Nov 8th, 11, 09:56 PM
Join Date: Mar 2009
Location: Lyman, SC
Re: Backfire exhaust issue
You should be able to get the pop tuned out and your friend is correct. Popping doesn't necessarily mean anything is wrong though, it's more annoying (to some people) than anything. Stock tune on cars turns fuel off or almost off during decel and retard timing for fuel economy and emissions but there is still a small amount of unburned fuel which makes it into the exhaust and it ignites. You don't notice anything with a stock exhaust. Some systems actually inject air into the exhaust to encourage the unburned fuel to ignite which lowers emissions. Seems Corvette owners liked the decel pop so much that GM changed the way the automatic exhaust valving works on those cars to allow it to pop MORE.
Anyway, without getting into much detail you no longer have anything muffling these pops plus with the free flowing exhaust you're pulling more air through the system as well. To compensate, you can increase the amount of fuel that is injected during deceleration with the throttle closed or just turn off decel fuel shutoff. My aftermarket system although not nearly as complex as an OEM system has this. I used to run with mine turned off but started experimenting with it and finally wound up with it set to inject a little over half of my normal idle pulsewidth value. An OEM system has much more programming for decel fuel in a manual transmission car for during shifts, mine is just on or off and doesn't know if I'm decelerating or just shifting so too low of a value gives a pretty good backfire between shifts when in it hard.
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
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'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled