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NVSmith · 04-26-2012, 07:28 AM

-This may be old news to many of you and maybe won't work with most electronically controlled cars unless you have a computer hookup, but...
-Way, way, back in the days of distributors & coils & carburetors and such a mechanic taught me how to adjust the timing of a car by using a vacuum gauge. He pointed out that a timing light actually timed only one cylinder since it was hooked to just one plug wire.
-He ran a vacuum guage from the intake manifold, ran the engine at about 2k rpm and then adjusted the distributor until it read max vacuum. He would then back off about 2" Hg on the guage and lock down the distributor and remove the guage. For kicks, he would again hook up the timing light and show how far off factory specs he was.
-Now this trick was particularly useful since we lived at about 5k ft elevation.
-In the days of JC Whitney tools that allowed one to adjust the distributor while driving, on my trips from Reno to Las Vegas (450 miles; two stop signs and four traffic lights, no speed limit) I hooked a vacuum guage to the dashboard and played with various settings close to max vacuum. This leaned the engine out and my Dodge Slant Six gave fantastic mileage. One just had to remember to back off a couple of inches when slowing down or entering town.
-Of course I wasn't driving at 110 mph either. 65-70 or so was good enough.
-Four stroke reciprocating engine airplane pilots know about this and they also know that they have to watch EGT (exhaust gas temperature) lest they start burning valves.
-I havent the faintest idea how to go about doing something similar with an ECU but imagine that the O2 sensor(s) would play a major part.
-Comments?

04-26-2012, 07:28 AM	#1 (permalink)
NVSmith NVSmith Join Date: Apr 2012 Location: MacDill AFB, FL Posts: 10 Thanks: 3 Thanked 3 Times in 2 Posts	Timing by Vacuum -This may be old news to many of you and maybe won't work with most electronically controlled cars unless you have a computer hookup, but... -Way, way, back in the days of distributors & coils & carburetors and such a mechanic taught me how to adjust the timing of a car by using a vacuum gauge. He pointed out that a timing light actually timed only one cylinder since it was hooked to just one plug wire. -He ran a vacuum guage from the intake manifold, ran the engine at about 2k rpm and then adjusted the distributor until it read max vacuum. He would then back off about 2" Hg on the guage and lock down the distributor and remove the guage. For kicks, he would again hook up the timing light and show how far off factory specs he was. -Now this trick was particularly useful since we lived at about 5k ft elevation. -In the days of JC Whitney tools that allowed one to adjust the distributor while driving, on my trips from Reno to Las Vegas (450 miles; two stop signs and four traffic lights, no speed limit) I hooked a vacuum guage to the dashboard and played with various settings close to max vacuum. This leaned the engine out and my Dodge Slant Six gave fantastic mileage. One just had to remember to back off a couple of inches when slowing down or entering town. -Of course I wasn't driving at 110 mph either. 65-70 or so was good enough. -Four stroke reciprocating engine airplane pilots know about this and they also know that they have to watch EGT (exhaust gas temperature) lest they start burning valves. -I havent the faintest idea how to go about doing something similar with an ECU but imagine that the O2 sensor(s) would play a major part. -Comments?