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Old 10-13-2017, 10:19 AM
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Marine timing curve

Curious about the timing curve on my boat....


It is powered by a pre-vortec 4.3L v6 which wears a 2-jet carburetor and a prestolite distributor. I upgraded the ignition with a pertronix igniter 2 and a MSD blaster 2 coil (which matched the performance requirements of the igniter 2)


so after the upgrade I reset the timing according to the attached graph.


reading the graph, the distributor offers only 12 degrees of centrifugal advance, and my initial should be set at 6 degrees for a total of 18 degrees.


this seems like it is much more conservative than what it would have to be. I understand the possible need for a more conservative timing curve for a marine application, but this seems downright lazy.


it seems like I should, at a minimum, be able to run 12 degrees initial and get a total of 24 all-in, but even that seems really conservative. I could try to get it up to 30ish total, but it seems like 18 initial would be far too much.


it would seem like getting 18-20 centrifugal would be more optimal, allowing at least 30 degrees total (which is higher than what this graph says for a 5.7) with running 10-12 degrees initial.


does anyone know anything about the prestolite distributor used in this v6? is it relatively easy to change how much advance the dizzy offers?


what kind of timing curve would you shoot for in such an application? I imagine marine service is possibly one of the most severe, so it probably should be approached with some degree of caution.


why am I posting this on hotrodders.com?
#1 the knowledge base
#2 my dream for this boat is to swap in a set of vortec heads and a 4-bbl carb and make somewhere north of 200hp at the prop (factory rating on the 2-bbl v6 is 150 at the prop)


FWIW, the attached graph is supposed to be the factory timing though I haven't been able to verify the genuine authenticity of the picture.


one theory about the lazy timing curve I've ran across is that they were purposely limiting the power on the 4.3 so that it didn't approach the power offered by the 5.0. theory being that if the 5.0 only make 10 more horsepower than the 4.3, no one would buy it. just a theory, but how else would you explain such an ignition timing curve?


thanks in advance.


mike.
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Old 10-13-2017, 10:39 AM
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You do know distributor degrees are 1/2 crankshaft degrees, don't you!
That means that you actually have 24 degrees crank plus 6 initial to give a total of 30.
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Old 10-13-2017, 10:59 AM
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Originally Posted by RWENUTS View Post
You do know distributor degrees are 1/2 crankshaft degrees, don't you!
That means that you actually have 24 degrees crank plus 6 initial to give a total of 30.
Yes, I am aware of the timing relationship between the cam and crank.

If you set the timing at zero and rev the engjnf, the timing goes to 12. The distributor is maxed out at 6 camshaft degrees and provides 12 at the crank.

Did you look at the graph I posted?

If what you are saying was correct, then the 5.7 would be providing 40 degrees centrifugal, and we all know that's not going to fly.

Trust me I've checked it. With the timing at 4 initial, the centrifugal puts the timing just barely off the scale which maxes out at 14. This distributor is designed to only provide 12 centrifugal at the crank.
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Old 10-13-2017, 11:57 AM
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Marine setups do need to be a bit conservative on the timing, although that sounds excessively conservative to me. The big thing is that you can't bring the timing in too early. If WOT RPM is, say, 4500, you probably don't want the timing all in until somewhere around 3500 - 4000.
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Old 10-13-2017, 12:54 PM
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Quote:
Originally Posted by meborder View Post

If what you are saying was correct, then the 5.7 would be providing 40 degrees centrifugal, and we all know that's not going to fly.

.
Why not?
My motors manual shows several different distributors that have 20 (40 crank) degrees in them .
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Old 10-13-2017, 01:08 PM
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Originally Posted by RWENUTS View Post
Why not?
My motors manual shows several different distributors that have 20 (40 crank) degrees in them .

The graph is pretty clear. They aren't mixing cam and crank degrees on the vertical axis, the numbers add up.

6 + 12 = 18, and that jives pretty well with what I see at the damper.

The question isn't whether I know what I'm taking about, but rather what would a proper timing curve look like and can I modify my prestolite distributor to produce that curve?
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Old 10-13-2017, 01:12 PM
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Quote:
Originally Posted by rslifkin View Post
Marine setups do need to be a bit conservative on the timing, although that sounds excessively conservative to me. The big thing is that you can't bring the timing in too early. If WOT RPM is, say, 4500, you probably don't want the timing all in until somewhere around 3500 - 4000.
That matches the graph above very well. My Max engine speed is listed as 4600 rpm, and the advance appears to stop slightly north of 3000. Same for the 5.7, though their engine speed was rated around 4800 IIRC, same as the 4.3 with the 4bbl.
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Old 10-13-2017, 02:47 PM
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I don't own boats.......But why not lock it out and forget it?
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Old 10-13-2017, 03:21 PM
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Originally Posted by johnsongrass1 View Post
I don't own boats.......But why not lock it out and forget it?
I have heard of some racing applications where they lock it out.


if I were to do that, where would I set it?


how easily does an engine start with 25 or more degrees locked in? Would 25 - 30 be too much at lower RPM?
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Old 10-13-2017, 06:15 PM
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Quote:
Originally Posted by meborder View Post
how easily does an engine start with 25 or more degrees locked in? Would 25 - 30 be too much at lower RPM?
Not very well sometimes, which is why a lot of them that don't know any better have trouble getting their cars started, especially hot.

I've never understood the fixation with locked timing. There's an advance mechanism in there for a reason, and with the right setup the timing will be where you want it at race speeds.

Same with fear of vacuum advance, "my car runs hot idling in traffic?" Well of course it does dummy, they do that with only 10 or 15 degrees of timing. Put a vacuum line on that can like it's suppose to have and let it idle at 30*. The vacuum will go away when you're on the loud pedal, so who cares.

Boats are set up to run for long periods at one throttle setting, often to keep them from rattling to death because their operators aren't often real bright engine wise. "Hey Kenny, what's that funny noise back there??"
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Old 10-13-2017, 07:37 PM
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We do it cause I don't want the weight and springs and stuff coming apart at 8200rpm and taking me out of a race.

We don't have hot or cold start problems. I could see it happening on a stock starter soaked in heat and poorly grounded wires that are too small to begin with.

If starting is an issue one can always add the starter and coil switch separately to get the engine spinning before flipping on the spark.

Vacuum advance doesn't help our race cars either but it may on a steady state constant load condition but only because boats hold that rate and load for longer periods (think long highway trips) than race cars.

I assume the RPM is about 2000 to 4500. At 2000 your prolly just cruising at a low load and 4500 your cruising at a high load. The timing is usually done helping at 3000 anyway so that's only 1000 rpm it might be a benefit however that negated by the steady state loads so I think I might set it at 32 locked out and see what happens. Then again I've only been on a boat like 3 times my whole life and 2 of those were outboards.
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Old 10-13-2017, 08:06 PM
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There's no centrifugal advance in boats. Mainly because they never run with a light enough load to use it. And also it's another thing to rust and stick in the wet environment.
All the advance is in the electronics.
Performance big block guys like the V6 module. It has the least advance of all the Mercruiser systems. It's 14 degrees advance can run wilder cams which need more initial timing. When the distributor is advancing 24 degrees like most v8 modules it can be a problem for them.

Stock for your engine is 8 degrees at idle so it's going to add up to a total all in of 22. I'm sure you can get away with a little more. But how much is up for debate.
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Old 10-17-2017, 10:01 AM
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Quote:
Originally Posted by 3repete View Post
There's no centrifugal advance in boats. Mainly because they never run with a light enough load to use it. And also it's another thing to rust and stick in the wet environment.
All the advance is in the electronics.
Performance big block guys like the V6 module. It has the least advance of all the Mercruiser systems. It's 14 degrees advance can run wilder cams which need more initial timing. When the distributor is advancing 24 degrees like most v8 modules it can be a problem for them.

Stock for your engine is 8 degrees at idle so it's going to add up to a total all in of 22. I'm sure you can get away with a little more. But how much is up for debate.
Thanks for the info.

Couple of points, though. My boat is an 88 so it did not come with electronic ignition. Factory distributor is a points style distributor with mechanical advance. Factory settings are to provide 12 degrees mechanical on top of 6 degrees base.

Good to know that in later years they upped it to 6 and 14, through electronic ignition.

Curious as to why 22 to 27 seems to be the limit used in marine application.

I guess I won't know until I get it on the water, but it seems like 2000-3000 rpm is going to be the critical point. Between those rpms is probably the highest load as the boat is trying to get up on plain. Above 3000 it is on plain and cruising nicely. My concern with setting a bunch of initial to get the total up where it should be may be too much advance in that 2000-3000 range where you are very deep in the throttle.
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Old 11-03-2017, 10:47 AM
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I'm a boater, for an older 262" engine like yours, I'd set the timing for the usual 36 degrees total at 3,000 - 4,000+ RPMs and let the marine distributor do it's usual thing below that... I'm talking measuring the timing on the front damper of the engine... Same as for an older Chevy car...

Wouldn't be surprised if an old base level 350" with big 76cc bathtub chamber heads, dished pistons, and marine camshaft needed 40 degrees total at higher RPMs to light the huge chamber mixture off in time to give full power...

The 4.3L/5.7L chart you're looking at may be considering engines with Vortec heads that work best with 28 - 34 degrees total timing because they are more efficient heads with high swirl ports, smaller fast burn combustion chambers, and higher compression ratio... They may also be assuming some electronic advance added in as well...

Your 262" V6 is exactly 6 cylinders / 3/4's of a 350" V8 and tunes about the same way... except for the V6 they use heads with a little bit smaller combustion chambers for a bit higher compression ratio to keep the HP and torque from being too ridiculously low... And base level marine cams are usually a little step up in spec.s from basic car cams... 2 steps above truck cams... because raw water marine cooling and marine 160 degree thermostats allows higher continuous HP outputs...

As 3repete mentioned above, marine, racing, and heavy truck distributors don't use vacuum advance because that's for passenger cars cruising at 15 - 25 HP... whereas the engines in boats, race cars, and heavy trucks may be cruising at 75 - 250 or more HP and need less cruising ignition advance to avoid detonation...

Last edited by BuzzLOL; 11-03-2017 at 10:54 AM.
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Old 11-03-2017, 04:56 PM
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Quote:
Originally Posted by BuzzLOL View Post
I'm a boater, for an older 262" engine like yours, I'd set the timing for the usual 36 degrees total at 3,000 - 4,000+ RPMs and let the marine distributor do it's usual thing below that... I'm talking measuring the timing on the front damper of the engine... Same as for an older Chevy car...

Wouldn't be surprised if an old base level 350" with big 76cc bathtub chamber heads, dished pistons, and marine camshaft needed 40 degrees total at higher RPMs to light the huge chamber mixture off in time to give full power...

The 4.3L/5.7L chart you're looking at may be considering engines with Vortec heads that work best with 28 - 34 degrees total timing because they are more efficient heads with high swirl ports, smaller fast burn combustion chambers, and higher compression ratio... They may also be assuming some electronic advance added in as well...

Your 262" V6 is exactly 6 cylinders / 3/4's of a 350" V8 and tunes about the same way... except for the V6 they use heads with a little bit smaller combustion chambers for a bit higher compression ratio to keep the HP and torque from being too ridiculously low... And base level marine cams are usually a little step up in spec.s from basic car cams... 2 steps above truck cams... because raw water marine cooling and marine 160 degree thermostats allows higher continuous HP outputs...

As 3repete mentioned above, marine, racing, and heavy truck distributors don't use vacuum advance because that's for passenger cars cruising at 15 - 25 HP... whereas the engines in boats, race cars, and heavy trucks may be cruising at 75 - 250 or more HP and need less cruising ignition advance to avoid detonation...

if I set my total at 36, my initial would be 24. is that going to be too much? there really isn't much curve.


if I hadn't spent about 100 bucks on the pertronix kit I'd dump the prestolite for something else. I should just pull the dizzy and see what it takes to rig it for more advance. it just has never been a priority. I would think getting the timing up to 32-36 would make a lot more power, though.
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