is built I am going to assume that nothing engine wise needs to be looked at.

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again, never assume. the guy assembling your heads may have checked the valve springs, and checked the rate at the installed height, and was getting ready to install the valve springs in your head when his day ended. if another guy came along and the first guy didnt lay out any shims to be installed, or the first guy came in the next day and didnt remember to check if he needed any shims, problems will occur. mistakes happen, even with the best engine builders. if the above items check out, or dont cure the problem, then have the springs checked for installed height.

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