1.... I did some research and found some specs 10-12 base and 32-34 all in or total advance but there still was not a specific all in rpm.
2..... MSD does have the electronic advance dizzy that works with a knock sensor but not sure if one is available for the early marine 318. It will retard the timing when detonation occurs and fully adjustable.........
3..... Another thread said if the timing is off it will make the starter labor real hard so that would be another consideration in base timing.
4.... Somthing in the back of my head is telling me the mopar curve takes two stages or two springs rather agressive up to 1800 rpm like 15 degrees then around 3000 be all in. Maybe looks something like this is just an example you have to correctly determine TDC?
5...... 10 degrees base at 800rpm
15 degrees advance at 1800rpm
7 degrees at 3000rpm
that adds to 32 dbtdc at 3000 rpm all in
6..... slack in the second spring allows the two stages of advance
7..... Someone must have the top secret clearance willing to leak the advance curve for a early marine 318. Maybe wiki leaks could find out or someone in the oval office.
1.... didn't someone post a BASE advance spec of 5* BTDC?
2..... That would be an EST system (electronic spark timing), such as the Merc Thunderbolt system, or the Delco Voyager. I don't know if EST is available for the 318/360 engines.
3..... That is correct. The early spark lead will cause the engine to "buck" against it. I'm sure that's why a BASE of 5* is being recommended.
We fire up on and idle on BASE advance..... and as you know, that's all the engine needs BASE advance for.
4...... Most all mechanical advance systems incorporate two flyweight return springs of different values, and perhaps the flyweight cam profile is slightly different from one another. This can create an initial aggressive ramp up, or a fairly linear curve throughout.
Just the nature of a centrifugal advance system.
I do think that you are correct in that the two together provide the complete curve, and then blend these together, so to speak, so that the actual mechanical advance appears rather linear when viewed plotted out.
5 ..... It looks like you are adding BASE of 10*, first ramp up of 15*, and then a secondary value of 7*.
I've not seen a Marine curve graph that lists this in terms of showing a separate curve for each stage of flyweight/spring value.
Most Marine curves show this as though being a continuous curve, even if it ramps up a bit in the beginning.
6..... see above.
7..... No kidding! But rest assured, we do have an agent working on this now.
found some specs 10-12 base and 32-34 all in or total advance
that adds to 32 dbtdc at 3000 rpm all in
That's too much for a 318; I wouldn't exceed 26 degrees total all in at 2,500- 2,800 rpms................. Going to 28 or even 30 degrees might improve gas mileage, but gas is cheaper than rebuilds!
Jeff, I'm not sure which of Kim's suggestion you make reference to. With the unknowns, that may be risky, especially re; the lower 2,500 rpm.
Getting completely side tracked and talking out loud here:
I promote the Quench Effect or Squish style combustion chamber in the SBC Marine.
In all the years that I've doing this, I have never used a piston that did not accommodate this.
Chrysler's 318/360 cylinder head offers a wedge section off to the side of the combustion chamber...... very similar to the SBC.
Chrysler's 318/360 Marine piston is apparently this flat top piston below... Yes/No?
The F/T can be considered a Q/E piston when the correct quench dimension head gasket is used. It can then offer a Quench Effect or Squish Zone.
(the Chrysler Wedge Head automotive guys have known about this for years)
With a Q/E built SBC, we can go up a point or so on static C/R, and can toss more spark lead at the engine and without increased detonation potential. (it's all about LPCP, detonation control, yada yada yada and so on)
Even with a good Quench, 32* @ 3.2k RPM is just about MAX in order to steer clear of Marine load detonation.
You can carry out the progressive some as RPM increase (35* @ 4k rpm for example), but we DO NOT dare bring this spark lead on any earlier than approx 3.2k RPM under Marine loads.
Point being:
If the 318 and 360 have some similarities with the SBC, then it's posible that the same principles may apply.... I don't actually know!
If so, then perhaps 32* @ 3.2k rpm is not out of line.
However, if there is NO quench area in this combustion chamber......, then perhaps 32* @ 3.2k rpm is rather aggressive and risky.
This is why GM's run-of-the-mill SBC Marine Engines (using the full dished pistons) are setup to hold the TA back to approx 26* @ 3k rpm or so. This build
CANNOT use 32* @ 3.2k rpm.... or it would most likely detonate!
Just to be clear.... I'm not recommeding any 318/360 advance numbers... just talking out loud.
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This thread needs an Intermisssion, like in the movie "Gone with the Wind".
We can go to the snack bar for popcorn and soda pop, and stretch our legs a bit!
Maybe the second half will include the OEM advance curve!
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