Saabscene Saab Forum - Saab Technical Information Resource banner

1 - 20 of 25 Posts

·
Registered
Joined
·
1,592 Posts
Discussion Starter #1
I have a full 3" system with sports cat fitted to my 9k Aero. Sometimes it will pop a little, on startup and when running. Out of interest, do others experience the same thing?
 

·
Registered
Joined
·
563 Posts
Had the same thing during the first two weeks after I fitted my 3" exhaust. It sometimes popped on startup, very loud
.

For some reason it didn't occur recently .
 

·
Registered
Joined
·
247 Posts
Very occasionally I get a pop from the exhaust when I start.

I also love the sound of the exhaust. It has a wonderful menacing sound when the throttle is opened from about 3000rpm (as a guy in a BMW 325 Ci witnessed today ).

BTW, I run my car without the cat and find that it is much less breathless at high revs. It saves weight as well
 

·
Registered
Joined
·
14,305 Posts
Originally posted by Alan_b:
[qb]BTW, I run my car without the cat and find that it is much less breathless at high revs.  It saves weight as well    [/qb][/b]
And therein lies your answer... I can't recall why at the moment, but a long front section of exhaust without attenuation (be it cat or silencer) will give popping, especially on overrun. Something to do with the way the gasses expand and contract IIRC. On my Abbott system, if I a straight thru pipe instead of CAT, I get the popping on overrun. If I put the cat back in or front silencer then the popping disappears.

Fuelling also has an affect- the first version of software that I had from Maptun caused an awful lot of popping until it was sorted...
 

·
Registered
Joined
·
1,044 Posts
I have just fitted the JT full system to my CD Carlsson and no popping, however I was getting exhaust leaks from most of the clamping areas due to me putting the clamps in the incorrect position to clamp the 2 pipes together, it was blowing out of the 2 slots cut into the pipes, I moved the clamps up to the solid section and now its aokay....but I would check your clamps close to the turbo by 'carefully' putting your hand around each clamp...best when the engine is cold!!
If you have any sort of leak there, on the overrun it will pull in air and cause backfiring...99.9% of the time backfiring in exhausts is due to a air leak...
 

·
Registered
Joined
·
2,041 Posts
About to fit a 3" front pipe - no cat - I take it that the popping is not a sign of anything harmful and somewhat like a Morris 1000 on the overrun.
 

·
Registered
Joined
·
963 Posts
Mmm, there's nothing like a Minor on overrun. As my brother once described it, "Wow, our car farts a lot!".

Sorry, please resume normal programming
 

·
Registered
Joined
·
247 Posts
I popped the cat on since the tester told me that it wouldn't pass without it. I knew all the stuff about the lack of cat not being a fail point unless it fails the emissions but this guy would fail it for the lack of cat regardless. The cat was removed just a little after the ink on the MOT had dried
 

·
Registered
Joined
·
6,531 Posts
Originally posted by Alan_b:
[qb]I knew all the stuff about the lack of cat not being a fail point unless it fails the emissions but this guy would fail it for the lack of cat regardless. [/qb][/b]
errrr then he's braking the law... for failure on that reason alone...
Now if it failed because the emissions were high thats another matter entirely...

But... as a note, if he failed it on emissions being high due to missing cat... well he'd be in trouble...
 

·
Registered
Joined
·
2,041 Posts
 errrr then he's braking the law... for failure on that reason alone  [/b]
I would agree from other postings I have read on this site - see also link at bottom of page - Bob McKay's MOT index.

Mike
 

·
Registered
Joined
·
2,599 Posts
But... as a note, if he failed it on emissions being high due to missing cat... well he'd be in trouble...  [/b]
Go on explain this one, is it just simply that he is making a statement without checking the facts? If he said the same thing after carrying out checks that proved the missing cat was the reason for the high emissions would he be OK?
 

·
Registered
Joined
·
2,041 Posts
My understanding is that provided the emissions are below the required level for a cat vehicle even if the cat is not there, then it will pass. I think Leon is confusing himself or it may just be funny phrasing - if tested and emissions too high through lack of cat, then its a fail.

Mike
 
1 - 20 of 25 Posts
Top