hopps

My 2 cents: I have an 86 N/A with a cat delete...no fancy test pipe or anything. I just took it to my local muffler shop because I was getting bad gas mileage and fuel mileage was decreasing. For ~ $60 he took my cat out and welded in a new pipe. The sound of the car is meaner, and a lot louder (I need a new muffler because I'm not to fond of that) and performance wise...Well its my DD, with the occasional AutoX, I've seen a slight increase in HP, but more noticeably, the mid section of your revs smooth out. Before the car would be slow up till 3500RPM, and then I would hit my power band and it seemed like all the cars power was unleashed. Not, it's straight power from taking off to redline. Or so it seems.

TL;DR Sounds louder, revs smoother.

P.S. I don't have any emission laws to follow where I live...and frankly, I could care less. Just an FYI because I don't want anyone telling me I'm going to Hell for polluting

odurandina

run a resonator about mid-way between where your cat was and your 45" bend... then a large glasspack muffler like a Hooker Maximum flow (the Borlas are way more $$$)... it will really make a nice sound. you can read my crass exhaust thread. JDS is one of a few guys who's heard it.... but you're really in luck cuz, i'll be at the 12 hours of sebring. if that doesn't work, i'll be coming right up i-75 shortly and you can hear it.

see post # 36;

https://rennlist.com/forums/924-931-...-heaven-3.html


Jegs has this resonator in a "single" but it's not on their site. amazing product, considering how simple it is.

http://www.jegs.com/i/SLP/847/31062/...ductId=1182214

the muffler shown in the photo is a 4" in/out/center/center. but one you'll want is the 3" in/out/center/center for making good sound and power.

http://www.jegs.com/i/Hooker-Headers...oductId=744871


;

V2Rocket

in the near-ish future i would be willing to run back to back smog tests on my car with and without a cat to see if a good tune can eliminate the need for one...if there's interest.

id probably run with one anyways in case of a freak roadside inspection but...it is for science

i could even do testing for gas and for e85.

hell, on sunday i ran my car with open headers and in open-loop (no O2 sensor = runs rich), and while cold (runs rich by default to warm up), the gases didnt smell that different from when theres a full system on there

86 951 Driver

I say do the test. Its always talked about on here that a car can pass emission without a cat.

m73m95

Couple things....

There is already proof that you can pass a smog test without a cat. Even in Colorado that uses the same dyno test that California uses. It requires a different tune (Which requires an ostrich, or some kind of eprom emulator), but it will pass.

Also, just unplugging your O2 sensor doesn't put your car into open loop. The DME is still trying to read the Sensor, even though its not there. Meaning the DME is adding 10% fuel to compensate for the missing O2. The only way to do "open loop" correctly, is to turn the function off in the DME.... which you can also do with the ostrich.

V2Rocket

got one



hard to fit in the hatch though

m73m95

HAHA, I know you have an ostrich.... Just adding to the thread info.

I got my ostrich squeezed under the dash. They fold up like an origami box. Head goes back, and stuffed in the ***. Legs tuck up under the wings. EEEEEEEEASY fit

V2Rocket

a woodchipper aimed at one of the rear cubbies greatly simplifies things

Rudeboy42

Are there any advantages or disadvantages to ditching the o2 sensor and switching the DME to open loop?

m73m95

I used to think that's what I always wanted. I couldn't wait to switch the stock O2 with a wideband, and tune my own setup....

...And now that I've done that, sometimes I wish I had the stock O2 back. I don't regret the change at all, but it is nice to have the DME compensate on its own. It is really nice to be able to tune the car how I want it to run, but especially when cruising down highway, when you don't NEED to tune anything, it would be nice to have the DME self correct to 14.7

It really depends on what you want, how your car is setup, and how you drive. If you just daily drive, a stock (or near stock) engine, and you want good mileage, there is absolutely no advantage to losing the stock O2...it might even be a disadvantage.

If you have a dedicated track car, heavily modded, and you drive "flat out", then yeah, there is no reason to have the stock O2, and it would be to your advantage (and necessary) to tune your own setup.

Those are the extremes. Just decide where in between those you fit.

I will say this. When I get my turbo engine built, I will be running both the stock O2 and a wideband. I'm going to have a modified engine that I will need to tune on my own, but I still want to get good mileage on the highway.

jcslocum

My daughter made her own "test pipe" this weekend after the pipe on her 944 broke right at the inlet weld. She does not have the budget for a new cat (big $$ if you want the full pipe section) but did have the $32 for 36" of 2-1/4" straight pipe and a clamp. She is becomeing a mighty fine welder and is proud of her latest weld!!!





We may weld in a new universal cat this winter once she has more cash. Time for her to not only do her own maintenance but pay for it too. :-)

M758

I have seen this happen a few times on track cars. Mine included and it is one good reason to run a track car without a cat. One less thing to break.

The only thing to watch is the joint is not a straight joint. There is slight angle where inlet weld is so if you replace it with perfectlly straight pipe it will cause problems with mounting it.

Rudeboy42

If your daughter wants more practice she can weld my muffler in

F40LM

:If you have a Autozone buyers card.....got a coupon for $5 off when you spend $5 yesterday via email.

http://p.p0.com/YesConnect/HtmlMessa...LViWlYGn7Xcfly

Stop by local autozone, two 18" long pipes with flared ends were $5.19 each. Walked out the door with both for less than 6 bucks. Will cut to fit and weld it up hopefully tomorrow.

Thanks for all opinions.

michael

hevquip

Wtf, do you guys not have to have emissions done or catalytic converters on yours cars in the states you live in or something? I live in Colorado where both are mandatory, though my car passes fine without a cat. I'm hoping they'll not think to do a visual inspection or I'll just bribe the emissions person to not write up that there's no cat installed...I might check into one of those fake cats that was linked in this thread too, though I'd rather not have to remove and install anything though, especially if I have to do emissions every two years or so and might have to keep swapping between a test pipe and cat just for the sake of passing emissions. The few reasons I miss living in New Mexico is for it's lack of emissions requirements and it's lack of traffic.