The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Help -- Old Fashioned engine tuning with vacuum gauge

mr48chev · 07-03-2018, 11:56 PM

On most older engines 16 to 18 inches of vacuum at an idle is considered Ideal. Some newer tight tolerance engines might pull a bit more but those generally fall into the computer controlled area anyhow or at least they were originally designed to be computer controlled.

The link that Nordic gave in post 3 is real good with one exception. The writer is ASSUMING that everyone reading it has an engine with a distributor that rotates the same way as the one he is describing. What he is describing is backwards for a Chevrolet engine.

Reading what he wrote here he is describing an engine with a distributor that turns counter clockwise rather than one that turns clockwise.
....4. Keep in mind when adjusting the timing, you have to turn the distributor clockwise to advance and counter-clockwise to retard.
Mr48Chev note: This works on a Ford V8 but is backwards for a Chevrolet V8.
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5. While watching the vacuum gauge, slowly turn the distributor clockwise (advance timing) and look for a maximum reading on the gauge. For instance, if the reading on your gauge peaks at 18 inches of vacuum, that is the maximum for your engine. (The normal range could be from a high of 20 inches to a low of 15 inches, depending on the internal condition of your motor). The reading will drop off if you advance too far, so turn the distributor counter-clockwise (retard timing) to go back to the peak reading on your gauge.

Outside of assuming that everyone reading it is working on a Ford V8 his info is good and moving the distributor to get max inches of vacuum and then backing off slightly should work and not ping. With cruddy gas you may have to back it off slightly more though. It may be a set it, go try it and adjust if needed deal.

A quick fiy, on any engine you aren't all that familiar with if you wrap your thumb around the vacuum advance and wrap your index finger around the distributor housing on the side the advance is on, your index finger will be pointing in the direction of distributor rotation.

07-03-2018, 11:56 PM	#9
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,284	Re: Help -- Old Fashioned engine tuning with vacuum gauge On most older engines 16 to 18 inches of vacuum at an idle is considered Ideal. Some newer tight tolerance engines might pull a bit more but those generally fall into the computer controlled area anyhow or at least they were originally designed to be computer controlled. The link that Nordic gave in post 3 is real good with one exception. The writer is ASSUMING that everyone reading it has an engine with a distributor that rotates the same way as the one he is describing. What he is describing is backwards for a Chevrolet engine. Reading what he wrote here he is describing an engine with a distributor that turns counter clockwise rather than one that turns clockwise. ....4. Keep in mind when adjusting the timing, you have to turn the distributor clockwise to advance and counter-clockwise to retard. Mr48Chev note: This works on a Ford V8 but is backwards for a Chevrolet V8. ___________________________________________________________________ 5. While watching the vacuum gauge, slowly turn the distributor clockwise (advance timing) and look for a maximum reading on the gauge. For instance, if the reading on your gauge peaks at 18 inches of vacuum, that is the maximum for your engine. (The normal range could be from a high of 20 inches to a low of 15 inches, depending on the internal condition of your motor). The reading will drop off if you advance too far, so turn the distributor counter-clockwise (retard timing) to go back to the peak reading on your gauge. Outside of assuming that everyone reading it is working on a Ford V8 his info is good and moving the distributor to get max inches of vacuum and then backing off slightly should work and not ping. With cruddy gas you may have to back it off slightly more though. It may be a set it, go try it and adjust if needed deal. A quick fiy, on any engine you aren't all that familiar with if you wrap your thumb around the vacuum advance and wrap your index finger around the distributor housing on the side the advance is on, your index finger will be pointing in the direction of distributor rotation. __________________ Founding member of the too many projects, too little time and money club. My ongoing truck projects: 48 Chev 3100 that will run a 292 Six. 71 GMC 2500 that is getting a Cad 500 transplant. 77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.