Site Partners: SpotterGuides Veloce Books  
Related Sites: Your Link Here  

Go Back   TenTenths Motorsport Forum > Racing Talk > Racing Technology

Thread Tools Display Modes
Old 5 May 2008, 21:50 (Ref:2194703)   #1
Join Date: Feb 2008
Posts: 755
1975DCS should be qualifying in the top 10 on the grid
Air mass meter on Rallycross cars?

Hi there,

I am watching Rallycross for 20 years now and noticed that even the current Div 1 cars don't have air mass meters. Kind of strang because all current road going cars seem to have one.

There must be a big downfall with using an air mass meter if they don't use them? I can understand it restricts flow, but a bigger one could be used right? Like Audi did with there S3 engines?

So what is the reason Rallycross car's don't use them and (modified) road car's (like an EVO FQ340) do? What are the pro's and con's?

Thanks in advance!
1975DCS is offline  
Old 6 May 2008, 06:40 (Ref:2194918)   #2
Notso Swift
Notso Swift's Avatar
Join Date: Apr 2006
United Nations
37deg 46'52.36" S 144deg 59' 01.83"E
Posts: 1,924
Notso Swift should be qualifying in the top 10 on the grid
I presume you mean turbo cars.
I bet they use a MAP sensor
No restriction and mass is calculated, self adjusting for pressure and heat, "all"* aftermarket and a lot of modern OEM systems use them. Flaps, wires and vortex meters are only used because they are cheap, also it stops people from playing too much, I think they car alaso good at low flow and hence allow better emmissions.
(Some cars are fitted with multiple sensors, then in competition they only use the MAP)

* when I say "all" I do not mean an absolute, but you get the idea.
Notso Swift is offline  
Contrary to popular opinion, I do have mechanical sympathy, I always feel sorry for the cars I drive.
Old 7 May 2008, 21:54 (Ref:2196426)   #3
Join Date: Feb 2005
Posts: 162
ian_w should be qualifying in the top 10 on the grid
There are basically 3 methods of measuring 'load' for an engine management system, namely - throttle position, manifold absolute pressure ( MAP ) and mass airflow meter ( MAF ). I have listed them in order of increased accuracy, it also also the same order as cost.

The pressure drop across a MAF meter is very small ( much less than 1% ) so there is no great performance gain by removing it. OEMs use them as they measure the airflow of the engine directly and are thus the most accurate.

MAP sensors as their name implies measure the air pressure in the manifold - from this, a reasonable approximation of air flow can be inferred. The relationship between MAP and airflow is however effected by lots of parameters as air temp, humidity, exhaust back pressure etc - all these relationships have to be characterised. For OEM type systems there is a trade off between accuracy and cost and it is not uncommon to find MAP based systems on cheaper cars.

On a turbo car you need a MAP sensor in order to be able to do any turbo boost control so you can actually kill two birds with one stone - although many turbo road cars actually have both a MAF and a MAP sensor.

Most of the aftermarket EMS systems don't support MAF and thus MAP is the next best option particularly if you have a turbo engine.
ian_w is offline  

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Air-con in race cars stoned pony Australasian Touring Cars. 43 10 Jun 2009 13:52
Rossi's Stress-o-meter. gfm Bike Racing 1 15 Oct 2006 18:41
Dig' meter readings Snapper Baz Motorsport Art & Photography 19 20 Apr 2004 22:47
Air Fuel Ratio Meter bradenc Racing Technology 7 5 Dec 2003 23:26
Cars getting air at Rockingham sicla National & International Single Seaters 1 12 Jun 2001 19:49

All times are GMT. The time now is 01:12.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Original Website Copyright © 1998-2003 Craig Antil. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2004-2021 Royalridge Computing. All Rights Reserved.
Ten-Tenths Motorsport Forums Copyright © 2021-2022 Grant MacDonald. All Rights Reserved.