Performance CDI by "Jaguar"

Technical Information:

Stock CDI: Basically the stock Grubee CDI is a high advance CDI made for low compression engines with carburetors that do a poor job of atomizing the gasoline. Both low compression and low fuel atomization require more advanced ignition because of the slow burn time in such an engine. And so the ignition spark needs to happen even more degrees before piston TDC (top dead center) in order for the peak combustion pressure to occur between 10 and 15 degrees after TDC which is the ideal for best engine power. Also the spark power is very low with the stock CDI which also reduces the engine power. It is low due to the small ignition coil in the CDI/coil combo. The hotter spark of our Performance CDI reduces burn time also. Excess ignition timing advance at high revs causes excess vibration and engine heat (read more) and wears out the crankshaft and conrod bearings too quick due to excess combustion pressure because with the stock CDI it is around TDC instead of 10-15 degrees after TDC. (Its pressure peak is higher because at TDC there is less volume between the piston and the head.) Click here to see a video demonstrating the function of our CDI. If the stock CDI had a little bit less ignition advance at top RPM then it would be ideal for the stock engine. But the reports of upper connecting rod bearing failure in the stock engine indicate that the timing is too advanced.

Performance CDI: This is a true 2 stroke CDI designed specifically for use with the Grubee engine. The amount of spark advance (in degrees before TDC) is near perfect for this engine and its timing curve can be set by the rider to best match the engine (stock or modified). Also the maximum spark gap is more than three times what the stock CDI gives. (read more) And the spark current is 50% more. This spark power increase causes around a 10% power gain from the engine. This is because of the bigger ignition coil that comes with this CDI.  From the research paper "Devices to improve the performance of a conventional two-stroke spark ignition engine" a 33% electrical spark power increase results in:
+2.5% brake thermal efficiency (engine power)
-30% carbon monoxide emissions
-38% ignition delay (ie: a faster burn)

Other Advantages:

Reliability: The stock CDI/coil combo is cheaply made and prone to failure. The Performance CDI is well made and much more reliable. The stock overly advanced ignition causes too much compression at high rpm by igniting the fuel mixture too early. This is very hard on the stock bearings (connecting rod and crank bearings) which are rather weak.

Higher RPMs: The Performance CDI increasingly retards (makes happen later) the spark timing at rpm's over 3600. At high RPM there is much more air/fuel turbulence which reduces the need for advanced ignition timing. (This is true of a small displacement engine whether or not the cylinder head has a squish band.) As a result of installing our CDI you will be able to run the engine to higher rpm's (ie: higher speed). To take the maximum advantage from it you can use a rotary tool to raise the exhaust port and lower the intake port to get even more RPM and more speed without risk of damage.

Aids High Compression Cylinder Heads: The higher the cylinder pressure of air/fuel, the higher the spark power needs to be to ignite it. If you modify your cylinder head for high compression or use an aftermarket high compression head then you are likely to have a significant amount of combustion instability and some misfiring if you don't also up the spark power. The Performance CDI solves that problem. Also if the head has a squish band then you need to be able to adjust the timing because squish bands cause a more rapid burn which necessitates later ignition timing to keep the peak cylinder pressure occurring between 10 and 15 degrees after top center.

Aids Expansion Chamber: The Performance CDI increasingly retards the spark timing at rpm's over 3600. An expansion chamber is not required for use with this CDI but there is an extra advantage with it. That advantage is an upper extension of the powerband. So if your pipe gives you an RPM range of increased power of 1500 then you may expect an extra 400 RPM of boosted power because of this CDI. Here's why: At high RPM the fuel/air turbulence is greatly increased which increases the burn rate. An increased burn rate causes the returning exhaust pressure wave to come back (from the final pipe cone) to the exhaust port too soon which hinders the entrance of the trailing amount of fuel/air intake charge into the cylinder which lowers engine power. This is remedied by retarding the ignition timing at high RPM which is what the Performance CDI does. Making the ignition spark happen later allows the pressure wave to return at just the right time for maximum engine power (due to a maximized delivery ratio of fuel/air).

Less Vibration: The Performance CDI reduces engine vibration at high RPM by retarding the timing. Reduction of the timing advancement to the correct amount keeps the engine from fighting against excess cylinder pressure each compression stroke which causes loss of power and increases vibration. You will see once this CDI is on your bike how much smoother it is at high RPM.

Customer Testimonies:

"Now there are no more misfires which were common with the stock coil, and about an extra 1500 rpm! Also a noticeable difference in acceleration and power as my engine no longer sputters along. It was a good investment, worth every penny!"

"Micheal, I just came back from a test ride, and I am very pleased with your CDI's performance. The power feels smoother and it feels like I have more top end. The bike runs like I visioned it would when I started the build. I don't think I could ask more from a single cylinder. I am very happy, will spread the word, recommend it to everyone, and after the Death Race I hope you will get more orders when I beat the Morinis." 

"I want you to know that your CDI works GREAT!  The motor pulls strongly at low and high RPM's  Thank You!"

"ALL my engines have had a consistent problem with bottom connecting rod bearing failure, but this was largely attributed to the standard CDI giving an ever increasing spark advance with increasing rpm's. Since fitting the Performance CDI I have not had any more bearing failures; in my case, the only reason why all 7 engines failed. All these engines failed at around the same time; between 700 and 750 kilometers [around 450 miles] - surprisingly consistent, and my oil/fuel ratio is 20:1 with the old engines and the new engine. With the Performance CDI I now have approx 3,000 kilometers on the 8th engine which was rebuilt with a new crankshaft, although the new crankshaft is of the crowded roller design."

Comparison to the standard Grubee CDI: On one long uphill I use for testing my bike went 20.5mph up it. 15 minutes later with the modified CDI the mph increased by 10% to 22.5! And at high RPM the standard CDI allowed too much engine vibration. The new CDI cut that in half for a much more pleasant ride. The stock CDI has an overly advanced timing curve which makes the engine run too hot and is hard on the bearings. If you raise the engine compression then the advanced ignition timing can cause detonation. The stock CDI may be OK for stock engines (power-wise) but is terrible for modified engines. The Performance CDI is better for both stock and modified engines because it is completely tunable to match the engine. Here is a picture of a piston with only two hours of running in an engine with detonation:

Here is Speed Concepts ignition curve analysis guide as a Word document: Guide
 

How does the Performance CDI compare to the Lightning CDI? Looking at the comparison timing curve graph below you can see the differnces. The Lightning is too advanced at the lowest RPM (allowing possibility of backfiring when starting) and at highest RPM (causing engine vibration, contributing to detonation, and being harder on bearings). And it is a bit too retarded around 3000 RPM.

The Rocket Racing Ignition: J.L. emailed me: "My bike is very limited with the Rocket Racing CDI presently installed. The unit is very ambient temperature dependent and only works well above 75 degrees F."

Although the Performance CDI is great for racing engines, it is not just for racing. It is made to increase the overall performance and reliability of these Grubee engines. But Steven "magrider" DeZwart, with the Performance CDI on his bike, competed in the June 2012 motorized bicycle race at Willow Springs, California. He has a 66cc Happy Times engine with few changes to it other than the Performance CDI and an expansion chamber. He emailed me: "I got 1st place in the China 2 stroke category and 1st place in the Trophy Dash which was the 8 top finishers of the classes. I saw your ignition on many bikes. Great job with this. I raced with the stock head temping out at 345 degrees." Here's his picture before practice with the 1st place trophy inserted in the picture:

Why doesn't this CDI come with two external switches instead of the on-board micro switches? Because you only have to make a few test runs to determine the optimum settings and thereafter you won't be messing with them. Also that kind of switch is prone to failure due to water intrusion and vibration. And if the contacts are momentarily breaking contact because of vibration then the engine will run erratically.

Other than having a weaker spark and more engine vibration why shouldn't I stick to the stock CDI? Because its excess ignition timing advance at high revs can cause excess engine heat (read more) and wears out the crankshaft and conrod bearings too quick due to excess combustion pressure because with this CDI the pressure peaks sooner than the desired 10-15 degrees after TDC.

Which engines can the Performance CDI work on? Any of these small two stroke Grubee engines that have a two wire output from the magneto stator coil to the CDI. It don't work with ignition systems that rely on battery voltage. My 48cc also has a third output wire (white) for use with a kill switch or lighting system. This CDI does not affect it at all.

Does it matter whether or not the engine is modified? Not at all. It improves performance of both modified and non-modified engines. But engines modified for higher compression and/or to rev higher will benefit even more. Click here to read about how to change the ports for higher RPM.

How can I test it to see that it produces a hotter spark? Just take out the spark plug, connect it to the spark plug cap, hold the spark plug onto the cylinder head so that it is grounded, and with dim lighting (best at night) push the motorbike and you will see the actual spark. Do this same routine with the standard ignition system before changing to this new system so you will have a point of comparison.
Here is a video showing the Performance CDI and Kawasaki motocross coil sparking a gap 5 times normal. Normal is .025" and the gap with the ground electrode bent out is .12" on this plug. The voltage source is the normal Grubee magneto rotated by an electric motor to power a Grubee stator coil. Read more

How do you know the timing curve change you made is all good? It is "good" because it is adjustable which allows the possibility of peak performance. It can only be "bad" if you do a crappy job of matching the jumper settings to your engine setup. Lucky for you I give recommendations on which jumpers to use. I used my Performance CDI for KDXes on my KDX200 both on the street and at the races and nothing bad ever happened and it gave better power. I have had the Performance CDI on my motorized bicycle for over two years now and it just keeps performing day after day after day!

What about your competitors CDI that has very little ignition retard at high RPM? That only works well with stock low compression and the crappy standard carburetor which has no true idle circuit and does a poor job of atomizing the fuel. In such a scenario it takes longer for the fuel mixture to burn and so needs more spark advance. But anyone that wants true performance from these engines should do these three things: 1) install a good carburetor, 2) increase the engine compression, 3) install the Performance CDI. The more the fuel is atomized (due to good carburetion and engine turbulence) the quicker it burns which produces more engine power because a greater percentage of the burn happens after top dead center if the ignition timing is correct. For it to be correct you need to retard the spark at high RPM so that the peak cylinder pressure happens around 15 degrees ATDC. So getting a good carburetor and the Performance CDI go hand in hand. With a good carburetor you will also have easier starting and a stronger idle that isn't erratic. And you can adjust the jetting for more power, less fuel consumption (in case of too rich jetting from the standard carb), and a cleaner running spark plug.

Shouldn't ignition timing be advanced at high rpm since there is less time available for combustion to peak at 10-15 degrees ATDC (the ideal spot for peak pressure to occur)? Although there is less time available, because of greater intake/transfer turbulence, the combustion happens faster. Admittedly though the shorter combustion time doesn't shorten as much as the shorter degrees time. There is a balancing act going on with the correct ignition delay. As rpm rises the fuel/air delivery ratio decreases leaving less power derived from each combustion cycle, but there is more mechanical pumping losses (if the ignition timing remains the same) to counteract. So retarding (delaying) the ignition at high RPM is a balance between reducing pumping losses without excessively delaying peak combustion pressure past the ideal 10-15 degrees ATDC (which reduces usable power).
The result is that some power is lost due to the peak pressure happening past 15 degrees but there are also two advantages to ignition delay. One is that less heat is transferred to the head/cylinder/piston for less likelihood of piston seizure, and the other is that the exhaust gases become hotter which causes the sound wave in the expansion chamber to travel faster and return to the cylinder faster, better matching the lessened cycle time which results in a broadening of the powerband due to the expansion chamber.

Why does a 4 stroke engine need the ignition timing the most advanced at high rpm? As RPM rises the delivery ratio reduces which, contrary to how a 2 stroke is, also reduces pumping losses. That is because there are no remaining exhaust gases, as a 2 stroke has, to fill the cylinder to make up for the reduction of fresh fuel/air delivered. Also there is no pressure wave returning from an expansion chamber to cause more cylinder pressure (causing more heat). Since the power strokes happen half as often as in a 2 stroke (given the same RPM) there is less potential for piston seizure. And since they don't have expansion chambers there is no point in making the exhaust gases hotter to lengthen the engines powerband. The latest technological recommendations is for some timing delay at high RPM for 4 strokes, but not near as much as a 2 stroke needs.

Is the Performance CDI adequate for a highly modified racing engine also? Of course it is. This CDI is good for up to 10,000RPM. But higher than 9000 is not recommended since the transfer ports are small on these engines. It is possible to reach 10,000 by raising the ports but the power will be noticeably less than with an engine with larger transfer ports. And porting for that high RPM kills low RPM power. My bike revs to 8500 and still has down low power for street use but I cheat by having a torque pipe I custom built.

Is this the "Jaguar CDI" I have read so much about on the motorized bicycle forums? Yes it is. We just had to change its name due to trademark restrictions.

What if I don't know how to solder? Then read these online soldering tutorials for beginners:
http://www.epemag.wimborne.co.uk/solderfaq.htm#howto
http://www.epemag.wimborne.co.uk/desolderpix.htm
http://www.epemag.wimborne.co.uk/solderpix.htm
For a soldering iron I recommend a dual output (20/40 watt) one, # 64-2184, for $23 from Radio Shack. A good cheap .05" diameter solder is available from Radio Shack (locally or online at www.radioshack.com, #64-015) for $3. Also it is possible to use a flame from a candle or match to melt the solder to join the wires.

How do I insulate the exposed connection afterwards? Included with the CDI is 4 pieces of heat shrink tubing (available also at Radio Shack). Please put the black heat shrink tubing on one of two wires before soldering them together. Then slide the tubing over the exposed solder connection and move the soldering iron back and forth over it so that the heat causes it to reduce its diameter and provide a tight seal over the metal.

WARRANTY - If the CDI or coil fails within 1 year of purchase then the failed part can be returned to Sick Bike Parts for a new replacement.