Mechanical fuel injection, any good information?

[sled_dog]

My cousin is switching from Modified racing to 410 Sprints. I want to learn a bit about the fuel injection system they run on the car. Staring at the engine makes me feel all tingly inside. 800HP never looked as good as that 350lbs all aluminum engine... mmmm

 

[ntsqd]

Those use a constant flow system of the Kinsler/Hilborn style (as opposed to the Bosch CIS). I know some have played with the timed mech injection (usually Lucas), but I don't know if they're legal or not. Timed systems were once rather common in open wheeled road racing, but I suspect that EFI has probably killed them in all but Vintage classes. Prime advantage of the timed systems over the constant flow systems, at the time of their being common, was better off the corner throttle response. Wouldn't surprise me if Sprint guys have that worked out now.

Basic lay-out is:
Pump -> on/off valve -> "T" fitting -> barrel valve -> Nozzles.
Pump is engine driven so pressure & volume are engine speed dependant.

Not sure if the Sprints use the fuel shut-off valve or not. All of the injected Drag cars I worked on used them.

At the "T" there is a jet called a "pill". This jets the By-Pass, so a larger pill results in a leaner mixture.

The barrel valve may be self explanatory with the barrel's slot allowing more fuel flow the further it is opened. Know that the shape of the slot in the barrel is a very carefully made feature. There is an adjustable length link btwn the throttle shafts and the barrel's lever. Baseline idle position is set using a leak-down tester and then how many "flats" the linkage was adjusted away from that baseline is kept track of.

The nozzles have a minor air bleed in them. This is to get some air mixed into the fuel for better atomization. Most of the Sprints I've been around had little foam air filters on the nozzles.

That's the basic stuff. Then there are High Speed Bleeds and all sorts of other stuff I know nothing about.

 

[76zimmer]

DAMN....those things are so cool. Like about 1250 lbs. or whatever, and 800hp......way cooler than Smashcar

 

[sled_dog]

Yea high speed pill is what I wanted to know a little bit more about. All of the things you described are present on his car. Little filters and all. I was surprised to see the engine is direct injection. Its really an interesting fuel system as long as your ignore the constant injection, ha. I am just trying to wrap my head around the way the high speed and low speed circuits work as well as the main pill. The car has 3 pills as far as I was gather. A main one, secondary one(manually actuated by the driver) and a high speed pill.

From the way my Uncle explained it, the High speed pill is like a bypass pressure valve. When you are revving say 8,000 down the straightaway and let off going into the corner, it bypasses the main/secondary fuel pills. Keeps from the engine throwing a ton of fuel through the engine while the throttle bodies are closed. Sounds pretty self explanatory, just thinking there has to be more to it. Like what controls the High Speed pill? No vacuum line or linkage on it.

 

[ntsqd]

The various by-pass pills are enclosed in check valves. When the pressure exceeds the spring pressure the valve pops open and the valve by-passes to the limit of the pill size. Or the valve by-passes until a set pressure is reached and then it closes off.

Dig out your auto trans valve body tech info. All the same things apply, it's just a mutated form of hydraulic logic.

 

[sled_dog]

hmm ok, interesting