coil for 250 racer

[DewCatTea-Bob]

By: Stu65...
" I use total loss and points on my race bike with a 3 ohm coil and ,
we did a 5 hour endurance on the 250 Monza, we changed the battery after 2 1/2 hours
but that battery still showed good output, "

____ Since you didn't bother to mention what TYPE of battery you employed, are we to then assume that it was a stock type & size battery ?
Cuz the last time this topic was brought-up (in another thread a few months back), I was then made-aware of new-type non-lead/acid batteries which were smaller & lighter and could last all day without recharging.
__ So since it seems that battery-charge/juice storage-capacity is not a real concern, (at least for racing-rounds lasting up to 2-hours),, then a racer who's concerned about battery-power & spark-quality, could install TWO separate batteries (of the most advanced/modern type), and add a switch to engage the second-battery towards the end of the race.
Then in such case, the amount of stored-juice usage which an ign.coil consumes would be of little concern, (thus the primary-coil's resistance would be of much reduced concern).



By: Harvey...
" I would go for a 4 ohm primary. On 12 V, that will run 3 amps, for 5 hours, thats 15 amp hr. "

____ Your statement has saved me from having to point-out such related math, however YOU've left-out one factor...
Since the ign.points are only closed about 40% of the time, that thus-then means that the ign.coil's AVERAGE current-draw is under half your stated "3 amps" ! _ So-then for the "5 hours" , there would ACTUALLY be more-like just 6 amp.hours consumed from the battery's stored-charge.



Dukaddy-DUKEs,
-Bob

[Jordan]

I'd avoid a Ducati coil because I've heard enough bad reports about them, and I've had a "dead" one.
Lucas motorcycle coils never gave me any trouble. The same for Japanese aftermarket points type m/c coils.
You probably don't want a car coil on a race bike because of size and weight. Otherwise they could be a cheap option.

Jordan

[flynbulldog]

" Can anyone recommend a coil? "

____ Why not simply use your stock

Dukaddy-DUKEs,
-Bob

I don't have one.

I don't have a battery yet either, but I was going to look into a lithium battery.

[wcorey]

Bosch 'blue' coils have long been a favorite for all types of hi performance stuff, they can be had pretty reasonably if you dig around. I used to get them from BMW's, Mercedes and such at the local boneyard for about $5. I've had extraordinary luck finding cheap Dyna coils at a big Harley-centric swap meet I usually hit every May, found a working pair last year for $1.

What primary resistance to use is also partly decided by what type of ignition device you're using, some can't handle switching the higher current required by lower resistance coils. That's likely why coil manufacturers don't want to sell you some random resistance value, too low and it can potentially fry your ignition module.

Bill

[Jordan]

He's using points, so there's no electronic module to worry about.
Using a condensor that goes with the coil could be a good idea.

Jordan

[Harvey]

" Can anyone recommend a coil? "

____ Why not simply use your stock

Dukaddy-DUKEs,
-Bob

I don't have one.

I don't have a battery yet either, but I was going to look into a lithium battery.

There are a few good options in the battery. The lead acid is not the best it looses its voltage as the change is used. Batteries like the Nicad, Metal hydri, hold their rated voltage till there they run out of current, so the spark doesn't get weaker. as the day goes on. A lot lighter, and don't shake to bits on a single.

Jordan . Using a condenser that goes with the coil could be a good idea.

The condenser is matched to the cam and points leverage. It provides a low resistance path for the primary current, for a limited time, till the points are far enough apart to prevent the primary current from continuing to flow across the low resistance of the parting points.

[jbcollier]

The Dyna green "3 ohm" coil has a primary resistance of 3 ohms. 4 ohms will still fire the plug and the battery will last longer. I use a Dyna green with a 1 ohm ballast resistor and have no problems spinning 10k+ rpm.

[ducwiz]

Hi,

in an old Cycle magazine article a test of different coils was published - showing significant differences in performance. The worst listed is the stock Ducati type, the best a second source type from K-Mart !
I have made the article available for download at http://ducwiz.minus.com/mIK7TfXpI/1g.

However, if you are unconditionally eager to run your bike solely from the battery, it helps to install an electronic (transistor) ignition with a fixed and minimised dwell time. This feature reduces the current consumption at low revs, thus prolonging the resilience of you battery. A 12V system is mandatory, as all components are less expensive and easy to find, and power loss due to unavoidable contact/cable resistances is less significant.

rgds Hans

[LaceyDucati]

We always used Lucas 17m12 coils (oil filled) 4.2 ohm. Very reliable but unfortunately now obsolete, but can be found secondhand.

We used 2x 17m6's in series for twin plug heads (still just about available in the UK).

Avoid PVL replica's (resin bonded) as we have found them unreliable.

The cheap Emgo coils ( I guess Chinese? ) seem to be reliable according to customers. I guess don't knock it if it works, especially if it's cheap!

Some of our customers have used Dyna 3 ohm coils, expensive over here and tend to fail after a few years of racing. Not ideal for long races like the Manx GP with total loss as they do drain the battery. Road riding customers have reported very short lives as the coils run hot with low speed riding.

NUMBER 1 rule with coils, mount them in fresh air. I always mount mine in front of the engine as far away from the engine as possible i.e. on the side of the front down tube or under the tank at the front. Another thing to ensure is not to crush clamped type coil by over tightening (esp the oil filled types). Spacing the clamp to ensure it can only close up enough to only just clamp the coil is the best bet.

Hope this helps
Nigel

[Jordan]

Great tips! Thanks Nigel

Jordan