Thread: can a motor backfire if you overwind it???

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Hello everyone, Can a motor backfire if you overwind it? I have blown 392 hemi in a '32 ford & it's been backfiring. I just found out today that I've been overwinding it.... Thanks! Bill

Yes it can. It's usually caused by the valves floating or the mixture leaning out because the fuel system can't keep up with demand (in the old days point float could also be a problem).

If it startsd backfiring all the time at lower RPM after it's been over reved chances are you have bent a valve or pushrod.

A blown mtr will also backfire when too lean

Backfiring with a blower is a bad combination.

They usually only do it ONCE!!!!!!!

I think I still hold the altitude record for a 6:71

when i over rev my 548 past 7000rpm it,s on the rev chip cuts out the cylinders and then i get off it.it will un seat the pop off valve on intake and pop then i put my foot back in it

Originally Posted by jerry clayton

They usually only do it ONCE!!!!!!!

I think I still hold the altitude record for a 6:71

i remember reading about a somebody who had a brand new pink blower and backfired it thru the O in the champion sparkplug sign on the top end i belive it was riverside?

Thank you Mike, Shoprat, Pro70, Jerry, Pat & Gassersrule, Then I think this is why my motor is backfiring at high RPM's. I've been overwinding it. I looked at the paperwork that came with my motor & redline is 6000 RPM. I've been winding it over 6000. I'm sending away tonight for a 6000 chip for my rev-limiter. I don't think it's running too lean cuz the motor was professionally built & tunned. And the guy who put the motor in set the fuel pressure regulator at what he said was the right pressure {6 pounds?}. It also backfires when I'm turning it over to start it but not once it's running {at lower RPM's}. So maybe the timming is also off? In fact, I think I read where blower motors should start in an instant. Why does mine turn over & over? Thanks again! Bill

Check the intake valve springs. If they are ok, do a comp. test, may have a bent intake valve. Backfire when cranking means something is allowing combustion into the intake. Not good with a blower!

Interesting... but not surprised... I'm not an expert in racing designs by any means... but by the time ones takes a big block and strokes it out another 100 plus CI or so... its getting a bit long in the stroke.... 7k is pushing it... isn't it?

No----------------

My Harley will do that especially at elevation! Scares the bejsus out of the people your trying to pass!

Dem, and others, the OP started this thread in 2010 and has made a lot of progress on the car since then........

Originally Posted by dem45133

Interesting... but not surprised... I'm not an expert in racing designs by any means... but by the time ones takes a big block and strokes it out another 100 plus CI or so... its getting a bit long in the stroke.... 7k is pushing it... isn't it?

your kidding right ? i have 548.565.589s 632.s running past 7000 .valve train is key

No I wasn't kidding... I was asking. But then its been 30+ years since I gave any real thought to high perf... but then that's what this forum is for (I thought anyway). 30-45 years ago in the Muscle car heyday... 7-8 k was a good way to pull rods apart, suck valves, and otherwise ask for general mahem when it flew apart in your average Joe affordable toy. But its changed a lot since then, I'll give you that. In my day it started with the 273, 318, 340, 360, 383, 413, 426, and 440s in the Mopars. Never been a big fan of GM although the Buicks and Pontiacs had some serious BBs in the 60s. Ford too... my wife had several Ford/Mercury products... her little Couger w/ a 302 was a nice runner... got me in trouble... pegged up under the 0 pin... they frown on that. I never saw her 429 T-bird (before me). But I am partial to Mopar... sorry, so shoot me if you have to.

So re-educate me. When I build my rod... I'm thinking stroked Mopar big block... likely decked. Maybe a paxton? or other supercharger. Not a fan of turbos per say... don't like the lag. My 5.9 Cummins has a terrible lag here at 7300 ft ASL. Want I want is what the old muscle cars had... instant torque... NOW. Not waiting on some computer to think about letting it run due to EPA... no waiting on a spool up on a turbo... NOW. Only way I know anyway to do that is CI... the more the better. Am I wrong? Remember...on the road... hp at 120+ mph doesn't matter... can't drive there ... at least very long anyway before your explaining to the judge.

And NO, I can't stand anti lock brakes and computer controlled drive lines... all that is in my feet! Yea I'm old school... and now a 61 year old kid... again.

I could get a ticket on a skateboard... I swear it!. My wife could pass em doing 30 over and they would do nothing... Humpt!

So where is a good place to start studying on building up a streetable 700+ hp Mopar BB?

Dave