Date:         Sat, 31 Aug 2002 22:21:05 EDT
Reply-To:     CMathis227@AOL.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Chuck Mathis <CMathis227@AOL.COM>
Subject:      Re: vanagon Digest - 31 Aug 2002 - Special issue (#2002-1058)
Content-Type: text/plain; charset="US-ASCII"

Were it not for the O2 sensor your assertion about a hole increasing power
would be correct.  When the exhaust gases are diluted before they reach the
O2 sensor the FI assumes a lean condition and increases the amount of fuel to
compensate resulting in an over rich mixture that reduces power.  A good
sized hole in the system after the O2 sensor could increase power but any
gains would be minimal unless the whole cat and muffler are gone.  Even then
it ain't much.

Chuck
'85 Wolfsburg Westy - 'Roland the Road Buffalo'

In a message dated 8/31/02 8:20:01 PM, LISTSERV@GERRY.VANAGON.COM writes:

>Date:    Sat, 31 Aug 2002 16:04:16 EDT
>From:    Kim Brennan <KimBrennan@AOL.COM>
>Subject: Exhausts...tuning.(was loud identity crisis)
>
>In a message dated 8/31/02 6:28:18 AM, clive.harman-smith@NTLWORLD.COM
>writes:
>
>
>> I'd suggest that most holes in exhausts actually reduce power. A weak
>> mixture is one result (hence coinnected to rough running and backfiring
>on
>> the overrun), splashy irregular shockwaves in the syetm etc. etc. Any
>> supposed power gains are usually psychological due to the loder noise.
>>
>It depends. My brother worked in a shop that built race engines. One thing
>he
>learned after joining that shop was how an exhaust can hinder...or help
>evacuating exhaust gases from the engine. This is the process of tuning
>the
>exhaust. Most consumer vehicles have an exhaust system that isn't tuned
>all
>that well (modern cars are better than older ones as emissions quality
>has
>forced manufacturers to look at all aspects of engine management). The
>main
>focus of the exhaust system in these consumer vehicles is to reduce emissions
>(catalytic convertor) and reduce noise (muffler). Race engines, on the
>other
>hand, don't have to worry about this (they also use different fuel, but
>that's a different issue). In Race engines, the length of pipe used in
>the
>exhaust system can have dramatic differences in the power output of the
>engine. And it isn't a matter of pure length, but the ratio of volume of
>gases passing through it to the length.
>
>The wrong length pipe can cause a standing pressure wave in the exhaust
>system, this means that is is harder for the engine to get the burnt fuel
>out
>of the pistons, and causes a loss of power. Block your exhaust pipe and
>you'll see what I mean. If the exhaust can't get out, the engine won't
>run
>for very long. ON the other paw, if you have just the right length, the
>exhaust system acts as a partial vacuum and actually aids in removing the
>spent fuel from the pistons.
>
>Why? Harmonics. You have pulses being caused by the pistons. These occur
>rhythmicly and as with any other rhytmic system, you can get reinforcement
>of
>the waves in a positive or negative fashion. In this case the waves are
>pressure points in exhaust gases. High pressure is a positive reinforcement,
>low pressure is a negative reinforcement.
>
>All of this explains the large market in sports car after market exhaust
>systems. It isn't just about noise, but various people trying to get a
>little
>extra "free" power out of their engine, by tuning the exhaust.
>
>Back to my original point. Depending on the size of the hole (and where
>it
>is) you will probably end up with more power because of a less restrictive
>path for the exhaust gases.