catless vs cat

[jayro]

Hi all,
I'm sure this has pobably been discussed before, but with the loss of the previous posts I can't find anything. I was wondering what kind of gains are seen with the catless y-pipe vs the catted one. I currently have the magna flow catted version and am wondering about replacing it, or cutting out the cats and welding in a piece of strait pipe. The car is a 94 mtx. It is a "toy" with the current mods:
y-pipe, BBB, P+P intake, 75mm MAF, Ted B LPM, ASFB and quite a bit of weight loss (no carpet, no ac, racing seats ect).

Wouldn't I need some tuning if I went with a catless unit? Are the gains worth it? Would I see any gains by just cutting out the catts, or would I need to by a full new unit?

I am wanting to hit 200whp. Last time I dyno'd I was at 195. With the UDP that is on the way and some intake fine tuning I think I should make it.

Jeremy

 

[Kens1992mtxSHO]

With those mods I'm surprised your SHO's not at 200whp already. Cat-less you'll lose a little on the low end (if I remember correctly) and gain on top.

 

[jayro]

Yeah, I thought it should hit about 200 too. I had replaced the tube going from the MAF to the throttle body with one of the crome looking ones from autozone when I panted up the intake cause I thought it looked cool. After the dyno I checked everything out since my power kinda choked up top and found that the angle was off a little causing the air to have to zig zag. I have since put the stock one back on, but havn't dyno'd agian yet. The day I went was pretty hot and humid too.

Anything as far as the tuning needed, or just cutting out the cats?

Jeremy

 

[Kens1992mtxSHO]

With those mods I would be tuning anyways. What was the LPM tuned for?

*edit* and what kind of MAF do you have?

 

[jayro]

It was tuned for the mods listed. I am seriously thinking of getting a tweecer though. Next time I take it I will make sure I get an accurate A/F and do a couple runs with the LPM and a couple without to see the difference. Probably after I get the UDP installed. I'm pretty sure that I will need to do something with the tune if I go catless.

Jeremy

 

[SuperHO]

Well, unless you have access to a welder, or know someone who does, good luck getting rid of those cats at a shop, since fiddling with cats is a federal crime. At any rate, with those mods, you should be at 200whp....chances are, if you went on a day that wasn't so hot, you very well make that mark. SHO engines don't particularly like hot days...

 

[shobote]

You will hate the sound of your exhaust if you cut off the cats; rasp city; think ricer fart cannon sounding.
Unless you track your car, keep them on, as you will only gain HP way up in the RPM range but lose low and mid range toque, which is something these motors need as much of as anything. Torque is what makes the cars fun to drive, making for less shifting and quicker accelleration from a stop and out of corners not revving above 6k with your loud exhaust and announcing your presence to the local authoities.

 

[jayro]

I would be able to cut them out and weld it up myself....we also don't have any emmissions testing. I just didn't know if it would even be worth it. The car isn't driven alot, mostly just for fun and some autocross.

And the heat definitly has an effect. In the morning when the temp are down it is much more responsive.

Jeremy

 

[SHOZ123]

If you get the TwEECer you should be able to modify the MAF curve to make more power throughout the rpm band without cats. Just get a WBO2 sensor.

 

[jayro]

You will hate the sound of your exhaust if you cut off the cats; rasp city; think ricer fart cannon sounding.
Unless you track your car, keep them on, as you will only gain HP way up in the RPM range but lose low and mid range toque, which is something these motors need as much of as anything. Torque is what makes the cars fun to drive, making for less shifting and quicker accelleration from a stop and out of corners not revving above 6k with your loud exhaust and announcing your presence to the local authoities.

Just thinking if it would net me some cheap performance, why not?
I think my $ would be better spent on bigger brakes and suspension upgrades.

Jeremy

 

[jayro]

If you get the TwEECer you should be able to modify the MAF curve to make more power throughout the rpm band without cats. Just get a WBO2 sensor.

Let's see, the sho christmas list:

Tweecer, performance differential, bigger brakes, suspension set up, triflow cams, adjustable sprockets, forged pistons and a zex kit.

My wife and bank account would hate me.lol

Jeremy

 

[jayro]

*edit* and what kind of MAF do you have?

I have the 75mm drop in one from SHOSource. It is made by a company named Professional Mass Air Systems (PMAS). I thought I read that it was made by the Pro-m people just under another name.

Jeremy

 

[Mad Celt]

If you're running a stock Y pipe, get the magnaflow unit with cats. Modern cats do not hold your HP back. It's a myth. period.

 

[Kens1992mtxSHO]

I have the 75mm drop in one from SHOSource. It is made by a company named Professional Mass Air Systems (PMAS). I thought I read that it was made by the Pro-m people just under another name.

Jeremy

At least you've got the MAF that doesn't require a tune.

I recently got the Tweecer R/T myself and am still figuring out how to use it.

 

[38SHO]

Modern cats do not hold your HP back. It's a myth. period.

thats a pretty ballsy statement... however you look at it there is still a restriction in the exhaust... I.E. it is not a hollow tube like the rest of the exhaust system...........

there is way more to exhaust systems though then chopping cats off this y pipe and comparing to this type of y pipe though.......... there are just way too many variables if you want to get scientific about it....

 

[SHOtime2511]

there is way more to exhaust systems though then chopping cats off this y pipe and comparing to this type of y pipe though.......... there are just way too many variables if you want to get scientific about it....

X2
the exhaust design,flow,velocity and scavenging come into play.
this has been discussed quite a few times.

 

[Mad Celt]

thats a pretty ballsy statement... however you look at it there is still a restriction in the exhaust... I.E. it is not a hollow tube like the rest of the exhaust system...........

there is way more to exhaust systems though then chopping cats off this y pipe and comparing to this type of y pipe though.......... there are just way too many variables if you want to get scientific about it....

You are 1000% correct. My statement is based on your logic as well (you are thinking of the entire system as just that, a system), whereas others just assume Cats rob power. When implemented in a well designed system, there is no loss.

RJ

 

[shobote]

I would be able to cut them out and weld it up myself....we also don't have any emmissions testing. I just didn't know if it would even be worth it. The car isn't driven alot, mostly just for fun and some autocross.

And the heat definitly has an effect. In the morning when the temp are down it is much more responsive.

Jeremy

Are you using the stock air filter or did you replace it with a cone filter under the hood ? If replaced, that probably explains why you lose power after the car is warmed up. Unless you have a sheild for the filter it is not a true cold air intake like the stock setup and you lose performance. BTW, I do have an extra heat sheild laying around from an ebay CAI.

 

[jayro]

Are you using the stock air filter or did you replace it with a cone filter under the hood ? If replaced, that probably explains why you lose power after the car is warmed up. Unless you have a sheild for the filter it is not a true cold air intake like the stock setup and you lose performance. BTW, I do have an extra heat sheild laying around from an ebay CAI.

I am using the stock air box set up right now. I have been thinking of going with the cone/heat sheild set up. While it doesn't give any hp gains I have heard that you get added throttle response and sounds meaner. Do you have a picture of the heat sheild you have? I might be interested. Email me or PM me the details. Thanks

Jeremy
[email protected]

 

[jayro]

If you're running a stock Y pipe, get the magnaflow unit with cats. Modern cats do not hold your HP back. It's a myth. period.

I am running the magna flow unit. It was the first thing I replaced.

Jeremy