I've seen some custom UIMs around this site and was wondering what people are doing to mount the BAC or similar device for control by the MS. I've read of people with no BAC tuning to compensate for it, but haven't heard of anyone relocating or using something from another car. Is this uncharted territory?

 

the biggest thing would be getting a flange to mount one. You could use an FD BAC valve (aka ISC valve) or a Ford BAC (aka IACV). They all work in the same basic way as the FC BAC. They are pulsewidth modulated solenoid valves.

 

I could make the flange if I had the BAC. I'm sure placement on the manifold is important as well, although my 300ZXTT has the IACV (same thing?) at the far back corner, and that manifold is pretty much divided except for a balance tube. One day I will check the junkyard for a compact one.

 

stand alone with custom intake manifold... Why would you want to keep the BAC still?

 

because he likes having a stable idle that isn't 1000+ rpms... leave it to Rx-7 owners to delete idle air control valves

 

Stable idle yes, but it's a Datsun 240Z with a T2 motor. UIM is custom to clear some strut tower-to-firewall bracing.

 

it's like people asking me why I still have cruise control with a standalone and big turbo upgrade. Uhh... because I don't want to have to keep my foot on the gas for long periods of time on the highway?

 

I don't have a BAC. And I still have the stock ECU. steady idle at 750... Never had a problem on any of my cars after removing the BAC.

 

Just mount a BAC to your custom manifold:



Having a BAC is always nice, for things like:
-cold start
-regulating idle under varying alternator loads
-A/C
-dashpot functions
-not accidentally stalling the car at intersections

 

While not a T2, I did a similar mod to my S5 NA engine using just part of the UIM. I kept the injector mounts and the BAC valve. and cut away the rest. Then I welded it to a custom log intake for my Lotus replica. Height of the manifold above the block is maybe 3-1/2" to 4". Cold starts using the BAC are easy to control with the MS.

 

I saw your build on the locost forums. It was a great read. Very nice work.

 

When people tune their own engines, they often don't get the warmup, idle, and cranking fueling right. Having the BAC helps work around that without having to get the rest of it exactly right.

Ken

 

Aaron,
I've read your manifold build thread many times, great write up. How do you determine where the BAC would go?

 

It really doesn't matter where it goes as long as it can let air in past the throttle body. I just placed it on the bottom of the manifold because that was a large flat area that is relatively hidden.

 

Thanks for the compliment Aaron. I wish I had the plates on the car so I could go out and start tuning the car under a bit of speed and power. Most likely, when I get to trying that, I'll be here asking more questions.

I don't know if it is "proper" to link to another site, but I'll try. There are several of us who have built using the rotary and MS. For anybody who is interested, this is a link to my build log:my rotary locost build

 

I personally don't like idle valves at all, as they can easily mask mechanical problems.

But if you wanted to run one and had no easy vacuum tap (such as a full independent manifold), I'd look into running a Cadillac idle control motor. It was used on basically every 4.1/4.5/4.9.

It's a stepper motor that opens and closes the throttle plate.

 

Thanks Aaron, I will have a flat section on the underside of my manifold as well. And thanks Peejay for the alternative solution. I don't have a TB or idle valve yet, so maybe can find a set for a good price.

 

I don't know if it proper either, but appreciate the link. Interesting how my engine mounts turned out very similar to yours, especially with the A shaped frames they're sitting on. Wish I had seen you site sooner, would've been less head scratching for me!