Jazsun

People keep telling me that speed density 93's are slower then the MAF counterparts. I also hear that 93's were the slowest year. I dont really understand why as the motor itself was basically the same except the 93's got some better parts like hardned pushrods. Anyone?

FuryZ28

I've heard the opposite. Of course, I'm no expert, but maybe someone can clarify, because I remember reading somewhere that it doesn't really matter @ WOT...

DavesLT1

the MAF system is just a bit faster in response time. I don't think the speed density would affect overall horse power.

FuryZ28

Most high-boost cars run speed density w/ an aftermarket ECM, are they not? I seem to remember this, because I was gonna upgrade to OBD-I, but after reading that I'd end up switching back to speed density anyways, I decided to keep what I had...

Injuneer

The only difference between speed-density and MAF is the way the PCM gets the mass air flow data. The MAF sensor measures the mass air flow rate directly, and sends it to the PCM. In speed density, the ECM/PCM needs to calculate the mass air flow rate by multiplying displacment/2 x rpm x volumetric efficiency (from a table) to get volumetric flow rate, and then figuring the density of the incoming air from MAP and IAT to get the mass flow rate.

As long as the VE tables are correct, they both end up with the same number for mass air flow. From that point on, both systems work exactly the same. There's no reason that, properly tuned, there should be any difference at all in the end results.

The difference become significant only when you start to make a change that affects volumetric efficiency.... e.g. improved intake or exhuast, different cam, etc. At that point, the MAF system is able to recognize the resulting increased air flow. The speed-density system can not. It requires that the VE tables be updated to reflect the improved breathing. You probably wouldn't notice the difference from a simple change, but for something that makes a major change in the engine's ability to move air, you need to update the VE data. But at the same time, you need to make other changes... timing, idle speed, etc, so you're going for a reprogram whether you have a speed-density system or an MAF.

Injuneer

The Bosch MAF sensor used in the 3rd Gen engines is a major POS. It severely restricts air flow with dual screens (one in the inlet and one in the outlet, both made out of heavy metal wire), and cooling fins that extend deep into the airflow channel. The single, thin "hot-wire" is subject to major flow measurement errors due to the slightest bit of dirt buildup, and incorporates a somewhat self-destructive "burn off" system that heats the wire to 1,000degF on shutdown to burn dirt off the wire. The electronics are very unreliable.

By contrast, the GM MAF sensor used in the 4th Gen engines is much less restrictive, and much more reliable.