Exhaust Pop

[Timon]

I installed a new Magnaflow exhaust ~2 months +/- 2 weeks, and ever since then the exhaust has *pop* sound. I've only been able to accurately reproduce it when shifting above 6k rpms from 1st to 2nd, or from 2nd to 3rd (due to third not rapping out until 90+ MPH I haven't tried it yet, but it probably happens there too). There is no actual backfire, and the engine runs smoothly.

I'm assuming since it only happens between gears that it's built up pressure being released... but it could be unburnt gasoline coming through the exhaust and only igniting at higher rpms due to the exhaust manifold getting much more hot.

Any ideas?

[Lil Blue Bastard]

Yes. You are hearing small amounts of unburnt fuel igniting in the exhaust system. Most highly tuned engines do this, sometimes even with stock tune, but you never hear it because the factory exhaust has been designed to cancel a noise like that.

For example, my 2008 BMW does it now that I have rear straight-pipe setup, as well as my MR2 with the Magnaflow.

[328FTW]

Yeah they do that with an aftermarket exhaust sometimes. I found higher duration cams made it worse as well. My old N/A race car is famous for it and I love that noise. People always identified it by that noise. Once there was 5 guys drinking on a corner at a hill climb and they were cheering everytime I upshifted out of the corner and backfired, god knows how drunk they were to be doing that.

[ve2dict]

yeah they all do that i think it increases with less back pressure ( the more open your exhaust the more and louder it will get) . mine did occasionally spit some fire out as well though exspecially when i ran an open pipe when i turned it into a dirt track car. mine did it more when engine braking from a high rpm

[328FTW]

Originally Posted by ve2dict

yeah they all do that i think it increases with less back pressure ( the more open your exhaust the more and louder it will get) . mine did occasionally spit some fire out as well though exspecially when i ran an open pipe when i turned it into a dirt track car. mine did it more when engine braking from a high rpm

That is where I started out. The officials told me to put a restrictor in because of the hill climbs through the forest that I did in off season. They were none to impressed with shooting flames in a dry forest lol.

[Maticuno]

Is it possible that a worn out O2 sensor is causing the engine to run too rich, pumping all sorts of unburnt fuel into the exhaust to be reignited in the pipe?

[mr3]

Maybe. I dont know for sure though. I replaced my o2 sensor and the exhaust still pops.

[Lil Blue Bastard]

Originally Posted by Maticuno

Is it possible that a worn out O2 sensor is causing the engine to run too rich, pumping all sorts of unburnt fuel into the exhaust to be reignited in the pipe?

If that was the case, I think you would be having a straight up BACKFIRE, not just the little pop pop pops.

[Timon]

Well I'd have to say, I completely agree with 328FTW - I love the noise it makes. I did my first track run, and almost every single shift it popped. Sounded awesome, especially compared to some of the other cars on the track.

[mr2tim]

The only time my N/A cars did this I usually found a loose fitting in the the exhaust assembly or a cracked exhaust manifold, burnt seal rings between the exhaust manifold and the downpipeb(2 ea). (1 tiny pin hole is all it takes?)

I've also noted thru the years that these engines have a tendency to throw the manifold nuts off at both ends of the manifold. Very, very hard to see with all the OEM cladding crap in the way.

20 year owner.

[Ray-088]

hey what kind of magnaflow did you put on? im in the market for a magnaflow right now but my car is in storage and its a 30 min drive to it, i just need the specs or if you could just give me the link to it, it would be fantastic!
thanks in advance. btw i got an 89 n/a

[Timon]

That's what it looks like.

I didn't order it directly from Magnaflow, so I'm not sure on the part number, but this one matches the specs perfectly MagnaFlow Performance Exhaust.

[328FTW]

That looks really big. How much does it weigh?

[Ray-088]

thanks soo much !

[Timon]

TBH, it looks bigger in the picture than it really is. I'm not sure on the exact weight, but it's a small portion of the stock muffler, trust me. The stock weighs loads compared to this thing.

[328FTW]

You could use an exhaust made from water pipe and it would weigh less than stock. They are soooooo heavy and have wimpy pipe.

There is a thing on mine that makes it quiet at low throttle. I hooked it up on my race car so I could get through inspection without them checking with the sound meter but when you went full throttle a flap opened up making it straight through. They are so awesome but I don't know where you get them otherwise I would say use one of them.

[hosh]

my last mr2 popped on up shifts and with engine braking. Nice little flame out the pipe too.
Course my entire exhaust system from engine to tailpipe was like 4 ft.

Exhaust manifold to y pipe to glasspack. Hated the exhaust sound except under overpasses. Only had it a short time before i blew a hole through both sides of the block.
Cracked oil cooler return line. I found out i was out of oil a 7400 rpm.

[Timon]

^They call it a dipstick for a reason .

[hosh]

dipsticks don't work while driving.
At least not for people my height who like to keep the engine deck on.

The really bad part was that I had oil filter and oil in truck for oil change that night. If I had stayed at work for lunch and not been hot rodding under an overpass I would have made it home and seen the oil leak and fixed it.

[Timon]

Wouldn't your oil pressure gauge have dropped off completely if it was running that low? My car is leaking a bit from the oil pan (I need a new gasket), and when it starts getting low, the oil pressure gauge reads lower than normal - hinting that the car needs oil.