New B10 BiTurbo exhaust? - The Unofficial BMW M5 Messageboard (m5board.com)

Gerg · 28th March 2007, 07:58

I'm having some of the SLS system parts replaced on my B10 BT. The parts I'm having replaced are the brake accumulators, the regulating valve, and some of the hoses. The mechanic called and said the stock exhaust weighs a ton. OK, maybe about 80 pounds. It also has about 140k Kms on it. He's recommending replacing it with a quality SS system. I have an Eisenmann rear box on my M5. It's quality is first rate and I love the sound. How bad would it be to replace the Alpina muffler with a high quality replacement? I know the importance of keeping these cars original. BTW, does someone know the approximate cost to buy a new muffler for a B10 BT?

Greg S.

kees · 28th March 2007, 15:13

Well on a turbo car it's important to have the correct amount of back pressure. Less is normally better but if you go too far it can end up stalling the turbo. Alpina is quite good at tuning their cars for utmost performance so it is unlikely that there will be much to gain from an aftermarket exhaust.

I don't know exact prices, but the full BiTurbo is supposed to be quite expensive.

Dirk BT · 28th March 2007, 16:44

I don´t think that there is an Eisemann available for the BT, but Rojer has an custom made SS exhaust under his BT. Perhaps he can help you out with some questions.

The original exhaust costs (5 years back) 2400DM +TAX....this is something around 1500€ I guess (price without the cat)

Gerg · 29th March 2007, 09:25

Quote:

Originally Posted by Dirk BT

I don´t think that there is an Eisemann available for the BT, but Rojer has an custom made SS exhaust under his BT. Perhaps he can help you out with some questions.

The original exhaust costs (5 years back) 2400DM +TAX....this is something around 1500€ I guess (price without the cat)

Thanks Dirk, I did a search and found Rojer's thread. new stainless box for bi-turbo

I won't delete the cats but losing 50 pounds and gaining flow sounds good.

Greg

m5 killer · 30th March 2007, 00:29

gerg i hope you read the whole thread, as kees said you have to be careful with backpressure but if you get it right you will see a difference a huge difference also depending on if you do just the back box or the whole system, personally i would do the whole system with the cats off, you will see a big difference just by taking the cats off, if you are not allowed by law to remoce the cats then put a system which allows you to take the cats on and off within 15 minutes that way if your car has to go in for a goverment test you can put the cats back on. ps it will be worth it you will see the difference and it will put a smile on your face

Cor-Jan · 30th March 2007, 00:56

Look for the video where a race Alex,when we both start in 4rth you can clearly see the difference a cat makes.

Yaninnya · 1st April 2007, 20:13

Quote:

Originally Posted by kees

if you go too far it can end up stalling the turbo.

With all respect but you absolutely wrong. Exhausts with quite low flow drag are often suspect for decreasing torque and power but the real reason is that with far improved exhaust you should remap the DME as after any other mod.
Jan

kees · 1st April 2007, 22:38

Quote:

Originally Posted by Yaninnya

With all respect but you absolutely wrong. Exhausts with quite low flow drag are often suspect for decreasing torque and power but the real reason is that with far improved exhaust you should remap the DME as after any other mod.

I'm sorry but you're wrong. The DME has virtually nothing to do with this.

In a well-designed exhaust the pulse of exhaust of one combustion cycle extracts the pulse of the next combustion cycle. Effectively by going to too wide a pipe the resulting flow drag is too low and kills the velocity of the exhaust gases going out the exhaust.

Yaninnya · 2nd April 2007, 22:20

Quote:

Originally Posted by kees

I'm sorry but you're wrong. The DME has virtually nothing to do with this.

In a well-designed exhaust the pulse of exhaust of one combustion cycle extracts the pulse of the next combustion cycle. Effectively by going to too wide a pipe the resulting flow drag is too low and kills the velocity of the exhaust gases going out the exhaust.

You are saying about normally aspirated engines (it is not exactly as you describe it - it is more dependence of pulses of pressure - but we have not enough space here on forum to touch all issues of na engines exhausts).
In turbocharged engine the turbocharger (or more precisely the turbine wheel) is exterminating the exhaust pulses. You can improve exhaust by fitting equal lengh manifold pipes but it is not so important as in na engines. After turbine housing you need only as low drag as possible. Of course car producers needs to obay the pollution and noise regulations and of course loud exhaust is not everybody taste and that's the reason why always you can improve factory exhaust.
I hope that my very basic english is enough clear (I'm still learning

).
Jan

kees · 2nd April 2007, 22:54

Quote:

Originally Posted by Yaninnya

You are saying about normally aspirated engines (it is not exactly as you describe it - it is more dependence of pulses of pressure - but we have not enough space here on forum to touch all issues of na engines exhausts).
In turbocharged engine the turbocharger (or more precisely the turbine wheel) is exterminating the exhaust pulses.

What applies for N/A engines also applies for turbo engines - but not after the cylinders like on a N/A engine, but after the turbo.

Yaninnya · 3rd April 2007, 00:11

Quote:

Originally Posted by kees

What applies for N/A engines also applies for turbo engines - but not after the cylinders like on a N/A engine, but after the turbo.

How? In na engine the whole story is beganing when the exhaust valve is opening exhaust gases are pushed out with some pressure. Right? The vave of that pressure is moving with around sound speed forward. Right? When it is reaching the point where is big difference in cross section (connection with another exhaust pipe) it is changing the direction and as vaccum vave is going backwards (for us is only important the exhaust pipe from another cylinder). And the lengh of pipes needs to be so long that when the vaccum vave reach the exhaust valve port in this cylinder this valve shoud open. Right? After that this vaccum vave is "sucking" the exhaust gases from this cylinder. Thats the very short and extremally basic theory of equal lengh pipes tubular manifolds.
Now tell me how it can work in exhaust after turbine housing when turbo is not giving any pulses (don't tell me that turbine wheel vanes are giving the pulses because at around 70 000 - 130 000 rpm and 7 - 9 vanes it will be around 49 000 - 108 000 super micro pulses per minute, just can't phisycally messure it).
Maybe my experience with Alpina engines is not impressive but I'm working on other engines over 15 years and four cars which I prepared (two Cosworth's, Integra and Fiat 126

) won polish race championship (two overall). I prepared many cars for fast road use too (last time mostly BMW). I'm very, very far from saying that I'm a engine magician, guru or whoever. I'm just the bloke which is working on engines enough long to have some experience and enough skills to not be shamed of it.
No offence at all only wish not mislead other forum members.
Jan