Oval track engine mis

[RCJ]

Having some trouble with my dirt track car .350 chevy ,flat top pistons ,angel milled vortecs ,solid cam,1 5/8 headers ,around 500hp at 6500,
Runs great in the heat races but after about 15 laps, doesn't matter if they are under green or yellow,the engine starts missing under full power.Have done a compression test and leak down both showed good ,checked all valve springs,Lash has not changed any on the shaft rockers.Plugs show a little lean went up one jet size in all 4 corners, didn't help.The ignition is a mallory 6al with a mallory 30440 e core coil,.These part were new but purchased for a different project,I've never used a coil like it on a dirt track car.On a 16 volt battery also.Is it possible for the coil to heat soak after a period of time and produce to much resistance and the voltage drop to low to fire the plugs?

[raceman14]

Sometimes 12v electronics don't like 16v supply. On that one I would call Mallory tech dept. they are pretty sharp.

Looks like you have done a good job checking out the basics.

Cheapest test is run the car with a 12v battery next week and see what happens.

[BAracer]

What distributor? Have you replaced the pickup yet? I've seen heat soaked pickups cause this more and more lately. They work cold, but not once they are at temp... Also could be too small of a power or ground between the box and battery.

[barnym17]

Checked fuel cell vent?

[Brian W]

Make sure you have a good ground cable from engine to frame and then frame to battery. Faulty grounds do weird things!!

[Strange Magic]

Sounds like a fuel delivery issue.

[joedoozer]

I agree it does sounds like a fuel issue. I might be wrong thinking this.....but. If you had an ignition miss at WOT, and the fuel was correct. Wouldn't the plug show "rich", because the fuel isn't being burned correctly?

If that is true you could try and figure out at what RPM the secondaries open, I assume it's mechanical and progressive. Then drive the car around at a lower RPM. See if the plugs are still lean. Usually your rear jets are a few sizes larger. 74 and 79 in mine.

[ZIGGY]

[quote="RCJ"]after about 15 laps, doesn't matter if they are under green or yellow[/quote

Sounds to me unlikely to be fuel delivery.

[MadBill]

I'd go with an electronic component checking out due to heat. The pick up would be my lead suspect. Another possibility is build up of ionized gas in the distributor. Drill a couple of big holes in it JIC.
(On the other hand, about 4 years ago we had a Ford powered Trans Am car that missed from ~ 6,000 RPM up. We changed everything electrical without success. Later the owner sent the carb back to the builder for a refresh and all was good after that. Unfortunately we got no feedback on just what was the issue.)

[TMSJoe]

My first instinct is fuel. Vent or fuel filter issue. BUT, battery also comes to mind. Do people run alternators with 16v batteries? Are you running an alternator?

[raceman14]

I am pretty sure the ignition system RCJ is running is similar to an MSD and has no module in the dizzy. Some of mallory's stuff is optical P/U and can be problematic but much of the newer stuff is magnetic and not real easy to overload.

Not knowing how it is wired or set-up, I still think power supply @ 16v could be problematic to the system.

Easy check would be swap to 12V battery and see what happens.

If that does not cure it I would swap out the coil and then the ign box to eliminate either of them. E-coils can be finicky, I have always used the old Huge Accel Yellow coil ( lotsa guts in there to absorb and dissipate heat ) if I had a problem as it will run almost anything without a miss.

[levisnteeshirt]

might try running the ground for the box to the head ,,,

[dfitz16]

I have seen tachs do this also fuel cell foam that got in to carb and bad fuel line where the inner wall was closing and restricting flow. Also incorrect spark plug heat range.

[governor]

make sure you dont have any fuel cell foam plugging the line between the pump and tank. Unhook and blow air from fuel pump back thru the the line, have seen this happen numerous times, car runs great until fuel starvation starts.

Gov

[BlitzA64]

As has been answered grounds can be crazy! A Tech that worked at Roush told me to always ground ignition to both heads as he has seen a head get partially isolated from the block due to sealers, thread lube etc. Seems unlikely but be advised it has happened......