Centrifugal advance

[Dave Neptune]

Hello out there fellow A-4 owners. Does anyone have or know the "advance curve" recommended by Universal? Of primary interest to me is at wht RPM should the distributor be pinned at the stop?

Twenty some years ago I adapted an Allison hi performance electronic ignition set up on my lil A-4 and it worked like a champ. The Allison set up was probably a little quick as the springs were set up for the drag of the points on the shaft. I have since gone to the Indigo electronic and installed their advance weights included with the kit. It has been working flawlessly for a few years now and it is time to lubricate the centrifugal advance weights and counter shaft. I found my old timing light and decided to check to see if and at what RPM the advance system is at max. Also of interest is what is the total advance (in the distributor) of the centrifugal system?

Thanx Dave

[lat 64]

Hi,
I downloaded some specs(below in blue) the other day from http://www.hessmarine.ca/a4specs.htm
I found two inconsistencies elsewhere in their piston info, so use this with caution.
I once modified an old Ford 460ci distributor with pieces of metal soldered in the flyweight stops. I needed to reduce the total advance to 29 deg. from a whopping 49 deg.! the factory work was that sloppy! it ran great on cheap gas after that. I was using 9.5 to 1 comp. ratio pistons then. I had double-checked this by ”ccing” the combustion chambers.
To check my work on the dist., I printed a degree wheel on my lazer printer and glued it to a piece of cardboard and then jammed it on the dist. shaft for a guide. I made a little pointer from some wire—it worked great.

Russ


Prestolite distributor:
IGW4116C / 60032E1X
Delco distributor:
1112446 - 2G11/6C16/3HI8


Stock Delco distributor:
Static: No advance = 0° BTDC / Full advance = 12° BTDC*
Dynamic: < 1,000 rpm = 2° BTDC / 2,000 rpm = 6° BTDC / 3,000 rpm = 12° BTDC*
*Note: factory specifications state full advance is 17°, but testing has shown the late model Delco distributor only advances
12° with standard weights. That is a another good reason to set the timing by slowly turning the distributor at full throttle
while tied to the dock or at top boat speed to get maximum engine rpm, rather than assuming setting the timing to 0° BTDC with engine off will be accurate at full cruise speed. (The other reason to set the timing at full speed is because optimum timing varies with elevation, fuel octane rating, compression ratio, and carburetor jet spec.)
Atomic Four Engine Service "Hi-Torque" distributor (for direct drive engines only):
Dynamic: 1,000 rpm = 3° BTDC / 2,000 rpm = 6° BTDC - maximum advance

[High Hopes]

Dave,

Here is a chart that Don gave me. I don't know what a stop is. Maybe the graph will answer your question. My A-4 sitting on the bench followed this curve rather closely. I set the timing at 16oo RPM as I estimated that to be my crusing speed.

Steve

[Dave Neptune]

Steve, Russ, thanx for the reply. The numbers of 12-17degrees seem awfully low for such a low compression engine. I can see the timing not being against the stops since we seldom see more than 2000 RPM's. I have built and run many high compression and superchsarged engines with more lead than that and in those getting a short enough curve required some work with a degree wheel and a dist. machine to shorten the total advance. I expected to see anywhere between 35-40 degrees of advance being about right for a constant load duty application with such low compression. This brings me to the next question---was the 12-17 degrees in the distributor which would be 24-34 total degrees on the crank? Thast would make more sence to me.

I do set the timing via the "POWER TIMING" method while underway so most of this is moot information. I was thinking of havig my distributor be against the stop at cruising so it (the total advance) would not waiver as the weights become sticky or looser due to the springs getting older and or dirtier. I am just looking for more cocsistancy in the timing sequence. AHHHHHH something to play with!

Thanx Dave
E35 MkII
39 years of running so far!!!!!!!!!!!!!

[High Hopes]

Hi Dave,

I like your comment "AH something to play with." I am with you there, a tinkerer at heart.

The timing was set with a "True Angle" tool centered on the flywheel PTO. Probably not what you wanted to hear. I did not use the power timing method yet - so there may be room for improvement and readjustment.

On using the stops... I have noticed that when the A4 is under way, she hums contentedly. A smooth idle is harder to achieve. But I have only been out once since the rebuild.

-Steve

[Dave Neptune]

Steve, judging by the apperance of your A-4, it looks like you did a good job. The rough idle will improve as the engine "breaks in". There is a lot of internal friction in a new or rebuilt engine and as it runs. A lot of the roughness in the bearings and the especially in the cylinders will go away giving the lil' engine less work to do to keep it spinning at idle.

As a tinkerer, I may try to get the best idle by shortening the advance curve so I still have the same top end performance and a little more lead at idle. I will be checking my advance mechanism in an hour or so when I reinstall my carb. this mornin'. I.ve been playing with the float levels and the mani jet trying to reduce the idle influence above 12/1400 rpm. I have the high end figured out and am about to start tinkering with the Idle air bleed to shorten its influence on the power curve. I installed the "Spring kit" with the Indigo ignition 4/5 years ago which I think had a little longer springs to shorten the curve. I can check them against the originals if I get ambicious enough.
TINKER TINKER TINKER

Dave

[High Hopes]

Hi Dave,

Did you ever finish your tinkering with the advance? BTW, I did not rebuild the engine, but did just about everything else (there were 5 oil leaks, 2 gas leaks, rebuilt the carb, POWER flushed the block, new head and exhaust manifold. Compression was good and the valves didn't even need adjusting.

I have a question about dwell. Here is a scope trace of the ignition primary circuit. 2/3 of the time the coil is conducting current. This seems excessive. Is this correct? Maybe I should move the igniter further away from the magnetic ring.

Steve

[Don Moyer]

Steve,

This is very interesting to me, and you're no doubt paving new ground for many of us with your scope. It's my understanding that electronic ignition systems get away with a longer dwell time by somehow lowering the voltage to the coil. Can you tell anything about voltage getting to the coil in your read out? If you have any pier buddies with conventional ignition, it would be interesting to see how their trace compares to yours with an Ignitor.

Don

[Dave Neptune]

Steve, no I didn't work with it as the distributor machine I was going to use doesn't work with a photo electric ignition like mine. I may play with a "degree wheel" and see what I come up with. I am also going to review the Indigo instructions as far as the spring kit is concerned. I think that when I talked to them they mentioned that their spring kit had longer springs to shorten the curve. What I would like to accomplish is to be against the advance stop at my max cruising speed for consistancy and let the idle fall where it may as long as it is a good idle somewhere near 0 degrees.

Don & Steve, I'm not to sure about an electronic ignition lowering voltage to the coil. I know that the early Transistorized ignitions used with points ran a very low voltage through the points so they would last longer (I remember cleanig the points by draging a piece of paper betwen them while closed as they never "PITTED") and sending the full current to the coil. In these point type ignitions the dwell was still controlled by the point setting. In the full electronic set ups the dwell is radically increased for a good strong spark. This increase in saturation time was with a consistant voltage for a good charge and the voltage did not vary as with a point type that has resistance building across dirty points and the spike in voltage from the condensor.

I'm really digging through the cob-webs to remember this stuff so it may be off a little. I wonder what the designers of the A-4 would think of all this?

David

[High Hopes]

Hi Guys,

A coil resists current changes. When the ignition coil is initially connected to the battery for charging, the coil looks like an open circuit. In an ideal inductor, as the current flows through the coil, the voltage drops until the maximum current is achieved. In our A4 coil, the resistance of the coil limits the current to about 4 amps. This internal resistance also means that the voltage across the coil will not go to zero, but remain at 12 volts. Unfortunately, the scope trace shows the voltage across the coil, not the charging current. So the trace sits quietly at 12 volts for the duration of the dwell and we have no idea what the current is doing.

[ Don, I think that the voltage was approximately 12 volts. But, the scope needs a calibration, so I don’t know for sure. ]

For the case of distributor points, the current flow would be an exponential curve, starting at zero and rising quickly, and then rising more slowly as the current approaches the 4 amp value.

If the igniter employs a "constant current source," the current flow into the coil would rise at a constant rate. There would be no initial current surge. That would be good for the electronic components. However, it would take a longer time to charge the coil. So maybe this explains the longer dwell.

Don, can you get a dwell figure from Indigo?

Dave, I think the older A4 guys would dig it.

Best,

Steve

[Don Moyer]

Steve,

I'll try to get a reaction from Pertronix tomorrow morning regarding the Ignitor dwell duration and what (if any) control their module exerts on the current as it (the current) builds up to 4 amps.

Don

[High Hopes]

Here's what I think is happening on my engine.