Carbureted 944 race car on eBay
#31
Nordschleife Master
You wouldn't measure MAP with ITBs. You could use MAF, but in a full race application it would probably be easiest to simply use TPS. But since this isn't necesarily a true ITB build it doesn't matter since you don't need to measure anything as fuel would already be metered.
Just curious and want to learn more about these set-ups.
#32
Three Wheelin'
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?
#33
Nordschleife Master
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.
#34
Campeck Rulez
Rennlist Member
Rennlist Member
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.
#35
Campeck Rulez
Rennlist Member
Rennlist Member
alpha-n (computer estimates fueling by throttle position and engine speed)
#36
Addict
Rennlist Member
Rennlist Member
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
Or something like this
http://www.msefi.com/viewtopic.php?f...it=map+average
#37
Addict
Rennlist Member
Rennlist Member
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).
#38
Nordschleife Master
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.
#40
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.
#41
Rennlist Member
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
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
#42
Campeck Rulez
Rennlist Member
Rennlist Member
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
Or something like this
http://www.msefi.com/viewtopic.php?f...it=map+average
ah!
That would fix those problems wouldn't it!
#43
Campeck Rulez
Rennlist Member
Rennlist Member