Coil gap on 6608 ARC Limited Mod Flywheel

G

GAKARTER

Member
What is the proper coil to flywheeel magnet gap to set on a 6608 limited ARC aluminum billet flywheel? With the stronger magnet from a stock flywheel, is the gap more or the same as stock flywheel?
 
Typically speaking, ARC wheels require more gap than stock. Being unfamiliar with the 6608, I cant speak for certain, but a minimum of .030 and max about .060 woul be the case I suspect. Give them a call, they are very helpful. Good luck
 
I run my open all the way out at the end of the adjustment. No problems with fire. Raceseng flywheel I'm sure the arc would be the same. I have the gapping tool, but had a coil explode when a clearance problem occurred.
 
MIN. .040. Recommended .... .060
Don't want to kill the stock coil with that all powerful rare earth magnet.
This forgives some of the crankshaft whip by keeping the flywheel off the coil.
 
PD Power said:
MIN. .040. Recommended .... .060
Don't want to kill the stock coil with that all powerful rare earth magnet.
This forgives some of the crankshaft whip by keeping the flywheel off the coil.
Click to expand...

Is the timing affected as you increase the coil gap? If yes, in what direction (advance or retard) and how much of a change occurs?
 
All of our Billet flywheels require a minimum .030 coil gap. Most people run .040 to .060. The actual static timing is not affected by running more gap up to around .080-.090. Then you "might" loose 1 or so degree. You will have less magnet drag with more gap and some coil brands will retard a little more at high RPM. The coil gap is a fine tuning procedure than builders are using more and more, especially on stockers.
 
JPR57 said:
All of our Billet flywheels require a minimum .030 coil gap. Most people run .040 to .060. The actual static timing is not affected by running more gap up to around .080-.090. Then you "might" loose 1 or so degree. You will have less magnet drag with more gap and some coil brands will retard a little more at high RPM. The coil gap is a fine tuning procedure than builders are using more and more, especially on stockers.
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Thanks for the info and tips Jody.
 
,040 is the magic number for me. Never had a flywheel hit yet. ARC is fine equipment also. IMO the more gap slows timing. Although minimal it still occurs. SVR
 
You guys should listen to what the man said. More gap equals less magnet drag or parasitic drag on the engine. The further away you run the coil there will be less drag. Those rare earth magnets are extremely strong.
 
Petree said:
You guys should listen to what the man said. More gap equals less magnet drag or parasitic drag on the engine. The further away you run the coil there will be less drag. Those rare earth magnets are extremely strong.
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Thinking along the lines of your quote here.....in the past, I tested this magnetic drag thing exhaustively.
On a running engine, there is no measurable drag effect created by the magnet.
IF there was, it would be easily altered by changing the weight of the flywheel.
It's compression and ignition advance that wants to drag down the rotational speed of the flywheel.....not the magnet.
 
Paul I appreciate your opinion. It would be an interesting conversation to hear about your testing. We need to talk sometime. I would love to hear what you found and how you came to your conclusion. My simple mind just imagines a crank mounted in the block with the flywheel mounted. Spin the crank with out a coil. Mount a coil and try different gaps and spin the crank again and see if anything changes? I suspect you will find it likes to keep spinning longer with no coil. I would think it would spin longer with a wider gap. Granted this would be a static test in comparison to the dynamics of a running engine. Not an engineer so I can't speak here with any real authority. My original statement is based on here say and my personal beliefs .
 
Just to add to all of what I have said, get the coil set too close and crankshaft flex will put some ugly marks on your shiny wheel from the coil touching and you can also kill the coil.
 
I never said the magnets drag down the engine, on a modified it is hardly even noticed. However in my last sentence I said this is something we have found in fine tuning on stockers which as you know every little bit helps. I will add that the magnets are strong enough to bend the coil legs down on some blocks, so drag is present...
 
I am sorry for putting words in your mouth. You did say however " There is less magnet drag with more gap" . I assumed we were on the same page. Forgive me for assuming. Just seems to me thats a real strong magnet. When it gets near the coil it wants to stick to it. It wants to stick to it a hell of a lot harder that a stock wheel does. Have you ever built a billet wheel with a stock magnet? That in my mind that would be the hands down test. Take a billet wheel with a rare earth magnet and put on it on your open and pull a run on the dyno. Then install your billet wheel just like the last one with a stock powered magnet. Make another pull on the dyno. I suppose my thinking is theory. I figure that strong of a magnet has to put drag on the assembly. I realize originally we were talking simply larger gaps . However lets kick it up a notch. Why do you install such a powerful magnet in the billet wheels to start with? Does it enhance the timing curve ? Has anyone ever built a billet wheel with a stock magnet and tested it on the dyno? Paul in comparison to the dynamics you described my theory with the larger gaps may not be measurable. Have you ever considered a billet wheel with a stock magnet? In your opinion would there be any difference in the results?
 
Petree said:
Paul I appreciate your opinion. It would be an interesting conversation to hear about your testing. We need to talk sometime. I would love to hear what you found and how you came to your conclusion. My simple mind just imagines a crank mounted in the block with the flywheel mounted. Spin the crank with out a coil. Mount a coil and try different gaps and spin the crank again and see if anything changes? I suspect you will find it likes to keep spinning longer with no coil. I would think it would spin longer with a wider gap. Granted this would be a static test in comparison to the dynamics of a running engine. Not an engineer so I can't speak here with any real authority. My original statement is based on here say and my personal beliefs .
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This is really not my opinion. This is engineering.....not guesswork. Your suggestion that I check out the resistance to rotation with no coil, seems to ignore the information that I gave you, regarding having tested this exhaustively.
Here's something for you to do. With the engine not running hold a bolt near the magnet. Notice how the magnet grabs the bolt....and holds it against the flywheel. Now, with the engine mounted on the kart, with the flywheel exposed, run the engine up to a fast idle.....say 3 g. or so. Now hold the bolt
near the flywheel, as you did when the engine was not running. See if the bolt gets jerked from your hand as it did with the engine off. Report back!
 
PD Power said:
This is really not my opinion. This is engineering.....not guesswork. Your suggestion that I check out the resistance to rotation with no coil, seems to ignore the information that I gave you, regarding having tested this exhaustively.
Here's something for you to do. With the engine not running hold a bolt near the magnet. Notice how the magnet grabs the bolt....and holds it against the flywheel. Now, with the engine mounted on the kart, with the flywheel exposed, run the engine up to a fast idle.....say 3 g. or so. Now hold the bolt
near the flywheel, as you did when the engine was not running. See if the bolt gets jerked from your hand as it did with the engine off. Report back!
Click to expand...


That is some sound advice right there, rev an engine up and stick a bolt near the flywheel. Before you do that you might want to be sure your Obama care and Homeowners insurance are paid up because when it grabs the bolt there is no telling where it will go after it bounces off the coil legs.

Will it snatch it out of your hand, probably not. Will you feel it pulling as the magnet moves by, yes. This is the same type of test that was done back in the 90s except with actual measuring tools and clamps, not free reving and your hand... well actually someone else's hand.
 
Interesting. Paul thanks for the repeat. I believe it if you say its true. Why do you need the stronger magnet? Is it more voltage and or amperage? Or is there a dramatic improvement in the timing curve? This is the reason I ask , when I got started in karting I used a 3hp stock wheel on a open flathead. I never went past 9000 rpms. I did not see any problems with the ignition system. Soon there after I started using billet wheels for safety reasons and have never looked back until now. Has there not been exhaustive testing done on the cause and effects of the stronger magnet? Could you not build wheel cheaper without the rare earth magnets?
 
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