383 missing at 5k rpm

[mdh250]

I recently bought a 86 IROC with a 383 stroker motor
Scat Crank, I beam rods,10.5 to 1 compression forged pistons,
High volume oil pump
Dart Iron Eagle heads,215cc intake runner,72ccchamber,
205”/160” valves
Solid roller camshaft, scorpion aluminum roller rockers, stud girdles, bow tie tall valve covers.
Victor aluminum intake with a Holley 750cfm mechanical sec.carb
Long tube headers with Brand new true duel exhaust with moroso bullet mufflers
Holley high volume electric fuel pump Adjustable thermostat.
When I bought it it would rev to 7500 no problem. I had the distributor rebuilt new high torque starter and new 2 1/2" duel exhaust. It seems like it would crap out at progessivly lower rpms like 7200 down to 7000 6500 and so on. Now it's down to 5grand and starts missing like it has a rev limiter or something. I've tried different plugs,distributers and a smaller carb no diff. Any Ideas

[maxwedge]

May suspect weak valve springs, if this is not traceable to an ignition misfire.

[MrPbody]

Agreed, valve springs would be the first thing to look at.

Are you running straight "pump gas"? Your compression ratio is too high for 93. Mix 3 parts 110 to 7 parts 93, and you'll get the 100 octane those heads need.

Jim

[BOZZZ]

I had this prob on my drag car put a GOOD Module and Coil in it and prob went away.

[bigblock665]

Id go check the plugs again.... My 79 camaro did this exact samae thing... Plugs my come out of the factory with factory faults!!!!

[SpinnerCee]

With solid lifters, valve lash is very important, if it's too tight the valves may not be fully closing at high RPM when you lean on it and engine heat is the greatest -- too much is lash is better than too little clearance in this case.