Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (February 1999, week 1)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:   Fri, 5 Feb 1999 10:50:51 -0800
Reply-To:   Doug Jones <duge4wd@EMAIL.MSN.COM>
Sender:   Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:   Doug Jones <duge4wd@EMAIL.MSN.COM>
Subject:   Re: extractor exhaust?

>Mac wrote: >I think I understand basically the concept of an extractor exhaust, >but how do they go about "extracting?"

I'll take a shot at this. The first thing you should notice about an "extraction" exhaust is that the primary pipes (those coming from the head flanges to the collector) should be of equal length. The individual pipes may appear snake-like and excessively long; but, there is a reason for this. This ensures the exhaust charge from each cylinder travels the same distance. This equal distance equates to equal timing of these exhausts charges passing through the collector, thus the charges from each cylinder pass through the collector in sequence...one right after the other.

As one exhaust charge passes through the collector, it goes from exerting a positive pressure in it's primary tube, and to exerting a negative pressure on the other primaries which feed into the collector. This associated negative pressure "extracts" exhaust gases from the affected primaries. This helps remove exhaust gases quickly from the primaries and from the combustion chamber. This is extremely important when large valves are used, and there is allot of valve lift and duration which increases the intake/exhaust overlap. So the extraction caused by each charge passing the collector and 'pulling' on the other exhaust charges helps remove spent gases from the cylinders and helps maintain sufficient intake charge velocity and fuel atomization.

In the case of large valves, long valve duration and lift, high intake charge velocity helps fuel aerosolized (which equals more fuel surface area and better, more complete burn), poor evacuation of exhaust gases would contaminate the high velocity mixture and slow it down, causing the fuel to drop 'out of solution.'

This is why most race engines (especially F1) tend to have a convoluted snake-like exhaust (especially when space is at a premium), b/c they run large valves, and hi-lift/duration cams; They also make a great deal of their power at higher rpms which helps maintain the intake charge velocity==>better burn, more power.

>Does anyone have enough >experience with these things to know whether or not I would get a >noticeable advantage on an air-cooled with one of these?

Yes, you should see instant results. Low restriction exhaust systems are one on the quickest bolt-on ways to increase power. I've put several on different autos. Corvettes, Jeeps, and aircooled VWs. You may have some fit problems with VW extractor exhausts, nothing major I think. I've never put one on a aircooled T4 engine; but, the fit on most aftermarket T1 systems leaves something to be desired. Just requires a little "persuasion" ( read that as a big hammer for some subtle bending). Maybe a torch in the extreme cases.

>What kind of noise level do these things put out? Is it going to >"muffle" at all or will it sound like those annoying (imho) glasspacks >that everyone around here seems to have on their trucks?

My experience is that they tend to be louder b/c the mufflers used with these headers tend to be less restrictive; This helps maintain the "extraction" and reduces backpressure. You could try single or dual quiet pack type mufflers. They are a little deep and throaty but not offensive. I don't have much experience with what low restriction mufflers are available for Vanagons.

I hope I helped somewhat, especially since this post was kinda long. I apologize for the length to those not interested in this subject.

BTW, where's Berea College? Just curious, up until two days ago I was a post-bac student at Univ of MD; I've had to take a leave of absence for medical reasons. I can't really miss classes already, can I?

Doug Jones No Vanagon, No Syncro; but, I hopefully see something in my future. I'm just tied up at the moment. The money is burning a hole in my pocket. I'll keep you posted.


Back to: Top of message | Previous page | Main VANAGON page

Please note - During the past 17 years of operation, several gigabytes of Vanagon mail messages have been archived. Searching the entire collection will take up to five minutes to complete. Please be patient!


Return to the archives @ gerry.vanagon.com


The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.

Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.