MAGK944

Agreed, but let's asume fuel injected itb's on a street set-up, running four independant air inlets . And you need a MAF/MAP measurement for the brain to control metering. Where would you take this from?

Just curious and want to learn more about these set-ups.

DarylJ

Now I'm confused. Why wouldn't you use MAP? You tap all 4 intake runners and grab MAP from there. MAF would be the problem - what do you do? Put a MAF in front of each TB and somehow average them?

MAGK944

That is what I assumed, thanks for the clarification Daryl. Yes MAF would be stupid unless you combined the intakes into a common plenum. So in effect you take the average pressure of the four intakes for the MAP.

Campeck

well that's the thing. Ideally on a street car you wouldn't put ITB's on. throttle control at low speed would be ridiculous. and itb's on race cars doesn't matter cause they are always going fast as hell.

Campeck

Maybe im wrong but everything i've read/seen has been that MAP on itb's isn't any better. you've got the intake valve opening and closing inches away and the pressure in there is all over the place all the time. Aren't most itb setups run off of alpha-n or a combination?

alpha-n (computer estimates fueling by throttle position and engine speed)

theedge

With ITBs you tap all the runners, run the hoses to a central location, and then theres various methods to "smooth" the pulses. One is those little clear fuel filters for lawn mowers, another is you have a vacuum pot that the hoses from the runners go into, then you have a common hose coming out.

Or something like this

http://www.msefi.com/viewtopic.php?f...it=map+average

theedge

Lots of street cars are running around with ITBs. The key is properly sizing it, then you use a different kind of throttle cam thats not linear (the term is escaping me).

MAGK944

Logrithmic?

So MAP & smoothing, sounds good. Is that how they do it on bikes? I see a lot of four cylinder bikes running fuel injection with ITB's these days and they seem to have very smooth idles.

ritzblitz

Yeah there are plenty of street engines on ITBs and all the ones ive seen have a smooth idle.

eman930

Yea I agree, Thats the way the 2.0L 924 Guys are doing it, They used modified Bike cars, Take the carb apart and just use the butterfly part of it, Weld a boss for the fuel injector to the carb, Then tap all 4 carbs and get a vacuum pot, and run the vac lines from the pot to all 4 carbs, Take your Map reading from the pot. MAF would be retarded on a ITB setup unless they are connected into a common plenum. Alpha-n or whatever its called "load fueling" Is ok for race cars cus your almost always at WOT or atleast 50% throttle or more, You dont need to really worry about smoothness.

white924s

I think some new BMW's use ITB's...I don't know for sure, but I believe that they use a MAF into the plenum (from which each throttle body sucks air). I think that using MAPs in the runners would be extremely difficult as the pressure waves from the valves opening and closing would introduce a tremendous amount of noise into the signal.

I agree that running off of throttle position alone would also be quite difficult as it doesn't account for changes in barometric pressure or temperature as well as other air metering methods do

Campeck

ah!
That would fix those problems wouldn't it!

Campeck

non-linear?