dillyman
Likes DAFs
Becky beautiful
Posts: 283
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Post by dillyman on Nov 12, 2008 17:06:24 GMT
I think it was Starrider when answering another query who mentions fitting a vacuum gauge.
1. Where does one get one?
2. What type does one get?
3. How does one fit it?
4. If mounted within car can one still use it for setting up things as recommended in handbook without the aid of a mate in the car? If so how?
5. What are the principles that lie behind its function?
6. Anything else that a silver haired old bloke like me ought to know about the thing?
Marcus H.
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spunkymonkey
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Currently waltzing Matilda
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Post by spunkymonkey on Nov 12, 2008 18:38:19 GMT
That's a good range of questions ;D so I'll start by agreeing with Starider's post elsewhere that they're a greatb addition to (just about any) car. Or toolbox, for that matter!
To take your specific questions in order:
1) Most car accessory shops will still stock them - they're still fairly popular with the "styling" freaks who want every gauge going. A quick Google search for "car vacuum gauge" will throw up a fair few online suppliers - expect to pay around £20 for one suitable for dash mounting. They also come up on EBay pretty often.
2) Pretty well any that takes your fancy. Unlike pressure gauges, where the range can vary, vacuum ones tend to all read from 0 to "perfect vacuum" (0 bar pressure) so it's really a matter of taste what dial size / colour and so on you want.
3) You can cut a hole in your dash (if you really want!) or fit in an under / over - dash panel or pod. Panels and pods should be available through whoever you get the gauge from.
4) The simple answer to this is not really. With one mounted in a pod on the dash, you could probably turn the pod to be visible while you're under the bonnet but really for tuning work you're likely to want a bigger dial than you'll want as a driving gauge. Servicing dials tend to be around 3" diameter, and that's a big dial to add to your dash!!
In terms of plumbing it in, it will need a single small-bore vacuum tube (not as heavy as the transmission ones!) running from a t-junction in one of the vacuum lines (the one from the carb is probably best) to the gauge. If you get a gauge with back-light you'll also want a wire from your instrument lighting to the gauge, and an earth from the gauge to the body, so it lights up at night.
5) How they work (with some serious simplifications of a few principles before anyone comments!):
For a given engine speed there will be a certain amount of power produced burning fuel which exactly equals the power used. If there's more power, the engine will speed up; if there's less power the engine will slow down. On the road, engine speed is directly related to road speed (once you're in highest ratio). So, for given conditions, your road speed is directly related to the amount of power the engine is producing.
The amount of fuel burned is also directly related to the amount of air sucked into the engine because the carburettor is designed to keep the air / fuel ratio (by mass) constant. So, less air = less fuel
As you close the throttle, you reduce the amount of air. This creates a partial vacuum and also reduces the amount of fuel supplied. The vacuum increases as you allow less air in and less air means less fuel will be supplied by the carburettor to keep the mixture right
So, for any given speed (ie: total power output), the highest vacuum reading indicates the highest efficiency (ie: lowest use of fuel for that amount of power).
Joe
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Post by starider on Nov 14, 2008 0:36:52 GMT
Hi,ref.purchase of vacuum gauge,Europa UK should be able to supply a v.gauge and also a 50mm mounting bracket.I fitted mine under the dash in the centre and is easy to see it in this position.The connection in the engine compartment requiries a tee- piece which has the bar of the tee the same inside diameter as the bottom vacuum hose on the three way valve[ at the rear of the carb.]The leg of the tee needs to be the same diameter as the pipe supplied with the vacuum gauge. Cut the vacuum pipe about 2" from the three way valve and fit the tee-piece,then run the pipe through the bulkhead and fit to the gauge.If a restictor is supplied with the gauge, you need to fit it, otherwise the excessive vacuum on acceleration will make the needle vibrate and rattle.If there is not a restrictor in the kit you can tie a knot in the pipe and by how much you tighten the knot you restrict the amount of vacuum acting on the gauge to prevent problems with the needle.If anyone needs to know how to set up the three way valve,post the question on this posting,I have set up these valves literally hundreds of times.The only accurate way to set the valve is on a quiet road!![may sound strange but thats how I was taught by DAF Service Engineers].Different of course on 55/66 better using a rev.counter. starider.
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daf44
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Post by daf44 on Nov 14, 2008 10:26:30 GMT
hi there.
sound good to me john. using the one t-piece is what i used to do on my beach buggy.
I did not tie a knot in the pipe like starider though. the vibration used to undo it fairly quickly. I warmed the tip of the plastic t-piece that was connected to the vacuum guage and crimped the end 3mm totally shut. then i pushed a hot pin through to open a tiny hole and refitted the pipe. Instant restrictor, steady needle on the vacuum guage.
I found that if i drove the buggy using the vacuum guage i could save up to 20% on fuel. well worth fitting.
happy motoring
paul44
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Post by starider on Nov 15, 2008 1:20:29 GMT
Hi,just ensure you fit the "T" piece in the bottom hose of the three way valve.I agree that the pin hole method is fine, but my "T" piece is metal so the knotted pipe works fine for me and does stay tight.As I said previously adjusting the valve by setting by driving is the most accurate. starider.
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dillyman
Likes DAFs
Becky beautiful
Posts: 283
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Post by dillyman on Nov 18, 2008 17:46:38 GMT
Thanks guys for all your help. I shall see what I can do soon.
Marcus
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