I'm purchasing a Hooker catback system for my T/A when I get paid this coming Tuesday. However, I am confused as to which one I am supposed to order. There are three of them and each one of them is 3" piping to 3" in/dual 2.5" out muffler. 16820 is listed for 83-92 305 non-HO 16822 is listed for 83-85 305 16823 is listed for 86-92 305/350 HO or TPI If all these systems are 3", why is there difference between which engine they are supposed to be used on? Are the bracket and hanger locations different between the early years and later years? Also, I've heard the non-HO version comes with a 2.25" reducer where the I-pipe meets the cat. Is this removable or would I have to cut it off? I'm aiming to make this installation as straightforward and easy as possible. The system will be hooked up to a 3" Magnaflow cat and Hooker 2055s.

16823, assuming the the cat is a direct-fit.

The differences are in the connection to the cat. The TPI version is the right one to keep it 3" all the way.

So there won't be any problems with the exhaust using the stock hangar locations?

The hanger for the cat on the tranny tailshaft housing may need modification.

I have a 91 GTA with a 5.0 TPI HO engine. I could have sworn that when I was under the car that the outlet to my cat (I am assuming it's stock) was the flange type. But yet the Hooker 16823 for a TPI car does not come with the flange. I am confused...unless I don't have a stock cat or I am mistaken.

Anyway I was wondering if anyone has installed a Catco 4115 cat and a Hooker 16822 together?

The Catco has a 2.5" outlet diameter with an outlet flange attachment and the Hooker 16822 cat-back has a 3" I-pipe diameter supposedly also with a flange attachment.

How will these match up if one is a 2.5" and the other a 3"? Will I need some kind of adapter?

I am so confused! lol Thanks in advance!

Well after trying most of the day I finally got ahold of someone at Hooker that could help me!

They said that as long as the cat is either stock or a direct fit (which the Catco 4115 is), everything should mate together just fine. I am not sure how things connect if one is 2.5" and the other 3", but I am willing to take their word for it. I am new into the aftermarket exhaust setup so I want to be sure everthing will fit together before I buy it.

If anyone has installed both of these products together, please share any input you may have. Thanks.

I am going to keep my stock cat. For those of you that purchased the Hooker 16822 and that had to cut off the I-pipe flange to fit your cat....

Did you have to get the end of I-pipe flared to fit up against the ball of the cat to seal properly?

A '91 TPI with single cat is not 3". The 4115 is the correct cat for the application, has a 2-1/4" inlet and 2-1/2" outlet.

The 16823 is not the correct cat-back for this application. That is the 3" connection system.

The 16820 is the correct system to use with the 4115 cat. It has a 2-1/2" connection at the cat, the pipe thereafter is 3". http://store.summitracing.com/largei...t=HOK-16820HKR

Thanks five7kid for the info. I decided to keep my stock cat though. I figured it has the 2-1/4" inlet and 2-1/2" oulet.

The Hooker 16820 model you mentioned lists in the application notes: Fits non-HO models with vin code H and E. I have the HO vin code F, so I figured my model is supposed to be the 16823. But the pic of the 16820 does look like the correct connection. What's up with that?

Downside of the 16820 anyway though is it's $60 more expensive than the 16822. So I figured I could save a few bucks and buy the 16822 and if I had to I can get the I-pipe flared for like $5 or even a reducer if necessary. I figured others have done the same thing so just wanted a heads up what had to be done for everthing to fit and seal correctly.

Hooker is incorrect calling TPI applications "HO" and "non-HO". The only HO model from GM was the L69, which was carbed. So, we need to get over that hurdle first.

Next, in '91, VIN F came in two versions, single and dual cat. The dual cat version made more power, so if any deserved the "HO" designation, that would be it. The single cat version used the same size exhaust as the lower performance versions, which included the LG4 and LO3.

I've never seen modifications such as what you're contemplating cost less than $60. I thought I'd be smart and buy a universal cat and have the parts flared/adapted to make it fit. I spent more than the difference making it happen. Get the bolt-on part, you'll only be sorry if you don't.

five7kid...thanks! Your advice paid off. I got the 16820 and it fit perfectly to the stock cat. Why Pontiac went to a 2.25" inlet and 2.50" outlet cat on a TPI engine is beyond me!! Didn't the less powerful engines (TBI, etc) have 3" cats????

Anyway the Hooker is a nice system. A little on the quiet side...but I was kinda looking for that. Maybe it will break in and get a tad louder over time.

I am not totally 100% fond of the stainless tips that come with the kit. Unfortunately, new ones are like $50 each so I plan on dealing with these for a while. At various angles it looks as if they are sticking out way too far. Plus already...pulled out of a parking lot today and the bottom edge of the tips rubbed the ground! I may cut 1" or 2" off the tail pipes to bring them in a bit. Has anyone tried that with success to these problems?

And my car failed emissions. HC are fine but the CO is high...especially at idle. Not that there are other things that could be causing this, but I was wondering if the burning of the oils left on the pipe from manufacturing could be throwing off the numbers any?

Thanks!