Deleting Motorcycle charging system

[regal7point5]

I am in the early early stages of a bike build for the Maxton Mile.  The bike is a 1981 Yamaha SR250 single cylinder.  Just like every streetbike, it has a charging system that I would like to do away with if possible.  This will be a race bike only.  I have no title, the bike's "street" accessories (headlight, signals, brakelight) and wiring was trashed by the previous owner.  I know drag cars will run with a battery and no alternator; can I do this on my bike?  I suppose I am looking for any advantage I can get on rotating mass.  How do I go about doing this?  Is this a dumb idea?

Thanks,
Aaron

[Jonny Hotnuts]

you are not looking for a rotational mass advantage, a lighter crank will spin up quicker but not make more HP. You should leave the magnets on the stator. A heavier crank will not hurt unless you are running a twisty road track or 1/4 mile. The added crank weight will help in LSR through the gears, even at the short maxton mile.
You will get some advantage at the stator because there is not a HP loss from charging draw but if the lights are not on they will not draw power from the stator. The charging system works as an "on demand" system (rectafier). The only thing you would be powering would be an ECU and coil.

I would be willing to bet that they are not drawing enough to see HP on the dyno.
The reason drag cars (and other LSR including mine) run batteries is because they run many electric accessories that WOULD cause a considerable loss in HP.

Personally I run 2 big electric water pumps, on board air compressor, 1 large fuel pump, ecu, 4 coils, injectors and data acquisition. The stock busa stator (400 watt output) would not handle the loads.

This is why I run batteries. (this year 1 16v rock and not 2 yellow tops). 

Good luck~

~JH

[regal7point5]

I suppose my thinking was based on my drag racing background...I suppose I could always wire a switch inline of the stator and see if it makes a difference on the dyno..or the mile.

Thanks again for the input.

Aaron

[JimL]

Remove the stator...the rotor magnets drag against the stator coil cores whether you make electricity or not.  My exercise bike uses magnetic drag....faster I go, the harder it is.  Bike alternators are very RPM dependant to make electricity....the more RPM, the bigger generation (and drag).  Bike alternators are like my exercise bike, not like the excited field alternator in a car.

Ever tried to pull a rotor out of the stator?  When it starts off the taper end of the crank, it grabs right onto the stator!

Regards, JimL

[slopoke]

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[slopoke]

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[regal7point5]

I'm not worried about exceeding the value of the bike with modifications...buying a can of spray paint will do that for me...I didn't pay a thing for it.  This is more of a learning experience/licensing/fun thing.  I do plan on good gear which will be used for future projects. 

As far as setting a record, it would be nice, but know that it is not the ideal bike for the class.  I do also have a ninja 250...maybe that will morph into a land speed racer as well.  I just like making things going faster than they were intended..its a disease, I know.

[slopoke]

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[willieworld]

  --you know sometimes on the computer its hard to tell if someone is being a smart ass or they are serious---i have never reccomended that anyone run 45 degrees of rake  and never will---- i run 55 degrees and wouldnt reccomend that either--its not the amount of rake that you should be concerned with anyway but the amount of trail---- although they are related they are not the same ----10 differant bikes with the same rake can all have differant trail

                   willie buchta

[Stainless1]

OK.... this is me being a smart ass....  (just so everyone knows)

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slopoke... were you and panic separated at birth... 

OK, back to our regularly scheduled program...

[willieworld]

just so everyone knows---before this last weekind i removed the charging system from both sheri and my bike trying to free up a couple horsepower ---sheris bike wouldnt run under a load (although it ran good with no load) she turned off the track ----my bike ran 6 miles per hour slower than last november  with no other changes---i dont think the battery had enough power to run the ignition--i will admit that was a stupid mistake and will put the charging system back on before the next race   just some thoughts                                  willie buchta

[McRat]

Weak spark running total loss is common.  I think it's because with the alternator running, you have 14-15 volts available instead of 13.  Perhaps get a 14-16v battery or fab one up from NiCAD's.  Two NiCAD R/C car packs is like 14.4v? 

[38Chevy454]

I also believe there is logic in running a charging system to keep the voltage up and a strong spark.  I always ran analternator on my old drag car for this reason.  Unless you have real large battery capacity, the voltage does drop off at the top end, right where you need a good strong spark.

Now previous discussion indicates the motorcycle charging is not like an alternator, so maybe it does have more drag.  Plus with only 250 cc to start?  Is the charging system on the bike actualy a generator?

[regal7point5]

My thoughts were that a 16v battery would help combat the "low" voltage of running without a charging system.  One other question, when running a battery only, does this mean the regulator/rectifier is no longer needed or would this be required when using the factory ignition module?

Thanks,
Aaron

[JimL]

The ignition module runs straight off the 12V battery, with timing typically fed by a pulse coil (rectifier etc. not needed).  Dwell time is probably preset (probably what Willie has) which means that high load (more throttle opening, more air compressed, higher compression = higher resistance) requires more secondary voltage.  I get it by running a 6V Mini-Trail battery in series to the B+ terminal of the coils.  Hook the 12V coil wire to the (-) wire of the Mini-Trail battery, and the (+) wire of the Mini-Trail battery to the 12V terminal of the coil (assuming you have a 12 volt system?)

The igniter does not see the 18 volts, and at high RPM the coil saturation time is so short that the coil is "down to about 12-14 volts" anyway.  I learned this trick from the American Indy Series guys (racing old Indy cars in club events).  The Menards ran the Mini-Trail battery to keep the spark alive at high boost....particularly when the driver had to lean out a little to stretch his fuel.

Lean compressed air in a cylinder is a good insulator in the spark plug gap.  The higher you compress it, the better it insulates....especially if your gasoline has a high 90% distillation curve!

If you know the primary voltage is pulled down a little, and the engine misfires or falls on its face....you are on the ragged edge of lean or your gas is too heavy...or both.  40 years ago, we used to test cars this way (I had a couple BIG low ohm resistors in my toolbox, and jumper wires to interrupt the coil B+ power).

Simpler is better!
JimL

PS:  Don't confuse heavy gas (high 90% distillation temp) with too high octane number...they don't quite equate and I ain't smart enough to tell you exactly why!!