wat is a manifold vacuum gauge for ? i saw one in my mates mum's bluebird and was unsure wat it would be there for.

It's just for fun.

Some say it is useful for watching fuel economy, that is if you watch the gauge and keep the vacuum as low as possible, you'll get better economy. But the same is true without a gauge if you just keep the throttle as light as possible without lugging the engine.

Others say it help you tell when the engine is not running correctly by having a gauge permanently hooked up. Then again you should be able to tell that there is a problem without a guauge, by the way it runs & drives.

Where it is useful is when there is a real problem, you'l want a professional gauge with a large face (diagnostic tool), so I say just keep it as part of your tools and use when necessary. Sometimes it will indicate the cause of unusual problems, like if a valve is sticking. Actually in several years of mechanic work, it rarely was needed. I wouldn't consider it a critical tool. A compression gauge and a vacuum gun are far more useful.

Yeah, it's a reverse boost guage

The higher the vaccuum, the better for economy. Ddgonzal is right about it being for fun. But if you are REALLY serious about getting every last kilometre out of a tank of petrol, go ahead and fit one. Most boost guages do vaccuum and boost, so on my turbo cars I also use them for economical driving, keep a turbo motor "off-boost" is a great way to get "Better than atmo" economy.

It's not unusual to get figures like:
6.5L / 100kms for CA18DET (my old stocker CA18DET)
7.0L / 100kms for an SR20DET (my dads's SR20DET @156RWkW trim)

My fat ass'ed N15 Pulsar with it's SR20DE gets about 11L/100kms.

I expect my worked CA will get a touch under 10L/100kms on the highway...thanks to 550cc injectors.

Chris

Quote:
ddgonzal
If i remember rightly, you keep the "vacuum" as HIGH as possible... or said another way, you keep manifold "pressure" as LOW as possible for good economy.
A vacuum guage works a treat on long hauls as it's something else to keep you amused along the way.

I ran one in my 1000 sedan with GX engine, you know, one of those little 1-1/4" jobs, & i managed to get over 50mpg on a trip to the ultralight fly-in at Holbrook one year [ i was looking to buy one, but now i want a Luscombe 8A, Circa late 30's to mid 60's] By driving on the guage i managed over 44mpg at an average speed of almost 72mph from Albury to Bendigo late one night. That was two-up with luggage for three days. I recomend them if you plan on long trips.

Whats the metric conversion for MPG? Bug***ed if i know,....or care,... i lust want to know how far my car will go on a quantity of fuel that i can easily visualise.
For our US friends, thats an Imperial gallon, which is 4.54609 litres [approx]

Isn't it about 1.6kms per mile, and if 1 gallon = 4.54609L.

Then your
50mpg = (100mi / 2 gallon) = (160km / 2 x 4.546) = (160km / 9.092 litres) = so we want to get the km part down to 100, so 10/16 of 9.092 litres = 5.68L / 100kms.

Not pretty..but welcome to my world of mathematics..

(454.6 / (MPG * 1.6) = L/100kms.

Chris

I never did understand this metric fuel consumption rubbish. I want it expressed as a simple distance to 1 unit of fuel figure. I got 1 gallon of fuel, how far can i drive before it runs out.
This rubbish of somethin point yadda yadda milk bottles of fuel to drive one hundred thousand metres just leaves me cold.
Gimme MPG any day, a real way to measure economy.