backfiring through exhausts. - Team Camaro Tech
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post #1 of 4 (permalink) Old Apr 17th, 01, 09:53 AM Thread Starter
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Join Date: Jan 2001
Location: B C CANADA
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having a problem on getting my engine to run right. its a 350 , weiand 7504 highrise manifold, 780 holley, Headers 1.7/8, and a reground cam the specs are as follows intake [email protected] 314 l, exhaust [email protected] .050 323L 108 degree loa..
This was to be a strong midrange motor from 3,000 to 6000, . The mechanic says that the stock lifters are creating the problems and that the engine should come apart. Before I do this I thought I would ask , we backed off the exhaust by a half a turn which seemed to help and the condition is worse when it is cold.
Sounded like the timing was screwed up but he checked that and reset the timing,it runs okay at idle when warm but as soon as I hit the throttle fairly hard it backfires..
any suggestions before I rip it apart..
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post #2 of 4 (permalink) Old Apr 17th, 01, 11:54 AM
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Join Date: Dec 2000
Location: Monroe, WA, USA
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if you have lifter's that are "pumping up" and not bleeding off fast enough you can get this!

what is your gross lift with a 1.5:1 rocker arm?

IMHO if you are over .500" you need "fast bleed" lifter's to help. the OEM/stock lifter's kinda go nut's with a gross lift over .500". they do not bleed down fast or enough to keep the valve closed right. all so the exaust valve has a tendancy to swell more then the intake as it get's hotter. this with the high lift causes the broblem with stock lifter's.

a long duration can cause this too. that is why most cam maker's want you to use there lifter's, not stock with a longer duration cam. they bleed off a little faster and they have a tighter control over there prodution to keep them right. OEM spec's are bitt looser then most after market lifter's.

your duration at .05 should work fine with oem lifter's, unless you have a few that are takeing too long to bleed off.

you can try to adjust the exaust lifter preload with no more then 1/2 a turn after you get resistance on the push rod. it might do the trick for ya. but if you have a high lift cam( over .500") IMHO you need diferant lifter's.

[This message has been edited by ilbl8 (edited 04-17-2001).]
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post #3 of 4 (permalink) Old Apr 17th, 01, 12:53 PM Thread Starter
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Hey my car came from Monroe- maybe you saw it on the speedway ( its an ex stock car I am converting to Vintage racing) I may even take it Back to Monroe on the 15th of JUly , as we have a race there that weekend on the speedway.
I dropped it off for paint today will try readjusting the exhaust valves as you suggest.
I dont want to really put a lot of $ in the motor as it came with the car and I really should have a 302 in the car. Thanks for the suggestion.
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post #4 of 4 (permalink) Old Apr 17th, 01, 06:55 PM
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no prob! give me a hoot and we can pull a few some time!
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