Tom928

Well I got the 84 running and back on the road last weekend after 10 months of transmission and drive train work. But...
Today it failed emissions:

HC limit=220 tested=236
CO limit=1.0 tested=3.38

Also there is a funny exhaust smell ... it's real sweet and strong!!
I see from searching the archives, this can be a bad cat or one getting ready to go bad. If so, I would need to replace it.

Sooooo, I have a set of MSDS headers hanging in the garage and have been threatening to get them coated.
Instead of getting a replacement cat..maybe I upgrade to headers (Headers are legal here) and get a cat to match.

For the cat, I was looking at the Magnaflow 94037 universal cat.
It's dual inlet (2") to single outlet (2.5") with O2 sensor hole between the inlets.
Website call's it out for the 928 for $245.00
http://www.car-sound.com/02product/d...niversal=94037
Has anyone used this cat, know anything about it, have pro's con's?
Looks like it would work.

The original cat-back is in good condition, so I would use that - for now. I had a chance on a Borla... but I waited too long.
I would need is a couple tubes from the headers to the cat inlets and a tube from the outlet to mate to the cat-back.
I'm sure any good muffler shop could handle that for me.

Those of you that have been here and done this, what are some things I need to do or watch out for?
Also for 16V, do I have to raise the engine to get the headers on?
From what I read, I just remove the air pump and the down tube?
So headers (with cats) will get me...what maybe 15-20hp?

Thanks in advance for the help.
Cheers,

Lopez

I have a 100 c.p.i. (cells per inch) cat I got from Roger. That is very free-flowing (do a search for "racing catalytic converter" and some are as high as 200). My car runs cleaner with it than it does with the stock ceramic cat which is way more restrictive. I just had this tested with both of them, and the car loses so much throttle response with the stock unit I could barely stand to drive it.

Anyhow, my point is that Magnaflow is probably more restrictive than you need it to be - if your engine is running and tuned properly at least. If you are going to the trouble of installing headers but still want a cat then why not get the least restrictive one you can?

You should really make sure that your car is not failing for other reasons first, though. Also, when doing the testing I also had the air injection system present and functioning with both of the catalytic converters - the headers would eliminate that unless you specifically plumbed it back in.

soontobered84

how about your O2 sensor? Has it ever been replaced?

Jim M.

If your going to modify the exhaust then going to an X-pipe to the stock manifolds or an X-pipe to your MSDS headers is a proven performance improvement. Then a single or dual cats. What Lopez says is very good advice about the cats.

dprantl

Before you start messing with the headers/cat/exhaust, check your O2 sensor.

Dan
'91 928GT S/C 475hp/460lb.ft

Leon Speed

How's the coolant level?

Tom928

Lopez - I will talk with Roger about the cats. I do want the least restrictive and if they are cleaner than the ceramic, that's even better. I have a feeling the reason the car is failing is either a bad O2 sensor or a bad cat (due to the funny smell).

Soontobebred - O2 sensor was replaced in 2/2004 according to maint records. Emissions passed when I got the car in 2006. I figure it's needs a new one anyway.

Jim - I hear an X-pipe is a good improvement

Dan - I will likely replace it. So this is another thing I wonder about. There are two types of sensors available that I know of. The low cost universal and the high cost original. Does everyone use the universal and solder it in or does anyone use the original?

Aryan - Coolant level is good, no loss and it is clean. I don't think it's burning anti-freeze. It's a hot burning smell but nothing looks burnt when I check under the car. It's right at the doors. Just this bad pungent smell when the car is running.

Cheers,

Tom928

Just a quick update on this.
I did some tuning, set idle, timing, replaced rotor and cap and went back to recheck emissions.
1st idle failed, but on fast idle.... I passed - just barely !!!
Here are the numbers:

HC limit=220 Tested 1st idle=262 - FAIL Tested 2nd idle=93 - PASS
CO limit=1.0 Tested 1st idle=2.16 - FAIL Tested 2nd idle=0.94 - PASS
(2nd idle =2000-2700rpm)

This 1st time 2nd idle failed just as bad as the first, but I only drove the car about 15 miles.
This time, I drove the car over 40 miles before going to the station, but I had to wait in long a line.

Anyway, I got my tags, but something is still not right.
In 2006, It passed on 1st idle with HC=32 and CO=0.

It seems like when the cat gets REAL hot it works like it's suppose to; however, if you just get it warm it doesn't do the job.
I am pretty sure this is the original cat as the records do not show it ever being replaced.

Thanks to everyone for the help.
Cheers,

Jim M.

These cars need to be fully warmed up (read hot) to be clean for emissions. When I drive mine for 15 minutes it just barely passes. When I drive the **** out of it and give it to the inspection station hot it passes with flying colors.