Megafire module vs points

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steveohara
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Re: Megafire module vs points

Post by steveohara » Sun Dec 20, 2009 12:29 am

Scott and friends,

In the old days some folks wired in a switch to break the connection between the points and the coil giving them the manual activated equivilent of floating or open points. The purpose was to trigger "maverick spark" at a user defined rpm or point on the track. I see no reason why the same method would not work with any of the modules unless doing so would damage the module in some fashion.
For high rpm performance on the Mac engines we have always set the timing effectively by our choice of flywheel and position of the coil so it looks to me like a module that would produce a spark timing in the range of 24 to 26 degrees BTDC and maintain that timing up to around 10,000rpm could be fitted with a switch that would take the module out of the system and allow the spark timing to jump up to the 30 degrees BTDC range that we get when using a typical Mac coil, crank and 5 degree flywheel.
The best type of switch would be a spring loaded button type that breaks the circuit when held down so the driver clould ingore the button for most of the track and only use it when running down the longer straights.
I have never messed with any of the modules... I'm a Mac purist at heart, but is does seem like it would be a simple thing to try. I know several people that claim they have used the TCI unit from a KT100 and they work well but I don't see how they can produce the advance in timing that Mac thrive on in the higher rpm range.
If anyone gets a chance to try the approach please come back and post your results. I only run the vintage karts once a year so I don't get many opportunities to try new things but I may have to find the time in January at Adams when I run my new reed open Mc 91 grenade LOL
Steve O'Hara

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Re: Megafire module vs points

Post by Scott Kneisel » Sun Dec 20, 2009 7:48 am

Good idea Steve, It should work exactly the same as with points.

Weren't these switches illegal back in the day? IKF rules or something like that. Of course for vintage, all those kinds of rules are out the window. Most 91's are 30 over now anyway...LOL

I will be at Adams in January and hope to meet you. I will be there for the whole event. Hope you don't grenade your 91 grenade!!!

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Re: Megafire module vs points

Post by Terry Sullivan » Sun Dec 20, 2009 11:00 am

Thanks Scott.

I guess I'll have to build an adaptor to mount my degree wheel on the crank.

AND make a dyno! I'll create new thread to see if anybody has plans for a decent dyno.

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Re: Megafire module vs points

Post by Russ Smith » Sun Dec 20, 2009 12:58 pm

I only have basic knowledge about Maverick spark. Can someone explain it in detail?

Thanks

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Re: Megafire module vs points

Post by steveohara » Sun Dec 20, 2009 5:28 pm

Russ,
In very simple terms "maverick spark" occurs when the points fail to keep up and bounce or float due to engine speed getting too high. If that happens there will still be a spark but it will occur sooner in the cycle (more advance) and the timing will be a function of the relationship between the coil legs and the magnets in the flywheel and is not controlled by the points.
Scott can probaly elaborate on the relationship between the condenser, flux generated by the magnets passing the coil legs etc but for real world appications there are just a few things that you need to know as follows...

At lower speeds the ignition timing is controlled by the points and can be "set" where the mechanic wants the spark to occur. At some point moving up the rpm scale the points will fail to consistently follow the cam on the crank and the control of the timing will be lost and it will become a function of the coil/flywheel positions.
The most common method of influencing when the transition occurs is changing the point tension. More point tension makes the points continue following the cam up to a higher rpm before they lose control. Other factors less talked about are lift and duration of the opening of the points. The lower the static ignition timing as determined by the points the less lift and duration (dwell) you get and less lift and duration also helps keep the points following the cam up to higher speeds. The downside to using lower static timing as a means to delay transition to maverick spark is that there is a larger change in timing once it occurs and that can produce some tuning challenges. Another factor is stator position and some influence can be achieved by rotation of the engine side cover as that also moves the points around the crank but the effect is very limited due to the physical constraints of the shroud mounting needs.
It should be noted that the transition to "maverick spark" is by no means a clean switch. There is no question that there is a range of rpm that the motor passes through where the timing is moving back and forth between the static timing and maverick timing as the points try to keep up but only manage to be in the right position say half the time. This is where the "switch" a talked about came into play. If you take the wire that runs from the points and plugs into the top of the coil and route it through a switch you can manually create the same effect as having the points float. My only personal experience with the complete break came at Ontario Motor Speedway back in 1976 or 77 when I had a point spring break during a race on a Mac 91. I was way out in the lead at the time and it created some tuning problems that I managed to address and continue running to finish the race but when I let off the throttle cruising into the pits after the checkered flag the engine died and we could not re start it.
When I took the motor apart for tech the points were just laying open. I relay the experience to point out that it takes a lot of engine speed to generate a spark with the points stuck open and it would be very hard to spin one fast enough with a starter to fire with the points out of the equation.
Hope this helps.
Steve O'Hara

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Re: Megafire module vs points

Post by Dan Flanders » Sun Dec 20, 2009 6:21 pm

We had a similar discussion a while back when MacBob talked about using an ignition module from a Ryobi string trimmer. Personally, it would be great if we could find a reliable, economical module that could replace the points. To do that we need the RPM and advance data. Walbro makes ignition modules, and I would imagine we could find or have one custom coded for the 91s and 101's....Just a thought.

http://69.16.165.8/category.aspx?id=17

I have an .pdf that maps the RPM and advance specs if anyone is interested. Too big to attach so PM me and I'll send it along.

Dan

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Re: Megafire module vs points

Post by steveohara » Mon Dec 21, 2009 12:45 am

dan,

I have never heard of an electronic module that advances the ignition as the speed increases... have you seen anything like that?
I'd like to see your file... if you can post it great otherwise email it to me direct.
Regards,
Steve O'Hara

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Re: Megafire module vs points

Post by Russ Smith » Mon Dec 21, 2009 7:54 pm

Steve,
Thanks for the clear and concise explanation.
Hey Dan, can you email a copy to me? You have my address.

Thanks,
Russ

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Re: Megafire module vs points

Post by Dan Flanders » Mon Dec 21, 2009 8:02 pm

Hi Steve-
No, I've not seen anything that advances. Quite the contrary, most seem to retard...That said, I wonder if Walbro could be approached with a custom timing curve and program a module that would work with a Mc? I don't know what is involved, but in the digital age I would hope it was just a matter of programming the parameters into an existing unit (I imagine that is a pretty naive view, but who knows until someone asks) Scott do you have any experience in this realm? With Atom modules no longer in production and the potential, albeit small, market for Mac's maybe they could be convinced of the need for the 820 and 91/101 series motors.

Dan

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Re: Megafire module vs points

Post by Tom Smith » Tue Dec 22, 2009 4:30 am

Mc-102 .JPG
(803.32 KiB) Downloaded 39 times
I've found that magnet polarity is important with modules where as points don't care. PVL makes both an analog and a digital system which has a programable curve.

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