[itsbrokeagain]

Originally Posted by Tarthuss

What problem?

the problem of being overly restrictive with the stock dp.

[Tarthuss]

Originally Posted by Matt@Camber-Toe

the biggest thing is where it connects to the exhaust. that big of a pipe will not clear the cross bracket on an xi model...its identical to the AR pipe.

It looks good, but i would increase the opening on the turbine outlet flange. Its the same size as stock and that is one source of the problem.

Originally Posted by Matt@Camber-Toe

If you take a look at AR designs N55 pipe, the inside diameter is a LOT bigger than this one.

Originally Posted by Matt@Camber-Toe

the problem of being overly restrictive with the stock dp.

Methinks some guerilla marketing from competitors is at hand.

[Constant.S]

Excellent Work. Real quality! It looks trick! Now if you would only fabricate some N54 Z4 downpipes... :P

[Pepe_pr]

i want a DP but not sure if i should wait or buy now ? dammmm

[madmanhiker]

Originally Posted by Pepe_pr

i want a DP but not sure if i should wait or buy now ? dammmm

same here.

[atlharry]

Originally Posted by Matt@Camber-Toe

the problem of being overly restrictive with the stock dp.

Not to knock you or the AR DP, but if you have to mate the stock turbo to both of these downpipes, wouldn't the openings both be the same?

Both downpipes delete the cat, so the source of the biggest restriction is gone in both DPs.

Is there something that I'm missing?

[Pepe_pr]

any check engine ligth? code?

[shiv@vishnu]

Originally Posted by Matt@Camber-Toe

the problem of being overly restrictive with the stock dp.

The restriction is from the high density catalysts, not from pipe diameter. And since we are talking about a turbo that flows a maximum of 360-370whp on a good day, extra inlet large ID isn't required.

As for n54 (dual) downpipes, the notion that 3" pipes will outperform 2.5"pipes is funny considering each downpipe only needs to channel half the exhaust flow. But the idea of "bigger is always better" sells to those who don't know any better.

Shiv

[Forcefed3]

Originally Posted by shiv@vishnu

The restriction is from the high density catalysts, not from pipe diameter. And since we are talking about a turbo that flows a maximum of 360-370whp on a good day, extra inlet large ID isn't required.

As for n54 (dual) downpipes, the notion that 3" pipes will outperform 2.5"pipes is funny considering each downpipe only needs to channel half the exhaust flow. But the idea of "bigger is always better" sells to those who don't know any better.

Shiv

So do you prefer 2.5"? Or does diameter not matter at all to you?

[shiv@vishnu]

Originally Posted by gbreeE90

So do you prefer 2.5"? Or does diameter not matter at all to you?

Dual catless 2.5" vs. dual 3.0" ID downpipes doesn't really matter to me. Both are adequately sized to easily support 250bhp (x2). Besides, the 3.0" downpipes taper back down to 2.5" where the meet up with the midpipes. Granted, the downpipes have a pretty sharp bend. Which makes 2.5" more appealing than the 2.25" that would usually be associated with that per-bank power level.

[Forcefed3]

Originally Posted by shiv@vishnu

Dual catless 2.5" vs. dual 3.0" ID downpipes doesn't really matter to me. Both are adequately sized to easily support 250bhp (x2). Besides, the 3.0" downpipes taper back down to 2.5" where the meet up with the midpipes. Granted, the downpipes have a pretty sharp bend. Which makes 2.5" more appealing than the 2.25" that would usually be associated with that per-bank power level.

That is true, I went ahead and got AR just because they have a good reputation when it comes to quality and performance. Just like you have with tunes

[shiv@vishnu]

Originally Posted by gbreeE90

That is true, I went ahead and got AR just because they have a good reputation when it comes to quality and performance. Just like you have with tunes

lol.. that's fine. I'm still running 4 year old 1st generation Riss Racing downpipes that I got for free

[IlChengis]

Originally Posted by shiv@vishnu

Besides, the 3.0" downpipes taper back down to 2.5" where the meet up with the midpipes.

Shiv,
Someone (sorry, don't remember whom) posted this link a couple of weeks ago and I found it extremely interesting.

Here's a quote:

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

...and...

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.

Based on the above, wouldn't you say that 3" catless DPs tapering down at the midpipe would be optimal as opposed to earlier tapering or plain 2.5" DPs? I understand that dual 2.5" DPs could easily handle 450-500hp, but wouldn't 3" DPs drop backpressure enough to yield quicker spool at Force-Inducted power levels below that range?

If I recall correctly, someone on this Forum had custom 3" midpipes done that tapered down to 2.5" at the mufflers. I suppose such setup could have easily handled over 500whp given the reduced backpressure caused by moving the taper so far down the exhaust.

-Walter

[Forcefed3]

Originally Posted by IlChengis

Shiv,
Someone (sorry, don't remember whom) posted this link a couple of weeks ago and I found it extremely interesting.


If I recall correctly, someone on this Forum had custom 3" midpipes done that tapered down to 2.5" at the mufflers. I suppose such setup could have easily handled over 500whp given the reduced backpressure caused by moving the taper so far down the exhaust.

-Walter

My brother who is a engineer, knows a lot about this topic said 3" downpipe even when tapered to 2.5" would yield larger gains than a 2.5" downpipe. Im not sure how he figured that, but I will ask him when I see him.

[shiv@vishnu]

Originally Posted by IlChengis

Shiv,
Someone (sorry, don't remember whom) posted this link a couple of weeks ago and I found it extremely interesting.

Here's a quote:


...and...


Based on the above, wouldn't you say that 3" catless DPs tapering down at the midpipe would be optimal as opposed to earlier tapering or plain 2.5" DPs? I understand that dual 2.5" DPs could easily handle 450-500hp, but wouldn't 3" DPs drop backpressure enough to yield quicker spool at Force-Inducted power levels below that range?

If I recall correctly, someone on this Forum had custom 3" midpipes done that tapered down to 2.5" at the mufflers. I suppose such setup could have easily handled over 500whp given the reduced backpressure caused by moving the taper so far down the exhaust.

-Walter

LOL.... smalll world. That post about exhaust design was made by a buddy of mine (Jay Kavanaugh) at my request several years ago to clear up some myths about "bigger-is-better" downpipe design on the Subaru forum. Back then, some people had the notion that a single 4" dump tube coming off the tiny WRX turbocharger is better than the more convention 3". The manufacturer quoted the Ideal Gas Law to defend an exhaust design that tapered down from 4" to 3". So Jay laid down some facts.

But it's true that you do want to push ID transitions as far downstream as possible since that is where the exhaust is coldest and has the least velocity. But in the case of the n54's dual exhaust system where each downpipe is only flowing half of the total exhaust flow, even 2.5" is sufficient. Running dual 3" exhausts (downpipe+midpipes) wont help or hurt you anymore than running dual 5" exhausts. It's all overkill above a certain point.

I think the most important point that Jay made is that you want to make the transition between the turbine output and the downpipe inlet as smooth as possible and then gradually flare it out from there. This would suggest that the idea exhaust system would start off at ~2.25" coming off the turbo, flaring out to 2.5" (or 3") and staying that diameter all the way to the dual tips.

Shiv

[Constant.S]

Originally Posted by shiv@vishnu

But the idea of "bigger is always better" sells to those who don't know any better.

Shiv

Spot on

[IlChengis]

Originally Posted by shiv@vishnu

LOL.... smalll world. That post about exhaust design was made by a buddy of mine (Jay Kavanaugh) at my request several years ago to clear up some myths about "bigger-is-better" downpipe design on the Subaru forum.

Holy cow, I just realized how popular that post is.

Based on the transition smoothness part, I imagine that in our case slight (perhaps irrelevant) turbulence might be created with DPs with collectors larger than ~2.25".

Thanks for the follow up Shiv.

-Walter

[shiv@vishnu]

Originally Posted by IlChengis

Holy cow, I just realized how popular that post is.

Based on the transition smoothness part, I imagine that in our case slight (perhaps irrelevant) turbulence might be created with DPs with collectors larger than ~2.25".

Thanks for the follow up Shiv.

-Walter

No problem

[HP Autowerks]

If any of you is counting your pounds, this DP will save you about 5 pounds off the front of your 135/335i

[E92White]

how's the install compared to the n54 ? is it a real bitch ? or is it much easier ?

[HP Autowerks]

Originally Posted by E92White

how's the install compared to the n54 ? is it a real bitch ? or is it much easier ?

it will take half of the time of the N54 install, there is plenty of working space in the N55. More info here...

http://www.e90post.com/forums/showthread.php?t=455010

[itsbrokeagain]

Originally Posted by shiv@vishnu

The restriction is from the high density catalysts, not from pipe diameter. And since we are talking about a turbo that flows a maximum of 360-370whp on a good day, extra inlet large ID isn't required.

As for n54 (dual) downpipes, the notion that 3" pipes will outperform 2.5"pipes is funny considering each downpipe only needs to channel half the exhaust flow. But the idea of "bigger is always better" sells to those who don't know any better.

Shiv

Have you taken the N55 downpipe off yet? If so you will notice that the backside of the hot housing is nice and open much like a turbo on an N54...the stock downpipe crams down to a little over 2" across the inside...so you are telling me that it's not beneficial for a turbo to open up into the turbine housing, the neck back down at the v band to get out into the open expanse of the downpipe.

And why did mr. 5 gain hp using 3" dps over 2.5s?

I'm not trying to hijack anything, I deal with HP Autowerks all the time and Harold is one of the best people I've ever had the pleasure of talking to and doing business with. I can't knock the fitment of it or the gains of it (18hp is nice), the only thing I'm criticizing is the use of an oem size flange which from the factory is a bottleneck to begin with.

And 360/370 hp is it? Are you so sure about that? 3 years ago you said you were uncertain if we could break 400hp in an N54, and look where we are at now.