If you were to run a roots style blower, like a Holley 144, at around 4-6 psi, how would you actually get the computer to sense boost. I do not want to run an FMU. Is it even possible to do with GM TBI and a roots blower?

EDIT: Not sure if a 2 bar map would even help since it would be a suck through setup instead of a blow through, with the TBI on top.

 

No expert on boost, but in theory, the roots blower should make the motor appear bigger to a carb or tbi thats parked on top. You could just try to tune it like you would any other motor and the extra needed fuel would be incorporated into the VE table.

 

the other option is to use the 749. It already has the tables set up to run boost. And there are several people already using it to run TBI injectors.

The thing I worry about, is providing enough fuel, even with the BB injectors, I don't know that it would supply enough fuel for the 400-500HP that one of those little blowers is capable of.

For what its worth, I really thought about doing this a roots blown TBI project, before the TT bug hit me. I think it could make for an absolutly wicked little street mouse.

 

But with a roots blower, as opposed to a turbo or cent. supercharger, how would the map sensor even sense boost? There really is no way, so the 749 would be pointless right?

 

Well maybe in that regard, but it would still give you much much better fuel and timing control than a TBI ECM. The tables extend much higher in the RPM range. It also has the fast baud rate for data logging and just the fact that its a P4 puts it way ahead of TBI ECMs.

 

I have the 7060; it is TBI and P4

Also, the program I'm using goes to 6400.

 

Just run the boost sensing line, to between the blower, and manifold.

For a boosted application, the 749 is the way to go, IMO.

 

Exactly, with the case of the roots blower, you would need to get your the pressure for the sensor from the manifold instead of the from the TB unit. not a major change at all. Really, any option other than a computer really meant to work in a bosted application is pointless, you are either going to loose the ability to compensate for boost, or lose resolution with your other options.

 

I don't think it was mentioned above, but the 749 uses a 2-bar map sensor, if that was your questions. So it can "see" to 14 psi, there is a patch out there some where to run a 3 bar sensor so 28 psi is an option, but not with a small roots blower.

 

Is the 749 a direct swap for the 746 ecm? Can you reuse all of your stock sensors?

 

you will need at least a new MAP sensor, I'm not sure what else you will need. I think that you need an injector driver out of the turbo 4cyl. application. Then you will need to repin your harness. I don't have all the info with me, some searching on the DIY board should give you more info that you need. I'm busy packing and getting ready for my trip to arizona, so I dont' really have time to do too much searching for stuff right now.

 

As mentioned, you'd want to use a "new" MAP sensor. The only other sensor that you might need would be a MAT sensor. I don't know if the 746 ECMs have these or not. Further, even if they're present on the 746, you'd want to make sure you're really measuring "Manifold" temperature rather than the temperature pre-blower. There are adjusments to timing performed based on manifold (post-blower) temperature you'd want to take advantage of....

All other sensors should swap with no problems.