Alright...I was thinking tonight about how important it is for a good air/fuel mixture for performance. Since the injectors on our cars are basically hugging the intake ports, would there be any gain in mixture if the injectors were say, right at the beginning of the runners? Would this throw off injection timing? Would this improve performance? I want to hear some opinions and theories here.

 

Actually, yes, you'll gain performance at the expense of fuel economy. You'll see this concept is used in many aftermarket individual throttle body systems.

The injectors on my TWM are right after the throttle plates.

 

ah, that's what I wanted to hear. Will the timing of injection be a problem at all? I didn;t think so, just curious

 

Two reasons I can think of why not to:

1- You want the injector more or less pointing as directly as possible at the valves. This ensures the maximum possible amount of fuel makes it into the combustion chamber, though as you pointed out says nothing directly about whether or not it's atomized and suspended in the mix. Generally though aiming it at the port wall or floor could only worsen matters. Also, this may not be possible to acheive on all cylinder head designs, but luckily for us Honda heads tend to have very high ports, allowing injector placement in the manifold runners while still having a direct shot at the valve(s).

2- Moving the injector further upstream also exposes you to the possibility of significant mixture reversion. During at least a few RPM ranges, some reversion is going to occur no matter what you do. The further upstream the injetor is, the more likely the mixture will be carried out into the plenum, where it can do no good. Ideally you never want any fuel in a manifold designed for dry running, and you also don't want the possibility of overfueling/underfueling one or more cylinders due to reversion carrying atomized mix out of one runner and into an adjacent one.

 

thats what I wanted to hear...precise with details. Thanks. Would there be anyway to run a setup like this? Or is it just wack thinking?

 

I know a lot more goes into it then thinking about it and welding up some runners, I'm taking a vehicle design class at WWU starting in the summer and will have access to ANYTHING...CNC, Mandrel benders, anything and want to start thinking of stuff to do.

 

 

aside from Texan's points, you have to worry about "dropout" at low RPM's. The atomized fuel may literally drop out of the charge as air speeds in the runners fall. Fuel cools on it's "long" journey down the runner and your charge contain less atomized fuel as it enters the combustion chamber.

Ideally, you have 2 sets of injectors. A set in the stock location that always run, and a set at the top of the runners that come on above a certain RPM. Now, the engine retains it's low RPM driveability. There's a book called "Engine Management" available through Motorbooks.com that talks a lot about injector placement and even tests the 2 injector set-up above on a Ford Zetec motor. Well worth looking into. If you have trouble finding it, I'll give you the author, just have to check my copy at home first.