MrDude_1

i mean, has anyone taken a diffrent throttlebody, say a TPI one for example...

all the TPS,IAC, ect hook up to it, and then just mount the stock injectors (or some other ones) to either spray the in plenum or throttle blades?

you could retain the ECM and harness.. you might not even HAVE to retune... but it would flow better....

plus you have room to add a 3rd injector if needed.

ShiftyCapone

iTrader: (7)

I can change the thread title to what you want. let me know.

MrDude_1

yea, please do... lol.


athough i was hoping for a much more in depth responce when i saw that you replied.

Dewey316

the biggest problem is obviosly mounting the injectors so they spray properly into the plenum, to get good fuel distrobution, and atomazation.

the next quesiton i would have is why? airflow is not the limiting factor of TBI units, it is fuel delivery. with only 2 injectors, it is hard to get the ammount of fuel needed to support high horse power. which i assume was your goal in changing throttle body's.

ShiftyCapone

iTrader: (7)

There ya go. You might want to edit the top of your post there as to not confuse anyone.

How would you mount the unit? On its side or level? I think by the time you add inejctors and such you will just have a "jerry rigged" TBI unit that similarly matches the stocker with the inejctors being in the way of the throttle bores. Am I imagining this right?

MrDude_1

but since the injectors are mounted seperatly and not in a pod over the TB, whats stopping you from adding another injector?


well, when i was talking with someone about this lastnight, we were envisioning somthing like this:

imagine a single plane carb intake... with a plenum on top... the TB is mounted facing forward (or to the side.. it could be point in any direction, but its at a 90* angle to the carb inlet... )

now on top of the plenum, spraying down like a carb would, is the 2, 3 or 4 injectors.. they arnt blocking the airflow, just going with it.

its like a midway injection system.. kinda like the early V6 vortec motors, but without the cruddy plastic poppet valves.
you dont need 1 injector per cyl, but you could run any number you wish.

and the injector pods arnt stopping airflow... and you know the TB and intake are good for big HP numbers...


anyhoo, it was just a random idea... i was curious if anyone has DONE it.

ShiftyCapone

iTrader: (7)

I get what you are saying now. It is a novel idea but I really have no idea how well it would work. It is similar to the multi port conversions out there where you use the stock unit but take off the inejctor pod because you put an injector in each runner. I am pretty sure there would be atomization problems since the fuel is not being sucked in with the air over the TB blades. It would only be carried along since it is not leaving into a low pressure zone.

1981TTA

I think you're right on this. The tendency (I think) would be for the fuel to spray "down" in big drops and stick to the floor of the manifold all the time. While this is virtually identical to what stock TBIs do at WOT, they do have the advantage of squeezing through the butterflies at low throttle openings to help atomization.

That being said, I, too, like the novelty of the idea!

MrDude_1

also what i think is somewhat intresting...

theres a guy on one of the vette forums that makes squarebore carb plenum boxes... if you added the injectors to the top of that, and you already have the carb intake mod done, you just bolt on a throttlebody and you're set.

heck, i'll GIVE someone a throttlebody (LT1 or TPI their choice) if they actually go thru with it... lol.

BronYrAur

iTrader: (1)

It sounds like a pretty cool idea. The issue presented saying that airflow is not the limiting factor of TBI but fuel flow is, is the biggest reason not to do it though. You say you can add another injector or two more easily which is very true, mechanically, but the ECM won't be able to run that extra injector. You would need to get a separate add-on injector driver board to run it. Or you would have to convert to a '749. I think by the time you figure out how to power the extra injector(s) you would be better off just buying a 4bbl TBI unit off ebay and figuring out the ECM the same way, but now you have a 4bbl setup.

dimented24x7

iTrader: (2)

Even cooler would be if someone made a 4 bbl tbi base that would accept two stock injector pods, mount up like a carb, and have progressive throttle opening.

Another problem which is possibly bigger then WOT fueling is fueling at low speeds/loads. Big injectors being run at high pressures deliver alot of fuel and its hard to meter the fuel down low enough at idle while still having reasonable pulsewidths unless some sort of vacuum referenced regulator is used. Having four injecgtors would allow for only two to be used at low speeds and then all four to be used under load to give the extra fueling. The tools are available now to enable the ecm to control the extra two injectors but the injector boards arent available anymore and the 4 bbl tbi units with the good delphi injectors are hard to come by for a reasonable price.

Oh, no matter what ecm is used an external injector driver will ahve to be used if more then two injectors are used.

BronYrAur

iTrader: (1)

Really? I was under the impression that a '749 could run more injectors in a TBI setup situation. Could you explain this to me a little bit?

r90camarors

I was trying to figure out a way to make something like this work a while ago, though never really came up with a cost efficient way of doing it. But basically had the same idea:

Use a TPI or LT1 aftermarket throttle body on a plenum base that incorporated two injectors centered over the plenum (front to back) of a standard squarebore carb intake. Pressure would be controlled by an external vacuum ref regulator. The injectors would also be slightly angled forward to counterset the airflow.

The problems I saw with this setup was possibly too much plenum, and the obvious added costs to include the "injector plenum", the throttle body and sensors, and custom fuel rail and regulator. I'll see if I can dig up my lamo drawings......

I also believe, and plan on prooving that it is indeed AIR flow that is the problem, and not fuel flow with the 2bbl tbi. I may prove myself wrong as this go around I'm going with a Super Victor single plane......, but my last setup used the rpm airgap on my 383, and I consistently beat my buddy's 12.7 sec mustang trapping at 114mph. The O2 readings read good, though an atomization problem was the ultimate end of the engine, though I think it was mainly do to the crap holley adapter plate. That was with 85pph delphi injectors at 25psi (static)

There is a reason the 454 SS guys are having success with the 2.2" tbis......

Dewey316

I said that fuel is the problem base on experiance.

I can tell you that the 305 injectors go static way before i pull vacume. i would love to see results with you PW, and pulling vacume at WOT, but i am betting that you go static before you start pulling vac. at WOT.

r90camarors

Yeah, I was going static, based on the horrible rev limiter feeling above 6k. However, that was also with very limited chip tuning. This go around, I'm using an external vacuum regulator that will make for more psi at WOT, as well as doing actual tuning via Prominator. If I can find my old winaldl data, I will send it to you if you want. Just let me know. Chip tuning was done by tbichips.com. Great to deal with, but something as radical as the 383 needs A LOT of attention obviously, thus the prominator.

r90camarors

All right guys, I told you these were lame drawings, thus why I decided to hide them away........but since the topic was brought up, here is a very crude look........Try not to laugh too hard

ShiftyCapone

iTrader: (7)

Ah they aren't that bad

The problem with this type of set-up is fuel atomazation. Our current TBI's introduce the fuel spray from an ambient pressure zone to a low pressure zone which helps automizes it. A set-up like the one drawn would leave the fuel droplets way too big and poor combustion would be a result.

dimented24x7

iTrader: (2)

It looks like fueling will always be the achilles' heel of tbi . The huge 2.2 units really increase the flow potential but all that air needs fuel to be mixed in with it.

Your problems where indeed indicative of lack of fuel leading to detontation and other damage. Its unlikely it was much of a distribution problem. At WOT things are happening so fast that the fuel really isnt atomized as a fine mist from shearing or a vapor from the low pressure in the manifold but in droplet form just surging in with the air and a slight bias toward the rear wouldnt make too much of a difference. Q-jets seem to work perfectly fine with their huge 2.25 in secondaries toward the rear of the plenum. Those delphi injectors are too small and they have the same nozzle design as the standard tbi injectors so there is really nothing special about them. Ultimatly in the end upgrading to the larger 90 pph standard injectors and a regular injector pod is probably a better bet. You could really push them with an external regulator in place of the stock may-pop regular and theyd probably flow quite a bit.

Another thing about the stock O2 is I have doubts about its usefullness as an indicator of the overall fueling. It really only tells lean, stoich, and rich. That and the fact that the stock ALDL is slow as hell really means that youll miss alot. In terms of the engines operation, the 1.2 seconds between each full frame is an eternity. Even upgrading my ALDL to 8 fps isnt really good enough. It still leaves only two or three frames to analyse things like AE.

dimented24x7

iTrader: (2)

AFAIK, it has two injector drivers just like the tbi ecms, which means that only two injectors can be run off it.

Dewey316

unless you use the injector driver from a quad4 application, the impedance works out correctly with that driver board.

Grumpy

The 749 has two injector drivers.
In the Quad 4 application they fire 4, 2.4 ohm injectors, so it will fire 2, TBI injectors, that are 1.2 ohms without modification. Some internal rewiring in the ecm can change the load it can fire.
In the DFI ECM board is a thread about how to rewire the 749 injector drivers.

jwscab

This is a pretty neat idea, a couple of things come to mind here, to solve a couple of the problems.

since the injectors are now in the manifold, and influenced by the manifold pressure differential, you will need to have a vaccuum referenced regulator, ala multiport applications, no biggie there, run an external unit.

you could simply use standard multiport injectors, and build a small fuel rail for them. that way you can use pretty much any ecm, and not be limited in lb/hr, also 4 injectors sounds like a nice number too.

using the mulitport injectors, gives you some room to maybe angle the injector entry to shoot at the ports, albeit at the top of the ports, rather than the floor. you won't probably get the benefit of hitting the back of the valve, but then again, carbs don't either(tho the fuel is sheared through the airstream).

the last thing, is if you use something that has a dominator carb mounting pattern, it could make shooting down the ports easier, since the throat of the plenum is bigger, which also gives you more plenum, so you wouldn't have to build as big a box on top.

r90camarors

The problem running multiport injectors, i would think, is the fact that they would be too small, even with 4 of them. remember that multi port injectors are rated at a much higher fp than low imp. injectors.
And like shifty mentioned before, atomization would be hard to achieve.

jwscab

yep, you'd have to bump up the fuel pressure, something that has to be dealt with.

with the available injectors these days, you could drive the injectors with two factory options,:high impedance, 4 60 lbs will give you the equivalent of 30 lbs/cylinder injectors, or 4 low impedance, using a tbi or '749, and go as high as you need. its totally doable that way.

just throwing out ideas in case someone decides to run with this, and i don't thing atomization would be as bad as you think, maybe at idle 'tho.