Nitroburn

I got thinking about a dual TBI setup when I was driving home from Tennessee to Rhode Island (long drive and the family was sleeping, so you know... the mind begins to wonder) and the problems where our ECM's can drive 4 injectors which makes it almost impossible to do.

I'm sure I'm gonna get my ball$ busted for this one, but what if you take two TBI units but only one unit is complete (FPR, TPS, IAC, Injectors, etc...) and the other unit is only there to to supply air (the FPR, TPS, IAC, Injectors are removed but the butterflies and linkage is functional).

Then, on the unit which is fully functional, you install some large, powerful injectors to compensate for the added air going into the engine via the two TBI's.

I have no experience (yet) in burning my own chips or even understanding what size injectors and duty cycle and all that other stuff that goes along with it. But, in my mind, I don't see why it wouldn't work if the injectors are big enough to supply the amount of fuel needed by the added air flow.

Only one TPS is needed since both TBI's are hooked up on the same linkage (like dual quad carbs).

Only one IAC is needed for idle.

Of course, you only have to worry about fuel supply to one TBI unit along with only having to deal with one FPR. I'm sure the pressure would have to be set up there pretty high compared to what most of us now run, though.

The ECM would only be driving two injectors and I don;t think the O2 sensor cares where the air actually come from as long as the injectors are large enough to handle the added air to equal out the AIR/FUEL mixture.

So.. am I really out there in left field or is something like this a possibility? Like I said, if the injectors are large enough, there would be plenty of CFMs from dual TBI units to supply a high horse motor.

Later,
-Mike

raggedout91RS

The first problem w/ that is your fuel and air distribution. I mean how would you mount the TBI's on the intake so that the cylinders got an even amont of air and fuel. It seems that the cylinders closest to the fuelless TBI would run leaner than the others. I am in now way a professional mechanic or an expert but that seems to me like that would'nt work too well on a conventional dual carb intake IMO. Beleive me when I say I would like to have a dual TBI setup that works also. I dont think anything could be cooler than that.

Nitroburn

Yeah.. I thought about that one, too... Ok, how about mounting one functioning injector in each TBI unit, but only one unit would have the TPS and IAC functioning. This setup would have to have a FPR on each unit, but I don't see to big of a problem with that. Also, as for the functioning injectors, one would be on the left side of one unit and the other on the right side of the other unit.

AJ_92RS

Actually I have been thinking the same thing. I just never posted it here.

My idea is basically the same..... but run a relay similar to how nitrous does, and have it kick in the other 2 injectors only at WOT. That way the ECM is already in WOT mode, and won't even read the O2 sensor.

You'd have to really be careful about getting the right size injectors so you'd have a pretty good A/F ratio at WOT, but it shouldn't be too much harder than jetting a carb.

It's just an idea to make it easier for the guys that know how to program this stuff. That way they only have to worry about the fuel maps and timing tables at WOT. The rest of the time the ECM would run only 2 injectors.

The only problem I could see is...... running only one injector on each TB would require an open plenum design, which I'm not sure if the dual carb manifolds (other than a tunnel ram) are set up that way. Then..... would the mixture just be WAY TOO LEAN with both TB throttle blades open, but only one injector filling the need for that much air. Know what I mean?

Perhaps it's something one of the TBI gurus can answer, or at least ponder.

dimented24x7

iTrader: (2)

better yet... I wonder if its possible to use an external injector driver that could power 4 injectors with each bank of 2 injectors running in parallel. that way you could use the holley 4bbl unit. Obviously the power load would be too much for the power transisters int he ecm to provide and there would be too much heat to dissipate. Instead, a set of power transisters and all the support circuitry could be relocated to an external case. With an external unit, the injector drivers could be mounted in an external case that could have dedicated power and provisions for impoved cooling such as a heat sink and forced venilation. The ammount of injectors that could be driven is solely up to the design of the external driver. Hell, you could probably even drive twin 4bbl tbi's to power even the most insane setup.

JPrevost

https://www.thirdgen.org/techbb2/sho...hreadid=150036
Of how about just mounting the injector pod on a 4 barrel carb with mechanical secondaries. Why use a spray bar like with N2o? Just use the carb to deliver the extra fuel and under normal driving the primaries are disabled leaving you with the 2 TBI injectors. Only issue would be to modify the carb for the TBI injector pod.

Nitroburn

I think it would be easier to make mods to a dual TBI rather then mess with mounting an injector pod to a carb.

I'll look into some of the dual-quad manifolds and see if some one has one as a single plane type. This might make for a nice summer project for myself.

As far as the system running lean with only one injector per unit, that's why bigger injectors would be needed. Also, during normal driving (in theroy, that is), you're not feeding any more air into the motor than you would with a single TBI setup. The only thing which would be different is the amount of travel of the thottle linkage is opened. For example, on a single TBI setup, let's say the blades are opened up 1/4 to run at a steady 60mph. With two TBI's, each unit would only have to be open 1/8 to allow the same amount of air into the engine.

The way I see it, it's when both unit are open more then 1/2 of the way is where an issue would come into play running lean. That's the reasons for the larger injectors and FP.

Hey NTchrist, when can I get that other TBI unit from ya!!

Dewey316

i understand the novilty in doing this yourself, but holley makes a command950 ECU addon, that will power 2 of thier 900CFM TBI systems for use on a 2x4 intake manifold. i have no idea on the pricing i bet it would run close to 2k for the 2 tbi's and the ECU, but that is a readdy to run system

Nitroburn

Dewey, I agree that it would probably be easier. However, the cost would not offset the power gain, IMO. If I could possibly do it with the idea I have, the most expensive part of the project is actually the dual-quad manifold (if it was purchased new, of course).

The hardest part would be tuning. That's where I have no clue as far as injector sizes, duty cycles, etc... But, it'll be fun to actually get it working, if at all possible.

jlbolin

i dont really know too much but a while back there was a post put on here for the CFI guys and it showed an intake made by Offenhauser(hope i spelled it right), this intake was only $237 for the lower part and the deck lid was $115 but the deck lid could be ordered as a single 4barrel or dual 4 barrel or tripel wbers. i sue too have pics on my pc but system restore had to be done and dont have pics any more but did print the intake up on paper and i think PAW sells this intake cause its an ad out of there catalog.but this is a cross ram intake. will this work so each tbi could feed the cylinders. what do you think of this, can you use two ecm and two tbi's and, two oxy sens, two temp sens,two mat sens,two map sens,two esc modules, and whatever else you need and maybe a tpi fuel pump. just curious, cause i can get the rest of this pretty easily, minus the funds but wouldnt be to hard i guess.i mean what does the ecm need to make a-f adjustments and open loop and closed loop mode and all that there stuff, sorry talking to my self, any recomandations.

Fast67chev

Turbo city had a dual tbi setup, I saw a Truckin article on it a while back, the setup made 405hp and over 400lbs tq on a dual quad manifold, they tuned it on a dyno. It did have a special computer and both tbi's ran off one fpr. also the article said they had to do a lot of tuning to get it leaned down to acceptable levels. But apperently the system could support up to 500hp.
that would be pretty sweet!
Jesse

JoBy

If you look at the Cross-Fire system you have two TBI's that are linked together. They are 1bbl with one injector each. They also have one IAC each and they are wired in paralell so the ECM can handle that. Only the rear TBI has a TPS sensor. They also share the fuel pressure regulator.

When using this setup with 2bbl TBI's only 2 extra injector drivers are needed.

I think that best thing would be to add another slave ECM to drive the extra two injectors. This slave ECM can be a bad unit as long as the injector drivers are working. It does not need a prom or any sensors at all. You cut the injector signal between the cpu and the injector driver. Then you run a wire from the injector signal in the master ( original ) ECM and connect it to the injector driver in the slave ECM. That way the master ECM will fire all four injectors at minimal cost and work.

This is the scematics for the 7747 and 8746.

http://www.cruzers.com/~ludis/1228746sheet5.gif

In the lower right of the picture CD_INJR and CD_INJL are going to the right and left injector.

U19 and U20 are controlling the injector current by sensing the voltage over the resistors R80 and R79.

INJOUT in U13 is the signal source. You 'steal' the signal from there, and duplicate the driver stage for each injector.


This is an exaple using the 1226026 ECM from a Cross-Fire, but the idea should be the same on other ECM's too.





If you use two stock ECM's, then you connect the two spots in the lower right to the same spots on the slave ECM. The signal is coming to those spots on two wires on the other side of the board. Cut those on the slave ECM. Then both ECM's injector drivers will use the same signal.


The original ECM stays the same exept that you open it up an connect two wires to the "Front and rear signal to driver IC".

The spliced signal will go into the same place in the extra ECM. The slave ECM will have to be modified ( original signal source cut ) so the original ECM is feeding the signal to both without interference.

On the slave ECM you only need the power wires and the two injector wires. 5 wires on the edge connector and the 2 signal wires.

jlbolin

that figures i have no experience in that field, but i can build everything else. have you guys ever seen that offy intake that PAW carries in thier catalog,ive seen pics of this intake from all angles compared to the original crossram from the cfi motors, its alot bigger,if i had a scanner i could get you some pics. it would be nice to get 2 tbi's running on that setup,.got to figure out how tow work on the ecm, and get them linked. thanks for the info, if anything else please tell, im going to give this a shot.All i need is the spare ecm and the intake and gaskets of course.

JoBy

An Offenhauser with a dual 4bbl lid and adapter plates to use two 2bbl TBI's instead would be a nice setup if you have hood clearence for it.

Using a 'slave' ECM to drive the extra two injectors and wireing the rest like a stock Cross-Fire would work.

Mecanically you link the throttles together and use an external fuel pressure regulator for both TBI's.

I have installed an Offenhauser Cross-Ram now using My stock 1bbl Cross-Fire TBI's.

Pictures here:
http://jobyteknik.homeip.net/corvett..._installation/

Click the links at the top of the page to read more about the Cross-Ram and see more pictures.


This is an Offenhauser on top of a Cross-Fire
(Click to enlarge)

V8Astro Captain

iTrader: (1)

So to to make an ECM a slave would I have to cut the trace from U13(INJOUT) before or after the splice as seen the .gif? The splice goes to U21 and U19.

Then I would run wires from U13 in the master ECM to where I just cut the trace in the slave?

thanks

JoBy

This is what I would do, but I have not tried it myself.

One wire from pin 1 on U19 (master) to pin 1 on U19 (slave).
One wire from pin 1 on U20 (master) to pin 1 on U20 (slave).

In the slave I would cut the traces going to pin 1 on U19 and to pin 1 on U20. That would separate the injector drivers from the rest of the slave ECM.

I would also mount the two ECM's close together to minimize wire length.

NTChrist

I'm working on it, I'm working on it.

Hell, if you want to give this 1.5 ECM thing a shot, you could have my ECM, too.

Do you still have that engine stand? I figure maybe I can trade you this stuff for a little bit of time on your engine stand.

jlbolin

correct me if im wrong but you cant use e-tec heads or vortech's with this manifold but could use edelbrock performer rpm am i right?then that means that i would just have to get the ecm and part of an orignal harness.

JPrevost

I'm lost and don't know what you're asking. So far there is only 1 intake manifold that could be used with vortec heads and have dual 2 barrel TBI. That's the stock OEM 96-98 intake manifold. It can be made to be just like the cross-fire intake. The only problem is that at around 300hp the intake runners are just too small and become major restrictions. In other words, there aren't any good crossram style intake manifolds for vortec heads. For my new website I've got a page dedicated to vortec compatible intakes and there are a LOT of em, just no large crossram.

jlbolin

sorry let me rephrase the ?, can or cant you use the offenhauser crossram intake on vortechs, without having any or no machine work done? or do yu have to stick with the 12-bolt instead of V's 8-bolt style and the raised runners.dont know 2 much about the vortechs. ONE VERY IMPORTANT THING TOO ASK, DOES IT MATTER WHAT TYPE OF TBI ECM YOU WOULD NEED TO HAVE. FOR EXAMPLE---- 4.3 ECM, 5.0 ECM,OR 5.7,OR CAR ,VAN,TRUCK.JUST AS LONG AS THERE IS TWO INJECTOR WIRES FROM THE HARNESS.

JPrevost

No, the off will not bolt right up. You need the v8. It might be possible to port the intake but I'm not sure how much material is there. Then it would be possible.
It doesn't matter what ecm so long as it's a c3 type and TBI specific. Example: Any crossfire, or 2 injector TBI (4.3, 5.0, 5.7, 7.4) ecm will work the same way. Those have the 2 peak and hold injector drivers. Personally I wouldn't do it until I had gotten experience tuning other cars but if you're up for headaches with idle quality then go for it. The problem is the injector firing rate is so slow that there are dry spots, not a very nice even "cloud" of fuel going. It isn't exactly dry but just lean, then rich, then lean etc. If you used really small injectors like from a 4.3 or 5.0 and low enough fuel pressure I bet there wouldn't be an issue, but then what's the point of having dual TBI. Get into burning your own eproms and I'll bet that a VacAFPR would be of great assistance in getting a dual TBI setup to run like a champ.

Nitroburn

Dude.. it's a little hard to be working on it when you're in Cananda and your car is in the States!!!

Yes, I still have the engine stand. You can use it (as long as I don't have the TRANS AM engine on it, which I don't see that happening for a long time).

scauffiel

I've been stewing with this idea for a while now, and still haven't gotten much further BUT I've got some pix on my website here.

I'll be using my Haltech to control the injectors. Sadly, there isn't enough time in the day...

S.

AJ_92RS

OK..... I have a question.

If someone were to use injectors that were higher in resistance, and flowed enough, can you run them in parallel to just one driver?

The reason I ask is I've found a pair that are 2.6 ohms resistance each. The stock GM injectors are 1.4 ohms, correct? If you wire the two 2.6 ohm injectors in parallel that would present 1.3 ohms to the ECM.

Could the injector driver handle that? Based on my electrical knowledge, there's no reason it wouldn't. Based on my lack of computer knowledge, there may be some other problem.

The injectors I've found are off a 3.8L Ford TBI system. They appear to be shaped different, and use a different style injector pod (they're top fed),

Actually, the Ford TB could be used. It bolts to a standard 2 barrel intake manifold so standard 2-4 adapters could be used (why couldn't GM do that ), and of course they have a TPS, an IAC, as well as a FPR. Plus it has a Schrader valve.

I know not many here would want Ford TBs on their car, but hey..... if it works...

JoBy

I looked at your web-page. It is looking good, but I found one problem.

That will not work. The IAC uses a stepper motor and each step is a fixed length. It uses two coils and by sending current thru them in the right direction, and in the right order you can move them forward or reverse. Just wire them in paralell like it is done on the Cross-Fire. You can change the stepping speed from the ECM or Haltech instead.

scauffiel

Ahhh, noted. Hell, that makes this idea even easier... Must... get... off... @ss...


S.

steve8586iroc

Does this shead any light on the dual tbi setup. https://www.thirdgen.org/techbb2/sho...hreadid=168041

Steve

ronnyinwaxhaw

saved

ronnyinwaxhaw

I see this thread is from 2003, but was it ever resolved? Here's a direct question: If you had a 383 small block with say a Thumper cam, an Edelbrock Performer 2X4 intake (like part#5425 for instance), could you put two 2 barrel throttle bodies from a 4.3 V6 on it and run it with maybe a Megasquirt controller? Someone said there needed to be a plenum area under the TBIs, would you mill out the 4 hole ports where the carbs go a few inches or put a two inch open spacer between the adapter and the intake to give plenum area? With 4 and 6 inch cowl hoods, let's say height isn't a concern.
I dig the look of two fours under the hood, and if you could do this with the two TBIs then you get the classic look of two fours and the benefits of EFI.

Darkshot

iTrader: (4)

EBL has been developed since this thread was made. It can power 4 injectors for a dual 2 bbl TBI setup or even a single 4 bbl TBI setup with 4 injectors.

RFmaster

It can be done (and was done in the past). The problem with dual TB setup is achieving balancing between the two to achieve stable idle. Balance modification for a cross fire is described in a current TGO thread and can be possibly adapted to a quad setup. Building a setup like this requires access to machine shop, materials, TB's, engine and plenty of time to experiment (the later I lack).

//RF

ronnyinwaxhaw

What is EBL?

Cflick

See http://dynamicefi.com

bucklee00

http://www.fullsizechevy.com/forums/...l-t-b-i-s.html

ronnyinwaxhaw

That's the link I needed. That's just what I have in mind. Thanks, bucklee00!

Birdstheword

it would probably lok something like this

http://snflupigus.com/Partspics/image152.jpg

RFmaster

The link above shows a pair of 2 barrel TB's each equipped with IAC. Based on well known idle misbehavior found in OE cross-fire setup dual 2-barrel setup will likely have the same idle issues. Instead, of paralleling a pair of IAC of the same control lines a modification similar to the the one described in this post should be contemplated:

https://www.thirdgen.org/forums/tbi/...-both-tbs.html

I have not looked (devil is in details) into modifying 2-barrel TB's to have a idle air balance feed line connecting the two TB. With holidays coming up I'll take a look at my local JY for a pair of 2.8L TB's and see if balance tube mod is doable. Another question is (practical) injector sizing.
Right now I am kinda toying with an idea for my 383 TB setup - dual 2-barrel TB's on 5425 EDL intake. There are several problems that I have to overcome with this approach - hence a single BBC TB on dual plane intake is a front runner at this stage.

//RF

bucklee00

at the end of that thread it says more info on main page, and i have read the thread on the main page but i couldent find it again. but ill look again because Fast305 goes into detail on how to control dual tbi

Here is the follow up to that thread i posted up earlier
http://www.fullsizechevy.com/forums/...bi-mockup.html

ronnyinwaxhaw

I am several months from trying this, so I'll watch and learn from your posts. I'm looking at this set-up for a 383 that's going in my El Camino. I have two TBIs from two 4.3 powered C1500 pickups that happened to be similarly equipped and sitting side by side in a JY.

Cflick

I thought about doing the dual TBI thing, but a few calculations show that the big block TBI ( about 750 CFM ) flows enough to keep my big block happy to 5000 or so. Watching the MAP very closely during a few WOT runs confirms the TBI itself is big enough, but changing the air cleaner did make a difference. I now show barometric ( no vacuum ) through 5000 on a hard pull. Good 'nuff for me ! Much simpler than fabricating a dual TBI of any flavor. Around 5000 vacuum just starts to develop, but I'm not spinning that kind of RPM with any regularity, and it's not a race truck, so .....

JPrevost

I posted this information up a long time ago with regards to TBI airflow... it is not the problem... but the fuel is. Any healthy engine will quickly run out of fuel as the injectors are already undersized from the factory. They are peak and hold injectors but are constantly used at near 95% capacity on a STOCK engine. The fact remains that there are not a lot TBI injectors out there big enough to support any kind of horsepower so you're best bet is to use EBL and at least 4 TBI injectors. Else put an RPM limiter on the engine so that it doesn't run lean. Bumping the fuel pressure helps but it makes things like idle and part throttle tuning difficult (unless you use RBob's EBL code).

Cflick

TRUE !
In my case, a couple hard pulls, a couple tweeks to fuel pressure, and the injectors stay in the high 80% range at WOT up to 5000. Again, that works for me, but also true tweeking the low duty cycles gets tricky, and critical.
I also happen to be a believer in that unused surplus capacity is a waste, that getting the injectors real close to 90% at max RPM and max load is enough. Any more injector capacity and tuning the lower regions becomes exponentially more difficult, if even possible. I do have a bit of surge at idle sometimes, but when the injectors are running between 0% and 1% at idle what would one expect ? I'd need a vacuum pressure regulator to corect that, but it isn't worth it for the operating range I'm staying in more than 90% of the time.