Duke

Been probably a year since I posted on this forum.

I tired once before to make a reliable duel TBI system, but it never ran right. It made good power, but ran kinda goofy on the street and was a PITA to burn PROMS for. A few of the older members here might remember what I'm talking about.

Anyone successfully make a good running duel TBI system? If so, what did ya use and how did ya do it?

raggedout91RS

Hey Duke, what did you do to your system to make it run? I mean, which sesnsors did you splice together and how did they work together? What does ran goofy mean, (stall out, bad idle, no low end power)? I'm very curious about this so any answers would be appreciated. Thanx

brodyscamaro

nobody has gotten it perfect

JPrevost

Give me lots of time and it should be done. The issue isn't so much the hardware and theorty as much as it is the software. Yes you need those extra injector drivers but you also need to figure out the injector firing strategy. A stock 2 barrel runs pulsewidths by firing the injectors every time a cylinder fires. You get each of the injectors firing twice a revolution. If you had 4 injectors on the same theory of opperation you would need to have exactly half the injector flow rate to keep the same steady idle quality and light throttle accuracy. This isn't easy unless you go with some really small injectors but then what's the point of having 4 injectors that flow as much as 2!!!!
This is where the software and source code makes the biggest difference. With such you can program the injectors to do whatever you please. It's the same with going with a 4 barrel TBI. The only difference is how the IAC and vacuum lines are hooked/wired up.

91Bird305

Give me 5 minutes and a few days for shipping and I can switch to carb.

raggedout91RS

A carb is the easy way out. I have a carbed street machine already and I want more of a challenge with the TBI. Carbs have been done to death and emissions controls are taking over so why not make it fast and legal, even though I know you would probably never pass a visual inspection with dual TBI.

91Bird305

If your making an engine that requires a dual tbi setup, I doubt the engine alone will be able to pass emmisios, TBI or not.

JPrevost

You didn't just say that. If you did, I'm going to have to do my little reach through the monitor and slap you .
A perfect example of a motor that can pass emissions and would require dual TBI or at least 750cfm at 1.5"; 383, afr 190 heads, lt4 hot cam need I say more. Anything pushing the 400+hp is going to need more cfm than a 2" bore TB would be able to support. General rule of thumb is stock 1 11/16" is good up until 300hp, 2" good till about 400hp, and anything more you should think about a 4 barrel system. BTW, was talking to RBob the other day and some guy had an idea to mount a TBI injector pod on one side of a 4 barrel carb. Mechanical secondaries so when you needed the extra fuel it was there and adjustable. Use the TBI for cruising around and it's a perfectly logical idea to the 4 injector controls. The ONLY way I would ever consider doing such a thing is if I had my wideband o2 sensor and lockers to make certain the carb is adjusted well enough to provide smooth transitioning and semi-accurate AFRs in all weather. It's very creative if you have an extra large carb you don't mind cutting up.

91Bird305

Hmm, ok Jon whatever you say bud.

Anyways, good luck with the dual tbi setup, seems like a lot of time and money invested into something thats not gonna be that great. But thats just me.

jwscab

Hey Jon, about that firing strategy....if you use an external driver(s) and basically split the two injector signals so that in effect, you have a 'double' injector fired on the left and right injector signals, you should be able to plug in the effective injector constant of twice whatever you are using, no? Say for instance, you use 4 55lb injectors, you'd set the injector constant to 110 lbs. Would this run into problems with idling due to the short pulse width? I would think that this would run OK, if you can use 90lbs injectors and get an engine to idle OK. I've got some of this stuff sorta worked on, just on hold right now, cause of other priorities. I actually have the throttle bodies ready to go(bead blasted, minus injectors), and the injector driver module built. I just need to get around to making a top plate for an offenhauser cross-ram, linkages, etc. Then of course, I have to think about an engine to put under it. I guess maybe its not as simple as doubling the constant? I haven't really had time to figure out all the pulsewidths or anything, so this is all just top level thinking.....

JPrevost

It's definatly not wasted money since it's ~$10 worth of parts to make the extra injector driver board but time, maybe. Here's the major issue, idle and near idle. Why run small 45-55# injectors when you could run 2 90#ers. If you used anything higher than 55 the pulse widths would get very small. It might not be an issue but with an intake other than a single plane you could get into some troubles. I haven't seen a big problem with lowering the pulse widths so low that it hurts idle quality but that's only with ~75# injectors on a 350. I've been able to get it to idle smooth down to 500rpm without stalling. Of course the oil pressure gets a little too low for my liking so it's back up to 650 for the winter.
Having 2 injectors firing at the same time isn't going to flow the same as one big injector that's rated at exactly double. There are opening, closing properties that make a big difference when you end up going really low on the injector pulsewidth. A single 90 would outflow 2 45's at low pulsewidths, at least in theory it would. I don't have a flow bench for injectors to prove this but from others experience it's been the case. For that reason alone I think you'd be fine running dual TBI or a 4 barrel with smallish injectors ~55. The only issue now is the fact that what good is 4 small injectors when 2 large injectors can't support much more than 400hp. When you sit down and figure out the cfm requirement for a 400hp motor, the 4 barrel or dual 2 barrel will only have marginal differences compared to a 2" TB. If I did go 4 barrel or dual 2 barrel it would be with a big motor that had to idle above 750. Then I'd do exactly what you're doing with the cross-ram and dual 2 barrel TBIs. It's a dream for me that is limited only by money right now. Time isn't such an issue but finding a similar manifold for vortec heads is like looking for gold in your gas tank . Which injector driver board are you using? There are several out there and are you keeping the circuit inside the ecm to utalize the case as the heat-sink for the transistors? Load me up with info, I'm giddy just thinking about it.

Duke

I used an external driver to run my injectors, it worked fine, my problem was programming the ECM. If you're going to do this, I suggest using a Haltec computer with the 4 injector outputs. It's easier to adjust IMO.

JPrevost

We use a Haltech on our Formula SAE car at school. It's not the best piece of equipment (DOS based tuning) but it's definatly accurate. Realtime adjustments but what a PITA it is to find the money to pay for em . I'll stick with GM ecm's.

jwscab

To answer your question about how I'm implementing the drivers, I've used the national injector drivers(lm1949), and placed them in their own chassis, with heatsinks on the transistors. This way, you can use it on any ecm, since the box terminates the two driver signals from the ecm, inverts them, and drives them into the national parts. Makes it easy to replace as a component, either the ecm or driver board. As for which board I'm using, its pretty much the application circuit from the LM1949, duplicated 4 times, with an lm7805 regulator for IC power, an '04 inverter, and some resistors to terminate the driver outputs(I think maybe 2K or something, I forget, but I checked it out on a scope and its a nice squarewave output.) They all fit in a box about 3x2.5x2 inches, and the heatsink is almost that big....if I can borrow a camera from my brother, maybe I can throw some pics up here.......

JPrevost

A picture would be nice. Thanks for sharing that info. Glad to see somebody is making it work. Now the next step is to keep the GM ecm for it's obvious street driven advantages (highway mode fuel and spark, tcc controls, source code )

White Ninja

here's the pics for JWScab...

White Ninja

2:

White Ninja

sorry little blurry...
#3

V8Astro Captain

iTrader: (1)

I think the injector driver is very cool.

You could also run a Holley Commander 950. It's capable of running 4 TBI injectors. Although that's not really in the "DIY spirit" of things I suppose...

BUT if you really wanted to run a 4 barrel TBI it's there.

By the way...do you have a schematic for that assembly shown above?

jwscab

Yes, I have schematics. I'll have to get them to scan them, I don't have them at the house right now. I'll post 'em as soon as I can. Yeah, as for DIY vs. the DFI; the whole driver board cost me about....nothing...I sampled all the parts I didn't already have, but the cost would only be about 15-20 bucks or so....the LM1949 was like $2.50 or something like that...and everything else is less than $.50...the beauty of this is that it works for any S+H type injector(or saturated), and you can duplicate the circuit as many times as you want...want 10 low-impedance injectors? go for it!....It's even prgrammable for current limiting, and S/H timing. I know Grumpy said that this part hasn't been available for awhile, but even now, when you check National's website, they have stock(full production), and it shows up in Digi-key's website as well...I had no problems getting them. In fact, the more people that buy them ensures that they won't stop makin' them. here's the website(and where I got most of the schematics):

http://www.national.com/pf/LM/LM1949.html#Datasheet

RBob

iTrader: (1)

Yes, this is good news (The LM1949 being available). Jon also mentioned that he was able to get some. National Semiconductor actually did stop production of these pieces. For a while there was nothing available for PnH type injectors.

I was wondering what companies such as Holley and Motec were using for drivers. Maybe they are using the National Semi parts and that is why they are back into full production. With DigiKey carrying the 8 pin mini-dip version it makes it all that much easier.

As a side note this is the same part GM used in the '8746 & '747 ECMs.

RBob.

jwscab

For those guys that asked to see the schematic I used, here it is....if its hard to see, sorry, its hard to get this down to an attachable size and still readable. If anyone knows of a good cheap schematic entry program that can be attained, I'd like to transfer this to a real schematic file....

aDFIguy

I know that it's not a homegrown solution, but the DFI Gen 7 will have a Dual-Quad TBI strategy in it's upcoming revision due to be out next month:

[edit: see below for screen image]

aDFIguy

Part of a screen capture:

Dewey316

also not a homegrown solution, but i got the 03 holley catolog, and in the catalog there is a add on pack for the holley commander 950 ECU, that is for a DUAL TBI setup.


EDIT: Here is the link http://www.holley.com/HiOctn/ProdLin...I/534-122.html

SC2camaro

hey jon


why can't he use a 89-92 TBI computer. I i do reecall they have 4 injector driivers in them. where the 88 computer only has 2 driver. The way i founnd that out was nobody had then binary file for the 88 chip/ecm. but there were out there for the 89-92 ecm's. When i looked at the wiring diagram from alldata the only diffrence in the 2 were it had 2 more injector wires coming off the ecm. i was thinking about this very same thing about going with a holley 4 injector TB.

RBob

iTrader: (1)

The '8063, '7747 & '8746 all have 2 injector drivers. Each driver is wired to 2 pins on the connector. Can then double up the wiring to each injector.

Best way to go is to use either an external driver box or add the drivers internal to the ECM. Can then use a single 4bbl TBI or dual 2bbl TBI's.

RBob.

iroczrockz

I remember posting one of these pics before but, unfortunately the dual tbi setup is not available yet. Apparently the crossfire is available though.

iroczrockz

The crossfire. These guys are a bit pricey though. I am not sure of the price of these but the company is pricey. I have bought from them though.

iroczrockz

Has anyone had this done to their TBI butterfly shafts?