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 :thumbsup: :grin:

For an interesting read....
 

look here here for Dinans take. Comes down to a couple of points.

• 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".

Sounds good to me!
Matt

Ive noticed on my NA cars that when I switched over to a straight pipe
the low-end torque was lost. it took a tad more rpms to get the car
rolling.

My observations too... less torque low down, pulls stronger on top..

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.

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.:grin: that's what I wish:lol: .
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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.:wink:

They make an exhaust dump tube. An actuator that opens a valve and dumps the exhaust usually before the cats. This is fairly common amongst the V8 drag racing crowd. The car is legal on the streets and the tube is opened for track day...

nice, nice, nice
 

nice :thumbsup:

Yoou need to think abou this more...
 

For a given flow of exhast gas (determined by the RPM, air and fuel burnt etc) the AMOUNT of gas coming out of the exhaust pipe is pretty much fixed. So what is happening is you need a much higher pressure gradient to achieve the same flow! There are some changes as at higher pressure the gas takes less space, but it's also true that the gas cools as it expandes.

Anyone have dyno graphs of the same motor with more and less restricitve exhaust systems?

Matt

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?

Our exhaust is going to have a tunable volume/power function (A nob inside the car). Look for it in a month or so, it's in very rigorous testing right now.

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 :thumbsup: .

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 :wink: .

The 03 360 modena challenge I used to detail had a exhaust with a regulator like that you see on a jet engine. VERY COOL once that thing opened! Man did it scream.:thumbsup:

Has anyone actually used this activated exhaust piece? I am curious about its actual performance from a daily spirited driving and monthly auto-cross perspective. Since I plan to add a new milltek exhaust soon I was wondering if something like this is even worth trying?

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!

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.

Not quite right....
 

this was a thread about backpressure.........

Sorry... did my question about the control piece not relate?

wow... people get so angry around here too quick. This is the reason I started to ignore NAM.

Oh well..:sad: i won't interfere or contribute again

yah...as the maker of this thread i will chime in. This wasnt a MC only thread. Both cars will have back pressure. You will notice i discuss the results of backpressure on NA AND supercharged engines.

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.

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

are those actuators on some of the cars mentioned more for noise levels than actual performance increases? I'm not too sure though so please correct me if i'm wrong!

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. :thumbsup:

Bomboasy

Thats not just for MCS :wink: :thumbsup: I plan on getting the OBX for my MC once they get back up on ebay. Sounds like your setup is working well :thumbsup:

Any updates on this? :confused:

Ditto!