cat delete questions? does it cause power loss....

[pearbmw325is]

thinking about custom making new pipes from the bottom of the stock headers going into my UUC exhaust. doing so will delete my cats and resonator. what size piping should i use. Last i have heard people having power loss when running test pipes. should i just delete the resonator and leave the cats to not have this power loss. I have a e36 328is auto. i also understand that i will not pass emissions and have a check engine light on.

[robjohnson]

I've never seen a loss on a BMW. If cats made more power racecars would use them...

[pearbmw325is]

i have heard that you can loss low end power/torque but mid to high is increased.

on my friends G35 we installed a track pipe and the power loss was crazy. it increased 1/4 mile time drastically.

[robjohnson]

I heard the price of tea in china is cheaper....

http://************/kn6wv5

[BMWParkingOnly]

Modern engines are tuned/optimized based on the existance of OE cats. A properly functioning modern cat will have very little restiction on the engine flow/power. In some cases removing them will yield positive results, but it usually isn't until other things have been modified (cams, headers, etc) that you'll see an appreciable difference in performance.

[pbonsalb]

Removing cats with no other changes may not yield any benefits unless the tune can accommodate the removal. They are an obstruction, so if they are removed and the engine is tuned for the removal, the engine will make more power.

[BlownM3Bill]

I saw a small increase in top end,but if you have no other mods(cams,airmeter,injectors) it wont make that much difference, and you will not pass emmisions ,it will also be a nosie magnet for cops, all that for a few HP up top? why? ????? is it a race car? or deticated track car? then ok

[oldMcR]

i also run a 328. why you would want to mod an auto i don't understand but anyway, i have been told by a reputable firm in VA that cat removal will cause a decrease in power in that motor.

[KnudsonsM3]

To echo the others yes it adds power and can cause tq loss...

On my 95 M3 i deleted the cats and noticed a lot of tq loss.

Mods on the 95: dinan stg 1 ecu, uuc pulleys, dinan cai, deleted cat

My 99 M Mods: Full NA....Noticed no tq loss with cat delete

[Kaiv]

From what I gathered online most E46 M3s dyno 275/235-ish stock

My car is stock aside from no cats; it did 288/229 so I guess it adds some power, but you do loose a tiny bit of torque.

Errr should've read the thread. I get too excited talking about my car If I were in your pants I'd leave the exhaust alone and do a manual swap + M50 manifold.

[Alex @ Miller]

spend that money on a chip and intake. I had my 325is dyno tuned and made something like 15rwhp on a completely stock motor minus an intake (MILLER PERFORMANCE)

[KnudsonsM3]

or save all your money and do an s52/5 speed swap

[pearbmw325is]

KnudsonM3 when you did your cat delete did you run a larger pipe. People have been saying if you run the stock pipe size from the headers back to the UUC you will not have a power loss and gain some mid to high power

[KnudsonsM3]

KnudsonM3 when you did your cat delete did you run a larger pipe. People have been saying if you run the stock pipe size from the headers back to the UUC you will not have a power loss and gain some mid to high power

on my 95 i ran dual 1.75in pipes where i deleted the cats

on my 99 i have dual 2in pipes with a custom mid section within my mid section. (make sense?) LOL

The stock exhaust is actually a 1.75in so me doing a 2in opens it up even more.

[pearbmw325is]

i dont think i am going to mess with it. dont want the tq loss. Just going to go with the E46 m 6 speed swap then later do the motor

[xear0]

I actually have the Schrick Cams, 3.5 HFM/intake, machined cyl head, and retune, etc (see sig). with the cams and such will there still be a tq loss?

was thinkin of replacing the cats with the stock 1.75" pipe and getting some long tube headers. thoughts?

[n2bimmer]

i have heard that you can loss low end power/torque but mid to high is increased.

on my friends G35 we installed a track pipe and the power loss was crazy. it increased 1/4 mile time drastically.

This

[pearbmw325is]

i replaced the pipe from the headers back to my uuc system U with 2 2.25in pipe. no torque loss and car sounds great. it improved 1/4 mile slightly. i also did the 5 speed swap, light weight flywheel, short shifter, selector rod, and m50 manifold

[KnudsonsM3]

I actually have the Schrick Cams, 3.5 HFM/intake, machined cyl head, and retune, etc (see sig). with the cams and such will there still be a tq loss?

was thinkin of replacing the cats with the stock 1.75" pipe and getting some long tube headers. thoughts?

did you read my posts above?