Replacement Battery?

[gbs55]

My E36 has a BMW battery. I live about 80 miles from a dealer. What aftermarket battery will be the best, when the time come?

Barron

 

[gbs55]

Muffler Butterfly valve?

The valve that opens and closes in the end of the muffler, why and when does it work? Would we get more power and sound if we remove the vaccum hose, so it would stay open? How do you test it?
Barron

 

[Big Daddy]

Any quality battery is acceptable just make sure it has the proper venting. As for a "valve" at the end of the muffler, I have no idea what you are talking about?

 

[gbs55]

On my 96 328IS , on my stock muffler there is two short tail pipes. One has a butterfly flap. A vacuum line runs to the vaccum valve that operates it. It open when the car not running. Closes when cranked.

 

[chief]

I believe the flap you refer to is closed to increase torque. It opens at highway speeds or when cruising.
As for the battery: I installed an Optima (yellow top) in mine and it is doing what it is supposed to do. Provide strong voltage for starts.

 

[jrt67ss350]

I believe the flap you refer to is closed to increase torque. It opens at highway speeds or when cruising.

That's pretty much right. That valve closes when the intake manifold vacuum is high. High vacuum occurs under light and partial throttle. Having the valve closed under light and partial throttle increases exhaust system backpressure, which results in increased torque. When you give a large amount of throttle or wide open throttle, the manifold vacuum falls, and this valve should then open to reduce backpressure and result in quicker revving and increased power output at higher RPMs. Depending on the valve's calibration, it probably doesn't open at highway cruising speeds as this will usually be a high manifold vacuum state due to increased RPMs and low throttle.

Removing the vacuum line may give you slightly more sound, but in all reality, it isn't going to increase your power unless it isn't working right. Remember that exhaust backpressure is good to some extent for building torque, particularly at low RPMs.

 

[Kirby]

I agree completely with what Justin is saying about vacuum, backpressure & torque. But I think BMW wasn't quite that sophisticated in their goals, at least according to the Bentley manual. As I recall, Bentley claims that the valve is closed below ~2000 RPM and opens by ~2500 rpm. They indicate that the goal is noise reduction at low speed (cruising the hood, lol) and freer breathing at highway speed.