Date: Thu, 16 Sep 2004 08:02:14 -0700
Reply-To: Vince S <gipsyflies@COMCAST.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Vince S <gipsyflies@COMCAST.NET>
Subject: Re: Exhaust Pipe Question
In-Reply-To: <vanagon%2004091609212877@GERRY.VANAGON.COM>
Content-Type: text/plain; charset="us-ascii"
Dennis,
I agree with your detailed mention of the proper resonant-tuning of a
proper designed exhaust system so it promote efficient extraction of
exhaust gas from the engine. VW automotive engineers are no dummies and
I would think they have done that to optimize the operation at the
intended sweet operating rpm range. Given the package constraints in the
Vanagon and noise emission they may have to make some compromises.
I have no doubt that is some room for improvement if one is willing to
go thru the trouble for a more complex mounting and perhaps live with a
louder exhaust. How many extra HP are we talking about with such system
with a bone stock engine operating in the max torque rpm of under 4k?
I think for most Vanagon owner the best exhaust system is stock, for
cost, longivity, and peace of mind.
It is common knowledge on the BMW Mini community that even the best
exhaust upgrade can only bring about 5-7 hp out from a 170 hp of the
Cooper S engine and this is near the red line of 7000. It is virtually
next to impossible to see this increase in dyno runs due to the many
variables that influence the reading. It is possible that the Mini's
exhaust is already quite optimized.
- Vince
http://gipsyflies.home.comcast.net
1989 Vanagon GL Camper
1993 Mazda Miata (for sale)
1996 Land Rover Discovery
2005 Mini Cooper S
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Dennis
Sent: Thursday, September 16, 2004 6:16 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Exhaust Pipe Question
I would disagree. A properly designed exhaust has low or no
backpressure. On the contrary, by taking advantage of resonant pressure
waves, a vacuum is actually created at the exhaust valves. Essentially
the pressure front from the closing of one valve travels down the header
pipe around the collector and then back up the next primary tube .. and
bounces off the next exhaust valve about to open. At that point you may
actually have a vacuum at the valve resulting in increased scavenging,
decreased pumping loss, and thus better efficiency.
I won't rehash the volumes of information out there on exhaust theory
but tube diameter, primary tube length and collector location all
require careful consideration to ensure both high gas velocity and the
aforementioned resonant effect. It's important to note that this tuning
is generally focussed to a particular engine's planned power curve.
Check out the dyno tests at www.techtonicstuning.com
A quick intro to the theory:
http://www.powerflowsystems.com/review/12-00.shtml
A properly designed exhaust means better torque, hp, and mileage. A
good example is my daily driver car. It started life as a 90hp 1.8L VW
Scirroco that maxed at about 35mpg (imperial). It now has a tuned 2.0
litre that delivers 145 HP, yet still delivers 39mpg (imperial) at 60mph
highway cruise. It's all about efficiency...and internal combustion
engines (particularly older ones) have lots of room for improvement.
My site http://my.tbaytel.net/guskers has a section on exhaust with
references to autospeed's muffler tests. It is possible to have a quiet
exhaust with straight through mufflers if designed properly. The
exhaust I designed has two straight through mufflers, one five inch OD,
and one six inch OD. It is only slightly louder than stock...although
the first design with a smaller OD 2nd muffler was obnoxiously loud.
