Which cats, 2-way or 3-way for 89 SC?

phils89sc

Registered User
I think with my new exhaust I am going to get some new cats and re-locate them slightly downstream from the factory location (eliminate the 90 degree turn at the cats, what the hell was Ford thinking anyway?). I am going to get some universal type, but am unsure if they are 2-way or 3-way cats? I think they are 2-way, but what is the difference?

I don't care if they are high flow or not, I just need them to pass emissions (Huntersville, NC). I am going to get my exhaust done by a custom exhaust shop here locally who have done work for me before and are very good, but I need to get the cats before hand as they want too much for theirs (I already have the FlowMaster mufflers too).

Can some one help me out here?

Thanks

Phil Stocker
 
Where's Huntersville, NC?

In relation to Burlington, NC, where is Huntersville? I'd like to keep up with your exhaust work progress and employ the talents of your exhaust guy when it's time for me to get mine done.

Keep me posted!!

Dale
Graham, NC
 
An 89 SC with AOD will have EGR. It was the 91-93 AOD's that didn't have EGR. You can put a 3 way on if you want, but it likely won't work right because the exhaust won't get enough O2 to light it up.
 
Include the 90+AOD on the no-EGR list. Hence, 3way cats.

But to answer phils ?, the difference is the 2 stage catalyst reduces hydrocarbons and the EGR setup controls the Nox. While the 3 stage is designed to reduce the Nox without an EGR setup. So, it sort of depends on whether or not you have an EGR. It was standard fare on the 5 speed, and the AOD typically didn't have it. So, its best to inspect and find out. If you have it, you'll have a tube running out past the exhaust manifold back up to a gizmo buried behind the intake.

Hate to see you spend $ and then not pass. :)
 
I appreciate the advice!!

I would also hate to spend a huge boat load of $$ and not pass too!! They are sticklers on inspections here in Mecklenberg county. I need to get something done because I fear that the factory cats are just a shell now, they have either broken apart internally or someone punched them out (don't ask me how).

I appreciate the advice and all you help.

Phil
 
WHAT TO DO ?????

HERE IN PA. I went with after market cats 2/1/4 can get from " JEGS, SUMMIT, & J C WHITHEY just name a few under 70.00 bucks......................had no problems with emissions..............FAST FREDDIE ;) ;) :rolleyes:
 
So does this mean that two-way cats on a non-EGR 90 AOD will not properly reduce the correct range of emissions? I just bought some two-way hi-flows from Jegs but have not installed them yet. I had asked around but was always told it didn't matter...
 
joenintiesc said:
So does this mean that two-way cats on a non-EGR 90 AOD will not properly reduce the correct range of emissions? I just bought some two-way hi-flows from Jegs but have not installed them yet. I had asked around but was always told it didn't matter...
Depends on the state/county you live in. In Dallas county, they test for Nox which is what the 3rd stage handles. Years ago, they didn't used to do that test.

If the person who sold you the cats states that is doesn't matter, then i'd get it in writing and ask them if they'll pay to have them replaced if you fail the test.

But the folks who make a living testing/fixing the cars know for sure. Muffler shops should know. Something else to know about is if you locate the cats too far down, the exhaust has time to cool slightly and they may not do the job. You may need to insulate the downtubes to keep the heat up.
 
Yes, it definately depends on the type of testing done.

In Ohio for example, they do not check NOx, so 2 ways are fine for any car.

However, if they test NOx, then you need to make sure that if you have an EGR, it is working, and if you don't have EGR, and you have a tube going into the side of the cat, then you have 3 ways and must stay with 3 ways. The tube is there to provide additional O2 for the 3rd stage. Some cars have air pumps, not sure how the SC does it.

As for moving the location of the converters, I moved mine downstream a good 36 inches (all the way behind the transmission) and passed with flying colors even with a HP cam and other stuff. I DID wrap the pipes with header wrap though. The testing here is done on a dyno at 25mph.
 
So what the heck is the difference between the two Dynomax cats below???

3-way converter

3-way converter with air inlet tube
 
I think from what Dave said, you probably don't want the 3way with air inlet tube. That setup is for Ford engines which have an air pump. The air pump on older Fords was a belt driven thing usually at the bottom of the engine which looked sort of like a power steering pump. I believe they called it a Thermactor pump. None of the SCs that I know of had that and the 90 AOD certainly didn't.

hope this helps.
 
Cool, thanks for helping to get to the bottom of it... Now my only issue is whether I'll have problems since I have the 2.5" in/out. I've heard they won't mate up properly to the down tubes - but I plan on getting custom downtubes - so maybe it won't be an issue?
 
Back
Top