175 Ignitions

Hi,

I was just browsing ebay and came across, [url=http://www.ebay.co.uk/itm/Petrol-Pit-bike-quad-Stator-rotor-main-cable-CDI-ignition-Coil-Kit-SR0911-/230880667258?pt=UK_Motorcycle_Parts&hash=item35c18f667a[/url].

Has anyone ever looked at using a pit bike ignition on a bantam ? certainly cheaper than a pvl may just require a small rule change to make them eligible, as Tesco say every little helps  

JC

Interesting comment? Whats the ignition curve on it?

Bare in mind the only lap record broken in 2013 was Cadwell Park and the new
Outright bantam lap record is held by a "175" !

Anyone else like to speak up?

Regards Mike

Way back in the day , Jan Thiel was persuaded to try his hand with the Garelli team . One of the things that he brought with him was a great big blue, oil filled Bosch ign. coil, up to that point the team were using trick, slim line Japanese jobs . These Bosch coils produced a massive spark of long duration, the efficiency of the subsequent initial combustion burn, at the rpm and cylinder pressures that the engine produced, gave an immediate power lift !
In a race engine you have to be able to depend the ign system to be able to ignite a mixture that is weak, rich, contaminated with spent combustion deposits, or when compression pressure is high from good filling or with a high compression ratio.
The gas molecules between the plug electrodes are non conductive, so to enable a spark to jump between the electrodes, ionisation of the molecules must first take place and only then can a spark arc ignite the gas to initiate combustion . Obviously as revs increase and pressures  go up, together with a reducing time cycle, the demand on the ign grows, only top quality gear will do a dependable job .
The 175/190 brigade have an additional problem in that the large diameter bore and its long flame path from plug to cylinder wall. If the spark is limp at the go get then rev potential will be compromised and becomes just another example of, what was missing at the start won`t be made up for later !
Combustion is the great unknown for garden shed tuners , in that you can only feel the consequences, be it good or bad, and is a phenomenally complex process .
The question I continually ask myself is why should the big boys be disadvantaged for no sensible reason by being denied the use of a fully retarding ignition set up ? Engine reliability and performance will both improve and increase with it`s use, and as the larger class is seen to be the natural home of newcomers, it will be no more expensive to use a system fit for the 21st century than one having it`s genesis in the 1970s !

Cheers,   Trevor

The pit bike ignition is a relative unknown, especially regarding the curve (if there is any at all) so it may pay someone like myself to buy one and fit to a known engine to check if a curve exists. Alternatively anyone with a pit bike out there who is willing to put a strobe on the engine (or let me?) so that we can find out?
I say we find out more and then we will have another source of 175 ignitions.
The 175 class can hardly be disadvantaged if they break lap records and also win races outright... can they?
The idea of the simple curve ignitions goes back to cost as (in general) they are the cheaper end of the market and allow more riders to get involved in Bantam racing at an affordable cost.
Long may they reign!
Cheers,
Alan

Courtesy & Property Of Trevor Amos.

To enable a racing 2t engine to give of it`s best, the ignition curve needs to at least approximate the inverse of the power curve . Low end timing can be pushed to 30*, as revs increase, and bmep with it, the pipe gets into phase and dynamic compression ramps up together with heat, to avoid self destruction timing has to be pulled back and in my engine peak torque timing is 14*btdc. As revs reach max, timing is further pulled back to help more heat to be dumped into the pipe to keep wave speed and power up for just a little longer in the over rev range . Any ignition change will influence the torque curve, which in turn alters the whole behaviour of the engine .
Every modern race engine uses this scenario, but far more sophisticated than my efforts, that it works is a self evident truth and keeps the engine safe at the critical edge of survival !
The red line on the simulation graph is my w/c engine with the straight line ign. of the Motoplat and in this guise Mark lapped lydden in 48secs, so yes, record breaking is indeed more than possible with this system. The blue line has the identical engine spec as the red but has the ign. timings of the Honda curve plotted in, the difference is remarkable ! Both igns. were timed for 14*btdc at 10500rpm, the two lines mesh at 11,000 but the retarding system helps keep power up for 500rpm more and contributes a little more power. After several pipe designs the one shown here filled in the droop in output and produced the green line, which was just what was needed .
None of this would be possible with a 175 type of ign. system, and the principle objection to a fully retarding system seems to be cost, but it is only the difference in the price between the two systems that warrants consideration, and in terms of " bang for bucks" it seems to me to be a no brainer !
As a foot note to this I asked Mark for his recollections, and if he would like to revert to the Motoplat , his initial reply was pretty predictable, but not printable, the most significant improvement he felt came in pure drivability, so much more controllable power with the wide spread of power available !

Catch you all a bit later ? Trevor