As it seems the BAC valve is responsible for maintaining idle speed, what can I expect from removing the thing, and blocking off the spot it once occupied on the UIM?

your car may stall out when you turn the steering wheel when it is parked.

or turn on the defroster

So basically, I should leave it there until I install a standalone?

standalone doesnt change the need for an IAC of some sort, unless you don't mind setting a relatively high idle and letting it fluctuate under the varying loads. (this is basically how my car is configured currently, but I am thinking about adding an IAC so I can setup fastidle @ cold start and at that point I might as well just use it for regular idle control too)



standalones support controlling an IAC, the haltechs support the BACV natively.

there is also no Horsepower performance gains of removing your emissions solenoids and lines.

It helped my car run better. I removed everything at one time. It really made the car feel better. Not a HP gain, but it was smoother. My car idles where it wants to now. But if I really wanted to, I could get it below 1500, but why would i do that.



The car wont stall out if you dont have power steering https://www.nopistons.com/forums/pub...#>/biggrin.png

i doin't understand why people go out of their ways to remove things that make the car less user friendly. THey are there for a reason.

I'm definitely not one of those people. The reason I'm asking this question is that I have removed the stock TID and turbo bypass valve and replaced them with a custom made TID and a Turbo XS type H34 respectively. Since the BACV draws air from the same fitting where the H34 is, I didn't want to add nipples where I didn't absolutely have to.

so u would rather remove the BAC, reroute the cooling lines? live with high idle instead of drilling a hole in your custom made inlet duct and epoxying a nipple on?

Nope! I be epoxy-ing!

Just wanted to make sure I had to, that's all.

I like my 750 RPM idle!

The reason why some people(if not most) remove those things that make the car "user friendly" are because those same things make the car not "mechanic friendly" as far as I'm concerned. When you are building an engine that isn't intended to be daily driven..and is directed more towards racing, you don't want all that emissions crap in your way everytime you have to pull something off, or replace the motor. It makes for a very clean engine bay, easy motor pulls, and as time goes on, it's one less thing that can break and have you wondering whats wrong w/ your car..the less you have under the hood, the less that can go wrong. Now, I'm not trying to tell everybody to run outside right now and rip their emissions off..it doesnt make sense to if your using your car as a fun weekend ride or daily driver...but from a racing point of view..emissions suck.

I agree with that but anyone in that type of application I think is silly to be using a stock EFI computer for that very reason. The whole system is designed to run stock with all those components there. To 'delete' the components is just a bandaid to the real problem.



And what's so complex about a BACV anyways? https://www.nopistons.com/forums/pub...DIR#>/wink.png

fair enough... so how many people race their cars more then 50% of the time legitamently?



The motorsports forum on nopistons.com doesn't get too much traffic.

My T2 is one of six cars (okay, four running cars, a running truck, and a parts T2) that my wife and I own. The T2 gets driven to and from the strip, and around the neighborhood every weekend or two just to keep rigor mortis from setting in. This cars sole purpose is to get down the strip in a hurry. We've put less than a thousand miles on it since we got it two years ago.

Getting rid of all of that **** makes working on the car so much easier. When the AE was together, I could remove the TB/UIM in less than 5 min. And like Rotaryman said it is one less thing to break.

True enough, but as with all things, there is a point at which one should stop. Sex with a hooker is okay once in a while, but you don't want her to move in...

LOL. I like the analogy, and I agree 100%

I would also rid my engine of all of the emissions equipment, but the BACV is not for emissions. It doesn't require any special concern when building an engine. I will put one on everyone of my vehicles race or daily driver. The purpose of the BACV or IACV (Bypass air concrol valve or Idle air control valve) is to take filtered air and move it directly to the combustion chamber bypassing the turbo, piping, intercooler, throttle body and upper manifold.



The result is imediate air to the engine when its starving to breathe. This would occur in low idle, high load situations. Such as A/C on at idle, power steering at low speeds, braking hard at low speeds, etc...



I would run it! It does nothing but help the engine and keep it at a certain idle speed. Whats not to like about it?



UsfDr

wrong, the purpose is to manage idle. It is implemented by adding a bypass of the throttle(s) that is controlled by the ECU.

What are you talking about. You might want to do some homework or something. The only thing wrong about my post is that on rx7's the BACV doesn't bypass the turbo, but thats besides the point. Everything else is accurate.



And yes the ECU does control the opening and closing of the BACV which I failed to mention but assumed it was common sense. and yes it does bypass the throttle body, but it bypasses the a lot of other items too. However, in general just bypassing the throttle body would be good enough to achieve the effect.



So yes it manages idle, as I stated. I was also stating how it does this to educate those who might want to take it off thinking its only for emissions and might hinder the engine in some way.



UsfDr

The BACV cannot lower the idle, its purpose again is to raise the idle under high load low rpm conditions. If you want to lower your idle turn the screw on the throttle body next to the throttle cable or TPS until you reach the desired idle speed. The only way the BACV will lower the idle is to shut off.



UsfDr

read your post, it has nothing to do with the turbo, intercooler, manifolds, any of the crap you mentioned other than the throttle body.



Thats what i'm correcting here, show me a car that has an idle air control circuit that bypasses the things you mentioned. They bypass the throttle, thats all it has to bypass to do it's job, for packaging reasons, this is usually done right on the TB with the circuit integrated into the throttle body casting itself on production vehicles. Some implementations bypass more than the throttle body, but I believe this is usually for other packaging reasons specific to the car, or costs.



What am I talking about? I'm talking about idle air control only needing to bypass the throttle to do it's job, and generally being implemented in this way.



I would especially like you to manifest an implementation that bypasses all you mention and leads ' directly to the combustion chamber ', thats an interesting statement considering most multicylinder engines will have runners leading to a plenum or individual throttles, so your idle air control only leads to one combustion chamber? what about the others? Perhaps now you see how it would not make sense to bypass the 'upper' manifold, as this is usually the plenum. Or maybe you think there are multiple IAC circuits, one per combustion chamber? right...



your statement didnt make sense to me, you're welcome to clarify if you think it should have.

First of all if your talking about a 3rd gen RX7 then yes the ACV is right under the throttle body just as it is on a 20B. However on a 2nd gen RX7 the BACV is mounted on the lower intake manifold meet and moves air straight from the intercooler to the lower intake manifold. Thereby bypassing some piping, the rest of the intercooler, the throttle body and most of the upper intake manifold.

well ok so its mounted where the upper and lower intakes meet





UsfDr

you asked for it, heres my homework:



http://pengaru.com/~swivel/duh/iac1.jpg



http://pengaru.com/~swivel/duh/iac2.jpg



how many more references do you want me to come up with that do not mention bypassing anything other than throttle with regards to idle control?

Ok dude, read my post. I've stated that bypassing the throttle body is what you would need to achieve the desired effect. I understand that all you have to do is bypass the throttle body, however look at the picture of the 2nd gen.

The 2nd gen does exactly what I said and I dont have to manifest it Mazda already did. You must be getting hung up on my choice of words using combustion chamber. I should of just said Lower intake manifold. Don't just regurgitate words, try and understand them. The qoute you posted says that the air bypasses a closed throttle. That doesn't mean that it has to bypass it right at the throttle body. Air just has to get to the combustion chamber without going through the throttle. My picture of the 2nd gen clearly demonstrates this which you thought was non existent.



What you are failing to understand is that the only way the IAC can lower the idle is if its already open and letting air get in. Once its off idle is controlled by the mechanical setting. In other words if you have mechanically set the idle to 800 RPM while the IAC is offthe IAC cannot lower the idle anymore.

What do you have to say for the fact that the 2nd gen doesn't have the IAC on or near the throttle body (relatively speaking)?

Peng and UsfDr:

It's clear to me how the IAC (or BACV) thing works. Clearly, what the bypass air needs to get around is the throttle, regardless of what else is bypassed and regardless of the device's physical location on the engine. I think you guys are basically saying the same thing, just in a different way with an emphasis on two different aspects of this particular IAC.



BTW, the BACV will remain on my car!



Thanks for all the info! Feel free to carry on this discussion. https://www.nopistons.com/forums/pub...IR#>/bigok.gif

Good, I think you will like keeping it on the car. It does make a big difference.



UsfDr

Do you have to have the coolant routed through the BACV/TB for it to do it's job?

Yes.