Hi-Flow Cat or Cut Out for LOWER ETs!! Need Help!

[MustangEater8251]

Cutout befor the cat will hurt your times(I know form expereince) The reason why I say a high flow CAt will help you over a your original cat is, when a CAt goes bad, it can get so bad your car will sputter and possibly not run.

I reccomend you get a high flow CAt, and put the cutout after it, or maybe a cutout after the CAT, and expect the cat to go out pretty soon and put in a OEM replacement or hi-flo in its ways(though highflows seem cheaper)


When the cat crapped out in my car at areound 115k, a chunk broke off went sideways, and blocked off the exahsut pipe, and pretty much almost stalled my car and I barely made it home.

I took off my CAT, and ran Open Y-pipe was a crappy setup I lost too much backpressure lost like 4 mph and .5 in the 1/4 mile consistant. Through on a $15 muffler(I have the exact same muffler for sale if you want one, new in box) on my y-pipe, took the Catback off and ran 15.7s, and worked down to my 15.4 thats the record. Afterawhile I had some road trips and the exhaust was a little loud to be driving like that consistantly, so I took a stock z28 catback I got for free, a CATCO cat, and a cutout and had it installed.

I went Cutout, then CAT, then custom s-pipe(with 2 45* angles instead of 2 90* angles) It was quet, but alot louder then stock and sounded mean, always got compliments. I ran 15.8-16.0 pretty consitant with entire catback on. With cutout open I rean 16.0s consitantly, with cutou and the block off plate with a gieant hole in the middle in, with some washers wedged in it to cause some backpressure, I rant consistant 15.6-15.7s, with a few 15.5s never a 15.4 again, and never the mph I had with my 15.4. If you plan on running a cable or elctric cutout not sure you could even do what I did with it.

If I were you I woudl run a CAt, then Cutout...

I ran 15.6s consistantly, with my catback unhooked, and run my y-pipe to my stock CAT.

I did numerous runs to test out the different things, and too much free flow kills your power, there is a fine line between too much and too little.


I know high flow cats do not flow much better then stocker ones, but any new CAT will flow 10X's better then a 110k original CAT.

[MustangEater8251]

Also for the Y-pipe is 2 in. the stock I-pipe is 2.25 in. and the in for the CAT is 2.5 in.

[Timbo1969]

My stock Y-pipe was 3"....Just FYI there.. :D I'm running no cats with an H-Pipe and my car runs much better than it did with a CAT.

[MustangEater8251]

Originally posted by Timbo1969:
My stock Y-pipe was 3"....Just FYI there.. :D I'm running no cats with an H-Pipe and my car runs much better than it did with a CAT.

In 3.8L... not a 3.4L

[BradC]

MustangEater8251 thanks so much for that info. I do agree that more is not always better. The cutout that I was plannig on installing before the cat is adjustable so if I need more backpressure I can always open it %30,%70, ect... The cutout will really meet or exceed the pros vs.cons relationship between the two I think.

[MustangEater8251]

if you can adjust it go for it, it should work great... mine was partially adjustable but I was not sure on how cable cutouts work...

only electric and regular ones.

[BradC]

I should say I assume it to be adjustable since it is cable operation. The physics of it should work, although I might have to rig up a locking nut and bolt or something on the actual control, but it's got to stay partially closed for backpressure reasons as mustangeaster said. On a side note I got my vette servo and It looks like I've going to have to take it somewhere for installation. I'm just afraid that I will get it apart and not be able to put it back together again :rolleyes: . All well, any idea on prices down here in Mississippi? Don't want to pay too much.

[Ted]

Well this is what I have experienced. I have now had a catco cat, carsound cat, and a brand new stock cat. I beleive that the post cat o2 sensor adjusts for low end or high end depending on the cat. I have noticed I have better top end with a carsound cat, yet my car feels really fast on the low end with a new stock cat. I don't think it makes a life or death difference with a cat. But aftermarket cats aren't as durable as you would get in a stock one. Of course there are a lot of factors, but in general terms... A high flow cat has less dense honeycomb then a stock cat that the honey comb is more dense. Anyway, with a cutout you'll see maybee 3/10ths of a drop off your ET, post cat (this was tested on a 02 camaro, so results may vary depending on the vehicle) I'm not sure about pre cat. But good luck in your search!

[MustangEater8251]

just for anyone getting confused, 3.4Ls only have 2 o2, and they are before the CAt on the y-pipe, nothing after the CAT like 3.8Ls

[BradC]

OK, I've heard some more negative things about cut outs. I've heard that you can't ever get them sealed completely. IF I had the cable operated one I could see that as a problem. Unless there is a lot of tension on the cable I don't see how it would stay shut. Anybody have ideas??? I'm leaning more toward a hi-flow cat now. I just don't know what size to get. The pipe going into the cat is 2.25in and going out is 2.75. Should I go 2.5 or 3? Could the 0.75 difference be welded? I also hate the fact that I went and spent all this money on a hi performance exhaust to just go and bypass it all with the cut out before the cat. Would a 3in hiflow cat to a 2.75in I-pipe to a Flow 80 flow about as much as mustangeaters y-pipe to a "$15 muffler"? If I do the cut out after the cat that would be kinda pointless given my large I-pipe and aftermarket muffler, right? The only size I can get the cable operated cut out in is 2.25in also.

[ March 31, 2004, 12:07 PM: Message edited by: BradC ]