DIY MPFI

[CobraSix]

okay...this thread is not for ECUs...but for actually making the MPFI set up for an Aussie head.

Does anyone know of any good reading material, or have ideas on just how I need to go about certain things for making you own MPFI.

Things like:

1) how far can the injectors be from the valves?
2) I know they are supposed to point at the back of the intake valves, but is there a good angle that anyone knows about?
3) Any other general MPFI info.

I'm still debating hacking up another intake manfold versus fabbing up peices that will fit between the manifold and the head that will be AL, and drilled for the injectors. It will allow me to experiment in a less costly manner, and also give the ability to make it an easier add on for other people in the future if I decide to try to market it (or sell the design to AzCoupe ) The only issue will be clearance between the manifold and the shock towers as there is only about 2-2.5" between the two. Unfortunately, that means another set of gaskets between the turbo and the valves.

Slade

 

[rickwrench]

The injectors don't have to point at the back of the valves, that's more of an emissions location. Injected fuel hitting the back of the intake valve cools the intake valve, allowing a slightly leaner mixture to be run without detonation. Hitting the hot valve also makes up some for lost atomization time in the runner, as some of the larger drops of injected fuel will atomize when hitting the hot valve. For very slightly better throttle response, closer to the valve is better. The best top end power can be had by injecting into the runner much further upstream. This allows the fuel to atomize completely before entering the cylinder. If you are constructing a high rpm individual runner system, just below the butterfly is best.
Rick(wrench)

 

[CobraSix]

good insight. I was also thinking that if I do mount them at an angle, I should be able to avoid wet well problems with my runners. Or is that not really an issue? How far should the other end of the wall be from the injector? basically, how far will the injector spray?

Slade

 

[rickwrench]

Most injectors spray about a 30 degree fan/cone.. "Ideally" you want them to shoot as straight down the runner as you can get them. But on a straight runner, I'd lay them over at about 35 degrees. That should keep the injector side of the runner dry. If I did my math right, the velocity of a 1.125" runner at 4500 rpm is just a bit more than 70 mph (on a 200 I6). Dammit, forgot about VE, so at 80% about 58 mph. The velocity of the intake air should keep the fuel from hitting the opposite walls. Gas mist doesn't have a lot of mass. Also, higher pressure fuel systems tend to make the spray finer. I wouldn't mount them perpendicular to the runner in any case.
Rick(wrench)

 

[Anonymous]

Jack posted a good link to SDS in the "Multi Port EFI" thread awhile back. They have some good general DIY ideas for making the intake runners, plenum, injector bungs, etc. I'm starting to work on a design, but it's only conceptual at this point.

--mikey

 

[CobraSix]

wow...I never saw the links on the bottom of hte page...holy crap, lots of good info

Slade

 

[Kstang]

Hey slade, about those 03 cobra throttle bodies, i got a friend who has one off a second Gen Lightning would that work?

 

[CobraSix]

if it's free...it'll work for me...

Slade

 

[Kstang]

i don't know about free but i can aks him how much for ya, i have another one lined up that has the intake elbow and all according to TJ. I will ask about price when i talk to them

 

[CobraSix]

thanks kevin.

Slade