[Shotimes] MAF vs. Speed Density

[Ron Porter]

Kinda reading between the lines, it's as I suspected........speed-density
does a better job of passing the EPA tests!!

Ron Porter 

-----Original Message-----
From: shotimes-admin@autox.team.net [mailto:shotimes-admin@autox.team.net]
On Behalf Of Don McKinnon (AST)
Sent: Wednesday, June 04, 2003 5:41 PM
To: Kevin & Cheryl Airth; shotimes@autox.team.net
Subject: RE: [Shotimes] MAF vs. Speed Density


It's not just GM, Subura is doing the same thing on many of the post 99
models, cheaper probably has every thing to do wit it I'm sure.   I found
this today on-line:

----
So which is better, MAP or MAF?
While Air-Flow systems are still favored by most manufacturers due to their
accuracy, speed-density systems are slowing gaining favor once again due to
advances in electronic engine management. In order for a speed-density (MAP)
based system to offer the accuracy in A/F ratios to pass the stringent
vehicle certification tests, advanced ECU technology must be used to cope
with the speed-density's inability to optimally handle transient driving
conditions (compared to an air-flow system).
...
The facts remain the same though, the air-flow systems are slightly more
accurate at calculating proper Air/Fuel ratio under a wider variety of
driving conditions. At Wide Open Throttle (WOT) though, they are both very
similar. It's primarily under transient conditions (partial throttle
changes/city driving) where they differ the most. Again, the differences are
primarily in theory and hardly sometime you'll notice by the seat of your
pants. Those of you with speed-density systems don't think your system needs
to be improved by going to a air-flow setup. Keep this comforting thought in
your head; nearly every aftermarket engine management system uses a
speed-density system (ie: Haltech, TEC II, Motec, EFI, etc.).
----

Don McKinnon
95 MTX - White/Mocha 91k miles
Stage 1 Power Package with Stage 1cams
Canyon Carver Road/Race Suspension
Quaife & HiRevs Competition Clutch


-----Original Message-----
From: Kevin & Cheryl Airth [mailto:clubairth@peoplepc.com]
Sent: Wednesday, June 04, 2003 4:38 PM
To: Don McKinnon (AST); shotimes@autox.team.net
Subject: Re: [Shotimes] MAF vs. Speed Density


Don:
 I am surprised that a new motor would have a speed density system on it?

The speed density is cheaper and simpler. Uses less sensors. It usually is a
stop gap setup used after carburetors and before a full on MAF system. Most
aftermarket EFI setups use speed density.

The MAF is a much more precise engine management system. Almost all vehicles
were forced to a MAF system to meet the fuel economy standards as well as
emissions and drivability.

Maybe GM found an advantage going back to the speed density?
.
.

> What are the advantages again of using a MAF vs. Speed Density, if any?
>
> My 2003 Trailblazer XL has a nice motor I wish could show up in a car,
DOHC
> 4.2l Inline 6 with VVT, coated pistons, etc., and uses Speed Density.
>
> Don McKinnon
> 95 MTX
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