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Old 06-15-2009, 06:14 AM   #1 (permalink)
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Vacuum pump basics

There is some talk here and there about vacuum pumps, gauges, lines, etc., but it's all in bits and pieces. I'd like to have as much info as possible in one place. Not only for myself, but for anyone who knows as much as I do, or even less. I know the answers to some of the questions below, but I state them anyway.
I'd like to know:
  • What the vacuum in an engine is for,
  • Is it the same for gas and for diesel,
  • How strong should it be,
  • What kind of pump is better - belt driven or electric,
  • What does a vacuum gauge measure and how does this help me,
  • What (and how) should be tweaked/changed for better engine operation,
  • Will this help FE and why...

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Old 06-15-2009, 07:45 AM   #2 (permalink)
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* What the vacuum in an engine is for,
To provide assistance to the braking system. It reduces the amount of effort to stop the car

* Is it the same for gas and for diesel,
No. Diesel engines have no throttle plate and therefore have no vacumn in the intake system. Brake assist is then done by a vacumn pump. Mine runs off the camshaft from what i can see. It's in the same position as the distributor in the honda civic.

* How strong should it be,
Not sure. Someone else may chip in with that.

* What kind of pump is better - belt driven or electric,
Direct drive to the engine would be safest but.... Ideally electric as there will be no belt losses incurred in driving the pump. Better control can be had over the pump if it's electric. You could combine it with a vacumn resevoir and pressure switch to switch it off when not needed. Good savings to be had while on the open road there!

* What does a vacuum gauge measure and how does this help me,
In a gasoline engine, it is a measure of how much throttle you are giving and how much load is on the engine. (i think!?) How it helps is by giving you feedback as to how hard you are on the throttle and can therefore ease off a little on the uphills and generally drive with as much vacumn as possible. I'm open to corrections here!

* What (and how) should be tweaked/changed for better engine operation,
Not sure what in particular you mean there Piwo. If it's vacumn then as i said above: Electric vac pump with resevoir and pressure switch to cut out unnecessary use.

* Will this help FE and why...
Should help a bit. Less work for the engine. Stick a solar panel on somewhere and you may drive it for next to nothing. If only solar panels were cheaper...

Hope this is of some help. If anyone wants to modify this then fire away.

ollie
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Old 06-15-2009, 08:39 AM   #3 (permalink)
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WOW!!!
Thanks Ollie. Just what I wanted
I quickly googled for electric vacuum pumps on the local market, but nothing seems to be from the automotive branch, mostly industrial pumps, 11kW and more Keep looking...
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e·co·mod·ding: the art of turning vehicles into what they should be

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Old 06-19-2009, 08:40 PM   #4 (permalink)
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The vacuum in the intake is caused by the throttle plate restricting the flow of air into the intake, while the engine is sucking from the other end of the intake. It can be used to do work (e.g., brake booster) but that is IMHO secondary. (Some smart engineer decided it was "free power".)

A vacuum gauge may be useful for getting fuel economy in that it can tell you (more or less) how much air is going into the engine. It gives you more precise feedback than you trying to figure out how far your foot is pressed down and how fast the engine is spinning.

A vacuum pump can be useful in a car that does not have vacuum-operated systems. In a number of high-powered engines, a vacuum pump is used to draw out some of the air from inside the crankcase of the engine. That means there is less air in there for the "back side" of the pistons (and for the crank and rods and such) to push around, which means that more of the engine's power can be used to move the car.

The same theory would say that it would require less fuel to move the car as well, since less of the work the fuel is doing is needed to push that "inside air" around. My feeling is that any gains from that will be too small to repeatably measure when you talk about the power levels that are used for steady-state cruising.

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Old 10-04-2009, 02:17 AM   #5 (permalink)
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Returning to thread...
Instead of buy a totally new electric vacuum pump, would converting the belt-driven pump to electric work? Would it be enough to take the belt off and attach an electric motor to it? If so, any ideas as to (1) how powerful the electric motor should be, (2) what rpm is best? I'm thinking that since the engine idles at 750-800rpm, the pump could be spun at no more than 1000rpm and still do its job.

The upside of this is that it could be wired to: (a) work when engine off coasting, and (b) slow down when there is enough vacuum in the system, reducing the load on the electrics.
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Old 10-05-2009, 08:23 AM   #6 (permalink)
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Some diesel engines (Toyota for one) have an alternator (belt driven as usual) with a vacuum pump attached to the back of it.
This provides a source of vacuum for brakes etc as a diesel engine provides none as already explained above.
This may help with your "vacuum-with-engine-off" idea.
Another option is to fit a vacuum reserve chamber as a short term vacuum supply which can be replenished after the engine is again running.

A normal car engine in good condition will provide vacuum equal to about 17 to 21 inches of mercury , normally expressed as in/Hg.

Apart from the uses already mentioned by Ollie a vac gauge can help identify and diagnose engine problems like mismatched carbs , timing not set correctly , worn rings and valves , air leaks and other items.
Google for what these readings look like with the gauge attached.

Pete.
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Old 09-17-2010, 02:06 AM   #7 (permalink)
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back from the dead thread.. I have a 1980 VW Rabbit Diesel.

I have tossed around the idea of an electric vacuum pump since mine barely does anything anyways so I have manual brakes all the time.

I was searching for vacuum pumps and ran across a few for hot rodders and what not at summit and jegs for $200 and up. This is not in my price range. I work at an auto parts place and have ran across this: vacuum pump off a 99-07 Ford F-350. They have these for the accessories on the truck but I wonder if it will work hard enough to run the brake booster and reservoir.

i would have posted a link, but my post count is too low.

A lot cheaper than summit, that's for sure.
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Old 09-17-2010, 03:25 AM   #8 (permalink)
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Welcome to EM, erice1984

I believe that electric vacuum pumps in trucks are meant to help the primary vacuum system, not as a stand alone source of vacuum. On the other hand, if it's powerful enough, then it might be worth a try.

Remember that just slapping an electric pump on won't help you much, since it'll be a constant load on the alternator. What you want is a reservoir (3-5 liter volume should be enough) and some way to switch the pump on only when pressure gets too low.

Quote:
Originally Posted by erice1984 View Post
i would have posted a link, but my post count is too low.
I found this for US $77.95: 2007 07 Ford F250 F350 Truck Diesel Vacuum Pump NEW - eBay
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e·co·mod·ding: the art of turning vehicles into what they should be

What matters is where you're going, not how fast.

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Old 09-17-2010, 12:32 PM   #9 (permalink)
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Info on Manifold vacuum - Wikipedia, the free encyclopedia

What kind of pump is better - belt driven or electric?
Depends on what you are using it for. For brakes electric, to apply a vacuum to the crank case belt driven.

A vacuum pump on the crank case removes the air spring in the motor and tightens piston ring seal while helping reduce/eliminate blow by. The amount of vacuum you would want to run is around 10-15"Hg
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Old 09-17-2010, 03:44 PM   #10 (permalink)
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...consider using a clutch-assembly from an airconditioning pump on the vacuum pump to allow you to electrically "control" when it's on & off.

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