Vacuum meter, wierd readings on 1.3l swift/barina

[bobo333]

Hi guys,

i just finished installed a Speco boost/vacuum gauge onto my 1993 Holden Barina (Suzuki Swift) after trying a few different places to tap the t piece in to the vac lines ive ended up with it here:


it seems to be hooked up ok. When i accelerate it goes up, the further down i push the accelerator pedal the closer to 0 it gets, and when decelerating it goes to around -25. But when idling it stays at -20, ive read it should be around -12 when idling, is this a problem with the gauge or my engine?

heres another couple of pics of the install for those interested:




thanks

[JellyBeanDriver]

Sounds fine. Your engine vacuum should be relatively high at idle and for our cars that sounds okay, maybe even a bit low.

For my 1.0L that would be a great number.

[bobo333]

thanks Jelly

is a bit low a bad thing? is there anything i should look at to get it up higher?

also what should i be aiming for while driving? is keeping the number as high as possible while driving best for economy? or is there a number i should aim for during acceleration/cruising etc?

[JellyBeanDriver]

No necessarily bad. My memory is from V8's with vacuum in the high 20's (like 28) but I hear this is normal for our cars.

You want to keep the vacuum as high as possible and still maintain safe driving. There is no target.

[bobo333]

ok thanks a lot, im just about to refill the tank so hopefully i can get a good idea of how much better im driving with the vac gauge next tank (although adding the grill block at the same time will affect the readings too, damn my old school carby car and its lack of instant mpg feedback! lol)

[Ecky]

Low vacuum = high load, high vacuum = low load.

High load obviously consumes more fuel but it's also more efficient, low load saves fuel but is less efficient.

The idea behind pulse and glide is to run the engine at high load (low vacuum) for an acceleration "pulse", and then put it in neutral and let it idle while you coast for a while.

[user removed]

20 is probably good for a 3 cylinder. You could try reducing the idle speed some and see if it goes up any.

No way you will see 28 inches at idle, not enough atmosphere to create combustion.

Higher compression, more cylinders, lower idle speed, as well as highest atmospheric pressure will give you highest readings at idle speed.

Best acceleration efficiency will probably be at 1-2 inches.

regards
Mech

[bobo333]

thanks guys,

its actually a 1.3L 4 cylinder, and i live pretty much on sea level, most of my driving would be under 1000ft id say

so i should accelerate at 1-2in then coat as close to 20 (idle) as i can? where should i be shifting gears? the last tank i shifted around 2000rpm but the vacuum guage shows the vacuum increasing at around 3000 with a constant throttle level, is this where i should be changing gears to get it back up to 1-2in until im at the speed i want to be at?

[rollercoaster]

My 4.3 V6 does about -19 "/hg. The higher the better at idle.

You should tap directly to the manifold for real time readings and to avoid interference from using existing vacuum lines.

Here is a general guide:

Vacuum Guide for Engine Conditions

[allenh318]

Rollercoaster,

Is your 4.3 a GM? My 4.3 TBI idles at 19-20, and it has 115,000 miles on it. Always wondered if it was the correct vacuum for it at idle.