Just a quick recap for vacuum assisted driving habit management. Below elaboration solely based on my personal experience and my usual reading in inches/mercury suction(in/hg). For example, if your vacuum reading is 20in/hg, you put your airintake pipe in a pale of mercury, it will suck up 20inches of mercury. Bear in mind, vacuum meaning suction, suction means negative(pressure is positive), so vacuum reading is TERBALIK. Smaller number means UP, greater number means DOWN. 0 vacuum meaning no suction,no pressure.

Idling-engine speed between 800-1000rpm
For Campor engine IAFM. Usual reading without aircon compressor, vacuum should stay between 17-19(more the better). Reading within this region read as the whole engine system is tightly sealed. Safe to assume engine is running on its full potential. Some older model EFI & carbureted engines allowed user to fine tune throttle idling position. Experienced magician normally able to tune the engine idling RPM at 800-1000rpm whilst vacuum reading stay below 20in/hg(below meaning 21,22,23 and so forth). With a vacuum reading on hand, you can withness the powerful SANDEN aircon compressor kick in, straightaway it chew off 4-7 inches of vacuum. Meaning that, the aircon compressor is heavy and took away 1/3 of the engine torque. Normal idling with aircon compressor, reading should be 13-15in/hg. Cold start not applicable.

Usual driving
When you're over taking, you slam on the gas pedal. Vacuum point at 0. Once you release gas pedal, torque will channel back from wheels to your engine, piston pull down hard and your vacuum reading become lower again(higher). When vacuum point at 0 meaning no restriction(lots of air going inside), also meaning petrol pouring inside combustian chamber! For picking up speed, I recommend to maintain vacuum below 10(11,12,13...etc). Do this more often, you'll soon realize no point going full throttle. Those cars that everyday annoys you, that makes you go full throttle to ditch them, you can still dtich them with vacuum pointing at 10.

up hill
When going up hill, even you did not increase throttle, but your vacuum pointer will start travelling up(9,8,7,6...).  This means you need more fuel to burn, in order to achive same speed. For manual transmission, when vacuum pointer go above 5(4,3,2,1,0) meaning your at the wrong gear. Please down shift. Sometimes you'll be surprise higher RPM does not mean you're consuming more petrol. The correct power transmit from engine to wheel is more crucial. That's why gearbox official term is TRANSMISSION.

down hill
Wheels is spinning faster than engine, you will get all sort of error in reading vacuum. Most of the time during down hill, your vacuum reading stay below 23(24,25). When vacuum reading stay below 26, also mean the combustian chamber burning lean. Lean burning can raise temparature up to 800'c. Despite your sensor reading as normal 400'c at the catcon, you wouldn't know what kind of harm done to your head gasket. Often I heard people going Genting come back with a wreck engine despite radiator didn't boil, there's a good chance that the head gasket was burnt during downhill due to ultra heat developed by lean burning. Manual transmission can opt of lower speed downhill. Or declutched at idling RPM. Auto/CVT, I have no experience, you'll have to figure it out.


A side note from previous midnight run with lhwj. Luke cleverly assumed the vacuum reading as KM/L, on an average bassis driving consistently at 15in/hg can actually represent 15km/l on an averaging bassis. The previous MRR2 midnight runs yielded Luke 20.5km/l, whereas I managed to clocked 16km/l kinda phenomenon FC on a BLM SE. Credit goes to Luke & his lovely BLM SE


Like it or not, vacuum reading is utmost important in our daily driving, and its the only thing that globally omitted without even realizing its importance. There are more technical knowledge in vacuum reading, which is too long story to cover. I will try to explain it in future.