Throttle body sync question

[Fred H.]

Someone posted three different links to throttle body sync a while back, and I am trying to find them.

Specifically, one made mention of adding a certain amount of height to the mercury column based on your altitude. Does anyone have the link to that article?

I want to say it was something like add one inch for every 1K ft above sea level. Is that correct?

 

[Fred H.]

I think I may be able to answer my own question, here goes.

At sea level, pressure expressed in mercury height is 29.92 inches. At 1,000 ft it is 28.86 inches. At 2,000 it is 27.82. That means that the mercury pressure level changes roughly 1 inch for every 1,000 ft.

However, this assumes you are syncing your throttles on a day with "normal" outside air pressure. If you are under a high or low pressure cell it could throw off your measurements a bit, though I don't know if it would be enough to matter.

I think I just found another use for my Garmin 376C. I can get the current ambient pressure readings from it, and then determine how much to add to the 25 centimeter measurement mark. For instance, the current pressure is 1011 millibars, which converts to 29.854 inches of mercury. So 29.854 - 29.92 = .07 inches or .17 centimeters (not even enough to fool with). There currently is a high pressure cell parked over me, so if I were to sync my carbs right now, I could use the 25cm mark and be just about right on target. You could also easily get current pressure data for your home town off weather underground, or any similar weather site on the internet.

Hows that for being anal?

 

[RadioHowie]

I think I may be able to answer my own question, here goes.
At sea level, pressure expressed in mercury height is 29.92 inches. At 1,000 ft it is 28.86 inches. At 2,000 it is 27.82. That means that the mercury pressure level changes roughly 1 inch for every 1,000 ft.

However, this assumes you are syncing your throttles on a day with "normal" outside air pressure. If you are under a high or low pressure cell it could throw off your measurements a bit, though I don't know if it would be enough to matter.

I could be wrong...I have been before...but if I recall, it doesn't matter where the mercury in any single column is...it's just that you want all 4 columns to be the same. That's what sync'ing is all about...equally high or equally low.

Since the height in the column IS affected by altitude, pressure, RPM, engine vacuum, etc., the whole point of the throttle sync is sync.

 

[chiri1]

That is correct ! The idea is to make all four cylinders the same. Also, the book says to sync them with #3 cylinder. So the ideal way is to get the highest vacuum possible on #3 and then sync the others to it.

 

[Fred H.]

There is a note in the manual that the intake pressure should be 9.8 inches of mercury or 250mm (25 centimeters) or 33.3 kPa. Number three cylinder is supposed to be set to this value and then the other cylinders matched to it.

In reality, I am not sure how much of a difference it actually makes, but that it the way it is specified in the manual.

 

[bmwhd]

There is a note in the manual that the intake pressure should be 9.8 inches of mercury or 250mm (25 centimeters) or 33.3 kPa. Number three cylinder is supposed to be set to this value and then the other cylinders matched to it.
In reality, I am not sure how much of a difference it actually makes, but that it the way it is specified in the manual.

So Fred, when's the TBS party B)

My right mirror is driving me crazy. TBS is my last best chance at making it better.

 

[Fred H.]

There is a note in the manual that the intake pressure should be 9.8 inches of mercury or 250mm (25 centimeters) or 33.3 kPa. Number three cylinder is supposed to be set to this value and then the other cylinders matched to it.

In reality, I am not sure how much of a difference it actually makes, but that it the way it is specified in the manual.

So Fred, when's the TBS party B)

My right mirror is driving me crazy. TBS is my last best chance at making it better.

You just missed it. I am buttoning it back up now.

 

[GreyGoose]

There is a note in the manual that the intake pressure should be 9.8 inches of mercury or 250mm (25 centimeters) or 33.3 kPa. Number three cylinder is supposed to be set to this value and then the other cylinders matched to it.

In reality, I am not sure how much of a difference it actually makes, but that it the way it is specified in the manual.

So Fred, when's the TBS party B)

My right mirror is driving me crazy. TBS is my last best chance at making it better.

BMWHD,

Grab the right mirror (within the blue body) and turn it clockwise as far as you can. 80% of the vibration disappeared. I thought some other forum member reported that moving them the other way would take care of it. It had no effect on mine. When i tried to rotate them down, it made a huge improvement.

GreyGoose