Aftermarket Injection, Why no MAF? Options

[McMark]

I was just thinking about how all the aftermarket injection systems all use vacuum signal which can cause problems with wild cams. How come nobody is using a Mass Air Flow sensor? It can't be that complicated. Famous last words.

[rick 918-S]

QUOTE (lapuwali @ Dec 20 2004, 02:51 PM)

MAF based systems get confused by the extreme reversion in the intake caused by lots of overlap (exhaust pulses can flow "backwards" all the way back out the intake valve and up the whole intake tract. However, even carbs get confused by this. This causes double carburation, with the backwards wave adding fuel just like the forwards wave. If you run carbs open, you can even see this as "standoff A modern hot-wire MAF with a long enough intake tract will be unaffected by the cam until it's very wild indeed.

It's my understanding that the "fog" is really fuel vapor that is blown back out of the plenium through the venturis by the reverse pulse. Carbs only work on a venturi principal and only in one direction. The problem comes from the cancelling of inward air drawing fuel vapor to the cylinders. That's why carbs with big cams are set up so rich. It's an attempt to cancel the harmonics until until the revs pass that point.

I agree with the intake plemium size and runner length theory. Hence the shoe box tunnel ram on my old BB Chevy. I had a 580 lift with a 490 duration and lots of overlap. The long runners and shoe box helped straighten out the vapor. Same theory should work with injection. In the factory publication "Chevrolet Power" They promoted the use of the Crower MFI. It was a crazy thing with long stacks. It had a big mechanical pump that was driven off the front of the cam. You adjusted the charge with a "pill" like meter. Crazy stuff in the day... (IMG:http://www.914world.com/bbs2/html/emoticons/aktion035.gif)