checking out TWM's website and stumbled upon this trick setup.....has 2 sets of injectors, regular set for idle, part throttle and the another set for WOT....supposedly the injectors mounted "outside" the throttle bodies give more HP....slight risk of fire if outside/top injectors spray when the throttle is closed

The holley TBI on my Mustang looks like that. Sprays onto the throttle plate at idle. Those are the only injectors, none inside. I don't like it, someday that car will get a complete modern 5.0 and EFI. No fires yet.

Mike,
Grab a copy of Bruce Anderson's 911 book. There are pictures of how Jerry Woods does it. Injectors are mounted in the airbox lids firing staight down into the TB throats, but the injectors are suspended above the TB's like in your picture. Airbox lid gives you something to mount the injector and fuel rail to. You also get to keep the aircleaner element.

-Ben M.

Brad was tuning in a V8 with one of those when I was with him at HPH. Made fir some great fireworks while getting the timing dialed in for the first time.

Mike...you putz with stuff enough you can figure out what's going on.......

1. With the injector stuck in the bend prior to the port, it presents an airflow restriction (just like the stem and guide), but gives good turblence for fuel/air mixing. Of course the turblence also has an effect on cylinder filling.

2. An injector above the body doesn't present this restriction, so you would get better air flow, less turblent and better cylinder fill.

3. The only problem with #2, is spraying a fine enough mist to get the fuel dispersed in the volume of air. The turblence of the air passing the valve head should provide for the "mix".






Yeh, I know it's kinda late at night and I got nuthin else to say.

injectors above throttle plates - 35 years ago...

Race-only item? Because it seems to me that unless you are at WOT, it wouldn't have a significant advantage over a carburetor.

QUOTE (Reiche @ May 20 2005, 09:59 AM)

Race-only item? Because it seems to me that unless you are at WOT, it wouldn't have a significant advantage over a carburetor.

The advantage is in airflow (unrestricted) and fuel/air mixing. An injector will create finer dropplets of fuel than a jet, plus the injector does not rely on air velocity thru a venturi to correctly pull the fuel through the jets.

QUOTE (Reiche @ May 20 2005, 12:59 PM)

Race-only item? Because it seems to me that unless you are at WOT, it wouldn't have a significant advantage over a carburetor.

not many carburetors in racing unless the rules decree such.
a properly tuned engine management system will always be superior to carburetors and distributors.

subtleties in PEAK power are used in racing, where much less time is spent at part-throttle than in street driving. Porsche only used the high-butterfly and high-injector induction on the racing engines. it could help understanding to know that with MFI, the fuel shot is about 15 Bar; atomisation isn't really a big problem. and MFI is a timed injection, which neither L-Jet nor D-Jet is.

the street MFI engines all ran port injection, below the throttles.

Thanks, I think you are saying I was correct, in my admittedly imprecise non-engineering way. This would seem to need a lot of intake air velocity to work well, i.e unless the throttle butterfly was wide open, it would cause a lot of turbulence below it. (Were the Porsche high-mounted injectors also used only with slide throttles?)

I knew the MFI ran very high pressure but I couldn't remember how high. I just remember being told that the fuel shot from a MFI injector could cut through your skin. I doubt this system uses pressure like that.

Looks like the fuel injectors on an F1 car. I'd say it'd be ok to have them on a race car, but for street....nah. If you look at the new gsxr 1000 motorcycles they have 2 injectors per cyl ...one high and one low:

QUOTE

Twin injectors per throttle body for improved throttle response and acceleration - primary injector operates under all conditions while secondary injector operates under high rpm/heavy load conditions to further increase engine output

Now that'd be the ticket, good luck writing that software to control it though.

In a high speed engine (one designed to stay above 6-7K rpm all the time, like a racing engine), you need all the time you can get to allow proper fuel vaporization and mixing. Mounting the injectors well away from the intake valve helps this. Experiments done quite some time ago showed that pointing the injectors backwards (pointing away from the valve) substantially helped high-rpm power. Low-mounted injectors work best at lower speeds and lower loads, which makes them ideal for road cars that spent the bulk of their time at low loads. You don't get the airflow to allow the vaporization and mixing the high-speed way, so you do things like squirt against the back of the (hot) closed intake valve to vaporize the fuel in the manifold. At high speeds, you can't inject 100% of the fuel at the closed valve, as you simply can't inject it fast enough, so some of it is squirted into the port with the valve open, and you hope for some vaporization in the chamber from hot parts in there. You can solve this by having a second injector much bigger than the low-load injector, that can squirt 100% of the fuel while the valve is closed, or you can exploit the air velocity at high speeds by mounting a second injector up high or backwards.

So goes the theory. It would be interesting to see actual results.

QUOTE (JmuRiz @ May 20 2005, 09:57 AM)

Looks like the fuel injectors on an F1 car. I'd say it'd be ok to have them on a race car, but for street....nah. If you look at the new gsxr 1000 motorcycles they have 2 injectors per cyl ...one high and one low: QUOTE Twin injectors per throttle body for improved throttle response and acceleration - primary injector operates under all conditions while secondary injector operates under high rpm/heavy load conditions to further increase engine output Now that'd be the ticket, good luck writing that software to control it though.

Staged injector code is fairly trivial (assuming you know how to write code at all). A number of aftermarket ECUs will do staged injection out of the box, using either % of throttle or MAP or revs (or a combo) as the trigger for the second pair of injectors. Some systems I've seen described simply use two injectors of the same size, and use one of them until it runs out of flow, then stage in the second one, so at 100%, both injectors are maxed out. Allows excellent fuel control at low and high speeds.

QUOTE

Now that'd be the ticket, good luck writing that software to control it though.

I already have it

The Link ECU comes standard with "staged" fuel injection capability so I could run a primary and then a secondary fuel injector if I wanted to......

Look at how many F1 teams do it....

BUT it's only good for super HI RPM IMHO..

I plan on doing a ton of testing with the injectore moved all over the place and see the results.. Myths soon to be busted and data logged too!

Now that's what I'm talkin' about, gotta love an engine builder with his own dyno and willing to test all kinds of combos!
That's cool that the new software out there already can control 2 injectors, very cool stuff...there you go, the hardest part is already done for ya.