I will be conducting some experiments tonight on a dyno that I thought I would share with you all.

I have the potential of putting my foot in my mouth, but in an effort to clear up some confusion about MAF. I am willing to put my neck on the chopping block

Here is the link to the whole story. I am on hold right now seeing if my Dad remembered to bring his video camera so we can tape the whole scenerio first hand.

I am gonna post this on the TPI Section as well. Hope you don't mind Mods, but I think all will be interested in the results.

http://forums.corvetteforum.com/zerothread?id=566349

 

Jesse,

You are forgetting one thing. A friend of mine () turned me on to this during a discussion with several other knowledgeable thirdgen guys. I'm not going to argue or belabor this point but it's at least important for me to mention it to you.

If you don't pull vacuum at WOT then that does NOT necessarily mean that you don't have a restriction. I was under this ASSumption also. Then a buddy spoke up. Here's what he turned me on to ....

The motor is a complex entity. We need to expand our thinking beyond the intake tract with regard to restrictions. A piston moving downward will not only be sucking air from the intake tract (plenum, TB, MAF, bellows, airbox) ... but ALSO from other cylinders and other intake runners. It takes air from the least restricted point. Thus, you could effectively have a motor that has an intake restriction but no vacuum produced in the plenum because one cylinder is stealing a little bit of air from another intake runner.

Just some thoughts.

Tim

 

If the motor is drawing enough of a vac to read on a vacuum guage you have a serious restriction.

Try using a MAP off of TBI anything, and see what the baro value is and then compare that to a manifold reading, that might get you close enough to accurate to get some meaningful measurements.

To figure out the MAF as a restriction, means removing it, and seeing the difference, if you want accuracy.

Mike Pitts had posted his results at GNTtype, about what he found when changing to a MAP system, and the system was calibrated with the MAF inline, and then removed with no other changes, and results noted.

 

Could you not tap in and use two vacuum guages, one a couple of inches on either side of the MAF? Then you know if the gauges read the same there is no restriction but if the guage after the MAF shows more vac. then there is. Just a thought.

 

1 thing about vacuum in a plenum. We tried to measure vac in a plenum on a 500 inch prostock, as well as an 800 inch prostock engine, both on the dyno, and going up the track. We had 10 vac taps welded into the plenum, as well as the runners. There were no 2 locations that had the same vac/pressure. Our best guess was The air is not in a steady state, but is very turbulant. This made for a bunch of individual "cells" inside the manifold, some having pressure, and some with varying degrees of vac. Also, going down the track, we could see pressure develop in the hoodscoop, and the plenum, at locations that had a vac on the dyno (ram air from scoop). I guess I'm trying to say that the plenum may not show a restriction at the location you are tapping it, or it may have a vac there whether its restricted or not (maybe the reason gm put it where they did ?). If i can find it, I have a very accurate formula to figure the flow of any sharp edged orifice (port, tube, etc). I will post if if i can find it. Im also interested to know the results.
Bob


Found the formula. Its 146cfm/in2. This is what alot of head porters use for a reference value for developing new ports. All you do is figure the cross sectional area (in2). An unrestricted port will flow 146 cfm per in2 (at 28 in h20, 29.92, 60 deg). Using relatively common conversions for hp, you should be able to get a close figure of how much air is needed to make X hp. If the number needed is higher than what the CA of the maf is, its a restriction. It is possible to make way more power than what is theoretically flowing thru an orifice however (think nascar rest plate <1" hole), just that more is available if unrestricted. Hope that made some sence, its gettin late here

Bob

 

Just a very good thought, I'd say

A single point pressure reading is next to useless for determining how the pressure got to that point, when there is more than one influence on pressure (Trax's point), so you either use Grumpy's method, or the info is almost irrelevant.

You have one equation, and about 4 unknowns. This is no way to "clear up MAF confusion." Listen to the junkyard dog bark

John