IcemanG17

To the fellow rennlisters who have a highly modified exhaust, say headers-Xpipe-high flow cats-custom after that. Do you just eliminate the air pump when you put on the high flow cats? I looked at some pictures of a couple other cars (George-Blau) and it doesn't look like they have a air pump fitting by the cats anymore? Do your cars still pass CA smog without the air pump? I'm sure there is a slight power increase (& weight loss) by removing the air pump, does it effect the LH brain or MAF in anyway?
Thanks

DR

Hi Brain,

>To the fellow rennlisters who have a highly modified exhaust, say headers-Xpipe-high flow cats->custom after that. Do you just eliminate the air pump when you put on the high flow cats?

I do, at that point in time the air pump is an anchor. Although some people do leave them on in an effort to "trick" the emmisons testers.

> I'm sure there is a slight power increase (& weight loss) by removing the air pump, does it effect >the LH brain or MAF in anyway?

Doesn't seem to.

Fastest928

No, we have air tubes with our ssingle 3.5" and dual 3.0 setups, with and without cats, and our X pipes.

IcemanG17

Marc
Will the car pass smog using just the air pump but no cats (assuming it got past visual) or vice versa? I have heard they will pass with "hollow" stock cats and airpump or no air pump with high flow cats?

DR

Brian,
That reminds me oh a funny story I had forgotten about. Many years ago I had an 84 928S and it had one of the single test pipes that had the air fitting on it. I took it in for emissions testing and it was failing miserably. Since the guys at the station were good ole hot rod boys they took their air hose and stuck it down the air pump line (just before the exhaust check valve) and pumped about 120 psi into it as they ran the next test. Passed with flying colors!!! I asked them why not just put another car on the tester instead of my car and they replied "now sonny, that would be illegal" .. :-)

On a separate situation at another test site with an old 79 Euro I had with a Test Pipe. It passed emissions testing (on a GA. dyno test) with flying colors. Just before he gave me the sticker he decided to jack my car up to verify it had a cat.( it was so low you couldn't look under it) and when he saw the Test pipe he failed me. I came back an hour later with a cat on it and he gave me the sticker.. an hour after that and it was breathing free again.

IcemanG17

DR
Thats the kinda story I was looking for...sounds like your emissions testing is about like the republic of CA's...luckily for me my car runs exceptionally clean! I'm just looking for some fairly inexpensive HP gains, but want to keep the "smog legal" status....it seems the HP loss from high flow cats vs test pipes is not that much, might as well be "legal". It appears that you can get around 40+whp gain with the right exhaust setup + a RRFPR... I would be happy with 300whp!

Fastest928

Brian,
Your engine is very tight I know!

You could pass with hooloowed out stock cats and gain anywhere from 10-15 rwhp pending condition of your old cats. I can sell you a used cat if you want to inveverify the condition of your cat

Also, you wanna be part of a test? Let me know.

All our exhaust products come standard with cats, and at the 400 rwhp level, only lose 12 rwhp over no cats, the percentage is about the same for our headers with single 3.5"

Hope this helps,
Marc

IcemanG17

Marc
Hmmm hollowed out old cat.....simple bolt on trick to gain some easy HP....easy enough to bolt back on the original cats to pass smog (for sure anyway)...hmmmm might have to think about that one...probably sound a little meaner too!