TBI on a Dauntless 225 V6 - a couple questions

I have read the sticky thread about TBI on a 225 odd-fire and still have a couple questions that you all may be able to help with…

I seems that a GM 4.3L TBI unit is most the popular set up - but a Ford CFI could also be made to work. I think.

My 225 has a Offy 360 Dual Port intake and headers. Is this intake workable with either the GM or Ford TBI/CFI systems? I know an adaptor would probably have to be found or made - but would TBI with adaptor use both the secondary and primary runners in the Dual Port 360? Is a plenum chamber under the TBI unit the right way to go?

ICU - do most people use the 4.3 control unit and re-map the parameters, or is Megasquirt's controller more adaptable - assuming there is a map available somewhere.

Trying to get a grip on the basics and I have more questions than answers, it seems. Thanks for your help.

Mike

 

Maybe not answering your questions, but a couple of relevant points.

First, realize that the throttle body is only a passive part of the TBI system. You can use whatever throttle body you want - GM, Ford, Holley, whatever - as long as you can interface it to your computer. The 4.3L computer can be triggered by a crank wheel on the odd-fire engine, while the MegaSquirt can be triggered from the crank or from the distributor (tach signal).

If you use the Ford CFI throttle body, you can use the MS1/V2.2 (Megasquirt 1 with the V2.2 board). The kit for this computer is $169, vs. the kit for the MS2/V3.0 at $279. If you use the GM throttle body, you need MS2 so you can control the idle air control (IAC) stepper motor on the throttle body. Or, you can abandon the IAC on the GM TB and use a separate external on/off idle air valve, which the MS1 can control.

I'm not as informed about the GM computer, but from the factory, it has a ROM chip with fixed programming for a single engine type. You must make your own programming to tune the computer to your engine. There are devices and programs to do this. The simplest - I believe - uses an EEPROM (electrically erasable programmable ROM) that you pop in and out of the GM computer. You also need some kind of data logging capability. So once you scrounge the pieces from the junkyard or donor, you need some additional hardware and software to make it work right.

The Megasquirt uses memory on its CPU to hold the programming, and you both program and log via a serial port on the computer, connected to your laptop. So you don't need to buy another device if you already have a laptop. You may have to buy a RS232 to USB adapter, if your laptop does not have a RS232 serial port.

There are adapters to 4V manifolds for both the Holley pattern (Ford CFI TBs) and GM TBs. Take a look at those to see where it places the throttle plates. The only reason 4V carburetors exist is because carburetors need to maintain a fairly high manifold vacuum to function, so a progressive opening makes sense. A throttle body does not use the vacuum to do work - it only measures the vacuum to determine current operating condition. So there is no need for secondaries.

I would take a look at the adapters on Jegs and Summit to see where they put the venturies. Bill Hamilton makes some nice adapters too - http://hamiltonfuelinjection.com/products/4-four-barrel-adapters.aspx - looks like he puts the TB centered between the primaries and secondaries.