will running on speed density help my gas mileage or just make it worse? or will it screw up the pcm? thanks

 

cuz i did it and it made it a ****load faster

 

Road & Track just had a little bit about MAF vs. speed density in the Tech Tidbits section. They said that running a speed density car with mods that increase intake airflow (CAI, high flow filter, etc.) will cause the car to run leaner and could actually cause serious problems, in some cases. This is since speed density infers airflow from throttle position, and increasing airflow at a certain throttle position would make the a/f mixture leaner.

Just something to think about, I guess...

 

isn't that why you lay the fuel to it?

 

Help gas mileage? I suppose, but at the cost of running a lean engine. I guess I'm not quite sure what you're asking . . .

 

What the heck is speed density?

 

Here I got a link here that may help...


Click Here

 

Partly true...Speed density uses the vacuum read by the map along with throttle position and coolant temp (and others) to determine the amount of fuel. The MAF setup has always been said to read the intake airflow more accurately than SD. If you have a MAF car and you remove the MAF sensor you need to be sure your programming is configured to run that way. There were a few posts a while back about folks configuring the VE tables a certain way to support being able to run with the MAF unplugged. If you unplug the MAF the computer is going to calculate the airflow to the best it can but if the calculation comes out below what the actual intake flow is then you could see a lean condition. I wouldn't recommend it unless you have a good logging tool and a dyno with wideband to dial it in first.

 

Look at the words.....

The SPEED part is the VOLUME of air the engine it ingesting, as a function of engine RPM, displacement and volumetric efficiency (VE).

RPM/2 X displacement X VE = cubic feet of air per minute (with proper volume conversions)

But fuel consumption needs to be proportioned to MASS air flow, not VOLUME. To get the mass of air flowing into the engine, based on the volume, you have to multiply the volume by the DENSITY of the air. Density of the air can be calculated by the perfect gas law PV=nRT. The variables in this equation are P = manifold absolute pressure, and T = inlet air absolute temperature.

So... to calculate the mass air flow into a speed-density engine, you need to know RPM, MAP and IAT. Then you need a table of VE, that has been determined experimentally by testing the engine.

The "mass air" sensor eliminates all the calculations. It directly measures the mass of the ingested air, using a hot wire anemometer. It needs no other information.

The reason MAF setups respond better to engine mods that alter VE (e.g. improved inlet system, improved exhaust system, altered camshaft events) is that the MAF sensor immediately sees the changes to the mass air flow. But the speed-density system falls on its face, because the VE table must be manually updated to reflect the improved breathing of the engine.

 

Well, I almost made it through the day without a headache

 

I got a ? for ya Fred...
Do you have alot of handy refrence books or do you remember all of this stuff? I learned all this junk awhile back but cant rattle off forulas like that, mabye I just haven't applied it as many times as you have...