Nismo280zEd Posted June 11, 2004 Share Posted June 11, 2004 alright.. i know for sure i'm not the only guy on here running an L28 with triple webers. My setup is as follows: N47 head mild porting and polishing Racing valve train and cam Slightly shaved head 1mm metal head gasket OEM bottom end 6-1 MSA style header into 2.5" pipe all the way to the back where i have a flowthrough Magnaflow muffler I run triple weber 40's with 38mm chokes i'm pretty sure. my timing is within' the norms.. nothing extreme. Ok so my car backfires when i decel. Now i know alot of you are going to say the carbs... thats not the problem.. i ran EFI with the same setup and it backfired. Now a mechanic told me it's the sign of a healthy engine. my fathers 911 does this and so does my friends 56 Ford both in excellent shape. I figure it is simply burning off the excessive gas in the pipe since i dont' have a cat. But now i'm just sick and tired of it and want to get ride of the popping. Surely i can't be the only one who has suffered this problem? I can't see room for another "standart" type muffler under the car so i was thinking maybe an 18" or 10" Glass pack style muffler would do the trick? or maybe two of them? I'm tyrn' not to hurt the flow here but come on guys.. you can't pick up chics when your car backfires.. they just dont' understand. Help me out guyz -Ed Quote Link to comment Share on other sites More sharing options...
datsunlover Posted June 11, 2004 Share Posted June 11, 2004 Hmm.. maybe a resonator pipe right after the header? Maybe it would create a little back presure, and possibly subdue the 'poping/backfiring' a bit.. I'm thinking just a piece 12-18" long, .5" bigger diameter than your 2.5" pipeing.. I dono..My car sounds simmilar.. I have a stock manifold, straight pipe (2" I think) out to the aftermarket 'twin tip glaspack' thing. I havn't actually driven my car yet, but even when I rev it up, it pop's as it's spinning back down to idle. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 11, 2004 Author Share Posted June 11, 2004 hmm... so like going to a 3" section of pipe then back to 2.5? woudln't this just make it louder? -Ed Quote Link to comment Share on other sites More sharing options...
TomsCoupe Posted June 11, 2004 Share Posted June 11, 2004 if it is a rapid type back firing like popcorn then it is a hole in your exhaust. If it is a LOUD backfire with a while inbetween each one then it may be a fuel issue Quote Link to comment Share on other sites More sharing options...
datsunlover Posted June 11, 2004 Share Posted June 11, 2004 I don't think so.. I would think it would 'trap' the pop sound and smoth it out a bit.. I keep thinking about the demo derby's where they run 4cys and just put a straight pipe from the maifold out the side of the car. (ditch the resonator/cat/muffler ect. MAN those little 4 bangers are loud! But with the stock exhast systems (before they get ripped apart to go to their death), they are prety quiet...and most stock systems I have seen have some sort of resonator pipe shortly after the maifold. But I might just be way out in left field here. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 11, 2004 Author Share Posted June 11, 2004 hmm hole in my exhuast eh? ....well i definatly have the loud pop, but i also have the popcorn. when you say hole in exhaust do you mean header? pipe, muffler? i found one leak by the muffler, but i welded it up. Could it be caused by the gasket leaking between my header and pipe? cause my intake/ header gasket is brand new.. and i didn't see any holes in the header. I guess i could check again. Ed well the 3" pipe thing is easy enough to try.. what if i went to a 4" for like 15" would that "capture" the pop even more? Quote Link to comment Share on other sites More sharing options...
TomsCoupe Posted June 11, 2004 Share Posted June 11, 2004 well, the popcorn popping sound is from the cold air mixing with the super hot exhaust and it explodes(from what i was told). So im gueeing it would be before your mufflers. it is usually like this POP...pop pa pop pop pop pop(POP is the LOUD one and the pop's ar the quieter faster pops) if that makes sense. I dont think it would be the leaky gasket at your headers because the air around there is already HOT as hell. im guessing it is a leak between your collector and mufflers...do you have cat converters??? if so, maybe it is leaking around there. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 11, 2004 Author Share Posted June 11, 2004 Yeah actually that makes alot of sense.. describes my car perfectly. Ok well the gasket between the header and the pipe under the car is definatly toast.. i'll replace that one and see what happens I'm assuming it doesn't take much cool air to do this. And no i have no other mufflers or cats on my car... a straight 2.5" pipe from the header to my muffler. with only two turns. I think i'm still gonna put in a glass pack style muffler with some SS guts on the inside to take some DB outta the exhaust on topend. Kinda ear piercing at the moment. -Ed Quote Link to comment Share on other sites More sharing options...
TomsCoupe Posted June 11, 2004 Share Posted June 11, 2004 good luck man, let us know if that solves the problem. Quote Link to comment Share on other sites More sharing options...
dot Posted June 12, 2004 Share Posted June 12, 2004 I have the same issues with mine. It farts on deceleration. Remapping my fuel map to zero on deceleration was a help however the instant fuel is reapplied just above idle it pops. Drives me nuts. The exhaust is made up of headers, resonators, and fat cans. It’s an air tight 2 ½ " system. The racing V12s and turbo Porches at the track do the same thing. However Ed is right, the ladies don’t like it. I now suspect it is ignition timing related. Fuel not sparked in the cylinder making it’s way into the pipes? Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 12, 2004 Author Share Posted June 12, 2004 yeah... that's what i suspected, excessive fuel not burned exploding when it hits a hot pipe, i don't know about yours, but cold mine really doesn't do it... but when it warms up it's alot of popn' So i guess just more mufflers? mines carbed i can't re-map anything bummer. yeah... the ladies definatly think your car is a piece when they hear that sh**. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 15, 2004 Author Share Posted June 15, 2004 replaced the gasket today.. so far no signs of improvment. Quote Link to comment Share on other sites More sharing options...
TomsCoupe Posted June 15, 2004 Share Posted June 15, 2004 replaced the gasket today.. so far no signs of improvment. take it in and pay $30 to have a mechanic check it out. Cheaper than replacing a bunch of stuff to find the problem. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted June 15, 2004 Author Share Posted June 15, 2004 Ugh... Negative ghost rider.. I dont' trust anybody to touch my Z anymore. Last time i took it to a mechanic they tried to charge me 170 bucks for new spark wires and and coil claiming that would fix my problem. When in reality the fuel pump relay was bad. I'm my own mechanic.. I look at it for free. my car has done this for three years now... not like there is something wrong with the engine. -Ed I just need to know where to put the damn muffler... closer to the header or farther? Quote Link to comment Share on other sites More sharing options...
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