308 snorting and popping

I have excessive snorting and popping on overrun. 1978 308GTS, with a custom true-dual exhaust by PO, currently running test pipes. i notice alot of air leaking around the test pipes, which i have been told contributes to the popping. i took the test pipes off, and they were loosely bolted on with no gasket material. i will replace those.

however, the union upstream from that (see below), is there a gasket there? and should i replace it, and if so is it the same gasket as with the test pipe. I stupidly didnt check to see if those two connectors were leaking. that junction looks like it hasnt been opened in 30 years, and before i wrestle it apart i thought i would check. any thoughts would be appreciated.
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Yes, there; should be a donut gasket on each end of the pipe. Pics below shows the gaskets I've used when I installed the test pipe.
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yes, but is there a gasket at the end of the header (see pic with arrow above), i am assuming there is, and was wondering if it is the same part number, and whether or not i should crack that union open in the interest of hoping to solve excessive popping (leaking air). it looks like it hasnt been opened in a long long time..

 

I believe there is a gasket there; when I first took off my factory muffler, all the exhaust gaskets had severely deteriorated. Perhaps your original has as well.

 

Note in Mike's pictures that both the original cat, and the test pipe have a metal "sleeve" on opposing flanges (left side in picture), and meets with a flange without the sleeve. Some manufactures of test pipes skip this sleeve, and without it, the gasket material is in actual contact with the exhaust gases. The gaskets are not designed for this, and WILL burn up and rot away. They are only for sealing, not for exposure to the exhaust stream. If your test pipes are missing the sleeve, there is a solution. Just get sintered metal gaskets instead. Most muffler shops will have them, and less than $5 each.

 

I hope this diagram helps
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Yes there is a gasket there you can see it in your photos it is a fibrous gasket made of a product like assbestos and it will deteriorate over time. It is fibrous so that it has some flex and so it can seal. They are available in various sizes from most exhaust shops or car parts shops.

 

well i took everything apart, and there wasnt a single gasket anywhere (a few were in there, but so severely corroded they werent doing anything). So i replaced them all.

the end of the test pipe that goes into the custom muffler doesnt have the sleeve bit, it just has mated ends, so i slipped a little exhaust gasket material in there, and we'll see in the morning if the all the popping and burping is gone.

 

i put everything back together again, and the popping is about cut in half. it sounds very good, and just having a major completed everything is really tight and the car runs up very nicely. I am not sure if i should continue to track down the rest of the popping, or just let it be. Here are two videos, it sounds alot different under load.

any thoughts are welcome

http://www.youtube.com/watch?v=hTROSgKhyzk

http://www.youtube.com/watch?v=uTxm-j1UI-w

 

Trust me, the test pipe I had also did not have the proper metal sleeve and the factory asbestos gaskets were consumed in about 4 to 6 months. You will need to get sintered metal ones at some point.

Something is definitely not right. Has the car run correctly before? I had a 78 and it sounded nothing like that.

 

The car runs amazing, screams effortlessly right up to redline. It just pops on liftoff. Bear in mind the exhaust system is a little more than two old cherry bombs, nearing the end of thier life.

 

The issue with the snorting and popping continues. And now sometimes under very hard acceleration there is a sidewalk clearing backfire (wha-bam!!). Not always, only sometimes. The popping on lift off is all the time. Entertaining, but a little too much.

I pulled the old exhaust off, a homegrown system, and where the mounting rods are welded to the exhaust there is a pretty serious hole, exhaust flows freely out of it, and it is before the cherry bomb on one side, and after the cherry bomb on the other (both side welds are broken). Would air getting in at this location (before the muffler) create or contribute to the excessive popping? The whole system looks shot (see pics).

I found a used Tubi on craigslist in minneapolis for a great price (see pics 3 and 4), and it should be here next week, so we will see if that cures the issue. it needs to be cleaned up, but seems like a great find.

I guess if it doesnt cure teh popping it must be the header gaskets. The back side gasket was just replaced.

Thanks for any help or thoughts.
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How about a pair of Hyperflow cats?? Goes great with a Tubi!

 

Looking into that Len - have a great weekend, hopefully you can get the 348 out, and the weather complies. 75 and sunny here in Marin!!

 

Yes, holes in the exhaust will cause a back fire, and excessive popping. Have the holes welded or, put on a new exhaust.

Jim

 

give this method a shot....... turn up your engine idle speed to about 1000 rpm test drive it see if there is any improvement

 

No leaks in your manifolds where the 4 plugs are, #52 in Mike's post #6?