Got a problem with a car, 408 engine, big cam, Dart heads, FAST intake, TB, made over 500 HP to the tires. One day, at WOT, third gear, about 5500 rpm, big backfire, shut off. Re-start all seems fine, roll into it a bit, past 5500 ok. We put it on the dyno to work on the tune, 1-2 runs, no backfire but down 40 HP, next run, backfire, shut off, re-start, same ****. One plug wire burned through at the header, turn it around, full pull, still down on power. Made several pulls up till about 5200, smoothing out the WOT A/F, no backfire, still down on power. Changed plugs, full pull, no backfire, still missing the power. Leave the dyno to scratch out heads, get on it, backfire, crap!!! Any ideas ?????

 

only backfire on heavy WOT? does it only do it past 5500? what do the plugs look like?

almost sounds like premature detonation. what plugs are you using?

 

The plugs are new TR5s if I remember right, we did a pull, no backfire on the dyno as I already said, still low on power, then it happened again on the street, yes, past 5500 rpm.

 

No ideas? I guess start with the basics, LOL