Nealio240z Posted March 21, 2008 Share Posted March 21, 2008 I run 350/350 in my 240z w/ 3.90 rear gears... 330 hp. I get a series of wicked exhaust pops (wrap) every hill I go down... The exhaust pipes are only 5 feet long, (16" purple hornies glasspacks with "H" pipe). Is this a sign of bad ignition timing? Sounds cool but i dont want to loose proformance... Any ideas... Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted March 21, 2008 Share Posted March 21, 2008 You could have an exhaust leak somewhere. And the engine could be running too rich, so the popping could be a sign of unburnt fuel burning. My STI sounds pretty wicked. 4" down pipe into 3" back. Combined with an exhaust leak, and the whine from the turbo it sounds like it shouldn't be coming from a car. Quote Link to comment Share on other sites More sharing options...
MJLamberson Posted March 21, 2008 Share Posted March 21, 2008 I get that pop whenever I am slowing down around 2500 RPMs, I am also unsure as to what causes it Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted March 21, 2008 Administrators Share Posted March 21, 2008 Gentleman, Ahem… Out the tail pipe, this popping is called after-fire, opposite of back-fire which is popping back through the induction. His exhaust pipes are only 5' long! Deceleration mixture is rich! This is not harmful to the engine, but can be stressful on the exhaust system depending on the severity of the after-firing that is taking place. Before anyone else attempts their best guess, please read this link; Before you guess at the answer, please click ME! Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted March 21, 2008 Share Posted March 21, 2008 My 240 used to do that when it was running rich and coasting down hill. Garrett was behind me in TN mountains at night, and I bumped the rich/lean knob on the sds to rich and it was popping fire out the tailpipe. I would imagine coasting down rich isn't the end of the world, but if your running rich under acceleration you are giving up ponies. Evan Quote Link to comment Share on other sites More sharing options...
MJLamberson Posted March 21, 2008 Share Posted March 21, 2008 My 240 used to do that when it was running rich and coasting down hill. Garrett was behind me in TN mountains at night, and I bumped the rich/lean knob on the sds to rich and it was popping fire out the tailpipe. I would imagine coasting down rich isn't the end of the world, but if your running rich under acceleration you are giving up ponies. Evan wait, so when we get a real good pop or series of, we are poping flames out our exhaust? Quote Link to comment Share on other sites More sharing options...
m4xwellmurd3r Posted March 21, 2008 Share Posted March 21, 2008 You don't always get flames. sometimes it's just a bit of smoke. At night though it would be more noticable if they were flames. I would think that the muffler would suppress any flames though. I know on my bug, if I turned off the ignition switch while cruising, then just kick it back on, it would shoot out quite a large flame haha. those aren't really mufflers though..it's more like a can with a couple pipes tacked on. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted March 21, 2008 Share Posted March 21, 2008 Only muffler on my setup was a dynomax race magnum. No muffler to stop the flames. I had to run it real rich to make it happen. Quote Link to comment Share on other sites More sharing options...
dig280z Posted March 21, 2008 Share Posted March 21, 2008 wait, so when we get a real good pop or series of, we are poping flames out our exhaust? but when you have a stuck open injector then you get a three feet long flame:eek: out the back. well that is what happened to me. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted March 21, 2008 Share Posted March 21, 2008 How about a serious case of a dead distributor with a mix of SUs needing rebuilding? My video(look at 40 seconds in...the third afterfire looks to have a hint of flame): It was soo freaking loud inside the car from the "afterfire" that I had temporary hearing impairment after driving the crap... It also blew out/compacted most of the muffler packing which made the car even louder. It was plenty loud already. I even contemplated wearing ear plugs when driving the thing. The video cuts out most of the noise so it sounds more reasonable...but its not. Quote Link to comment Share on other sites More sharing options...
capt_furious Posted March 22, 2008 Share Posted March 22, 2008 I blew out the manifold-to-pipe gasket on my Z, ever since, it pops much more than usual on decel. Often I get a shotgun-like blast out the back after letting off from a hard run up to speed. If it happens at night, I'll occasionally see a flash light up the road behind me in the mirror. The pops are unburnt fuel lighting off, like BRAAP said, it's normal for decel to be rich, but make sure it doesn't blow out your mufflers or gaskets. I've neglected the gasket because the motor is coming out next weekend. I kinda like the gurgling when I slow down, anyway...sounds cool. I'm such a ricer at times. Quote Link to comment Share on other sites More sharing options...
olie05 Posted March 22, 2008 Share Posted March 22, 2008 I have the whole bottom row of my spark map set to -5 degrees, above 3000 rpm... and I have about 15% ve in the bottom row. Makes for some pretty decent flames. One time a friend reported roughly 12" long flame from my exhaust tip. This is through a turbo style muffler. Sounds like a gunshot when the flame makes it all the way out, and it's fun to watch the people back off when they see it edit: i guess I didn't make it clear that this only happens under deceleration. Quote Link to comment Share on other sites More sharing options...
Nealio240z Posted March 24, 2008 Author Share Posted March 24, 2008 K. Thanks for the input. I know im running rich- 750cfm on a smallblock.. And that would explain the pop. Thanks again. Quote Link to comment Share on other sites More sharing options...
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