[e90AW335i]

Is it possible to lose power from a DP back catless exhaust? I put an exhaust system on this weekend and I honestly think I have lost power. It feels slower in the low end and doesn't launch nearly as hard as it used too.

What do you guys think, is this just in my head or is my butt dyno correct?

[scalbert]

If properly designed, no. The best exhaust for a turbo system is no exhaust at all behind the turbine. However, sound increase does not always equal flow increase. Lastly, sound increase may be drawing attention away from the feel; i.e. a placebo affect.

[cn555ic]

Did u make sure you capped the vacuum hose from the OEM exhaust flap tightly....I heard someone on this forum also had this problem and it was the vacuum hose not completely sealed

[e90AW335i]

Originally Posted by scalbert

If properly designed, no. The best exhaust for a turbo system is no exhaust at all behind the turbine. However, sound increase does not always equal flow increase. Lastly, sound increase may be drawing attention away from the feel; i.e. a placebo affect.

This is basically no exhaust. It is 2.5" piping all the way back with the minimum number of bends and then flow-thru mufflers.

What could make it be not properly designed?

Originally Posted by cn555ic

Did u make sure you capped the vacuum hose from the OEM exhaust flap tightly....I heard someone on this forum also had this problem and it was the vacuum hose...

I have a small BB in there from doing the "golf tee mod" and I thought that would be fine but maybe not. Also, I didn't think that would have any bearing on the power that the car puts down...

I will clamp it up tightly in the morning tomorrow.

[cn555ic]

Originally Posted by e90AW335i

This is basically no exhaust. It is 2.5" piping all the way back with the minimum number of bends and then flow-thru mufflers.

What could make it be not properly designed?



I have a small BB in there from doing the "golf tee mod" and I thought that would be fine but maybe not. Also, I didn't think that would have any bearing on the power that the car puts down...

I will clamp it up tightly in the morning tomorrow.

I know I read on the forum that a OP has this problem when he installed his catback exhaust and the installer didn't completely seal the vacuum hose, when he dyno'd the car it showed power decrease...He went back and fix the leak and re-dyno'd and it showed increase in power...I would do a search, but i know the OP was from this forum that had the same symptoms as you do..

[scalbert]

Originally Posted by e90AW335i

This is basically no exhaust. It is 2.5" piping all the way back with the minimum number of bends and then flow-thru mufflers.

What could make it be not properly designed?

Most likely nothing, it may be fine.

Let me tell you a quick story of a GN racer who was on the cutting edge at the time. He made some changes to his car and on his first pass was sure he was slower. But when he picked up his slip he was shocked to see he went 3 tenths quicker and set a new personal best. What changed was the shape of the curve which didn't feel as quick but actually was.

Not saying this is the case but is something to consider.

[e90AW335i]

Originally Posted by scalbert

Most likely nothing, it may be fine.

Let me tell you a quick story of a GN racer who was on the cutting edge at the time. He made some changes to his car and on his first pass was sure he was slower. But when he picked up his slip he was shocked to see he went 3 tenths quicker and set a new personal best. What changed was the shape of the curve which didn't feel as quick but actually was.

Not saying this is the case but is something to consider.

Interesting....

Maybe I will just go dyno again and see what has changed.....

Thanks guys

[mistermojorizin]

i bought a g-timer off of amazon for $45. now i know what acceleration g's my car pulls in each gear at the various rpms. its pretty consistent in similar wheather. if i changed an intake or an exhaust, i would be able to tell very easily how my car's pulling - not depndent on launch or technique. for a guy who changes his mods all the time, i'd think this would be a great investment.

[e90AW335i]

Originally Posted by mistermojorizin

i bought a g-timer off of amazon for $45. now i know what acceleration g's my car pulls in each gear at the various rpms. its pretty consistent in similar wheather. if i changed an intake or an exhaust, i would be able to tell very easily how my car's pulling - not depndent on launch or technique. for a guy who changes his mods all the time, i'd think this would be a great investment.

And what makes you think I change my mods all the time?

I think I am just going to go and get another dyno done soon to see if there was a loss in power.

[PresaMat]

I dont know if its the same with turbo cars as much as NA... but on big HP NA cars putting a full out exhaust dropped some low end torque (not a ton but some). It made up for it in the higher end. Dyno and see if there is any difference... also check with terry there may be an A/F issue that could be causing it. Hmm another thought could be the spool up time - its a faster spool with no exhaust so it may have a little less "jolt" ie may be smoother. Not step on it wait a sec and it hits... it spools and makes power smoother. Just a couple ideas. Hope it works out kyle!

Mat

[e90AW335i]

Originally Posted by PresaMat

I dont know if its the same with turbo cars as much as NA... but on big HP NA cars putting a full out exhaust dropped some low end torque (not a ton but some). It made up for it in the higher end. Dyno and see if there is any difference... also check with terry there may be an A/F issue that could be causing it. Hmm another thought could be the spool up time - its a faster spool with no exhaust so it may have a little less "jolt" ie may be smoother. Not step on it wait a sec and it hits... it spools and makes power smoother. Just a couple ideas. Hope it works out kyle!

Mat

Thanks Mat. I will probably go and get another dyno after I get it remounted and stuff.

Thanks guys...

[scalbert]

Originally Posted by PresaMat

I dont know if its the same with turbo cars as much as NA... but on big HP NA cars putting a full out exhaust dropped some low end torque (not a ton but some).

It is different, the turbine acts as the back pressure for the engine. No exhaust is the best one for a turbo set up.