I'm wondering if anyone is equipped with a vac gauge and could test something for me, i smashed my 2 dollar handheld gauge when trying to perform a test.

I would like to know what reading you get when accelerating from lets say, 20 to 50 kph with standard gentle driving.

one might say, thats like asking how long is a piece of string, but in reality the difference between 2 people performing this test on very different cars should actually be pretty minimal.

My car idles at 50kpa and full throttle is obviously around 100. Id say 70 or 75 kpa.

no thats no help I'm affraid, a particular throttle opening vacuum will be different for varying loads. I need to know what it is when accelerating normally, not at a particular throttle position.

Accelerating normally?

 

Go and buy yourself another vacuum gauge

i know it sounds like a stupid question, but the truth is, when i last did the test, there was not much difference between gentle acceleration, and hard acceleration. on the vac gauge.

Because load makes such a huge difference on a vacuum gauge it overrules current speed and throttle position by a-lot in the equation it is down somewhere about 5 or 10 hg i just can't remember which.

I can not access a new one, as i am in the jungle in the Philippines.

Its ok i think this answered my question

I love how I study my logs and give the answer but its "no help". Buy yourself another 5 dollar gauge and do your own tests if you don't believe the answer.

https://www.avs.org/AVS/files/ae/ae66e4af-9b98-47fb-b166-77d28a4bb3d2.pdf

I love how I study my logs and give the answer but its "no help". Buy yourself another 5 dollar gauge and do your own tests if you don't believe the answer.

 

For 5 dollars he could get 2 and a half gauges!

 

I'm confused at the point of this thread.

but little red, your figures are backwards to what I'm after.

If it idles at 50 kpa (15 hg) on a vacuum gauge. then under load it should be less than 15 hg, less than 50 kpa. less vacuum, higher static pressure yeh,

so maybe you are reading a manifold pressure gauge, which works differently, and reads the difference between pressure outside and pressure in the manifold.

Thats not the same as a positive vacuum gauge reading which tells me simply the amount of vacuum.

 

The point of the thread is i am trying to prove a point in another forum that accelerating brings the vacuum down significantly as any load, even a small load greatly changes the vacuum in the engine when the rpm is maintained.

i assure you there is sound logic in my question, perhaps I'm not asking the question clearly enough.

Can anyone tell me what their 4k pulls in terms of manifold vacuum (not pressure), when under about 25 percent throttle in 2nd gear.

it should be somewhere near 5-10 hg.

or are you turboed litle red?

NO, google units converted is wrong haha.

And your figures are sound my appologies!

no, i think you'r pdf table is wrong. sorry now I'm ʞ©$ɟing confused.

HG is used as a positive measurement increasing with pressure, and a vacuum gauge simply reads the same in negative, away under 0.

So your figures make sense, but the conversion to hg mercury is complex and that was my fault.

your table pdf shows inches of mercury going up with corresponding pascals going down... huh?

Edited March 12, 20179 yr by rebuilder86

You gotta remember that atmospheric is 101.3kpa absolute pressure approx.

 

Little red saying he is getting 50kpa absolute prrssure at idle is less than atmospheric prrssure of 101.3kpa.

 

Now if you start talking gauge pressure that assumes atmoapheric pressure is zero. So another way of writing 50kpa absolute pressure is -51.3 kpa gauge pressure.

 

It all depends where you assume the zero pressure value is.

Can't you just get another gauge from eBay? They're like 20 bucks