Hey there folks.Need to know how strong the vacuum is on a 1.3spi (136) engine.Apparantly I need 6 inches of mercury vacuum whatever that means!!??Also where would this vacuum come from? Would it be the little hose that clips under the air filter housing?Thanks

You would get a vacuum effect from the inlet manifold. If you trace the hose from the front of the brake servo to the inlet manifold, that's where the brake servo gets it's vacuum from. From what I can tell 6" mercury is equivalent to around 3 PSI.

anewman is right, Vacuum in %, torr, mm Mercury, psi and kPa if you have a nipple off it you can connect a vacuum gauge to that to check, even a boost gauge with -ve would do for a temporary check.

Don't really want to you the brake servo's vacuum supply tbh unless there is a seperate feed from there besides the brake servo.

If I can't get the required pressure from the inlet manifold it isn't a big problem. I can work round it!

Thanks

Em, you do know that manifold depression is a variable with throttle setting and enginre revs (can't remember if it's direct or inverse with revs, but it's inverse with throttle)?

Yes I know its variable.

The stated pressure that I need is during acceleration I forgot to mention so obviously won't be at that value when idling etc.

Thanks

Under hard acceleration it can get under 2PSI from atmospheric to manifold, and that's inculding the loss in the filter assembly. You'd really need to fit a vacumn gauge to check it, and there's no way of doing that properly without drilling and tapping the manifold for the take-off.

Vacuum is a very important thing, it can tell you most anything about your engine

first of the felicia i have is a carburator felicia 1.3 the GLX, its normal vacuum reading is of 24 inches of mercury

please read this page and click on the senarios > How to Use and Interpret a Vacuum Gauge

you have to have a vacuum gauge that goes up to or higher than 30 inches of mercury.

if your valves are a little dirty the needle will wiggle just a tiny bit,

you can accelerate the egine to 2000 rpm's and check vacuum reading, then let idle and check the reading, if vacuum reading are the same and the needle is not twiching your in good shape.

vacuum reading varies from engine to engine depending on bore piston travel etc.. and of course wear and tear, so trust your engine and let it tell you his vacuum, you can try several rpms to make sure, again vacuum is the same on all rpms if engines is in top notch shape.

google "vacuum reading" and you can learn how to diagnose most everything on your engine with that little tool,

another great thing you can do is mount a vacuum gauge on your instrument panel, like races have, and if you learn to accelerate while keeping the needle steady (without droping a lot) your going to save buckets of gas, i read that on one of the pages, looking for a gauge myself to do just that (gas is to expensive, better train that LED foot i have)

Edited 11 November, 200817 yr by Cepheuz
made it more practical for reading

Yes I know its variable.

The stated pressure that I need is during acceleration I forgot to mention so obviously won't be at that value when idling etc.

Thanks

vacuum reading during hard acceleration will fall to nearly "0" then climb back to normal

during soft acceleration vacuum reading will fall up to 4 inches of mercury and then climb back to normal

durrina an acceleration followed by a release vacuum will drop, then climb higher that normal and afterward slowly settle into normal reading

to correctly read the vacuum choose the closest vacuum hose to the plenum (thats where the manifold joins from all the pistons) i detach the hose that goes to the air conditioner acceleration switch on mine, you can also tap the hose that comes from the manifold to the engine

Reading this thread reminded me of my old 100 E Fords where the wipers ran of vacuum from the manifold, later ones had an additional reserve tank but didn't make any difference. Anything approaching hard acceleration and the wipers would stop dead. Wiper boxes and motor from a mini was the normal swap, I used same from a Rover 3500 so you could have variable intemitment..

Apologies for off topic meanderings :(

Reading this thread reminded me of my old 100 E Fords where the wipers ran of vacuum from the manifold, later ones had an additional reserve tank but didn't make any difference. Anything approaching hard acceleration and the wipers would stop dead. Wiper boxes and motor from a mini was the normal swap, I used same from a Rover 3500 so you could have variable intemitment..

Apologies for off topic meanderings :(

Not that o/t; where did you think I got the point about the variable depression from originally?

Vacuum is a very important thing, it can tell you most anything about your engine

first of the felicia i have is a carburator felicia 1.3 the GLX, its normal vacuum reading is of 24 inches of mercury

i would like to apologize for the wrong information, the correct vacuum for a skoda felicia is not 24 inches of mercury, if you advance the timing on you felicia you will get this amount of vacuum, but, correct vacuum on the correct timing mark for spark is about from 18 to 22, depending on your engines health, anything below 15 is considered a faulty engine (this is at idle wich should be measured from 700rpm to 1200rpm) also a load condition will reduce the vacuum while a rich condition will increase it