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murbas
331 hemi with backfiring problems


i have a 331 hemi bored .040 over with 9 to 1 compression ratio, cam is an isky .485 lift 232 duration, 108 degree seperation, with dual holley 450cfm 4bbl's . headers are fenderwell exit with 3" collectors and baffles. car has a street/strip turbo 400 with a 3000 stall converter and 4.11 posi rear with 30" tall tires. i get backfiring occurring on ocasion under hard acceleration. can any help me with this problem ?
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on: Sun 28 of Mar, 2021 [03:13 UTC] reads: 1220

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Webmaster
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Re: 331 hemi with backfiring problems
on: Wed 07 of Apr, 2021 [16:42 UTC] score: 0.00
Murbas: Sounds like you're running too fat. According to the calculations I use, your 338 at 6,000 rpm will wants 587 cfm. Try a smaller carb and see if that fixes it. Have fun, Bob






> i have a 331 hemi bored .040 over with 9 to 1 compression ratio, cam is an isky .485 lift 232 duration, 108 degree seperation, with dual holley 450cfm 4bbl's . headers are fenderwell exit with 3" collectors and baffles. car has a street/strip turbo 400 with a 3000 stall converter and 4.11 posi rear with 30" tall tires. i get backfiring occurring on ocasion under hard acceleration. can any help me with this problem ?

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hemistude
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Re: 331 hemi with backfiring problems
on: Tue 06 of Apr, 2021 [19:47 UTC] score: 0.00
Is this a new build or has it been in place for a while and has run well in the past? Is it popping in the exhaust or through the intake? What does a compression check show? Is the vacuum steady or bouncy? Lots of clues can be had from those tests.

Does the mechanical advance work on your distributor? Have you confirmed the base and full advance timing settings? It should at full advance by 3000 rpm. You can rule out vacuum advance as the culprit -- it is not in play under acceleration.

If your full mechanical advance is between 28 and 32, then it shouldn't be popping because of SPARK timing. I always suspect VALVE timing next. Those "2 deg advance-straight up-2 deg retard" timing sets can be confusing to install. If that was set up wrong, it'll run but may give the symptom you are experiencing. Not necessarily the easiest thing to confirm but if everything else is right, that's all that's left.

Don't ask me how I learned this. confused Hope it helps,

Dave

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DaveBlakeman
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Re: 331 hemi with backfiring problems
on: Thu 01 of Apr, 2021 [15:35 UTC] score: 0.00
Lean condition ,, leaky plug wires . Bent valve stem .


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