Just curious if there is any relation on stock MAF and stock MAF calibration tables if there is a way to estimate approximate power based on the MAF grams in DataMaster?

 

Obviously, HP is going to increase with air flow. You could come up with some crude relationship. Say a stock 275 (flywheel)HP LT1 use 230GPS peak. That works out to about 1.2 HP/GPS. Using that, 300GPS would indicate 360HP, 350 GPS would indicate 420HP. But that's a very crude assumption. While you need the air to burn the fuel, you have to have the right amount of fuel. Add in the variations in thermal efficiency, volumetric efficiency, the effects of ignition timing, and your E85 having a different heating value than gasoline, and it becomes sort of meaningless..... other than to say more air = more HP.

If would be interesting to see if anyone can post their peak GPS vs. peak flywheel HP numbers to see if a more accurate correlation could be developed.

Just a thought.

 

G/Sec while a decent indicator needs quite a lot of correction to be of any use at all. First things first you have to verify that the mass airflow meter is calibrated correctly, I do this with a wideband to verify I am getting what I am commanding (this assumes that your injectors flow what they say they do). The most useful thing to do with it is use the atm conditions shown at the time measurement to figure out air density, and then turn your grams/sec into a volumetric flow rate. You would then have to correct the flow rate back to g/sec using the standard density of air at sae conditions. You can then sort of crudely calculate what kind of power you're making. So you have your g/sec airflow now turn that into a fuel flow at the stoich ratio. Multiply that by the energy content of the fuel and then multiply by about 0.3 for thermal efficiency and you would have a VERY crude smack at what kind of hp the engine is making. I can name the majority of the unknowns and why this is only a crude guess at best, but lets just say don't count on it making that at the flywheel on the engine dyno. Which btw that is what we were calculating is flywheel hp.

When comparing one car to the next, the volumetric flow rate is pretty much as far as you need to go if the builds are similar (peak rpm and stroke are the same).

A dirty maf or wild pe values will scew it, and so will different length strokes and peak engine speeds.

 

Gm/sec can be used as a fairly close measure of how much power CAN be made, like a turbo's rating in lb/min.

 

I just don't like grams/sec because of the variation in air density due to things like temp and altitude. Volumetric flow is more meaningful in terms of how well put together you combo is, although its still subject to issues with altitude due to less efficient cylinder filling.

 

That's exactly why volume flow means nothing to the motor/PCM, mass flow is what matters.

 

I figured there would be a lot of other variables, factors, error that would make it hard to estimate from just grams/sec. Just figured I would see if anyone has ever calculated a correlation or not?

New idea then, if viewing my datalog from a dyno run, where the rwhp is then given along with a grams/sec value, then, in similar weather conditions with no driveline changes, only engine changes, such as heads/cam, and then doing say a 3rd gear WOT or track run, would one be able to calculate/infer a rough linear correlation between AFGS and rwhp using the known variables?

 

The pcm cares about mass flow because it is trying to fuel the engine. The volumetric efficiency of the engine is going to be a constant set by the hard parts of the engine (and baro pressure to a degree), which equates to a pretty much constant volumetric flow rate no matter what day it is. If you have g/sec in December when the air is dry as hell and 15 degrees vs one in july when its 105 the difference in air density between those days is huge. So your grams/sec changes in a big way, but you know what doesn't, the volume of air the engine consumes. Absolutely right, charge mass = power, but raw power numbers in uncontrolled conditions is not worth a damn in terms of comparison. This is why when on the dyno we use SAE correction factors to normalize the numbers for comparison, and what I described was a crude way to do that with the limited ecm channels/info we have.

kgkern01, I laid out how to do what you asked for in order to get fwhp. You'll have to do the leg work yourself to get the numbers from it. Dont get hung up on rwhp numbers, a chassis dyno is just a tuning tool and no real basis for comparison.

This will be my last post in this thread.