Ignition timing question
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More Turbo
Joined: Jun 2015
Posts: 578
Likes: 111
From: New Hampshire
Ignition timing question
1975 F250 Highboy, 360 engine 2 barrel, automatic tranny, bone stock with a freshly rebuilt top end, timing set and new dizzy.
Upon setting initial ignition timing(with vac advance unplugged) at the spec of 6 degrees BTDC
The truck doesn't seem to idle smooth enough, bogs down a bit on acceleration and a vac gauge shows steady vaccuum but on the low side around 16" at idle.
Bumping up the initial timing to 10+ Degrees BTDC, truck seems to run lots smoother with lots more pep, vac gauge reading 19" at idle; idle speed seems a bit high though(about 800 RPM vs 650) at this 10+ degree setting.
Am I ok to keep running the truck at this 10 degree+ timing stetting?
I have not noticed any pinging or detonation when shutting down.
Any other ill effects I should be aware of for running this modified ignition timing?
Thanks
Tbruz
Upon setting initial ignition timing(with vac advance unplugged) at the spec of 6 degrees BTDC
The truck doesn't seem to idle smooth enough, bogs down a bit on acceleration and a vac gauge shows steady vaccuum but on the low side around 16" at idle.
Bumping up the initial timing to 10+ Degrees BTDC, truck seems to run lots smoother with lots more pep, vac gauge reading 19" at idle; idle speed seems a bit high though(about 800 RPM vs 650) at this 10+ degree setting.
Am I ok to keep running the truck at this 10 degree+ timing stetting?
I have not noticed any pinging or detonation when shutting down.
Any other ill effects I should be aware of for running this modified ignition timing?
Thanks
Tbruz
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Run as much timing as she'll stand, at all times, under all conditions. That is, without ping or predetonation of course. It's a little more complicated than that though not much.
The crankshaft damper (where timing marks are stamped) has an outer steel ring this will often slip off clock when the rubber bond starts to rot. That makes the timing marks useless. Use of a vacuum gauge is a good way to check for overall initial timing because of that.
Most V8 like somewhere between 10 and 20 degrees of initial timing. Too much and the starter will kickback, especially when engine is warm. 12 to 14 is usually right in there as a good number.
Run it up to 3k to 4k with the vac advance disconnected and plugged. See to it that there is no more than 36 degrees or so of total timing, and just let the initial fall where it may. Might need to change the mechanical advance inside the distributor in order to get there, because "more than 10" is not what the factory had in mind.
The crankshaft damper (where timing marks are stamped) has an outer steel ring this will often slip off clock when the rubber bond starts to rot. That makes the timing marks useless. Use of a vacuum gauge is a good way to check for overall initial timing because of that.
Most V8 like somewhere between 10 and 20 degrees of initial timing. Too much and the starter will kickback, especially when engine is warm. 12 to 14 is usually right in there as a good number.
Run it up to 3k to 4k with the vac advance disconnected and plugged. See to it that there is no more than 36 degrees or so of total timing, and just let the initial fall where it may. Might need to change the mechanical advance inside the distributor in order to get there, because "more than 10" is not what the factory had in mind.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
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