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Discussion Starter · #1 ·
Hello everyone ~

I recently removed my resornators and replaced it with two straigt pipes on each sides.

After car felt like very slow in picking up speed and takes a lot longer reaching 140 mile/ hour!! even with FULL WOT!!!!

THIS IS 10000000000% FOR SURE !!! Its that obvious !!

Just to let you know my car has only 6000miles on it so far and did 341 rear wheel horse power on Dynojet.


Any how I thought this was happend obviously because of removing the resornator and this led to reduce the exhaust pressure.

However after speaking to one of my close friend who is curreltly working for Nissan in Japan, developping engines and programming ECUs

told me that "no exhaust is best exhaust~!"

I asked him why and he told me that giving the minium restriction to exhaust flow is the best for engine performance. So basically no exhaust

from the engine. Which obviously is impossible setting for street cars.

So whats happening with my e39 M5 ? I replaced the restrictive and heavy resornator from the system and replaced it with two totally straight

pipe ~ making it so easy for my beast to breath out ~ plus no muffler ~~

Why is my car dirves like a MINI COOPER????????

My friend told me that the setting I did actually increased the exhaust pressure and thats why my car feels slow ~~ He said he can only give me

a perfect answer if he can cut open the resornator and see the structural design of it.

He told me that if I add an x type piping , like SS xpipe will decrease the pressure and make the car better ~~

because of difference in engine banks firing order when bank 1 fires and exhaust gas comes through to x piping the other side has no gas

and this drops the exhaust pressure ~


IS THIS TURE ???????????????????????????????????????

I know my friend has Dr degree in engineering and duh thats why his working for Nissan ~ but it was hard to believe ~

i seek to be educated by board members!!

Thank you reading my long thread and you have a self a awsome day !!!


My friend is safe from the Earthquake!!
 

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Hello everyone ~

I asked him why and he told me that giving the minium restriction to exhaust flow is the best for engine performance. So basically no exhaust

from the engine. Which obviously is impossible setting for street cars.

So whats happening with my e39 M5 ? I replaced the restrictive and heavy resornator from the system and replaced it with two totally straight

My friend told me that the setting I did actually increased the exhaust pressure and thats why my car feels slow ~~ He said he can only give me

a perfect answer if he can cut open the resornator and see the structural design of it.

He told me that if I add an x type piping , like SS xpipe will decrease the pressure and make the car better ~~
quote]


I think he is right if you are planning to run your car at wide open throttle and 7500 RPM all the time. Less back pressure will improve top end horsepower but at the cost of some low end torque. This would be great for racing but for streetability you want torque down low so you do need some backpressure. This of course is my opinion so FLAME SUIT ON :haha:
 

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Discussion Starter · #4 ·
Less back pressure will improve top end horsepower but at the cost of some low end torque.
Thank you for the advice ~ does this mean that my car would actally be faster in top end??? even though it is slower in low end power bands????
 

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Discussion Starter · #5 · (Edited)
Having a quality X-pipe would do a better job at equalize both banks than the stock H-pipe does. The stock H-pipe basically is ineffective at high rates of exhaust flow, as the gases just flows right by the H section.

Take a look at SS or Magnaflow 10791.



Or have your exhaust shop make you a custom one similar to this:
my shop where I did my straight pipe ~ they are keen on chopping pipes and welding ~ But still would it be better to purchase the Xpiping from supersprint? I mean they develope their products from actuall numbers ~ not from experience ~~

What shall I do ???? custom X piping job would cost me $190~ SS xpipe cost some where $400 + shipping + custom tax ~
 

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my shop where I did my straight pipe ~ they are keen on chopping pipes and welding ~ But still would it be better to purchase the Xpiping from supersprint? I mean they develope their products from actuall numbers ~ not from experience ~~

What shall I do ???? custom X piping job would cost me $190~ SS xpipe cost some where $400 + shipping + custom tax ~
If you have a shop that is capable of making you a custom X-pipe, go with that.

Thank you for the advice ~ does this mean that my car would actally be faster in top end??? even though it is slower in low end power bands????
In theory, yes, but no data to back that up. We are talking 1-2hp, which is insignificant.
 

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Look up exhaust scavenging. Lots of reading to be found out there in the interwebs. And that will be able to explain it better than I. Fluid dynamics is a complex science...
 
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Interesting post. You can run the car at 140 mph and it has only 6000 miles on it? Pure race car? Anyway, have you confirmed it is has lost power by a scientific method, e.g. dyno, 1/4 mile time? I only ask because any time I make a car noisier, it feels slower.
 

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What happened with your system is the different exhaust velocities from the cylinders are basically running into the backs of eachother - imagine the slow exhaust from 5000rpm is causing back pressure to the exhaust pulse coming out now from 7000rpm. By connecting the two bank's exhausts together you allow greater movement, and will dissipate the exhaust more effectively.

A poorly designed X-pipe will also increase backpressure as the exhaust slows to make the "turn" so to speak. As will an H-pipe

I also was curious if an H-pipe with rounded out inners (like an X pipe) matched to a decreasing radius exit pipe (venturi effect) would help in any way... see rough image below

Im no expert, fluid mechanics and aerodynamic principles just really interest me. The idea with my cross-pipe is that it has the smooth airflow of a straight H pipe, but with the smooth crossing over effect from the X pipe, while the venturi effect maintains exhaust speed past the turbulence
 

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Discussion Starter · #11 ·
Interesting post. You can run the car at 140 mph and it has only 6000 miles on it? Pure race car? Anyway, have you confirmed it is has lost power by a scientific method, e.g. dyno, 1/4 mile time? I only ask because any time I make a car noisier, it feels slower.

sorry ~ what I meant was 60000 miles~ouich units of measurements are always confusing ^^

I did not perform any scientific method ~ however it was that obvious to feel it was unnecessary. !! Even my wife who always seats at the

back told me "whats wrong with your car? It feels slow and num. " !! So I must have felt it immediatley since I my beast is a Daily driver ~
 

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Discussion Starter · #12 ·
I also was curious if an H-pipe with rounded out inners (like an X pipe) matched to a decreasing radius exit pipe (venturi effect)
Thank you for your thoughts~!!!

I know exactly what you mean by the "round out inner pipes"~ on a oem exhaust pipes~ I was also curious why that specific part of the

exhaust piping had a different diameter ~ !! If what you say is true ~ BMW did this to add a venturi effect ~ even with Supersprint Xpipe

witch has very smooth pipping , wouldnt it be less effective than the stock piping? Since stock system has something to push out exhasut

gas more faster than straight style X pipes ~ ?? Is my car running slow than before when it had stock piping ???

I forgot to mention , after doing a straight pipe I went back to the shop made them install X piping just a little bit behind where stock

resornators used to be ~ After car felt MUCH MUCH stronger than with straight pipes ~ Also sounds much more refiend and tasteful!!

Please let me know what you think ~ I would like to know about it more ~!!

Thank you ~
 

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It shouldn't feel significantly slower with that mod, there may be another issue at hand. At most you lost MAYBE 5lb/ft of torque, something you shouldn't be able to feel
 

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Bumping an old thread.

After my exhaust work using an x-pipe and two resonators straight to exhaust tips, I too feel like I lost some low-end grunt that used to be there before. When stock, the car would just freight train from 2.5K RPM all the way to redline. I honestly feel noticeably down on power in the low revs. Weird, because I also installed new spark plugs and did an oil change at the same time.

Any thoughts, or am I just insane? Lol.
 

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You are not insane but the real problem has not really been touched on here. This is just an opinion because I can't figure our how to measure the EGR volumes on this engine. Any time you mess with the exhaust back pressure you are messing with something that can't be fixed.
The vanos is the egr valve on this car, It opens the exhaust valve on the vacuum stock to allow exhaust gases back in to get the right volume of exhaust gas and air for the fuel it will blast in. I can't tell you if you have too much or too little exhaust gas but it will not be correct and that is where your torque went.
You could see if a tuner has a tune for this back pressure and by the tune but that is your only re-coarse.
 

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You are not insane but the real problem has not really been touched on here. This is just an opinion because I can't figure our how to measure the EGR volumes on this engine. Any time you mess with the exhaust back pressure you are messing with something that can't be fixed.
The vanos is the egr valve on this car, It opens the exhaust valve on the vacuum stock to allow exhaust gases back in to get the right volume of exhaust gas and air for the fuel it will blast in. I can't tell you if you have too much or too little exhaust gas but it will not be correct and that is where your torque went.
You could see if a tuner has a tune for this back pressure and by the tune but that is your only re-coarse.
Sailor,

If you are right, could this contribute to a poor score on the MAF test ? It would go some way in explaining the MAF score on my M5 (purchased with X-pipe already installed).

Asb9987,

what MAF score are you getting now? Do you have a score for before the X-pipe install?
 

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:dunno: But likely. Really have not sat down and tried to figure it out. Don't think it would be the X pipe as it reduces pressure. It will be the change in the cat back.
 

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Sailor,

If you are right, could this contribute to a poor score on the MAF test ? It would go some way in explaining the MAF score on my M5 (purchased with X-pipe already installed).

Asb9987,

what MAF score are you getting now? Do you have a score for before the X-pipe install?
I don't think so. The MAF test is done WOT. There's no demand for EGR at WOT. VANOS is controlling the exhaust cams for maximum scavenging, You need to be looking at the usual suspects for a low test result, bad MAF's, plugged fuel filter, etc.
 

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:dunno: But likely. Really have not sat down and tried to figure it out. Don't think it would be the X pipe as it reduces pressure. It will be the change in the cat back.

X PIPE ,Depends on which company you choose will either have resonated or non resonated setup!If it has no resonators, it will loose back pressure.Muffler delete will also kill the low end grunt,it's a fact not a myth.Only way to get back tq in a tune is a adjusting the peak and low end tq *,tuning will not add back pressure due to the exhaust volume changing from the deletes.N.a need back pressure.
 

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This thing people claim that cars need back pressure is a wives tail. It comes from the old days when we use to burn valves. Back pressure plays a role but only in the way it effects egr.
There is this thing you can do on something called the internet called searching. If you have some know how you can usually find the right answer.
 
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