Drivetrain Back pressure on N/A cars
#1
Back pressure on N/A cars
The issue was sorta raised in another thread, but i figured i would open up a new thread to start a discussion on the subject.
I have personally always heard (no one super-reputable) that N/A cars require a certain back pressure from the exhaust in order for the car to work properly. I have also heard that on superchargered cars it doesnt matter about the back pressure.
Turbo cars do in fact need the back pressure based on the requirements of the turbo.
So....can an MC owner create a custom exhaust like many MCS owners have. TonyB has his custom straight-back exhaust with an aftermarket muffler. Can i do the same thing with my MC without worrying too much about creating the "correct" amount of back pressure? Or should i stick to aftermarket exhausts who may have found the right backpressure?
Just figured it would be a good discussion... enjoy
I have personally always heard (no one super-reputable) that N/A cars require a certain back pressure from the exhaust in order for the car to work properly. I have also heard that on superchargered cars it doesnt matter about the back pressure.
Turbo cars do in fact need the back pressure based on the requirements of the turbo.
So....can an MC owner create a custom exhaust like many MCS owners have. TonyB has his custom straight-back exhaust with an aftermarket muffler. Can i do the same thing with my MC without worrying too much about creating the "correct" amount of back pressure? Or should i stick to aftermarket exhausts who may have found the right backpressure?
Just figured it would be a good discussion... enjoy
#2
For an interesting read....
look here here for Dinans take. Comes down to a couple of points.
Matt
- tuning is done in the header
- The best exhaust past the header is the shortest, largest possible.
- Other issues (like sound) drive other disign compramises.
- For any condition other than max load at high RPM, the exhause is "overcapacity".
Matt
#4
#5
Originally Posted by mikem53
My observations too... less torque low down, pulls stronger on top..
#6
How about this, dominicminicoopers
:smile:
A boost activated exhaust cutout;
[size=2]http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
I wish everyone would drop/stop using the term backpressure to describe a loss of exhaust gas velocity or exhaust gas reversion which causes lost power. that's what I wish .
[/size]
Of course very restrictive pipe/mufflers would cause a measurable pressure but this is really only the result of a lack of exhaust gas velocity.
Originally Posted by dominicminicoopers
How about some sort of solenoid action, where one pipe is used down low and another is used up high? Kinda like what John Cooper did with the JCW Intake, where at a certain rpm, a gate is opened to allow more air to flow into the intake.
[size=2]http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
I wish everyone would drop/stop using the term backpressure to describe a loss of exhaust gas velocity or exhaust gas reversion which causes lost power. that's what I wish .
[/size]
Of course very restrictive pipe/mufflers would cause a measurable pressure but this is really only the result of a lack of exhaust gas velocity.
Last edited by norm03s; 06-21-2005 at 08:32 AM. Reason: add text
#7
Originally Posted by dominicminicoopers
How about some sort of solenoid action, where one pipe is used down low and another is used up high? Kinda like what John Cooper did with the JCW Intake, where at a certain rpm, a gate is opened to allow more air to flow into the intake.
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#9
Yoou need to think abou this more...
Originally Posted by norm03s
Of course very restrictive pipe/mufflers would cause a measurable pressure but this is really only the result of a lack of exhaust gas velocity.
Anyone have dyno graphs of the same motor with more and less restricitve exhaust systems?
Matt
#10
Mugen has those trumpet looking exhaust systems for Honda's. those are
pretty cool.. and sound real good too. :smile: costs a fortune though.
Don't most higher performance cars these days come with a gated
muffer where it open/closes based on the amount of exhaust flow?
pretty cool.. and sound real good too. :smile: costs a fortune though.
Don't most higher performance cars these days come with a gated
muffer where it open/closes based on the amount of exhaust flow?
Originally Posted by dominicminicoopers
How about some sort of solenoid action, where one pipe is used down low and another is used up high? Kinda like what John Cooper did with the JCW Intake, where at a certain rpm, a gate is opened to allow more air to flow into the intake.
#12
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No dynos here, but I lost nearly 2 pounds max boost when I went from the fairly restrictive QuickSilver catback, to my straight one. However, I subsequently began turning quicker times from point-to-point on my canyon runs, and also on a music-based run that I do (floor it at song begin, and note landmarks at key audible points). Not highly scientific, I realize, but it does offer me some validation. More power with less boost is a good thing .
IF I suffered anything off the line, I certainly can't tell. Being that I've lost nearly 170 lbs, and have reduced tire rolling diameter just over 1", quickness from a stand still (not a biggie for me anyways), is quite good.
A dynamic exhaust is very interesting indeed, esp for a NA engine. Looking into my crystal ball... I would bet that one our tuners might have something for us in the not-so-distant future .
IF I suffered anything off the line, I certainly can't tell. Being that I've lost nearly 170 lbs, and have reduced tire rolling diameter just over 1", quickness from a stand still (not a biggie for me anyways), is quite good.
A dynamic exhaust is very interesting indeed, esp for a NA engine. Looking into my crystal ball... I would bet that one our tuners might have something for us in the not-so-distant future .
#14
Originally Posted by norm03s
:smile: A boost activated exhaust cutout;
[size=2]http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
I wish everyone would drop/stop using the term backpressure to describe a loss of exhaust gas velocity or exhaust gas reversion which causes lost power. that's what I wish .
[/size]
Of course very restrictive pipe/mufflers would cause a measurable pressure but this is really only the result of a lack of exhaust gas velocity.
[size=2]http://www.atpturbo.com/Merchant2/me...egory_Code=BCS
I wish everyone would drop/stop using the term backpressure to describe a loss of exhaust gas velocity or exhaust gas reversion which causes lost power. that's what I wish .
[/size]
Of course very restrictive pipe/mufflers would cause a measurable pressure but this is really only the result of a lack of exhaust gas velocity.
#15
#16
#17
Not quite right....
this was a thread about backpressure.........
Originally Posted by rednwhitecooper
its just disgusting how fast this turned into MCS exhaust chat.........
we dont care about MCS exhausts right now(or anything boost related, for that matter), were trying to figure out how to custom make MC exhausts!
we dont care about MCS exhausts right now(or anything boost related, for that matter), were trying to figure out how to custom make MC exhausts!
#18
#19
Originally Posted by rednwhitecooper
its just disgusting how fast this turned into MCS exhaust chat.........
we dont care about MCS exhausts right now(or anything boost related, for that matter), were trying to figure out how to custom make MC exhausts!
we dont care about MCS exhausts right now(or anything boost related, for that matter), were trying to figure out how to custom make MC exhausts!
Anyways, this all seems like good information. The loss of torque makes sense...and would go along with the dinan article posted which discusses doing the tuning at the header.
#20
Originally Posted by Motoring
The Audi TT 3.2 and the VW R32 both have vacuum controlled diverters that open above 3500 rpm, allowing exhaust gas to flow through a second passage in the muffler. I've also seen a similar application on a 911 (I think) that bypassed the muffler.
You can hear the change in exhaust note.
You can hear the change in exhaust note.
I believe that i have seen this product sold in one of the aftermarket japanese tuning mags. I will go back and check to see what company is making them
#21
#22
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Please do not kill me for adding this, but for the MCS folks. Going to the OBX header helped everywhere in the power spectrum, but with the catback I lost some obvious torque at the low end. I already had the RP#2 mod and when I read that some evidence existed that the exhaust mod would result in loss of boost, I added the VGS also. This has helped a LOT on the low end. I can not explain it, but you should try it, specially if you have RP#2 already. The result was NOT RP#1. I know, since I tried that set up before. MPG has not suffered greatly, 25 MPG in the city.
Bomboasy
Bomboasy
#23
Originally Posted by bomboasy
Please do not kill me for adding this, but for the MCS folks. Going to the OBX header helped everywhere in the power spectrum, but with the catback I lost some obvious torque at the low end. I already had the RP#2 mod and when I read that some evidence existed that the exhaust mod would result in loss of boost, I added the VGS also. This has helped a LOT on the low end. I can not explain it, but you should try it, specially if you have RP#2 already. The result was NOT RP#1. I know, since I tried that set up before. MPG has not suffered greatly, 25 MPG in the city.
Bomboasy
Bomboasy
Thats not just for MCS I plan on getting the OBX for my MC once they get back up on ebay. Sounds like your setup is working well
#24
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