10 replies to this topic

[photographymatt]

Found this on ebay just
http://cgi.ebay.co.u...1QQcmdZViewItem

and was wondering...how would you fit it and how does it work? looks groovy to be honest.

[bloomers]

If its a brand new one, Or all parts are supplied for fitting, Then you cut the 52mm hole, then pop the guage in, and then there is like a 'U' shaped bit that fits on the back which pulls it tight at the front.
Easy job. hope this helps.

Ian

[dklawson]

That's a vacuum gauge. It connects to the intake manifold either by using tap into the manifold itself... or a barbed fitting on a carb spacer.

I cannot comment on this particular design of Smiths vacuum gauge, but in general the 90 degree sweep gauges of this type are less accurate "diaphragm" types. The more desirable vacuum gauges (from Smiths and others) have 270 degrees of sweep, have a scale calibrated in inches of mercury, and use a bourdon tube mechanism.

There's probably nothing wrong with this gauge and it will be accurate enough for the basic purpose that it's marked. However, you may want to at least write the seller to confirm the size. Something about this one makes it look larger than the standard 52mm diameter you're used to seeing in a Mini.

Personally, I think 20 GBP is a bit expensive for this gauge but to each his own. For comparison, go back to eBay and look at these gauges:
290234552821
270239674184
380031222953
270240533557
All are used, all have 270 degree sweep, and all have calibrated scales. The prices aren't bad at the moment but you never know how high things like this go for. I really like the last one, 270240533557.

[coyttl]

That's a vacuum gauge. It connects to the intake manifold either by using tap into the manifold itself... or a barbed fitting on a carb spacer.

Showing my ignorance.. I thought those vacuum gauges were for turbo'd / supercharged Minis? Could those be connected up to an injected model, or would a carb be needed (for the vacuum)?

Good luck getting the gauge, I'm odd enough that I like the colored ones.

[dklawson]

You are thinking of a Vacuum/Boost gauge. Those have a needle that rests on a center position (zero) and the needle moves clockwise or counterclockwise depending on whether the car is driving normally or under boost.

A regular vacuum gauge can be hooked up to any (normally aspirated, non-turbo) engine. The gauge will be measuring the manifold vacuum which is present regardless of whether you're talking about a carb or injected car.

[coyttl]

You are thinking of a Vacuum/Boost gauge. Those have a needle that rests on a center position (zero) and the needle moves clockwise or counterclockwise depending on whether the car is driving normally or under boost.

A regular vacuum gauge can be hooked up to any (normally aspirated, non-turbo) engine. The gauge will be measuring the manifold vacuum which is present regardless of whether you're talking about a carb or injected car.

Ah! Well, thanks for that! Learn something new from you guys every day. So then a gauge like would, effectively (but not too accurately or specifically) tell you your gas usage. (Simply, less vacuum, less gas being used, and vice-versa.)

Mike.

[dklawson]

So then a gauge like would, effectively (but not too accurately or specifically) tell you your gas usage. (Simply, less vacuum, less gas being used, and vice-versa.)

Actually... exactly the opposite.

When your throttle is closed the engine is drawing very hard against a closed throttle butterfly (high-vacuum, low airflow). When you floor the accelerator pedal the butterfly is wide open, the airflow is high, and there is almost no vacuum, but high gas consumption.

A vacuum gauge can be used as a driving instructor to help you get the most out of a gallon of gas. Generally, what I do is keep the car in a gear that allows me to drive with the highest vacuum reading possible. I also limit how hard I accelerate to keep the vacuum "up". Lastly, once you know the vacuum level at which your car idles, you can decide when it's best to push in the clutch and coast. On decel the vacuum can go much higher than the idle value due to the closed throttle and high engine revs. That's when I push in the clutch and coast for a bit.

[il-barba]

so engine breaking does not waste petrol?

[coyttl]

So then a gauge like would, effectively (but not too accurately or specifically) tell you your gas usage. (Simply, less vacuum, less gas being used, and vice-versa.)

Actually... exactly the opposite.

When your throttle is closed the engine is drawing very hard against a closed throttle butterfly (high-vacuum, low airflow). When you floor the accelerator pedal the butterfly is wide open, the airflow is high, and there is almost no vacuum, but high gas consumption.

A vacuum gauge can be used as a driving instructor to help you get the most out of a gallon of gas. Generally, what I do is keep the car in a gear that allows me to drive with the highest vacuum reading possible. I also limit how hard I accelerate to keep the vacuum "up". Lastly, once you know the vacuum level at which your car idles, you can decide when it's best to push in the clutch and coast. On decel the vacuum can go much higher than the idle value due to the closed throttle and high engine revs. That's when I push in the clutch and coast for a bit.

Well crackers. That makes perfect sense when described like that. I always thought it was the other way around. (I'm very basic on engines, but getting there!)

But then that leads to this question - would all Smiths gauges work? Wouldn't one engine (998) have different vacuum levels than a 1275?

[dklawson]

so engine breaking does not waste petrol?

That's not exactly what I said. You'll note that in my last post I stated (in different words) that when the vacuum reading on the gauge shows HIGHER vacuum than normal idle, I push in the clutch and coast. Anytime you see the vacuum reading higher than idle, you are decelerating. You may not be pulling in extra fuel from the higher vacuum because the gauge connection point is on the other side of the closed butterfly, HOWEVER... you are making the engine run at a higher speed than it needs to.

Coyttl, you asked if one engine would have a different vacuum displayed based on displacement. The answer to the displacement effect is: no.
There are a lot of factors that make one engine's vacuum reading different than another but displacement in not one of them. Changes in cams, timing, and carb settings will all affect the vacuum reading but not displacement.

We're getting way beyond the purpose of the original intent of this thread but at this point it's worth mentioning that you can also use vacuum gauges for troubleshooting, diagnostics, and tuning. I don't tune my Mini by vacuum but years ago I had a Toyota that I could tweak to get much higher gas mileage by vacuum tuning. For more info, see:
http://www.classictr...cts/vac/uum.htm
http://www.free-ed.n...p?iNum=01030305
and
http://www.centurype...ge-spg-148.html

[coyttl]

We're getting way beyond the purpose of the original intent of this thread but at this point it's worth mentioning that you can also use vacuum gauges for troubleshooting, diagnostics, and tuning. I don't tune my Mini by vacuum but years ago I had a Toyota that I could tweak to get much higher gas mileage by vacuum tuning. For more info, see:
http://www.classictr...cts/vac/uum.htm
http://www.free-ed.n...p?iNum=01030305
and
http://www.centurype...ge-spg-148.html

Thanks for the links and info. Looking through it all now.

I'll stop this hijack now, tho.