460 ford timing
- Thread starter arebilly
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US Marine? I have the specs for an OMC Cobra Ford 460 if that helps....
using regular gas-->10*BTDC
using premium gas-->15*BTDC
ignition advance--> at 4600 rpm full centrifugal advance is 25*, so if you are using the 15* base timing, at 4600 your total should be 40*. If you want to check it at a lower rpm, at about 1500 rpm you should be at about 19*, at 2500 rpm approx about 20.5*, at 3,000 about 21*....use an advance timing light to check....
using regular gas-->10*BTDC
using premium gas-->15*BTDC
ignition advance--> at 4600 rpm full centrifugal advance is 25*, so if you are using the 15* base timing, at 4600 your total should be 40*. If you want to check it at a lower rpm, at about 1500 rpm you should be at about 19*, at 2500 rpm approx about 20.5*, at 3,000 about 21*....use an advance timing light to check....
Lou - I have 0 experience with Ford 460's , but just noting a quick search turns up a post on a performance boats site that suggests a starting point of 30-32* BTDC total ( initial + advance) timing at 3000 rpm. That's probably with "regular". If increasing timing , if there is any question of detonation/pinging, back it off.
These tune up specs for the 7.5L agree with your initial timing figures .
http://www.hors-bord-stern-drive-inbord-service.com/omc/omc-cobra-86-93-quick-references-data.pdf
But wouldn't the advance top out closer to 3000 or well under 4000, with total timing readings higher at 3000? Could your figure of 21* at 3000 really be advance, not total at that rpm? Just asking. It sounds like you have personal experience observing your figures and I surely do not.
These tune up specs for the 7.5L agree with your initial timing figures .
http://www.hors-bord-stern-drive-inbord-service.com/omc/omc-cobra-86-93-quick-references-data.pdf
But wouldn't the advance top out closer to 3000 or well under 4000, with total timing readings higher at 3000? Could your figure of 21* at 3000 really be advance, not total at that rpm? Just asking. It sounds like you have personal experience observing your figures and I surely do not.
george smith
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Do not go more than a max of 36 degrees total advance on that 460. I would set it at 28 to 30 degrees. If you go more than 36 degrees you will destroy that engine in a boat.
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The numbers I got off of OMC's advance curves in my 1988 OMC factory shop manual....it shows it peaking at 4600 rpm.
Looking at that spec sheet, it appears that they changed the timing specs...
the '87 and '88 used 15*,
the '89 used 10* even with high octane fuel. Might be safer to go that way, seeing as how it is hard to hear detonation in a marine engine. My manual lists full centrifugal advance at 4600 as 25* so if you used a base timing of 10* you'd be at 35* total. I think it also depends on the octane of the gas used to a large extent and carb jetting. If all you can get is regular then I would use 10*. I use premium on my '88 4.3 and set it at 6* which is the spec OMC had listed for premium gas. Never had any issues with detonation.
Looking at that spec sheet, it appears that they changed the timing specs...
the '87 and '88 used 15*,
the '89 used 10* even with high octane fuel. Might be safer to go that way, seeing as how it is hard to hear detonation in a marine engine. My manual lists full centrifugal advance at 4600 as 25* so if you used a base timing of 10* you'd be at 35* total. I think it also depends on the octane of the gas used to a large extent and carb jetting. If all you can get is regular then I would use 10*. I use premium on my '88 4.3 and set it at 6* which is the spec OMC had listed for premium gas. Never had any issues with detonation.
I use mid grade or reg. fuel so I was going to set total advance timing at 34* but seeing this info I think 32* max would be much safer. Both engines are inboard 460 Fords and all my manual said was base timing was to be set at 10* , no numbers for total advance.
Base timing or initial timing is just the starting point for starting the engine.
The formula for setting timing according to GVP is determined by the fuel octane rating. 87 octane at 30*. 89 octane at 31* and 91 octane at 32*. I'm really not sure how alcohol affects these numbers being that alcohol is itself an octane booster. Increasing octane quiets the explosive nature of fuels under pressure. That fuel/air under compression just wants to explode and will do so with just the slightest provocation in a very uncontrolled nature. Controlling that explosion is what increasing octane does by slowing the burn rate and allowing more fuel to burn more completely.
Different distributors or electronic ignition systems have different advance curves with different timing advance built in with an average between 12*-18*. At, say 30* advance with 18* advance, that would put your base timing at 12* but with 14* advance, your base timing would be 16*. Basically, you set your timing for full advance for the octane rating you use and let the base timing fall where it will.
I have a TBIV ignition system with a module that continues to advance to around 4200 RPM. That means it has a slow advance curve. Not my favorite but it works so I leave it alone. For my cam, I would like my advance to be all in between 2200- 2600 RPM. I could even live with 8* of advance with my advance being all in at 1800 RPM.
The formula for setting timing according to GVP is determined by the fuel octane rating. 87 octane at 30*. 89 octane at 31* and 91 octane at 32*. I'm really not sure how alcohol affects these numbers being that alcohol is itself an octane booster. Increasing octane quiets the explosive nature of fuels under pressure. That fuel/air under compression just wants to explode and will do so with just the slightest provocation in a very uncontrolled nature. Controlling that explosion is what increasing octane does by slowing the burn rate and allowing more fuel to burn more completely.
Different distributors or electronic ignition systems have different advance curves with different timing advance built in with an average between 12*-18*. At, say 30* advance with 18* advance, that would put your base timing at 12* but with 14* advance, your base timing would be 16*. Basically, you set your timing for full advance for the octane rating you use and let the base timing fall where it will.
I have a TBIV ignition system with a module that continues to advance to around 4200 RPM. That means it has a slow advance curve. Not my favorite but it works so I leave it alone. For my cam, I would like my advance to be all in between 2200- 2600 RPM. I could even live with 8* of advance with my advance being all in at 1800 RPM.