jkamtan909

Anyone done a primary cat delete with straight pipe in its place with stock headers?

I have Secondary and resignator delete with x-pipe already.

just curious if anyone has done this.. have u gained hp or torque from what your butt dyno told u? or lost power and low end torque? If anyone's done this.. please chime in. Not trying to start an argument or anything just curious cause my cats are cracking on the passenger and I plan on re-welding them or cutting them out completely.

current mods:

77mm sc pulley
bwk
1 step colder plugs
k&n filters
3pc idler pulley set
FTP Heat Exchanger
bosch 010
ECU tune from Eurocharged

layzie12g

Yup. I had primary cat delete and 200 cell metal race cats in place of my seconarys on my SL55 . It had a smaller s/c pulley and an EC tune. It ran 12.40 at 116 if I remember right. I don't think you'll pick up much power from the cat removal. It will make the car louder though.

jkamtan909

high flows don't seem bad but I would rather just stack up for some headers.. my cats are fine. I just need to weld it up and its good to go..do u know anyone who actually went catless with no high flow cats, and just straight pipes?

jkamtan909

No one has an input or done this?

M3diesel

You need to get rid of the stock exhaust manifolds. They are choking your engine. Do Kleeman/EC mid length or step up and put LT's on. These exhaust manifolds will go down in history as the worst manifold ever on a FI car. They are puny under the cover that you see. There are threads on here where iirc Shardul cut the covers off and showed how small the primaries were.

jkamtan909

Just curious if anyone's done this thanks for everyone's input.

Max.H

#1 worst exhaust manifold in the history of all FI exhaust manifolds. The pipes are so tiny it is an absolute joke. Headers will be first engine mod, If I ever get around to mods. I'm fine the way it is.

MACEDON

I have straight pipes (up to the muffler) and I don't know any better because the car came like that... the car is very loud under load and I am going to keep it that way.

I didn't know the headers were that bad. I think that's going to be my next upgrade.

Will an X pipe give any advantage over the stock H config? I should show you a picture of my exhaust's welding job if you guys want to laugh...


How much of a gain would you see with EC, and how much with Kleeman midlength? I don't think I can afford the luxury of full length ones...

E55amg0220

Im sorry while these are some pathetic exhaust manifolds their is absolutely nothing worse in my mind than the 01 to 06 exhaust mannys of the bmw non Ms these are horrid

Not only is the cat right at the exhaust merge but even the point of the merge is squished almost an extra 1/2 inch before the merge is ridiculous!!!!

MACEDON

Wot that is annoying to look at, what were they trying to achieve?

PieRat

Kleemanns and eurocharged are the same headers basically. People like the flanges on eurochargeds better and they usually have sales (cheaper). With your primaries already taken out you will probably net 20+whp.

E55amg0220

Honestly they wanted to get the ultra low emissions rating so needed very early cat light off other than that i have no idea why such a ****ty design.

How much power do the EC mids give up over like a set of MBH LTs? Just curious

PieRat

Not sure, ive read as little as 9whp and as muh as 40! Maybe someone who switched has a definitive answer. Removing cats adds 10-15 each. Maybe its fair to assume longtubes improve flow over mids to a similiar degree as removing 1 cat? X pipe is good for 8-10 wheel as well I believe..

MACEDON

So my rough idle is pretty annoying honestly, it shakes the car like a muscle car... could it be a faulty crank position sensor or do you guys think it's just normal because of the lack of back pressure?

To recap: 180mm cp, EC tune, stock heads, no cats, no res.

jkamtan909

I did mines today after installing my EVOSPORT shorty's. And haven't had any issues or rough idle or Check engine light. Definitely better response and low-end torque on the butt cheek dyno. Don't regret it wat so every

PieRat

Is it consistently bad? What are your fuel trims doing at idle?

MACEDON

I'm gonna check with the torque app and screenshot what i find

PieRat

Only rough idle prpblems ive had is with mounts (engine and trans) there is a way to check yours if you haven't.

Pop the hood, jump in car, put car in reverse foot hard on brake, slowly give it gas so the engine torques but car doesn't move. See how far the engine moves should be a inch or so. Since reverse mount is usually fine you can use that as a baseline. Now do the same in drive. Mount lifted like 3 or 4 inches on the driver side :o.

the other problem I had was with a loose vaccum hose going to the surge tank. Car wouls drive fine normally until the ecu spazzed ( crash?) out from dealing with incomprehensible fuel management parameters and would start pulling fuel. All my fuel trims would shoot up to +25% and sit there. Car would shake and buck. It would also jerk and surge on deceleration while in gear. The dealer plugged the vaccum hose in and prpblem solved...

hope some of that helps!

MACEDON

If you removed the cats you're gonna get a CEL soon. Get a tuning cable from Shardul for $400 and get a tune going if you haven't alraedy. Mention you deleted cats and list all your mods, easy af to do and it will get rid of your CEL's as well (it really changes up the car, feels like a monster)