High Flow Cats Installed

[Don Nguyen]

Does anyone have high flow cats installed on their cars or know of any good brands to look at? I was gonna just run straight pipes, but I don't think I can deal with the smell at idle. Do most guys who run high flow cats on the boards just run universal high flow cats welded in place of their stock cats? Any insight would be great.

thanks.

-Don

[Bernanke]

..

[Don Nguyen]

You have an e30 now? I have a set of midpipes that I had the cats cut out of but left the resonators on there. Should I take the resonators out and put the cats in place of it? Or should I just put the cats in front of the resonators? I just don't want a raspy exhaust sound. I also can't seem to find them on ebay. Who sells them? Should I also go with 3" piping all the way through or should I keep the stock diameter, which is smaller at where the cats meet up with the rest of the midpipes.

thanks.

[souroull]

take out resonators, add high flow cats

[equate975]

Im running a magnaflow seems good to me :dunno

[arakele]

i have not personally used them.. but..

a buddy of mine runs 2 carsound/magnaflow #54905

http://www.car-sound.com/02product/parts/54904.jpg

[M3PowerE36]

Magnaflow FTW

[Don Nguyen]

Shuold I go with 2.5" or 3"? I heard if you take out the resonator it gets kinda raspy, anyone have any input?

[ZLUJ]

wheres the resonator on a cat located?

[Gregg]

Everyone I know uses 3" straight back. Of course they are turbo cars. LOL

[MasterM3]

that girl with the black e36 m3 at UCI had her resonators removed. lemme know if you want her number so you can check it out.

[techno550]

This is for the OBD-I 325 in your cars list?

if replacing the two cats with a single cat, a 2.5 inch cat is probably your best size.
The best overall solution is a set of factory OBD-II midpipes.

[Don Nguyen]

This is for the OBD-I 325 in your cars list?

if replacing the two cats with a single cat, a 2.5 inch cat is probably your best size.
The best overall solution is a set of factory OBD-II midpipes.

No, that's my old car. This is for my OBD2 M3.

[Don Nguyen]

Oh yea, my car is NA right now with a slight chance of possibly going FI, but I dunno.

[GEN3RIC]

Don I seriously think you are fabricating some idea of how terrible it smells at idle. Unless you are running 87 or something, I dont see an issue with the smell. Higher octane usually results in a better smell anyways, but thats beside the point.

I have the Active Autowerke track pipe and yes I can smell it at idle but it is not overpowering at all. The only downside is that you get a good amount of soot built up in the exhaust sometimes and you will sometimes get a black soot cloud shooting out your tailpipe during WOT. It doesnt mean your car is not running right.

[Don Nguyen]

Don I seriously think you are fabricating some idea of how terrible it smells at idle. Unless you are running 87 or something, I dont see an issue with the smell. Higher octane usually results in a better smell anyways, but thats beside the point.

I have the Active Autowerke track pipe and yes I can smell it at idle but it is not overpowering at all. The only downside is that you get a good amount of soot built up in the exhaust sometimes and you will sometimes get a black soot cloud shooting out your tailpipe during WOT. It doesnt mean your car is not running right.

I had it installed on my car for a while and the smell was not just me. Everyone I drove in front of said it smelled and that smoke would come out at every gear no matter how much or little I was on the gas. I am running 91 octane. I don't smell it at idle, but when I come to a stop, all of the smoke/smell/gas or whatever comes forward also and then into the cabin if I have the windows down. Maybe you got lucky and your car runs really clean, but my car is a different question. I lay a thick smoke screen on the ground whenver I go WOT and shift hard.

[GEN3RIC]

Hmm. Maybe you should check your cylinder compression just for fun :) I have 11.0:1 compression, maybe mine just burns more of the fuel than yours does.

Good luck in your decision Don

[Don Nguyen]

Do you shoot out flames?

[GEN3RIC]

Can't say I know for sure. I'm usually ahead of the exhaust tip at this point :tongue

Nobody's ever commented flames but I'm sure its happened a time or two :dunno

[Don Nguyen]

So the search for high flow cats is now on. Probably gonna go with 2.5" diameter ones, but now the question is, should I take my resonators out?

[QuestMCoupe]

Please keep us informed. I've been under the impression that trackpipes and such dont do much for OBDII M3s.

[EstorilRoc3060]

I just saw straight through pipes for a OBD2 M3 by SS on the Turner Motorsport website, anyone know anything about those?

[JLac]

So the search for high flow cats is now on. Probably gonna go with 2.5" diameter ones, but now the question is, should I take my resonators out?

(2) 2.5" diameter cats are going to be overkill and you will probably be loosing even more low end torque than you would like.

I think adding high flow cats in general will make your car raspier. I have 1 single 3" high flow cat and my car is pretty raspy especially with my AA gen III exhaust.

[Don Nguyen]

Please keep us informed. I've been under the impression that trackpipes and such dont do much for OBDII M3s.

Yea, it was mainly for sound and whatnot. I did feel a bit slower putting around town, but on the freeway and higher speeds it felt like I was faster. But who knows, maybe it was just all in my head.

[Don Nguyen]

(2) 2.5" diameter cats are going to be overkill and you will probably be loosing even more low end torque than you would like.

I think adding high flow cats in general will make your car raspier. I have 1 single 3" high flow cat and my car is pretty raspy especially with my AA gen III exhaust.

What should I go with then. Isn't stock 2.25 or so? Does that mean you have a custom exhaust from the headers back since you have a single pipe?

[arakele]

as i mentioned in our convo, 2.25 would be fine, and 2.5 depending on mods


also id leave the resi's out.. but then again i like exhaust to be loud. :evil2

[Don Nguyen]

Well, current mods are 3.5hfm, m50 manifold, AA software, fan delete, ASC delete, 3.5" intake, System U UUC exhaust, and well, the midpipes I guess.

[techno550]

Yea, it was mainly for sound and whatnot. I did feel a bit slower putting around town, but on the freeway and higher speeds it felt like I was faster. But who knows, maybe it was just all in my head.

Ah, OBD-II M3. Yes, your car is now slower than it was. Best bet is to put stock midpipes back on.

Your ideal size for a pair of cats will be 1.75 inches. A single 2.5 would be close. (just slightly too big.)

[JLac]

What should I go with then. Isn't stock 2.25 or so? Does that mean you have a custom exhaust from the headers back since you have a single pipe?

I'd hafta do some calcs to choose a right sized cat for you when I get off of work since I am not 100% sure how s52 midpipes are designed off the top of my head. I do have a custom midpipe. I have the two header pipes going down into a single 3" pipe through a single 3" MagnaFlow highflow cat and back out to 2 50mm pipes out to the stock resonators back out to the catback. This setup makes my car pretty sound pretty damn raspy.

My bends, inlets, and outlets are not the best in my midpipe, but I paid real cheap to get this done so I can't really complain. Plus I actually did feel an increase on my BUTT DYNO. But who knows how well my BUTT DYNO is calibrated. :dunno

I'm gonna be coming back down to Irvine this Thurs. and Fri. if you want you can come check out my car and get a ride in it if you want. My car pulls pretty hard up top.

[Mr.M]

My bends, inlets, and outlets are not the best in my midpipe, but I paid real cheap to get this done so I can't really complain. Plus I actually did feel an increase on my BUTT DYNO. But who knows how well my BUTT DYNO is calibrated. :dunno

The butt dyno is almost always poorly calibrated ;)

[Don Nguyen]

I'd hafta do some calcs to choose a right sized cat for you when I get off of work since I am not 100% sure how s52 midpipes are designed off the top of my head. I do have a custom midpipe. I have the two header pipes going down into a single 3" pipe through a single 3" MagnaFlow highflow cat and back out to 2 50mm pipes out to the stock resonators back out to the catback. This setup makes my car pretty sound pretty damn raspy.

My bends, inlets, and outlets are not the best in my midpipe, but I paid real cheap to get this done so I can't really complain. Plus I actually did feel an increase on my BUTT DYNO. But who knows how well my BUTT DYNO is calibrated. :dunno

I'm gonna be coming back down to Irvine this Thurs. and Fri. if you want you can come check out my car and get a ride in it if you want. My car pulls pretty hard up top.


That'd be cool if you can calc what size is ideal for me. I think if I ever go FI in the future, i'll just swap out the cats again for whatever size is most efficient for me then. I'll just put in the size that is the best for what I am running now. Doesn't cost too much.

[Bernanke]

optimal system is 200 cell cat one bay for $37, 22" long magnaflow resonator, 14-18-22" magnaflow muffler depending on sound volume u want. use all 2.5" mandrel bent piping for NA, 3.0 for FI. simple as that.