A. EXHAUST BACK PRESSURE
The simplest way, is to describe exhaust back pressure, as follows: The exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. Back pressure is the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream. Back pressure in the exhaust system is caused by (exhaust manifold, catalytic converters, mufflers and connecting pipes and even X-pipes if it is not properly configured)
However, we need to be aware of the environmental concern: By removing the restrictions that cause back pressure we release more CO2 pollution into the atmosphere as well as creating heavier chemical by-products (smog) and noise pollution by removing the cats and mufflers. This can be hazzardous to humans and animals in a concentrated area. Smog testing policy/laws are currently under review in South Africa.
B. WHAT DO THE CUT-OUTS DO?
The cut-out system - also called electric exhaust cutout, exhaust dump or e-cutout. The exhaust cutout bypass the remaining exhaust system after the point at which the cutout is installed. When you bypass the remaining exhaust system you eliminate the restrictions and reduce back pressure. The cutouts are fitted into your stock or modified exhaust. They can be placed anywhere after the headers (where space allows). To open the cutouts you press a switch in the cabin, which opens the cutouts, releasing your exhaust. This makes it easier for the engine to work and result in an increase in horsepower and torque.
With this system you can go from stealth quiet to wide open power. You control the volume, you control the power. Open your exhaust with the flip of a switch. Run it closed, run it all the way open or any position in between.
C. ORDERING, SHIPPING & PACKAGING
I ordered the cutouts from a company called [DMH Performance]. But placing an order on the DMH website was concerning. I tried a few times using the online store but to no avail. I then sent an email to DMH and after a few days got a response with a confirmed price including shipment. After payment with Paypal, I had to wait another week or more before I heard back from DMH on shipment dates. Then there was another delay because they had to manufacture the flowtechs and length of wiring according to my order. When the cut-outs eventually arrived it was well packaged and the quality of the units including the flowtechs were outstanding. The wait was worthwhile after all.
:thumbs:
D. DECIDED ON A CUSTOM EXHAUST
While waiting for the DMH package to arrive I decided to do away with the BMW Performance exhaust and have a complete custom exhaust built that meets my criteria and expectation. At the same time I wanted to keep the BMW performance rear muffler for its lovely and unintrusive tone. In fact, I did not have a choice to go for a custom setup because I wanted to place the electric cutouts in the same location as the BMW performance exhaust X-Pipe, and I did not want to cut the performance exhaust.
I approached All Speed Racing (ART) to fabricate the exhaust for me as well as ensuring that all the mods and the tuning come together for best performance.
Here are my previous exhaust reviews for reference:
* Downpipes install review
* BMW Performance Exhaust Review
Without sparking a debate. I am not an exhaust expert but I know what I want and what sound I want to hear when sitting inside the car and from the outside. I participate in all aspects of modifications or tuning to my car. And my views are not always orthodox. Exhaust tuning is an ART (excuse the pun) but it is also a "try test - test try" until you get what you want.
Bigger or wider pipes are not necessarily more effective at clearing the combustion chamber than narrower pipes. Sure wider pipes will flow more than narrower pipes. But you may not get the (exhaust velocity). A tricky balance between flow capacity & velocity has to be found. You want the exhaust gasses to exit as fast as possible yet you want the right size piping that continues to decrease back-pressure up to the point of exit.
But there is another issue that one has to be congnisance of. The exhaust piping has to be narrower where the power band is located in the BMW 335 between (2500 - 6200rpms) than if the powerband was in the 7 - 8000rpm range. So for quick boosting cars narrow piping is more ideal. "A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of back pressure at high rpm."
For my purposes we increased the piping diameter from 60mm (this is the BMW performance pipe size) to 67mm as well as placing the X-Pipe after the resonators and before the cutouts. The X-Pipe location is roughly about 15cm before the original BMW X-Pipe location. Planning the exhaust system was fun but our aim was: The exhaust and all the other power mods on the car as well as the tune - All these parts have to come together in a beautiful yet powerful noise.
:inlove:
E. THE DMH DUAL E - CUTOUTS WITH FLOWTECH'S 2.5'
The cut-outs can be ordered to fit various exhaust sizes from 2.5', 3.0', 3.5', 4.0' The vital specs of the cutout-outs are:
• CNC Machined 6061-T6 aircraft grade aluminum body
• .375 diamiter 316 Stainless Steel Shaft
• Torrington Needle Bearings for years of trouble free service
• High torque gear motor
• 4 year replacement warranty!
A close-up view of the cut-outs and the plug and play 16GA Belden wiring harness on the right. Notice the small black rocker switch on the cable which is only .75" X .50". You can order the wiring to your requirements. I needed at least 2 x 3 meters due to the wiring route from the back of the exhaust into the cabin. This is important because you do not want to fall short on the length.
F. FLOWTECHS 2.5" or Y-Pipes
You can order the cutouts without the flowtechs/Y-Pipes. I would recommend this because the DMH flowtechs were too heavy for our purposes. Keeping weight in check was paramount. So we custom made our own light weight flowtechs and could bend them to fit in the allowable space.
The cut-outs were bench tested on arrival to make sure everything was in working order. It was fun to play around with the new toys as well as refining our exhaust diameter measurements to ensure a proper fit of the cut-outs:
G. VIDEO: Revo holding the camera...:
:=):
<iframe width="560" height="315" src="
" frameborder="0" allowfullscreen></iframe>
H. IN THE CABIN
One switch rule them all. This is the last part of the install but I am putting it first because I love switches, lights and gauges that tells me what is going on with the car. This switch has a huge convenient factor. In the past you had to shuffle under the car to open or close the cutouts. Now you can simply press a switch (the one @ the bottom) to open or close the cut-outs. You can hear the cutouts open or close when holding the switch down for a quick 3 counts or 1 second. You wont be able to hear it whilst driving though. You can also press the switch briefly for a partial opening of the cutouts, if you so wish - the noise is still the same but the exhaust tone changes when partially opened as oppose to full blast.
I. ART DPs & Midpipes
These DPs are based on the Rissracing 3' DPs that was first installed on my previous 335 but we refined the pipes for better fitment as well as tweaking the flanges and positioning of the lambda sensors. All the flanges used in this custom exhaust uses the "AR Design" bomb proof gaskets. They really great in preventing leaks.
I initially imported two resonators from Vibrant Performance in the US but these resonators did not fit the space available after we factored in space for the X-Pipe. So we sourced two resonators from Powerflow and were lucky that they fitted the space as well as working perfectly in reducing drone and excessive noise when the cut-outs are closed.
In the picture below you can see (on the right hand side of the pic) that our custom brace must still be fitted.
J. CUT-OUTS INSTALLED
Our own custom made flowtechs with adjustable down-turns and 1/4' thick flanges. The down-turns can rotate 360 degrees. We decided to point them downwards to the ground yet pointing to the back of the car, to create a vibrato, rumbling & echo effect as the sound reflects off the ground. In the pic below on the left you can see we took caution in attaching the cut-outs wiring away from the hot exhaust to rubber or insulated piping that does not relay heat.
The BMW performance rear mufflers/boxes. The BMW mufflers only flow 25% more than the stock 335 exhaust but the sound from these babies on a stock exhaust in the higher rpms is really exciting with an exotic pitch. But after installing the cutouts the sound from the BMW performance mufflers are totally different. The sound is deep, loud and uncivilised but with a unique rumbling character that forms deeper in the lower rpms. And as you build the rpms so does this sound increase into a boom. The lovely crackling sound of the turbo car exhaust is also amplified when you downshift.
Closeup of the inside of the cut-out. The pic on the right: We fitted flanges to the mufflers for easy removal. The original "joint" for the BMW performance muffler has a slip on clamp, which is not very secure and can easily leak when the exhaust shifts. This problem is now solved.
After some run-in time, the exhaust changed into this stunning golden hue colour. Notice the joint between the DP flanges to prevent vibration or the flanges from touching. On the right: The stock brace was replaced with a custom brace which cleared the bigger mid-pipes.
K. VIDEOS
The first video is of the completed exhaust after installation. Before the testing started:
<iframe width="560" height="315" src="
" frameborder="0" allowfullscreen></iframe>
Car being fired up on a cold start with the cutouts open & closed. If you listen carefully you can hear the cutouts being activated with the switch.
<iframe width="560" height="315" src="
" frameborder="0" allowfullscreen></iframe>
L. SOME DRIVE - BY FUN
You can clearly hear the difference when the cutouts are opened and closed:
<iframe width="560" height="315" src="
" frameborder="0" allowfullscreen></iframe>
M. VERDICT
* The freeflow custom exhaust transforms the car. The turbos spool quicker and the car revs freely through the rev band.
** The standard JB4 maps were not adequate and the car felt sluggish due to the loss in torque. We had to readjust tuning settings for each rpm on map 6 to take full advantage of the freeflow exhaust system. We were able to fine tune the exhaust and the car really woke up!
*** When the cutouts are open the turbos spool up so fast it is one manic driving experience. You just cannot believe how the rev needle shoots through the rpms. Its crazy. My brother accompanied me on the initial testing and we giggled on each gear shift. It was crazy.
**** The exhaust is extremely loud when the cutouts are open. No video will do this noise justice. Its freaken loud. The noise will turn heads - period. Its an uncivilised, rumbling, noisy experience but oh so fantastic.
****** The sound is well contained when the cutouts are closed due to the resonators but still loud, yet bearable. As the exhaust warms up so does the noise levels settle.
******* When the cutouts are closed there is plenty drone under 3000 rpms in "D" mode. But in sport mode or "DS" mode the sound is racy and quiet and climbs to an enthusiastic racy pitch in the higher rpms. You have to experience this in the cabin. The sound is simply intoxicating in "DS".
N. POST INSTALLATION CHALLENGES
1. When ever we open or close the cutouts (on the fly) the car would go into limp mode. We checked the battery voltage and cutout wiring but the issue persisted. We operated the cutout off an external power source and the problem continued. All indications were that the ECU could not adapt quickly enough to the opening of the cutouts when activated on the fly. We thought of moving the cutouts further away, closer to the rear mufflers but space did not allow this option.
2. However, when you open or close the cutouts (before) starting the car then the car drives fine with no limp modes.
3. This was a let down. Because part of the fun was to open the cutouts on the fly; when you next to the Honda or GTi boyz at a robot; and you want to give them a good skrik before you pull away.:=):
4. I have said this before but it is worth a repeat. The noise levels inside the cabin when the cutouts are open is crazy loud. For short stints and racing at the track, I guess it should be fine but not for long term use.
5. So I decided, that I would only keep the cutouts if I can open the cutouts from the cabin while driving (on the fly) and since this did not work out; we sadly had to remove them.
6. A MercFanatic that has been following the progress on my car, purchased the cutouts from me and seem to be having plenty fun with his CLS 500 without limp sessions. See the video below.
O. CUSTOM FREEFLOW EXHAUST SYSTEM WITHOUT THE CUTOUTS:
So how does the custom free-flow exhaust sound without the cut-outs? The car screams the same hotness as when the cutouts were closed but the tone is different. Its less racy yet awesome. On downshifting the exhausts breaks loose a wonderful crackling rumble that turbo cars are known for. I will now definitely consider my favourite brand Eisenmann rear muffler set instead of the civilised BMW mufflers to round off the package.
:thumbs:
Here is a video of a cold start with the cutouts removed. This is how the car is now. Note it was a very cold and misty morning.
<iframe width="560" height="315" src="
" frameborder="0" allowfullscreen></iframe>
Video of my cutouts on another BMW/Merc fanatic. He has zero limp issues when opening the cutouts on the fly:
<iframe width="560" height="315" src="http://www.youtube.com/embed/9YZ3xFN1C84?rel=0" frameborder="0" allowfullscreen></iframe>
P. SOURCES
* Wikipedia
* DMH
* QTP Performance
* Back pressure myths
* Cut-out installs
Thanks for reading.
:ty:
The simplest way, is to describe exhaust back pressure, as follows: The exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. Back pressure is the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream. Back pressure in the exhaust system is caused by (exhaust manifold, catalytic converters, mufflers and connecting pipes and even X-pipes if it is not properly configured)
However, we need to be aware of the environmental concern: By removing the restrictions that cause back pressure we release more CO2 pollution into the atmosphere as well as creating heavier chemical by-products (smog) and noise pollution by removing the cats and mufflers. This can be hazzardous to humans and animals in a concentrated area. Smog testing policy/laws are currently under review in South Africa.
B. WHAT DO THE CUT-OUTS DO?
The cut-out system - also called electric exhaust cutout, exhaust dump or e-cutout. The exhaust cutout bypass the remaining exhaust system after the point at which the cutout is installed. When you bypass the remaining exhaust system you eliminate the restrictions and reduce back pressure. The cutouts are fitted into your stock or modified exhaust. They can be placed anywhere after the headers (where space allows). To open the cutouts you press a switch in the cabin, which opens the cutouts, releasing your exhaust. This makes it easier for the engine to work and result in an increase in horsepower and torque.
With this system you can go from stealth quiet to wide open power. You control the volume, you control the power. Open your exhaust with the flip of a switch. Run it closed, run it all the way open or any position in between.
C. ORDERING, SHIPPING & PACKAGING
I ordered the cutouts from a company called [DMH Performance]. But placing an order on the DMH website was concerning. I tried a few times using the online store but to no avail. I then sent an email to DMH and after a few days got a response with a confirmed price including shipment. After payment with Paypal, I had to wait another week or more before I heard back from DMH on shipment dates. Then there was another delay because they had to manufacture the flowtechs and length of wiring according to my order. When the cut-outs eventually arrived it was well packaged and the quality of the units including the flowtechs were outstanding. The wait was worthwhile after all.
:thumbs:
D. DECIDED ON A CUSTOM EXHAUST
While waiting for the DMH package to arrive I decided to do away with the BMW Performance exhaust and have a complete custom exhaust built that meets my criteria and expectation. At the same time I wanted to keep the BMW performance rear muffler for its lovely and unintrusive tone. In fact, I did not have a choice to go for a custom setup because I wanted to place the electric cutouts in the same location as the BMW performance exhaust X-Pipe, and I did not want to cut the performance exhaust.
I approached All Speed Racing (ART) to fabricate the exhaust for me as well as ensuring that all the mods and the tuning come together for best performance.
Here are my previous exhaust reviews for reference:
* Downpipes install review
* BMW Performance Exhaust Review
Without sparking a debate. I am not an exhaust expert but I know what I want and what sound I want to hear when sitting inside the car and from the outside. I participate in all aspects of modifications or tuning to my car. And my views are not always orthodox. Exhaust tuning is an ART (excuse the pun) but it is also a "try test - test try" until you get what you want.
Bigger or wider pipes are not necessarily more effective at clearing the combustion chamber than narrower pipes. Sure wider pipes will flow more than narrower pipes. But you may not get the (exhaust velocity). A tricky balance between flow capacity & velocity has to be found. You want the exhaust gasses to exit as fast as possible yet you want the right size piping that continues to decrease back-pressure up to the point of exit.
But there is another issue that one has to be congnisance of. The exhaust piping has to be narrower where the power band is located in the BMW 335 between (2500 - 6200rpms) than if the powerband was in the 7 - 8000rpm range. So for quick boosting cars narrow piping is more ideal. "A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of back pressure at high rpm."
For my purposes we increased the piping diameter from 60mm (this is the BMW performance pipe size) to 67mm as well as placing the X-Pipe after the resonators and before the cutouts. The X-Pipe location is roughly about 15cm before the original BMW X-Pipe location. Planning the exhaust system was fun but our aim was: The exhaust and all the other power mods on the car as well as the tune - All these parts have to come together in a beautiful yet powerful noise.
:inlove:
E. THE DMH DUAL E - CUTOUTS WITH FLOWTECH'S 2.5'
The cut-outs can be ordered to fit various exhaust sizes from 2.5', 3.0', 3.5', 4.0' The vital specs of the cutout-outs are:
• CNC Machined 6061-T6 aircraft grade aluminum body
• .375 diamiter 316 Stainless Steel Shaft
• Torrington Needle Bearings for years of trouble free service
• High torque gear motor
• 4 year replacement warranty!
A close-up view of the cut-outs and the plug and play 16GA Belden wiring harness on the right. Notice the small black rocker switch on the cable which is only .75" X .50". You can order the wiring to your requirements. I needed at least 2 x 3 meters due to the wiring route from the back of the exhaust into the cabin. This is important because you do not want to fall short on the length.
F. FLOWTECHS 2.5" or Y-Pipes
You can order the cutouts without the flowtechs/Y-Pipes. I would recommend this because the DMH flowtechs were too heavy for our purposes. Keeping weight in check was paramount. So we custom made our own light weight flowtechs and could bend them to fit in the allowable space.
The cut-outs were bench tested on arrival to make sure everything was in working order. It was fun to play around with the new toys as well as refining our exhaust diameter measurements to ensure a proper fit of the cut-outs:
G. VIDEO: Revo holding the camera...:
:=):
<iframe width="560" height="315" src="
H. IN THE CABIN
One switch rule them all. This is the last part of the install but I am putting it first because I love switches, lights and gauges that tells me what is going on with the car. This switch has a huge convenient factor. In the past you had to shuffle under the car to open or close the cutouts. Now you can simply press a switch (the one @ the bottom) to open or close the cut-outs. You can hear the cutouts open or close when holding the switch down for a quick 3 counts or 1 second. You wont be able to hear it whilst driving though. You can also press the switch briefly for a partial opening of the cutouts, if you so wish - the noise is still the same but the exhaust tone changes when partially opened as oppose to full blast.
I. ART DPs & Midpipes
These DPs are based on the Rissracing 3' DPs that was first installed on my previous 335 but we refined the pipes for better fitment as well as tweaking the flanges and positioning of the lambda sensors. All the flanges used in this custom exhaust uses the "AR Design" bomb proof gaskets. They really great in preventing leaks.
I initially imported two resonators from Vibrant Performance in the US but these resonators did not fit the space available after we factored in space for the X-Pipe. So we sourced two resonators from Powerflow and were lucky that they fitted the space as well as working perfectly in reducing drone and excessive noise when the cut-outs are closed.
In the picture below you can see (on the right hand side of the pic) that our custom brace must still be fitted.
J. CUT-OUTS INSTALLED
Our own custom made flowtechs with adjustable down-turns and 1/4' thick flanges. The down-turns can rotate 360 degrees. We decided to point them downwards to the ground yet pointing to the back of the car, to create a vibrato, rumbling & echo effect as the sound reflects off the ground. In the pic below on the left you can see we took caution in attaching the cut-outs wiring away from the hot exhaust to rubber or insulated piping that does not relay heat.
The BMW performance rear mufflers/boxes. The BMW mufflers only flow 25% more than the stock 335 exhaust but the sound from these babies on a stock exhaust in the higher rpms is really exciting with an exotic pitch. But after installing the cutouts the sound from the BMW performance mufflers are totally different. The sound is deep, loud and uncivilised but with a unique rumbling character that forms deeper in the lower rpms. And as you build the rpms so does this sound increase into a boom. The lovely crackling sound of the turbo car exhaust is also amplified when you downshift.
Closeup of the inside of the cut-out. The pic on the right: We fitted flanges to the mufflers for easy removal. The original "joint" for the BMW performance muffler has a slip on clamp, which is not very secure and can easily leak when the exhaust shifts. This problem is now solved.
After some run-in time, the exhaust changed into this stunning golden hue colour. Notice the joint between the DP flanges to prevent vibration or the flanges from touching. On the right: The stock brace was replaced with a custom brace which cleared the bigger mid-pipes.
K. VIDEOS
The first video is of the completed exhaust after installation. Before the testing started:
<iframe width="560" height="315" src="
Car being fired up on a cold start with the cutouts open & closed. If you listen carefully you can hear the cutouts being activated with the switch.
<iframe width="560" height="315" src="
L. SOME DRIVE - BY FUN
You can clearly hear the difference when the cutouts are opened and closed:
<iframe width="560" height="315" src="
M. VERDICT
* The freeflow custom exhaust transforms the car. The turbos spool quicker and the car revs freely through the rev band.
** The standard JB4 maps were not adequate and the car felt sluggish due to the loss in torque. We had to readjust tuning settings for each rpm on map 6 to take full advantage of the freeflow exhaust system. We were able to fine tune the exhaust and the car really woke up!
*** When the cutouts are open the turbos spool up so fast it is one manic driving experience. You just cannot believe how the rev needle shoots through the rpms. Its crazy. My brother accompanied me on the initial testing and we giggled on each gear shift. It was crazy.
**** The exhaust is extremely loud when the cutouts are open. No video will do this noise justice. Its freaken loud. The noise will turn heads - period. Its an uncivilised, rumbling, noisy experience but oh so fantastic.
****** The sound is well contained when the cutouts are closed due to the resonators but still loud, yet bearable. As the exhaust warms up so does the noise levels settle.
******* When the cutouts are closed there is plenty drone under 3000 rpms in "D" mode. But in sport mode or "DS" mode the sound is racy and quiet and climbs to an enthusiastic racy pitch in the higher rpms. You have to experience this in the cabin. The sound is simply intoxicating in "DS".
N. POST INSTALLATION CHALLENGES
1. When ever we open or close the cutouts (on the fly) the car would go into limp mode. We checked the battery voltage and cutout wiring but the issue persisted. We operated the cutout off an external power source and the problem continued. All indications were that the ECU could not adapt quickly enough to the opening of the cutouts when activated on the fly. We thought of moving the cutouts further away, closer to the rear mufflers but space did not allow this option.
2. However, when you open or close the cutouts (before) starting the car then the car drives fine with no limp modes.
3. This was a let down. Because part of the fun was to open the cutouts on the fly; when you next to the Honda or GTi boyz at a robot; and you want to give them a good skrik before you pull away.:=):
4. I have said this before but it is worth a repeat. The noise levels inside the cabin when the cutouts are open is crazy loud. For short stints and racing at the track, I guess it should be fine but not for long term use.
5. So I decided, that I would only keep the cutouts if I can open the cutouts from the cabin while driving (on the fly) and since this did not work out; we sadly had to remove them.
6. A MercFanatic that has been following the progress on my car, purchased the cutouts from me and seem to be having plenty fun with his CLS 500 without limp sessions. See the video below.
O. CUSTOM FREEFLOW EXHAUST SYSTEM WITHOUT THE CUTOUTS:
So how does the custom free-flow exhaust sound without the cut-outs? The car screams the same hotness as when the cutouts were closed but the tone is different. Its less racy yet awesome. On downshifting the exhausts breaks loose a wonderful crackling rumble that turbo cars are known for. I will now definitely consider my favourite brand Eisenmann rear muffler set instead of the civilised BMW mufflers to round off the package.
:thumbs:
Here is a video of a cold start with the cutouts removed. This is how the car is now. Note it was a very cold and misty morning.
<iframe width="560" height="315" src="
Video of my cutouts on another BMW/Merc fanatic. He has zero limp issues when opening the cutouts on the fly:
<iframe width="560" height="315" src="http://www.youtube.com/embed/9YZ3xFN1C84?rel=0" frameborder="0" allowfullscreen></iframe>
P. SOURCES
* Wikipedia
* DMH
* QTP Performance
* Back pressure myths
* Cut-out installs
Thanks for reading.
:ty:
