Mongo

Hey guys I noticed something interesting while I was doing an exhaust system on a 928 this weekend which inspired me to inspect my 944's system. The 928's system uses 2.5" piping to the cats from the header which is then reduced to 2 1/4" after the cats for sound purposes.

I believe the 944 is the same way but I can't confirm this quite yet until I know for sure. Can anyone verify for me real quick that the piping diameter actually is 2.5" dia before cat after header on an 8v 944 NA? I already know that it's 2 1/4" after cat. I just need to reassure myself since I may be planning to do another exhaust system for my NA since I'd like to keep my catalytic convertor on the car, but go with a high flow cat instead.

Mongo

bump.

Mongo

bump again. nobody?

Mighty Shilling

should be 2.5 IIRC...

Mongo

Thank you! Someone finally answers a question that I've had on this board 1 whole day!!

Manning

Nope, not 2 1/2, it is way smaller than that. I have a cat out in the garage, I think off a >85.5 and the pipe after the Y is a little over 2" then immediately in front of the cat right ahead of the weld is 2 1/8, after the cat it steps up to 2 1/4 and then it steps back down right before flange to 2 1/8 again.

Mongo

it can't be, 2 1/4" mates directly up to the flange piping. The gasket at the end of it supports only 2 1/4" in piping... I'll have to look underneath as soon as I'm done with my homework.

Manning

Well, I know there are at least 3 cats for the 8V NAs, one for 83, another for 84 - 85 and then a third for the late 85 cars on. I am pretty sure the flanges are slightly different dims as well. The cat I have in my garage, which thinking about it now must have been off an early 85, was used for a while on my car when the stock cat cracked a weld and nearly fell off. When I bolted this cat up the holes in the flange did not seem to line up just right. So probably the earlier cars had smaller pipes than the later cars. That said, I can assure you the cat in my garage has a pipe OD of 2 1/4 right after the cat and then for about an inch ahead of the flange it is swaged down to 2 1/8 OD. I can also assure you that when I had a 2 1/4 in/out cat welded onto the broken original Y pipe the 2 1/4 ID was almost too big to fit the pipe where it broke at the weld, and if I measure that section of pipe it clearly necks down to a smaller diameter ahead of the cat (near the front hanger).

Mongo

wow I cna't believe they dropped it to 2 1/8"!!!! that's like KIA Sephia sized piping! Ok I'm definitely redoing the exhaust now! Thanks for your help Manning, it's much appreciated!

Mighty Shilling

Manning is a great guy...very helpful and very nice...

Manning, this is for you...

Manning

Stig,

The thing I don't get is why they step up the size from the Y pipe to the cat and then step it back down again to the flange. Why do that? Increase velocity maybe?


Geoff,

Thanks.