cat bypass

[juanbenae]

if a cat by pass is installed on a 78sc will there be CSI tunning required after the install? will the oxygen sensor and pump be required to be disconnected ?

[Thomas Owen]

Sounds like you need a John Walker response on this one...

[jmohn]

A '78 has no O2 sensor, and if you're removing the cat. you may as well remove the air pump (be sure to block the openings or the air lines). Sorry, I don't know if any change to the CIS tuning is required, my guess is ... not much.

Jerry M
'78 SC

[Jeremy Cottrell]

You should check the mixture now that you have no cat, you can get a true reading - 1.5 % CO works well with CIS.

[Calspeed]

Hello,

How about removing them on an '85 Carrera? Is there any real performance gains. I already have a filter, Autothority chip, fuel regulator and BB Exhaust. Should I consider the removal of the Cats too?

Calspeed

[juanbenae]

bump

[ChrisBennet]

Originally posted by Calspeed
Hello,

How about removing them on an '85 Carrera? Is there any real performance gains. I already have a filter, Autothority chip, fuel regulator and BB Exhaust. Should I consider the removal of the Cats too?

Calspeed

Removal of the cat will help. According to some, it is as good as SSI's on a 3.2. Now that filter will do nothing but let in more dirt on a 3.2. If you get a chip made for your (new) setup you probably won't need the adjustable fuel pressure regulator.
-Chris
3.4L twin plug, stock filter,

[juanbenae]

I am pretty sure the 78 has an 02 sensor. it is the one wire model sensor if i have understood it right in the past. that may not be the case but,,,,. has anybody heard from mr. walker in the last day or two?

[MotoSook]

Anyone have an euro pre-muffler on a 78 SC?

I here the euro p-m is better for HP gain??

Any dyno results of the p-muff on a 78?

[juanbenae]

not here. i have a stock system that is due for a smog test in a couple of months. i figured a by-pass would complement my otherwise stock exhaust system. i would get a little over 2 years before i had to swap it back out for my 2 year test.

[tsuter]

No O-Sensor on 78SC. Only 1980-83SC. The 1978 doesn't need a cat, air injection, EGR. None of that stuff. Got rid of all that years ago.

[juanbenae]

does not need a cat for smog testing?

[JavaBrewer]

Originally posted by ChrisBennet
Removal of the cat will help. According to some, it is as good as SSI's on a 3.2. Now that filter will do nothing but let in more dirt on a 3.2. If you get a chip made for your (new) setup you probably won't need the adjustable fuel pressure regulator.
-Chris3.4L twin plug, stock filter,

I swapped the cat for a straight bypass pipe - not the Euro pipe others seem to be running. I did this ONLY to perserve the cat for when I really need it (once every two years at registration time) and to eliminate it's heat sink qualities. Performance gain was nill based upon my seat of pants measurements. MPG did not change however my exhaust has a slightly tougher sound, not louder, just tougher. If you're only looking for more power then you will be disappointed.

The biggest performance gain I got was to reconnect my O2 sensor. I didn't even know it was disconnected until my local wrench discovered it. I immediately realized sharper acceleration and another 3-4 MPG.

If your filter is one of those oil/foam types (KN) toss it and put the stock system back on. There's too much test data around indicating that the only thing you increase is the level of crap (stuff filters are supposed to block) your engine will eat. I read a report some time ago where they tested a 3.2 car with no filter and with the stock filter and the results were practically identical. Choices choices choices.

[tsuter]

You might need a cat or something that "looks" like it for a visual. But not for the sniffer. Set your CO to go in and pass. Then reset your CO back to where you want it after you pass.

[Jdub]

I have a '78 with a cat bypass from Pelican.

Ideal CO is 3.5% as per John Walker's recommendations. Do readjust your CO if you go bypass. As above there is no O2 sensor, though your bypass will have a plug for same: you need to plug that.

Go to a muffler shop, have them pull and replace all nuts and bolts attaching the cat. to the system. Get fresh gaskets for your work from Pelican and put these in when you go home after the muffler shop to R&R the bypass. Save your cat. for the next owner.

David is correct in that the sound is tougher. There is no hp or mpg gain or loss. The heat aspect of the cat. was something I also wanted to get rid of. My left exhaust valve bank doesn't need the abuse.

I also pass emissions with this setup no problem.

John