[AmuroRay]

Originally Posted by wilson kop

good stuff.

Before and after dyno of this would be incredible Ray. I know that’s not free but as a man that loves data, you know you wanna! I got $5 on it!

First run

[///393]

Nice. Hopefully we get to see what if any impact the larger diameter exhaust has. Would be awesome.

[AmuroRay]

SAE correction


STD correction

[AmuroRay]

Originally Posted by wilson kop

Nice. Hopefully we get to see what if any impact the larger diameter exhaust has. Would be awesome.

Because the diameter isn’t much larger than stock unfortunately, I’m not expecting a huge amount. - I believe I would need to get a 3.5” (and ideally a matching 3.5” outlet for the downpipe) for real gains.

We’ll see.

[///393]

Looks like Supersprint makes a 80mm unit in both resonated and non-resonated as well.

Anxious to see what if any gains a midpipe can deliver. Thanks for doing this.

[AmuroRay]

Originally Posted by wilson kop

Looks like Supersprint makes a 80mm unit in both resonated and non-resonated as well.

Anxious to see what if any gains a midpipe can deliver. Thanks for doing this.

Son of a biscuit, you're right. I would love to get the SS stuff and return this...but we are talking 4mm and .14"s - not sure it's worth $300 for me. (restocking fee + purchase of the new stuff)

ECS has the SS stuff on sale right now.

mike@x-ph.com - Do you carry Super Sprint?

[mike@x-ph.com]

Originally Posted by AmuroRay

Son of a biscuit, you're right. I would love to get the SS stuff and return this...but we are talking 4mm and .14"s - not sure it's worth $300 for me. (restocking fee + purchase of the new stuff)

ECS has the SS stuff on sale right now.

mike@x-ph.com - Do you carry Super Sprint?

I do not

[AmuroRay]

I’m out of the return window for my exhaust, so I’ll try to sell it and grab the SS stuff. Still have to install the MILVS, HPFP, the exhaust AND get a retune.

[AmuroRay]

3LiterBeater - I don't mean to thread jack!

So I found this:
https://f87.bimmerpost.com/forums/sh....php?t=1610213


Stock M2 vs BM3 Stage 1
Baseline numbers (we'll use the smoothest line of 347whp/403wtq

And this

https://f87.bimmerpost.com/forums/sh...3+stage+1+dyno



Baseline numbers 340whp/375wtq

Finally:
https://f87.bimmerpost.com/forums/sh...highlight=dyno


Baseline includes an Akrapovic Exhaust
355whp/384wtq

So what does this conclude? Absolutely nothing
I'm now worried my exhaust experiment will end in failure.

[F87source]

In regards to the larger exhaust diameter discussion, my thoughts are there is only so wide you can go before you start experiencing deminishing returns to maybe even seeing some negative effects.

Ok so lets say the opening at the end of the turbo is 4" in diameter, and the stock exhaust is like 2.5" just for the sake of putting out numbers. If you got to a larger exhaust diameter like 3" you increase the flow. This also allows more exhaust gas expansion creating a suction effect (just like a diffuser on a car would) and this improves exhaust scavenging at the cost of exhaust velocity (at first it will be fine because back pressure was too high). However at some point when you go too wide the suction effect doesn't scale anymore, and back pressure drops so much that exhaust velocity will decrease. At this point there is no difference between running without an exhaust entirely. So imo you have to balance between exhaust velocity and diameter, and at some point the exhaust gets too big you no longer get any benefits.


I measured the mid pipe on my m2 and it was over 81 mm (3.1") wide at the smallest point but it was an oval so it isn't exactly an 81 mm pipe. But I think at 3" you are reaching the upper limits of where you will see a benefit of going larger.

[AmuroRay]

Originally Posted by F87source

In regards to the larger exhaust diameter discussion, my thoughts are there is only so wide you can go before you start experiencing deminishing returns to maybe even seeing some negative effects.

Ok so lets say the opening at the end of the turbo is 4" in diameter, and the stock exhaust is like 2.5" just for the sake of putting out numbers. If you got to a larger exhaust diameter like 3" you increase the flow. This also allows more exhaust gas expansion creating a suction effect (just like a diffuser on a car would) and this improves exhaust scavenging at the cost of exhaust velocity (at first it will be fine because back pressure was too high). However at some point when you go too wide the suction effect doesn't scale anymore, and back pressure drops so much that exhaust velocity will decrease. At this point there is no difference between running without an exhaust entirely. So imo you have to balance between exhaust velocity and diameter, and at some point the exhaust gets too big you no longer get any benefits.


I measured the mid pipe on my m2 and it was over 81 mm (3.1") wide at the smallest point but it was an oval so it isn't exactly an 81 mm pipe. But I think at 3" you are reaching the upper limits of where you will see a benefit of going larger.

I’m going to disagree - on a turbo, you can’t go too large, but you’ll likely reach a limit of packaging.

I think I cited the test of the Supra elsewhere: same headflow, same configuration (3 liter inline 6) and it saw gains even in the 300whp range with a 3.5” exhaust. The gains were even larger (100whp) when the Downpipe was sized up .5” to match with a 3.5” exhaust on a 600whp build.

I was a HUGE N/A guy, to me, building a balanced and linear N/A motor is like having a fine time piece. Tony Colletti from Motordyne Engineering did a test about exhaust velocity back in the day. Now, Tony was a former rocket engineer, so all his parts were research based, unlike what we have in the BMW world.

But he was able to show how the exhaust velocity worked on an N/A car - his findings were there was no power to be gained after the exhaust gas merger: basically after the header collectors merged (merge diameter and length had an impact) no power was gained with any pipe, they just limited velocity and of small enough, power. The only exception was having a “trumpet” muffler, which could potentially diffuse the exhaust, lowering pressure and increasing power.

He also tested a restriction plate that allowed him to test how “back pressure” (I know we are taking velocity) impacted power.

Now this is on N/A cars, and you can do the reading for yourself if you’re interested:

https://my350z.com/forum/intake-exhaust/438890-jic-ti-80mm-ok-for-n-a.html

(iIhave a lot of this burned in my head from when I read it while it was active 13 years ago )
Basically, you’re not going to large on a turbo, which is why real “full race” cars, they will just have a dump that terminates right after the downpipe. On street cars, the exhaust is there for emissions and noise suppression, and that’s basically it. You’re not losing velocity because this is already spent exhaust gasses after the “merger”

[AmuroRay]

If my 2.4 liter 4 cylinder N/A motor could gain from a large 3” exhaust at a modest sun 200whp level, I can’t be convinced that a 3” exhaust is adequate for a near 400whp turbocharged 3.0 liter 6cyl

[F87source]

Originally Posted by AmuroRay

I’m going to disagree - on a turbo, you can’t go too large, but you’ll likely reach a limit of packaging.

I think I cited the test of the Supra elsewhere: same headflow, same configuration (3 liter inline 6) and it saw gains even in the 300whp range with a 3.5” exhaust. The gains were even larger (100whp) when the Downpipe was sized up .5” to match with a 3.5” exhaust on a 600whp build.

I was a HUGE N/A guy, to me, building a balanced and linear N/A motor is like having a fine time piece. Tony Colletti from Motordyne Engineering did a test about exhaust velocity back in the day. Now, Tony was a former rocket engineer, so all his parts were research based, unlike what we have in the BMW world.

But he was able to show how the exhaust velocity worked on an N/A car - his findings were there was no power to be gained after the exhaust gas merger: basically after the header collectors merged (merge diameter and length had an impact) no power was gained with any pipe, they just limited velocity and of small enough, power. The only exception was having a “trumpet” muffler, which could potentially diffuse the exhaust, lowering pressure and increasing power.

He also tested a restriction plate that allowed him to test how “back pressure” (I know we are taking velocity) impacted power.

Now this is on N/A cars, and you can do the reading for yourself if you’re interested:

https://my350z.com/forum/intake-exha...k-for-n-a.html

(iIhave a lot of this burned in my head from when I read it while it was active 13 years ago )
Basically, you’re not going to large on a turbo, which is why real “full race” cars, they will just have a dump that terminates right after the downpipe. On street cars, the exhaust is there for emissions and noise suppression, and that’s basically it. You’re not losing velocity because this is already spent exhaust gasses after the “merger”

I guess the only way to find out is with more data.

[3LiterBeater]

AmuroRay you’re good man! I appreciate some data, always

[///393]

I’m with Ray on this one. The Mk4 Supra community has dispelled the idea of there being a need for “back pressure” on turbo applications. You’re seeing the same thing with large diameter exhausts benefiting big power Honda K motor builds as well.

I don’t expect to see a huge power jump but, it ain’t gonna hurt.

[David.m]

Making any comparisons against the stock M2 N55 exhaust need to take into account the oem valve operation which closes at "high" rpm (we can only assume it's noise emission related) effectively halving the muffler output diameter.
I don't know that anyone has ever tested/measured the affects on power of the valve open/closed, for the aftermarket manufacturers that may negate any performance increase..
Early days when I tracked with the valve operating on oem settings the valved side was always a lot cleaner indicating it spent a bit of time closed. I ended up keeping it open by pulling the fuse & now with BM3.

[AmuroRay]

AWE midpipe is sold, so let’s see what else I can do instead?

[AmuroRay]

I don’t know a shop who will do what I want, so I guess Super Sprint it is.

[AmuroRay]

Been sitting on pulling the trigger on the SuperSprint Parts, but I’m hoping something else pops up.

I might just grab them this week, my inaction caused me to miss a sale and now the price is 50-100 higher than before