Did anyone use this method? Ill try this on my 248 straight 8 with good results. According to the manual it should be 4-degree btc and with this number the vacuum reading was a steady 14 hg. I advance the timing and reach the top limit at 22 hg and then back down to a steady 20 hg. The engine runs smoother then ever before and absolutely no sign of detonation when test driving uphill and no hard start. The compression on these engines is like 6:1 and with todays fuel (95 octane) compared to the 70-75 octanes on the late forties it seams logical to use a little higher advance or am I asking for trouble here? What you think?
It sounds like your motor likes it at 20Hg/in. The condition of the motor, if it was rebuilt, has better made parts, better ring sealing and machine tolerances better than originally mfg. Too many variables like higher rpm at idle, cam type and timing, compression ratio, oil type (SYN) and iginition parts. Drive like you stole it.
been using it for years especially since the decline in gasoline quality. Way back when (early as mid 70s) used it as confirmation in conjunction w/ timing light...still do. BTW, also handy in adjusting carbs.
Can you shed some more light on the details of 'the procedure'? Do you find highest vacuum reading, and then back off by two or to a steady reading? At idle? Something else?
Yes, youre right. I advance the timing for the highest vacuum at normal idle (400 rpm) and then back off 2 hg/inch. The idle will pick up, so you'll have to back it down so the centrifugal weights in the dist dont interfere. Test drive your car and listen for any ping under light acceleration as well as under heavy acceleration and back off if needed.
I use this method on every car that I have. When finished, you can put a timing light on it and see where it is at. Nine times out of ten, it will be dead on where it should be. Robert
When you set the timing with a vacuum gauge, do you disconnect the vacuum advance like you do with a timing light?
attach vacuum gauge to the intake manifold after it has reached proper operating temp. loosen the dizzy, with the car at idle, everything attached, trun the dizzy to atain the highest steady vacuum reading. depending on your cam shoud be between 15 to 21 inches of vacuum. Once the highest steady state vacuum is reached, tighten the dizzy, the re adjust idle speed as necessary. If you can not attain a steady vacuum reading you got other problems that need attending to. Check the secongchancegarage website for the section on what the vacuum gauge readings mean. If you can not conveniently attach the vacuum gauge to the intake, try attaching it to your power brake booster tube if so equipt. The vacuum wiper port is also a handy spot.