EFI Gurus, need help with injector setup

[Chuck Moreland]

I'm putting EFI on my 2.7 "S" motor.

I'll be using MFI throttle bodies and stacks. The stacks will be modified to accept the injectors, positioned above the TBs. I realize this is doing it the hard way, but I'm keeping the stock intake setup for racing rules.

Basically as follows:



Here are my questions/concerns.

- I find injectors available with narrow cones down to 15 degrees dispersion, others with perhaps 30 degrees. I'm a bit worried about fuel hitting the side of the stack and dropping out of atomization. What is best for my application?

- What angle between injector/stack is best? I'm thinking it should be the straightest possible shot, perhaps 30 degrees to the stack.

- I expect the motor to put out about 240HP. What should my flow rate be? Formulae I've seen suggest about 25 lbs/hour. Assume 43.5 psi and I'm guessing .5 BSFC.

- Recommended injectors?

- Recommended place to buy injectors?

[KobaltBlau]

RC engineering has a good reputation with injectors; they use the lucas type (not manufactured by lucas, just the original design) which is a plate type valve as opposed to the slower reacting pintle type, main difference here is the pintle type might not keep up with 8000rpm. buying new from them will not be cheap though, you could probably get away with junkyard injectors just fine.

as far as mounting angle and injector spread, you might try to find more information on the factory MFI with injectors mounted high above the butterflies. I don't know what injector spread they used (probably regular MFI, what's that?), but I agree that the straightest possible shot from up that high is a good idea. modern fuel injection sometimes tries to spray the back fo the intake valve head but your injector is much higher so that doesn't apply. I also agree that the narrower spray would probably be better for your application.

My concern is that your 73 is still street driven part of the time (isn't it?). I have heard people recommend against butterflies below the injectors for a street driven car for driveability and fire concerns. Whether these are valid I can't say as I haven't built such a system.

Would you be allowed to run Webers or PMOs in your class, on the same engine? (not suggesting it, just trying to clarify rules)

[Kanipso]

I would buy Bosche 30lb red tops and calibrate your regulator at 3.0bar that should be perfect for your 240HP... You can raise the pressure later to support up to 300hp with these injectors..

[steand]

One off the reasons to inject directly at the intake valve (like in the 74-83 CIS cars) is that fuel that do not get into the cylinder at first, as the intake valve closes, get sprayed to a hot surface that helps evaporate the fuel for the next intake cycle. This helps fuel economy.

If you put butterflies before the injector, the air stream in the throat will be slow with nearly closed throttle, and that impact the blending of air/fuel, and some off the fuel gets sprayed on the butterflie that is relatively cold (compared to backside of intake valve) and then it condese to clean fuel (i assume) running down the intake.
ALL off this leading to a poor idle and low throttle running.

[smdubovsky]

Chuck, I think Im running 24lb injectors in my 3.32L (or maybe 28's been a long time). I bought new from Accel - probably not the best ones out there but MUCH cheaper than bosch or even used carrera or 993 ones. Buy something cheap or used to get the car running. If you then need to go bigger or smaller you can get just the right ones.

Wouldn't it be simpler to do the jerry woods/madonna type injectors in the filter top plate? That seems alot simpler to machine/weld than the round & angled stacks. Plus, you'd get a straight shot. Makes the most sense for race applications. Others are right about the fire/diveability issues for a street application, but what you're planning isn't much different than the rsr high injection setup is it?

The low throttle driveability has to be better than carbs. They dump unatomized fuel right on the throttle plate right?

SMD

[304065]

I second the madonna setup. Straight shot right through the stacks, and easy to remove and inspect.

[Chuck Moreland]

I'd like to do Madonna, 'er the setup, but I don't know how I'd sync the TBs.

I don't see how to put a synchrometer on top of the stacks with the fuel rails in the way.

Any bright ideas?

[Chuck Moreland]

This is the "madonna" setup.

I think it would be ideal to achieve this center spray. If I could only get a synchrometer on there.


SMD, good point about carbs - fuel sprays right onto the throttle plate. Though they do have a seperate circuit for idle.

[svandamme]

get really fancy : 2 injectors per stack !! one above one below the TB
upper one only for WOT , and the one below the TB will ensure you don't loose bottem end

[KobaltBlau]

Originally posted by Chuck Moreland
I don't see how to put a synchrometer on top of the stacks with the fuel rails in the way.

How does Jerry do it?

[pwd72s]

Chuck, you might give gammer a ring. He has a trick EFI unit he's been using on customer cars, but hasn't used the MFI stacks AFAIK...but he has good knowledge of the system itself.

[304065]

Chuck,

You could synch the throttle bodies on the flow bench first, then fine-tune them with a vacuum gauge. If you look at the TB's there's a boss on the port (left) side where they were drilled for the sportomatic vacuum setup, and the 2.4's with a vaccum advance have similar ports. A careful drill and tap of the TB's with a nipple to which you could attach a vacuum gauge would do it, followed by removal of the nipple and insertion of an allen-head pipe plug of identical diameter.

Or you could get some "carb sticks" as used by the motorcycle types, these are basically water manometers that use plastic tubing to measure the vacuum level. As long as you located them at the same place in the throttle body, e.g. at the top you would get the same vacuum signal. Hell, with your mind you could MAKE a set of water manometers to measure the vacuum.

[BoxsterGT]

Can you use alum spacers between the throttles & heads that accept the injectors?
That would simplify things if they are legal.
I am planning to do this myself. For me it doesn't matter about legality.
I got a quote of $100 each. Perhaps less if they make more at one time.
PM me if any interest.

[smdubovsky]

Chuck,
I've NEVER though of the problem how to synchronize. I would have put the whole system together and sat there w/ my synchrometer going hmmm....

But, everything is solveable. How about putting a set of vacuum ports below the throttle bodies? You'll need them anyway unless you're running pure alpha-n. Just unplug one from the MAP manifold at a time and and run into a seperate pressure gauge. Or use a multi-tube water/mercury manometer like what is used to synch motorcycle and E30 M3 throttle bodies? Problem solved

SMD

[smdubovsky]

Dangit, I don't type fast enough. What John said

BoxsterGT, For $600 ($100x6) your only about $150 shy of a set of TWM throttle bodies. Doesn't seem cost effective unless you want to keep a single throttle body/plenum system esp once you add the custom fuel rails needed for your adapter setup.

SMD

[Chuck Moreland]

Vacuum! Is that an accurate way to synch?

I have no experience with these motorcycle carb tools. Anyone have a link?


Boxster, I'm not sure if the spacers would slide by. They would increase the stack height, and I suspect this would be objected to.

[304065]

Chuck,

Yes, vaccuum is an accurate way to synchronize. To reassure you on this point, take a look at page 49 of Check Measure Adjust.

Here is a fine article on how to make a water manometer.

http://www.obairlann.net/~reaper/motorcycle/manometer.html

Related ideas below.

DIY Flow Bench

[Chuck Moreland]

Like a virgin, I'm sold on Madonna. That manometer looks like the ticket.

This will be easier to implement then fabbing and welding bungs to the Mag stacks too.

Thanks all, the collective input/knowledge on this board rocks!

Now that we've got that solved, how about my other questions:

Best injectors and best place to buy?

And how about those Madonna funnels?

[KobaltBlau]

Originally posted by Chuck Moreland
And how about those Madonna funnels?

Call Jerry and see if he still sells that stuff. nothing to lose. If not, you can look at making something similar.

[KobaltBlau]

Hey Chuck, have you seen this photo?



it's CamB's engine. not sure if this setup would be legal for you or not.