E92 Race Exhaust Project

[Gjm127]

Hey guys,

I'm a 4th year Mechanical Engineering student and as my final year project I've chosen to design a full race exhaust system for the E92 M3 (instead of choosing a boring wind pump ). I know I won't be manufacturing it but I need to thoroughly design this product.

Well this is how far I went... I just wanted to know if any of you had any information on the steps after-market manufacturers have to go through to actually analyse performance, safety, ecology and sound specifications on a full exhaust system.

Any information (ANYTHING, I have 20 pages worth of analysis haha) would be greatly appreciated!

[mkPOTO]

very nice!

[MikeE92M3]

Doesnt look like your pipes would clear the lower suspension components--after the X pipe

[m3an]

Looks pretty sweet. Regarding your concerns, mufflers are not really "safety" oriented w/ regards to design> except notably for the M3 cars (don't know about other BMW) The riveted tips actually collapsed towards the muffler in the event of a rear end collision.

Your mockup looks pretty nice, but overlay the x-pipe center section more. You want a scavenging effect created here. An example I really like is the Mastermind X-pipe. Google it and take a look at the crossover.

Looks like a fun project that you should def at least make a couple; good luck@!

[Gjm127]

Originally Posted by m3an

Looks pretty sweet. Regarding your concerns, mufflers are not really "safety" oriented w/ regards to design> except notably for the M3 cars (don't know about other BMW) The riveted tips actually collapsed towards the muffler in the event of a rear end collision.

Your mockup looks pretty nice, but overlay the x-pipe center section more. You want a scavenging effect created here. An example I really like is the Mastermind X-pipe. Google it and take a look at the crossover.

Looks like a fun project that you should def at least make a couple; good luck@!

Originally Posted by MikeE92M3

Doesnt look like your pipes would clear the lower suspension components--after the X pipe

Perfect, thanks for the feedback guys! Again, if any of you know analytical stuff about performance specs please fill me in!

[cposk]

I'm no engineer so don't take everything I say as fact (and please correct me if you do know).

I see scavenging was already mentioned, and I think the flow rate (which related to back pressure) is a huge player in exhaust design. Least resistance is not always the best design. You would need to run the motor on an engine dyno and see what flow/scavenging combo produces the most power (taking into account what type of power you are after). Then use your engineering and math skills to get your exhaust as close as possible to it.

As for sound, the math is pretty simple to figure out what size/shape of pipe is needed to cancel out certain wave lengths. Testing for those wave lengths is the issue here, as I imagine you don't have an M3 to fit a bunch of sensors to and run different types of systems.

To test safety, you would need to compare rear end crash results with/without the stock muffler. Then with your design. Also not feasible... This could be a big issue, as some cars are even engineered so the spare tire absorbs energy in an accident. And with the size/weight of our stock mufflers...

If ecology means fuel economy, then that would be part of the flow/back pressure testing. Figure out what produces the best fuel economy results and design around that.

Lots of work and $$ involved in correctly designing/testing car parts. The reason race cars costs millions to develop, and why aftermarket parts can have such a big price range. Good luck with your project, I went to VT and all of my friends wanted to do stuff like this for their senior design project. Most were turned down because it isn't feasible without a huge market (aka too expensive)...

[Malek@MRF]

Start by re-working that "x" you have in that drawing.

I remember projects like this in engineering school, they were always fun. I also suggest get the car on a rack, and start taking actual measurements for your drawings.

[s14_kev]

I wish my senior project ME was as cool as this. I made a dolphin toilet Good luck!

[Protocav]

I got to twin turbocharge a VR6 engine for my mechanical engineering senior project, so it is nice to see people actually doing stuff that they are interested in.

I suspect that there is little to no engineering calculation that goes into aftermarket exhaust design, and it is more driven by packaging. They are probably pulling from tried and true exhaust designs, dynoing the prototypes and boxing them up as an "engineered" product. The key (i think) is to design the exhaust for a certain RPM range, and not for peak horsepower. Figure out your flowrate based on Engine size and RPM to properly size the piping, and keep your bends smooth...remember that 90 degree bens are bad

If you look at a true dyno plot of an aftermarket exhaust, you will find gains and losses compared to the OEM exhaust. The plots that show HP curves with gains across the board are typically fictional...especially on a car like an M3 that was designed with performance in mind from the start.

Good luck, and have fun man!!

[Gjm127]

Big thanks to all of you for the helpful information!

Would any of you know where the hooks are to actually install this system (muffler and xpipe) ?

Also, where I can get initial values (such as mass flow rate, speed, temperature, etc...) of the air coming out of the manifold into the primary pipes before the x-pipe for given RPMs ?

[Protocav]

Mass flow rate would be approximately calculated by taking the size of the motor, multiplying it by the RPM that you want to focus on (i suggest making a spreadsheet to see the mass flow rate across the RPM range) and dividing by two since the engine only exhausts every other rotation (since it is a 4 stroke). These calculations assume 100% volumetric efficiency also.

Remember that you must divide this final answer by two, because you are making a dual exhaust.

[Gjm127]

Originally Posted by Protocav

Mass flow rate would be approximately calculated by taking the size of the motor, multiplying it by the RPM that you want to focus on (i suggest making a spreadsheet to see the mass flow rate across the RPM range) and dividing by two since the engine only exhausts every other rotation (since it is a 4 stroke). These calculations assume 100% volumetric efficiency also.

Remember that you must divide this final answer by two, because you are making a dual exhaust.

Yes, I researched and that's exactly it for the mass flow rate!
Now I need to make a thousand assumptions to actually start calculating stuff...

Any idea on how I can estimate the manifold air temperature for given RPMs?

[S65B40V8]

Sounds like a great engineering project. Hopefully you have access to an M3 for measurements and photos? If not, contact your local BMW club or service shop and ask around. Since you are specifically targeting the M3, it would be best if you could design something that sort of looks like it would actually fit on the car.
Why a "full race exhaust"? The best race exhaust is probably just straight pipes -- pretty boring project Why not set your design as a "flow and sound optimized street exhaust"? You could first model the factory exhaust and then compare flow (sound is more difficult) to your own design. The factory muffler has 2 roughly 90° bends for each pipe inside. It is claimed that these restrict flow. Do they? How much?
What CAD system do you use? Solidworks for instance has a nice flow modeling package that would be very useful for this but for your project, maybe it's better to calculate what you can on your own.
It seems that most street exhausts for the M3 that don't drone (unpleasant resonating noise heard in the cabin) in the 2k-3k RPM range use Helmholtz resonators -- that right there is a great engineering design exercise for your project (examples include: AA, Dinan, Corsa). Some good info. to get you thinking (click on the M3 exhaust link): http://www.dinancars.com/university/
You can also search the posts here and other sites for some good discussion on Helmholtz resonators in exhaust systems.
Good luck!

[Gjm127]

Originally Posted by S65B40V8

Sounds like a great engineering project. Hopefully you have access to an M3 for measurements and photos? If not, contact your local BMW club or service shop and ask around. Since you are specifically targeting the M3, it would be best if you could design something that sort of looks like it would actually fit on the car.
Why a "full race exhaust"? The best race exhaust is probably just straight pipes -- pretty boring project Why not set your design as a "flow and sound optimized street exhaust"? You could first model the factory exhaust and then compare flow (sound is more difficult) to your own design. The factory muffler has 2 roughly 90° bends for each pipe inside. It is claimed that these restrict flow. Do they? How much?
What CAD system do you use? Solidworks for instance has a nice flow modeling package that would be very useful for this but for your project, maybe it's better to calculate what you can on your own.
It seems that most street exhausts for the M3 that don't drone (unpleasant resonating noise heard in the cabin) in the 2k-3k RPM range use Helmholtz resonators -- that right there is a great engineering design exercise for your project (examples include: AA, Dinan, Corsa). Some good info. to get you thinking (click on the M3 exhaust link): http://www.dinancars.com/university/
You can also search the posts here and other sites for some good discussion on Helmholtz resonators in exhaust systems.
Good luck!

I am so thankful for all the information I'm getting from you guys. You're helping me make a very fun project out of it!

That Helmholtz box is very interesting, I would love to integrate that into my project. You are right, the best "race" exhaust would be straight-piping the whole thing heh, I could write a one pager and that would be the end of it haha. You're right though, I'm gonna look into resonators to eliminate the drone, etc... I think it gets rid of unwanted pops as well...

I use Catia V5 (from Dasseault Systemes) as my CAD system, it's very much like Solidworks (actually brought by Dasseault Systemes as well). It's gonna help me calculate lots of things.

I am amazed by the amount of information Dinan has released to the public too. That website is gonna help me a lot too.

All in all, big thanks to all you guys!