kcrunner

I put an aftermarket exhaust on about a year ago at the local muffler shop. While we were working on it, we noticed that the cat had been hollowed out, no baffles. I just went with the El Cheapo exhaust that was recommended, and ran 1 3/4" exhaust.

My question is: Do I really need to have a new cat (other than for environmental purposes) or will it be fine to go without? I assume some backpressure is needed, but how much?

Thanks guys!!

DaveInDenver

Your truck does not /need/ a cat to run. IOW, it's not providing any function specifically to make the engine run well. You need a cat to keep the air clean and having a good one has a minimal affect on your performance, so there's just no reason to hollow them out or remove them.

InternetRoadkill

Oh god. Not another back pressure thread. Short answer is that it depends on the cam profile.

dcg9381

I think it depends on more than your cam profile.
Corky Bell had a good book that gave rule of thumb on power and exhaust size required... Short answer is that for a 100-120hp 2.4L motor, you don't need huge exhaust.
The recommended size is no more than 2.25". That little exhaust system isn't optimal, but it's probably not killing you either.

Ganoid

from a performance stand point it would be worth noting that a Cat actually increases exhaust temperature (by burning off the extra fuel) and hot exhaust gas flows faster than cold.

kcrunner

I didn't hollow the cat out myself, and I think from a moral standpoint the benefits are there. I just found out that my 87' Runner has a pre-1985 22R and I'm trying to squeaze the best performance out of it as I can. Sorry to start up a thread that's probably gone around the block a few times . I did the search, didn't find my answer, and that's what you guys are here for.

Much appreciated!!!!

chimmike

Problem with this is, while your statement is true, the cat is a big enough obstruction to not allow the hotter gas to expel any faster from the engine. Simplest way to do this with a straight exhaust would be to use exhaust wrap from the header to the muffler, keeping the hot gases in and trapping the heat for faster flow.


you DO NOT want to add things to create backpressure, EVER. Backpressure is bad. Some people will say some is okay......for the health of the motor, it's bad.

Zealot

You do though want some back pressure on an engine. Especially 22-r(e), if you do not have any back pressure you will have no low-end torque. Few months back my exhaust split in half at the neck in the down pipe, resulting in no back pressure. Not only was insanly loud but I got really bad gas mileage and it barely got up normal hills. Believe me back pressure is needed.


I now run a 4 into 1 header with hollowed out cat, and a normal muffler. In the engine I have a 260* cam with the head ported and polished and with O/S valves. I get excellent low end power.

stormin94

Well, this shouldn't even be a problem, 22-RE's have no torque anyway. jk. But in all seriousnes, don't go puttin a 3 inch cherry bomb on a 22RE. You should stick with a 2.25. I have a 3.slow, and headers, and hi flow cat, and flowmaster all the way back, and i run 2.5 inch. Flows just great. I would hollow my cat out for more MPG, more torque, more HP and deeper sound. Cats do obstruct your exhaust tone. Check for a sensor after the cat. too.

RustBucket

iTrader: (1)

Your cat does ALOT as far as reducing emissions... none of us can pretend like that's not our responsibility.

AH64ID

First off 1.75" is way to small, for being concerned about performance gains.... The best setup for the 22R(E) is 2.25" pipe, with a 2.25" cat and 2.25" muffler. Get a carsound(magnaflow) cat of summit for like 55 bucks, and a then go to a shop and have a full 2.25" exhaust made with that cat, and a good muffler. That will yield you the best results as far as improvements and increased efficacy..

If nothing else put a decent cat back on, the effect on performance isn't noticeable, and they really do work..

chimmike

if you get a crush bent exhaust, get 2.5" diameter piping, as the crush bends SEVERELY reduce the diameter of the pipe.

No, ideally, you want NO backpressure. Backpressure is bad, it can ruin valves, mmmkay?

2.25" with a high flow cat and a good high flow muffler will do wonders for economy and power.

Eventually I'll buy headers for my 3vz and get rid of this flowmaster muffler and run a 2.5" mandrel bent setup all the way back ( I have mandrel bends left over from my turbo car days...so I'll just fab it myself). Probably get a nice magnaflow muffler for it.

NC-B17A

Back pressure is bad on any motor
needing back pressure is an old wives tell. It came from people putting larger exhaust pipes on their cars & loosing tq. The loss is due to the loss of scavaging not loss of back pressure.
Exhaust works in pulses with a vacuum in between each one.
The captions below are based on piping sizes for an Integra but you get the idea




http://www.nsxprime.com/FAQ/Miscella...austtheory.htm
http://www.uucmotorwerks.com/html_pr...torquemyth.htm

AH64ID

Well, yeah... but backpressue is the commonly misused term

Nice diagram

DaveInDenver

What is the right definition, then?

AH64ID

Commonly its referd to the proper amount of backpressure, when really you want the proper amount of flow.....

chimmike

Isn't this what I said? lol.

MudHippy

From http://www.nsxprime.com/FAQ/Miscella...austtheory.htm
Good stuff, thanks NC-B17A.

This is why I have no muffler. I wouldn't have a cat either, but it's too loud without it. I've taken it off a few times for kicks.

Ganoid

What you are looking for is a balance. You want a small enough pipe to keep your VELOCITY up so you can take full affect of the scavenging aspect of your exhaust design. If your pipe is too big you get reduced velocity and a reduction in scavenging. If you pipe is too small you get "Back pressure".

In response to a cat adding to much restriction to an exhaust system its pretty common knowledge that a modern cat will not add any significant resistance (back pressure) to an exhaust system. But it will keep exhaust temps high enough to be a performance value however slight.

AH64ID

Sure, but do you run in the 4500+ rpm range? The exhaust with a muffler has a better bottom end, thou maybe a few less hp at redline....

I have run open header on a 22RE and the performance sucked compared to a header with a cat and good muffler.