Max timing advance

[Bill Van Steenwyk]

Jerry and Anthony:

The whole length of time I ran alky motors from the late 60's to 2003 or so, timing was set staticly for as much as the engine would stand up to about 6-7 thousand or so, because if it was set any higher, at the higher RPM past that, burned or stuck pistons were sure to result. When the CD ignitions came out, even the early Phelan self excited type used on the Konigs, they supposedly had electronic means in the "porkchops" that the flywheel passed by so as to retard the spark at higher RPM electronically. In the mid 90's I had a 125 made from Honda and Yamaha road race bike cylinders, and we used an MSD ignition on it that came with small plug in modules that allowed retarding the spark at higher RPM to keep from burning/sticking. These modules allowed different degrees of retard at different RPM's, and worked very well, but for some reason MSD went away from that type system, and then you had small switches on the box itself that could be arranged in different sequences to do the same thing. If you did not use that those type devices after they became available and tried to run the same static timing (high)you set for best acceleration all the way to top RPM, without some way to retard it past 6-7 K RPM you would be replacing pistons very regularly. Most of the explanations to this point I have read on this thread say basically the same thing, more advance at lower RPM for acceleration, but it you run it high pushing the envelope too far up the RPM range without some way to retard it, either mechanically or electronically, it gets costly very quick My experience was the same as Fred's, and I am not near as smart, so I think he knows of what he speaks, cause I had those boxes of burnt pistons also, as did others that tried to push the envelope. Of course if you want to run up front, that is what you have to do.

There are several manufacturers of ignitions out there that have these features. Whether they could be adapted to work on a Yamaha of the type described is another matter, although where there is a will, there is a way most of the time, with enough money.

[50sFlash]

Thanks guys. I get the picture. I got a ton of learnin' to forget. A thought on a solenoid, OMC choke solenoids are small and might work.

[Bill Van Steenwyk]

Jerry and Anthony:

Please be sure and notice the part on my earlier post about the adjustable retard capability of the MSD boxes. Don't know if it is still availiable but their website should give your the info.

I have no interest in MSD other than knowing that they are a reputable company and their product worked well for me in the particular application I posted about earlier. One thing about them is the tech dept at the time was very willing to work with us to provide us with the components to make the ignition work after they understood what we were doing. Perhaps they could work with you in the same way if you want to try to upgrade the existing ignition you are working with. We were using a battery total loss system to fire the ignition (very small light wgt l-2 lb battery) and a trigger mounted on the flywheel. They make ignitions for both self excited and battery systems and could probably provide some type control box that would allow you to time the motor statically and then retard at higher RPM to accomplish what you want. There are probably others out there also, but this is one I am familiar with, that would probably work with a minumum of work. They also make most of the ignitions the NASCAR folks us also, so they are certainly technically capable. There is a company called Rapair that also that makes ignitions for Mercury and possibly might have something for you also.

If you are not familiar with a website called Scream and Fly, they have good tech forums for pleasure type outboards and a lot of folks that chime in with good answers to questions such as yours. Good luck.

[Powerabout]

Dont forget the exhuast pulse will be changing as the rpm changes.
This can do different things on different engines.
If it leans it out you want less timing or
if it stuffs charge back in the cylinder so the bmep goes up you also want to back off the timing.
The speed of combustion/flame front will most likely be different at different speeds as this depends on how homogenous the mixture is.
And this will all be happening at different rpms depending on the atmospheric conditions on the day...dew point/speed of sound and all that...

[50sFlash]

So it really is just a crap-shoot, and until you have a box of burnt pistons, you're just guessing?

[Bill Van Steenwyk]

As previously mentioned, MSD for one, and possibly others now, make PROGRAMMABLE ignitions that allow you to electronically set the RPM point and also the amount of degrees the timing would be retarded at top RPM, to keep from filling up those boxes with those stuck and burnt pistons.

BUT, it is like anything else in racing, testing and trial and error while figuring out what your engine likes in the way of timing depending on the pipes or exhaust tuner, porting, prop, length of course, and all the other variables involved in racing, boats or othewise. Going along with the testing, is keeping good records regards temperature, humidity, etc., so you can refer back to when you did stick or burn a piston and not run the engine at that static timing again if you dont have the capability of retarding it at top RPM, or set the retard if so equipped, to start at a lower RPM and/or retard more degrees, or a combination of both.

It is still a testing process no matter the state of the art equipment you have, test or otherwise. I think anyone who has been in this game for any length of time at all would tell you if burnt or stuck pistons scare you or you don't have time or money for them, you are wasting your time trying to get every last bit of performance out of an engine, because based on 40 years of doing and watching, they all run best right before they come to a sudden stop. The hard part is figuring out where that point is, and tuning right up to it but not beyond, no matter whether it is pipes, ignition, or carb fuel/air mixture. Nothing will tell you that like it happening to you so you recognize that point and don't go beyond it the next time.

As to calling it "guessing", I wouldn't go that far, as anyone who is familiar with engines knows the basic limits to start with, either thru someone else running the same kind of equipment, or information funrnished by a manufacturer or selling dealer of the engine. But when you get to the point where you are trying to extract that last bit of RPM and speed, then to use "guessing" implies that you have no idea what you are doing. I doubt you would be on this forum talking about your engine unless you had some basic knowledge. Better to call it "parts investment speculation". That sounds more engineering oriented, don't you think. It's probably not going to be any cheaper on you in the long run,, but like the guys on Wall Street, "Investment Consultant" sounds better than "THIEF".

[Powerabout]

"parts investment speculation"
Good one!

[50sFlash]

Been there. In our Pro/Stock Camaro we spent hundreds of hours building a 538 Cu in, "monster Motor" (1970) We had over $5,000 in heads, stroker crank, everything the best. The engine builder clearanced the deck for steel rods, and then put in M/T Aluminum. Well they stretch .005 more at 7,000 RPM. Piston, meet head. 1 full pass, box of parts. Don't need to do that again.
The good news, I'm not racing it, just trying to get a couple extra out of a 1958 Johnson. I have a lot better idea of what not to do now.

[Fastjeff57]

I hope you made those morons compensate you!

Jeff

[Powerabout]

I think only 2 hp Jonrudes had aluminium rods so no problem there