Vanagon EuroVan
Previous messageNext messagePrevious in topicNext in topicPrevious by same authorNext by same authorPrevious page (November 2004, week 4)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Sat, 27 Nov 2004 15:59:32 -0800
Reply-To:     syncrolist@BOSTIG.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Bostig Engineering <syncrolist@BOSTIG.COM>
Subject:      Re: Intake air flow, improvement possible?
In-Reply-To:  <001401c4d4d3$fb61dfe0$e10cfea9@9100d>
Content-Type: text/plain;charset=iso-8859-1

Hi Gary,

You make some good points, but let me clarify a couple things.

> 1. The volume of air required by a gasoline engine is directly > proportional > to RPM. > The higher the RPM, the more air needed. A gasoline engine needs to > maintain a relatively constant air fuel ratio.

True, however above and beyond the volume, we're really concerned with air mass, which is derived from volume as you point out, temperature, and pressure. It is the mass of air not just volume that affects air/fuel ratio which like you say, the ECU likes to try to keep in range. This is the primary problem with the vanagon stock system, it measures force on the vane spring(crudely measuring volume), and tempurature, and then back calculates mass. This is the reason why vanagon guys have problems at altitude, because the stock system isn't *measuring* mass and does not calculate the value correctly when not at sea level.

> 2. The stock air filter - throttle body - intake manifold system is > capable > of flowing enough air for the stock engine up to redline.

True, but any given intake system, isn't just qualified for flowing X CFM, at X pressure drop. The vanagon system at the CFM needed by a running 2.1 at redline creates about a single PSI of drop. This is in effect running your engine at well above sea level. At lower flow, it isn't as much of a drop, but it's significant enough to make a substantial gain in power possible by increasing flow and decreasing that drop. Think of it this way, do you get more soda by sucking the same through a wendy's straw, or do you get more by sucking through the sewer pipes they give you at McDonalds?

> > So, increasing the volume of air the intake tract can flow will have no > affect on power or fuel economy (in a stock unmodified engine).

Again, we want to talk about mass. not volume, as I could put the engine in a vacuum chamber at 1 PSI, and you'd pump the same volume but couldn't produce 20 HP.

> > If you drive your van at less than redline, increasing the size of the > throttle body and/or increasing the size of the intake tract will have no > affect > on performance.

It has an effect in multiple ways, not only is the pressure drop reduced, and mass increases, but the volumetric efficiency of the engine increases because the exhaust backpresure (which is always at or higher than atmospheric) to intake pressure ratio is closer. Additionally pumping losses will be less as a result of not having to suck air from a lower pressure and pumping into a higher presure (intake to exhaust). If you don't buy this stuff, I'll hook you up when we're shipping and you can feel it for yourself :)

Certainly everyday city driving is far below redline, > well > within the capacity of the stock AFM and air filter. Even if the stock > system is > restrictive, there should be lots of headroom for normal driving with a > stock engine.

True, but this is akin to saying you don't need/want more power, which is a personal thing.

> If you do not accept the above, then some related questions are: > - just how bad is the stock system?

So bad that when we flowed it the first time, we had to go back and triple check because we didn't believe the bench... and so bad that I don't think it would be possible to find a system that performs this badly on ANY car produced today.

> - do things like K/N air filters really honestly offer more hp and better > mileage?

They can, but the entire system has to be considered as a whole, and just the K&N while in one application yields great results, may not in another... but basically the answer is yes because the surface area of the filter is much higher lending itself to better flow/less drop... now just to compound your head scratching... and for everyone on the list to consider.. brownie points to anyone that comes up with the correct anwser to the following FACT:

WHY does the vanagon air box/meter flow BETTER with an air filter, than wide open without one? :) (While we're on the sibject of filters and flow)

Hope this helps,

Jim Akiba Bostig Engineering


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.