Multiple TBI's (revisiting)

[ski4evr]

I sent in a question to Holley a while back about multiple tbi's. Below is some cut and pastes:

I'd like to modify my intake (it is integral to the head) to direct mount 3 holley 1 bbl TBI's or 2 holley 2 bbl TBI's. I understand that this is a custom application and that I would need to modify the intake and/or make the adapters myself. Can the Pro-Jection and/or Commander 950 ECU's control multiple throttle bodies? Can I buy the 1bbl throttle bodies (3 of them) or the 2bbl throttle bodies (2 of them) and plug them into a holley ECU? The reason I ask the last question - the 1 bbl throttle bodies are listed a an OEM replacement for GM vehicles.

What would I need to get - i.e. a custom stand alone kit?

What is the bolt pattern / base plate of the 1bbl and 2bbl throttle bodies? Do you have drawings with dimensions? I'll need this to determine how to modify the log head (also the throttle body height - for hood clearance).

Thank you,
Scott

Hello
The commander 950 ECU will control up to 4 low impedance injectores or 8 high impedance. Unfortunately the 1bbl TBI units are no longer produced. You can run multiple T-bodies you only need TPS input and IAC for one. The over all height of the 2bbl TBI is 4.5" Unfortunately due to patent resrictions I can not provide any drawings. The bolt pattern is the same as a stock GM TBI.
Thanks

So..... since the 1 bbl TBI's are no longer an option, maybe I could do the two 2 bbl TBI setup. One centered over the #2 cyl and the other centered over the #5 cyl.

But..... a new question: In multiple TBI setups, would only the TBI unit that has the IAC connected be maintaining idle operation? If the Commander 950 can only control one IAC, would the other TBI not contribute at all for idle fuel and air? If so, this would lead to a lean mixture for the cylinders beneath the non-contributing TBI and a rich mixture for the cylinders beneath the controlling TBI (the one connected to the ECU).

Am I out to lunch on this one? And would it really matter if only one contributed at idle?

Scott

 

[Stubby]

Think 82 Camaro and Corvette they had two TBI with one TPS. The Holley four barrel injector has four injectors with one throtle pos sensor.

You should be able to run a multiple tbi setup, however it would be sensative to proper adjustment and tuning issues as were Camaros and Vetts. I would think it would still be easier than carbs.

He said they don't make them anymore. He didn't say that they aren't available thru wrecking yards and parts stores. You would just have to run something compatible and might say AC delco on it.

 

[ski4evr]

I'm not concerned with the TPS. Both throttles would be set up to move together (synchronous). I'm concerned with idle control - when the throttles are shut. With the IAC not functioning on one of the TBI's, I'm assuming that throttle body would not have air nor fuel moving through it. This would give non-uniform fuel air mixtures throughout the intake at idling conditions. Right?

As far as the wrecking yard option... that would allow me to use three 1 bbl throttle bodies and the "non-uniform" idle stuff is not an issue. I'd just use the center TBI to control idle. And if the outer TBI's played at idle (or not) it wouldn't matter. I'd like new, though. It's a nice thought to get new stuff every now and then.

Scott

 

[Stubby]

The GM setups idled on both TBIs and I think this would be better, but it would have to be very precise on an engine this small.(very small TBIs) I don't have alot of experiance on EFI.

 

[ski4evr]

I'm going to do it! Order the Holley Commander 950 with a 400 cfm 2bbl throttle body. Direct Mount on a D8 head. Once that's running with all the bugs worked out, I'll figure a way to add another throttle body.

scott

 

[Stubby]

Cool

 

[Anonymous]

I am kicking around the idea of mounting a 2 bbl to my 1982 head, but with the barrels side by side, not front and back like most direct mount 2 barrels.

The left barrel would be over the hole in the log, and the right barrel would feed another manifold "log" that would be fabbed together and feed the areas of the log near 2 and 5.

I am going to see when I can get together with my machinist friend to see if that is doable. We have both been pretty busy lately.

 

[Stubby]

I would try to make the outer log meet inbetween 1/2 and 5/6. Two plenums and two logs It doesn't sound conventional, but then again I like living outside the box.

 

[Anonymous]

I would try to make the outer log meet inbetween 1/2 and 5/6.

Good Feedback!

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