[e90AW335i]

I decided to get another dyno done since I got my DP back exhuast put on. As some of you might remember I said that I thought the car got slower. Below is a comparasion between Catless DPs w/ stock catback and Catless DPs w/ catless DP-back exhaust.

Obviously the car is not slower, but this test just goes to show that a DP back is not worth it for performance gains alone.

Feel free to ask questions about the testing, setup, etc....

[sleepdoc]

thanks for the info. I have thought maybe that would be the result.....

[lucassilva]

What exhaust did you go with?

[longodj]

Did you modify your tune to account for the lack of back pressure?

[BMW_TT]

I'm assuming the DP back exhaust had the 2nd cats deleted?

[Driver72]

Kyle, unless those two dynos were done on the same day (or on different days with pretty much identical conditions) that conclusion is not accurate.

There have been tests done long time ago with "catback" exhausts that have shown power.
One of the first was with me and my buddy back in early 2007.

We both got our 335i sedans in December 2006.
On a few occasions we did some "roling runs" when we were both stock.
We both had 6AT trans.

Each time we pretty much ran side by side.

He then had a prototype "catback" exhaust put on his car.

We dynoed his car and it made like 12 whp more than mine. (But he did not get a stock baseline).

We then also did some side by side runs.
Some of the runs starting in 1st gear at 10 mph.
By 90 mph he had pulled a bit over 1 CL on me (there was maybe 2-3 feet of air between his rear bumper and my front).

And even when starting at higher speeds and gears, his car would begin to pull a bit.

***Then on a side note, being one of the first people to ever get a PROcede, we then did runs again, and I'd pull several car lengths on him.

In anycase, he clearly gained power with the catback exhaust he added.

There's also the fact that in most cases you'll drop 20-30 lbs in weight with just a catback exhaust too.
I wouldn't say they are not worth it.
I wouldn't spend more than $1000-1200 for them.
But if you figure 1/2 that amount is worth the sound, and 1/2 the added performance and weight loss....to many that is worth it.

[e90AW335i]

Originally Posted by Driver72

Kyle, unless those two dynos were done on the same day (or on different days with pretty much identical conditions) that conclusion is not accurate.

Here is a graph with the run conditions displayed. As you can see it was very similar conditions, today was actually a little cooler....

[e90AW335i]

Originally Posted by sleepdoc

thanks for the info. I have thought maybe that would be the result.....

Yep, sucks....

Originally Posted by lucassilva

What exhaust did you go with?

Borla cat delete pipes, and magnaflow mufflers.....

Originally Posted by longodj

Did you modify your tune to account for the lack of back pressure?

The JB3 auto adjusts for these things....

Originally Posted by BMW_TT

I'm assuming the DP back exhaust had the 2nd cats deleted?

That assumption is correct.

[e90AW335i]

Here is another graph that makes me laugh. The PROcede one was when all I had was PROcede and Dual cones, the other graph is from today. The top end taper is different between the tunes but as you can see by adding DPs and fully catless exhaust I gained alot of power!

[PresaMat]

Thanks Kyle for a really good thread. I think this has shown the biggest reducer of back pressure is the DPs. I wonder if just freeing that up helps enough to overcome the standard exhaust backpressure... Meaning if you dont have DPs cat-back helps reduce some backpressure - but if you do have DPs the majority is reduced there and there is enough velocity to really not make a difference with the rest of the exhaust. Kind of hard for my to explain in words but its just a thought...

Again thanks - I think this shows that we can stay with the stock exhaust and DPs just fine - I know I would prefer not to have an extremely loud car - at least an i6. If it were a v8+ thats another story... but the loud i6 just sounds a little to close to rice for my personal taste.

[Driver72]

Originally Posted by PresaMat

Thanks Kyle for a really good thread. I think this has shown the biggest reducer of back pressure is the DPs. I wonder if just freeing that up helps enough to overcome the standard exhaust backpressure... Meaning if you dont have DPs cat-back helps reduce some backpressure - but if you do have DPs the majority is reduced there and there is enough velocity to really not make a difference with the rest of the exhaust. Kind of hard for my to explain in words but its just a thought...

That's probably exactly it.

Adding a catback exhaust with the stock intake and DP's and you see the 10-15 rwhp difference it makes.

But adding a catback exhaust to a car with intake and catless DP's already on it, probably doesn't do a whole lot since the biggest part of the air restriction (the DP's) has been opened up and therefore the stock exhaust flows well enough to not make too much of a difference.

But if you've seen the stock exhaust with all it's bends, you know going with an aftermarket one will free up that air exhaust and gain power (as well as drop some weight since you are using quite a bit less metal.)

[e90AW335i]

Originally Posted by Driver72

That's probably exactly it.

Adding a catback exhaust with the stock intake and DP's and you see the 10-15 rwhp difference it makes.

But adding a catback exhaust to a car with intake and catless DP's already on it, probably doesn't do a whole lot since the biggest part of the air restriction (the DP's) has been opened up and therefore the stock exhaust flows well enough to not make too much of a difference.

But if you've seen the stock exhaust with all it's bends, you know going with an aftermarket one will free up that air exhaust and gain power (as well as drop some weight since you are using quite a bit less metal.)

It might just be my car as well. With DPs and exhaust I have added about 5rwhp, and 5trq....

Oh well, hopefully this thread helped some people. I will be putting the stock exhaust back on soon so my car wont sound like a ricer for much longer....

[e90AW335i]

Originally Posted by PresaMat

Thanks Kyle for a really good thread. I think this has shown the biggest reducer of back pressure is the DPs. I wonder if just freeing that up helps enough to overcome the standard exhaust backpressure... Meaning if you dont have DPs cat-back helps reduce some backpressure - but if you do have DPs the majority is reduced there and there is enough velocity to really not make a difference with the rest of the exhaust. Kind of hard for my to explain in words but its just a thought...

Again thanks - I think this shows that we can stay with the stock exhaust and DPs just fine - I know I would prefer not to have an extremely loud car - at least an i6. If it were a v8+ thats another story... but the loud i6 just sounds a little to close to rice for my personal taste.

No problem Mat. I dont like my car being very loud either so that is why I said if I didn't see a decent gain (10rwhp) with exhaust than I would go back to the stock setup. I will be doing this very soon....

[Former_Boosted_IS]

Honestly, this is one of the main reasons I haven't got DPs. The dynos all show power increases, but they also show boost increases. The problem is you will obviously gain power if you increase boost, so the DP's were not necessarily gaining any power. The reality is these turbos are not large and the stock piping may be more than sufficient for stock and higher boost until someone stuffs larger turbos in.

[PresaMat]

One more thing I thought of... it could be the dyno. I have seen a car dyno the exact same - same day going from stock to catback on the BHS dyno.

[e90AW335i]

Originally Posted by PresaMat

One more thing I thought of... it could be the dyno. I have seen a car dyno the exact same - same day going from stock to catback on the BHS dyno.

I could always try a different dyno just to see what my power numbers are elsewhere.....

[Tuned335i]

Gotta give Kyle a big hand for this thread

If more people approached N54 performance modding with the open mind and qualitative measurement approach that Kyle has consistently used, there would be a lot less on this forum and a lot more useful information.

Anyway this is all good info and helps people make better informed decisions about which mods will get their car where they want it to be, performance-wise.

I'm hoping we get to see another dyno with the UR CAI installed!!!

[dim135]

Originally Posted by Former_Boosted_IS

Honestly, this is one of the main reasons I haven't got DPs. The dynos all show power increases, but they also show boost increases. The problem is you will obviously gain power if you increase boost, so the DP's were not necessarily gaining any power.

+1

the catless dp's decrease the exhaust temperature when you increase boost. this is a good reason to use them

[JoeyFiasco]

Originally Posted by Driver72

That's probably exactly it.

Adding a catback exhaust with the stock intake and DP's and you see the 10-15 rwhp difference it makes.

But adding a catback exhaust to a car with intake and catless DP's already on it, probably doesn't do a whole lot since the biggest part of the air restriction (the DP's) has been opened up and therefore the stock exhaust flows well enough to not make too much of a difference.

But if you've seen the stock exhaust with all it's bends, you know going with an aftermarket one will free up that air exhaust and gain power (as well as drop some weight since you are using quite a bit less metal.)

I didn't even realize that you gained so much from it, but it makes sense if you have stock DP's.

[e90AW335i]

Originally Posted by Tuned335i

Gotta give Kyle a big hand for this thread

If more people approached N54 performance modding with the open mind and qualitative measurement approach that Kyle has consistently used, there would be a lot less on this forum and a lot more useful information.

Anyway this is all good info and helps people make better informed decisions about which mods will get their car where they want it to be, performance-wise.

I'm hoping we get to see another dyno with the UR CAI installed!!!

Thanks man, I appreciate that. You will be seeing another dyno once I get the UR intake put on, you can bet on that....

[Bubbles]

Nice work, with all those mods I hope you have made a track day or two, and by track day I do not mean "1/4 vrooms".

[Flat Out 32]

Man this is a great topic and with great timing. I just installed an intake and was looking into the "obvious" next step: exhaust. Should I go for DPs and leave the OE mufflers or get a cat-back with stock DPs? Reading from this thread DPs are the logical step but what pointers can you give me? Hope the new setting works for you and keep posting useful topics!!