Excitor coil signal conversion

bradrs

Joined Jan 23, 2023
17
It's almost impossible to create "better" performance than
the original factory installed Ignition-System.

You will not gain any Engine-Power by changing the Ignition-System.
It is fairly easy to create better performance than the original factory installed systems. You can extract higher voltage from the original stator, making kickstarts much easier. Improved timing curves can be optimized for different exhaust pipes, which is especially important on 2 strokes. This can give more peak power, as well as allowing it to rev a good bit higher. I designed programmable ignition systems for dirtbikes/quads from the late 80s to the early 00s that made good power over stock, dyno proven. I no longer work for the company that still sells them. But they are legitimate performance boosters. There are lots of lower quality ignitions out there that really are no benefit over stock. But a quality one can get gains, proven on a dyno.

As far as swapping out the stators, does the new one come from an engine that runs at the same RPM? Something to consider is that some of those stators will drop off power output at RPM higher than they were intended to run.

If making your own circuit: Inductive pickups increase amplitude as you increase RPM, so if you trigger at any set voltage, you will get some angle drift as the RPM changes. If the tooth you are sensing is shorter than the pickup, you will get a large negative, then positive voltage swing. And the zero cross should be at a consistent angle. Alternately, using an integrating circuit can work, but it is a good bit more complex.`

If you are trying to set up your system to work with this programmable ignition, instead of building one from scratch, you will want to use whatever pickup they use, and make sure the rest of the hardware mimics what they are expecting. I seem to recall even swapping to different inductive pickups on OE circuits was enough to mess the ignition up, as they were usually designed just for the signal from that pickup.
 

LowQCab

Joined Nov 6, 2012
4,029
Improving upon the factory Engine "Package" can certainly be done,
and it's reasonably easy,
just install a "MicroSquirt" Fuel-Injection-Computer,
along with a single, generic, Fuel-Injector, and an Electric-Fuel-Pump,
and an Ignition-Coil-Module from a late-model GM Truck .

Smaller-Scale Fuel-Pumps and Injectors come on many late-model "Street-Bikes",
which may be more convenient than the usual "full-sized" parts.

This setup does require a small LifePo 12V Battery for starting,
but it gives You complete and repeatable control over all aspects of Fuel and Ignition parameters.
Then You need to have a reliable and repeatable Dyno to verify whether or not
a particular change has a desirable effect ...... or not so much.

This will eliminate the vast quantities of "Old-Wives-Tales", and "Bench-Racing-Blarney"
that is so prolific on the Internet, ( and at races ).

But this is not where the significant Power-increases are to be found.
Compression-Ratio,
Combustion-Chamber-"Squish" size and clearances,
Porting-work,
Camshafts, ( for 4-Stroke-Engines ),
or,
Expansion-Chamber-design, Reed-Valves, Power-Valves ( for 2-Stroke-Engines ),
are where the biggest Power-gains are to be found.

Then there's playing around with different Fuels and Oils.
Then there's Tires, Suspension, and Handling.

Everything else is just "a-Lick-and-a-Promise".

The Thread-Starter is very unlikely to go to this extent,
and changing Ignition-Boxes in the "hopes" of gaining a provable Power increase
is most likely going to be just a waste of time.
.
.
.
 

bradrs

Joined Jan 23, 2023
17
But this is not where the significant Power-increases are to be found.
Compression-Ratio,
Combustion-Chamber-"Squish" size and clearances,
Porting-work,
Camshafts, ( for 4-Stroke-Engines ),
or,
Expansion-Chamber-design, Reed-Valves, Power-Valves ( for 2-Stroke-Engines ),
are where the biggest Power-gains are to be found.
Much of the time, the gains from those mechanical changes are minimized by the stock ignition curve being a bad match for those changes. Especially as people were heavily modifying the engines, like the shifter cart racers we dealt with. It has been a while, but I recall the gains from adding the ignition on top of those parts, being at least as big as the difference from adding the other parts. Maybe not in peak numbers, but in usable area under the curve.

The Thread-Starter is very unlikely to go to this extent,
and changing Ignition-Boxes in the "hopes" of gaining a provable Power increase
is most likely going to be just a waste of time.
Is it an otherwise stock bike? I am guessing if he wants to play with powervalve timing, it has already had some mechanical upgrades. It is a project to change the ignition, but not as much as adding megasquirt.
 

LowQCab

Joined Nov 6, 2012
4,029
Ignition-Timing is a very exact thing,
and advancing the timing can provide substantial gains over the factory settings,
but few people have the resources to actually set it in a manner
that provides the maximum gains in Torque across the entire RPM/Load range.

I would recommend simply keeping the factory Ignition-System intact and
simply advance the overall Timing a few degrees at a time until Lap-Times
stop improving, then back it off to the last setting that showed an improvement,
keeping the factory Ignition-Advance-Curve and Rev-Limiting-RPM.
But You might just find zero Lap-Time improvement because of
the "Bottle-Neck" being elsewhere in the system, ( the system also includes the Driver ).
.
.
.
 

bradrs

Joined Jan 23, 2023
17
Ignition-Timing is a very exact thing,
and advancing the timing can provide substantial gains over the factory settings,
but few people have the resources to actually set it in a manner
that provides the maximum gains in Torque across the entire RPM/Load range.
That is a good point. If he starts with one of the RS125 specific programmables, it may have the original timing curve in there as a reference/base starting point. But if he starts with the programmable he selected, or something like a microsquirt, it wouldn't even have the original curves to start with. The systems I designed, and some of the other aftermarket programmables in that time frame, would include a set of timing curves precalibrated for a few different mods, in addition to stock. Those could be used as a reference for making your own.


That LS truck coil you mentioned as part of a microsquirt system is potentially the riskiest coil to use. Most transistorized coils go out of saturation and just overheat the coil if you accidentally overdwell it. That coil fires when it hits a certain current. So it can fire way advanced of your settings, if you accidentally overcharge it. I found that issue myself on a test bench, and others have reported it as well. Not a lot of people pay attention to that issue, but its an unecessary risk when there are any number of other coils out there that don't do that.




I would recommend simply keeping the factory Ignition-System intact and
simply advance the overall Timing a few degrees at a time until Lap-Times
stop improving, then back it off to the last setting that showed an improvement,
keeping the factory Ignition-Advance-Curve and Rev-Limiting-RPM.
But You might just find zero Lap-Time improvement because of
the "Bottle-Neck" being elsewhere in the system, ( the system also includes the Driver ).
It can be tougher to just advance timing with these setups. You may have a little free play in the pickup, or you can slot the pickup bolt holes in some cases. Offset crankshaft keys are another way. But a programmable is better. On most 2 strokes, you gain power down low by advancing timing. But you lose power at the high RPM by advancing timing. If anything, retarding timing will potentially give it a bit more top end power, at the cost of a weaker low end. With a programmable, you can add 2 degrees down low, take 2 degrees from the high RPM, and get more performance everywhere.
 

shortbus

Joined Sep 30, 2009
10,045
On most 2 strokes, you gain power down low by advancing timing. But you lose power at the high RPM by advancing timing. If anything, retarding timing will potentially give it a bit more top end power, at the cost of a weaker low end. With a programmable, you can add 2 degrees down low, take 2 degrees from the high RPM, and get more performance everywhere.
Thank you for saying that. This is the same thing I have been seeing said on most 2 cycle sites. Not what I learned on 4 cycle engines but really interesting.
 

bradrs

Joined Jan 23, 2023
17
Thank you for saying that. This is the same thing I have been seeing said on most 2 cycle sites. Not what I learned on 4 cycle engines but really interesting.
It was an interesting learning curve on them. Their timing curves are opposite of a typical 4 cycle. Most advance at idle, and you decrease timing as RPMs climb. If you quickly bring timing back in at high RPM, it is basically like a rev limiter, it just won't go past it.
 

shortbus

Joined Sep 30, 2009
10,045
It was an interesting learning curve on them. Their timing curves are opposite of a typical 4 cycle. Most advance at idle, and you decrease timing as RPMs climb. If you quickly bring timing back in at high RPM, it is basically like a rev limiter, it just won't go past it.
That's what the TS is up against, a rev limiter. He's using a inner rotor ignition(MVT brand) that is from a 50cc bike on his 125cc bike. He want's to use a different DC CDI box that's programmable with the inner rotor for lighting and the trigger for the DC box. He can't put a slug on the outside of the rotor without putting it off balance.

I suggested using the trigger coil built into the inner rotor to triger the DC box, but so far haven't found if the two trigger voltages are compatible. All the 2 stroke stuff I've worked on was before CDI, and didn't have any power valve exhaust, just expansion chamber exhaust.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
I have already installed all the performance parts that you can think of.
Programmable CDI is one of them. This is just final touch to complete the bike and fun project to do, or what i thought it would be :p
The last try would be to ask zeeltronic if they can make or have in stock CDI for the MVT ignition type.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
The reason for using this type of ignition is 50% lighter rotor, i know that lighter rotor causes harder start on stop but since this is a small cc motorcycle, you spend all the time in the higher RPM and the throttle response is much better. Also two strokes are sluggish up to cca 7000 rpm so you want to get out of that range as soon as possible.
 

Thread Starter

Vforce94

Joined Jan 11, 2023
21
I didn't understand that was his reason to do this ignition swap. Derestricting a bike with a low rev limit is usually much easier.
Many of these race bikes have ways to derestrict them built in to the original ECU, or an ECU only swap that you can buy.

Here's one for an RS125. I don't know if it is applicable to his year or version, just an example.
https://hartrusion.com/en/aprilia-rs/remove-power-gap-from-qca91/
The most important reason is that it has lighting coil because i want to keep it street legal, none of the aprilia rs 125 racing ignitions have lighting coil
 

bradrs

Joined Jan 23, 2023
17
I have already installed all the performance parts that you can think of.
I dunno, I can think of a lot of performance parts. Nitrous? Turbo? 250cc swap?:)

How much adjustment have you made to the timing on your existing programmable CDI?

The reason for using this type of ignition is 50% lighter rotor, i know that lighter rotor causes harder start on stop but since this is a small cc motorcycle, you spend all the time in the higher RPM and the throttle response is much better.
A lighter rotor is definitely noticeable when you rev it with the bike in neutral, actual power difference is negligible. Some 2 stroke racers here add flywheel weight instead of taking it off. But if I was building a Bosozuku bike I'd want the lightest stator possible.

If you really want to go with the lightweight stator route, then contacting the manufacturer of that ignition to see if they can help with the pickup selection makes sense. Does their ignition have a coil built in, or is it separate? You may need to change the coil to whatever that MVT ignition needs. Some ignition boxes have higher output voltage than others, and that is scaled up by the ignition coil, so the coil needs to be matched to the box.
 
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