[NoDOHC]

So now that I am nearly certain that I have squeezed every single possible horsepower out of my engine with the stock ignition. I am looking for ignition options.

I have a limited budget for this (I do not want to exceed $200.00 for new ignition).

I have heard mention of LS1 coils, Some have mentioned that MSD coils work pretty well, but I don't know if I could use one for the rotary.

Explanation:
Because the leading plugs are wasted spark, the leading plug coil must fire 2 times per engine revolution. Because the coil requires approximately 0.5 ms to fire and at least 3.5 ms to charge (or the spark is very weak), The leading plugs can not reliably fire above 250 Hz 1/4ms = 250 Hz.

{** IGNORE THIS PARAGRAPH IF YOU ARE NOT AN ELECTRICAL ENGINEER**}
The current through the leading coil peaks around 4.8 ms, indicating saturation. Because the current through the inductive coil increases at a nearly linear rate, the coil energy (0.5LI^2) can be computed based on charge time. If maximum charge occurs at 4.8ms, the current at 3.5 ms will be 3.5/4.8 times the peak current or 0.729 times the peak current, 0.729^2 gives 0.532. Thus at 3.5ms charge time the coil contains 0.532 times as much energy as at 4.8ms charge time.

Unfortunately, 250 Hz equates to 7500 RPM. (7500 ignition events/rotor/minute = 15000 ignition events per minute = 250 ignition events per second). This means that the leading coil is not charging adequately to light the fuel mixture. The trailing coil is similar as the charge signal must travel a common line for both rotors, even though neither coil is close to saturation.

Now I can give some actual hard data for mechanical guys who don't care about EE formulas.

I have attached a graph of normalized torque output for my engine.
Normalized Torque = Wheel Torque/VE of the engine as a decimal (IE: 1.1).
Most engines will have a very constant normalized torque as it is basically a measure of chemical efficiency (which depends on combustion chamber dynamics, engine displacement, compression ratio, Air/fuel ratio, etc.), all of which are fixed for an engine (if the AFR is tuned consistantly).

A good number for a piston engine that I have heard is 1.0+((CR-8.0)/30) lb-ft/cid at 100% VE (1.0).

The chart is included as a .jpg. These numbers are listed for anyone who wishes to check my work.

Engine Speed (RPM),Fuel,AFR,VE,Torque,Normalized Torque
5000, 4.85, 13.3, 103.05, 145, 140.7
5500, 5.02, 13.3, 106.67, 151, 141.56
6000, 5.21, 13.2, 109.87, 155, 141.07
6500, 5.4, 13.1, 113.02, 160, 141.57
7000, 5.5, 12.8, 112.47, 154, 136.92
7500, 5.3, 13.3, 112.62, 148, 131.42
8000, 5.1, 13.4, 109.18, 139, 127.31

From this trend, it is clear that the engine makes very consistant torque/VE below 7,000 rpm, but this number starts to decrease abruptly as the speed exceeds 7,000 rpm. (Interesting that this is a very similar speed to that computed above, isn't it?)

Interresting Side Note:
Using the formula above, the 100% VE torque of this engine should be:
1.0*((8.2(Compression ratio)-8.0)/30)*160 (effective displacement in cubic inches)= 1.007*160 = 161 lb-ft at 100% VE (1.0).

If you use an 20% drivetrain loss calculation (standard for Mustang Dyno and IRS car) you get a flywheel torque number of 176 lb-ft at 100% VE
Thus this rotary engine makes 10% more torque than an equivalently sized piston engine (with the same compression ratio) would make.

{** IGNORE THESE 3 PARAGRAPHS IF YOU ARE NOT A DATA ACCURACY FANATIC **}
The injection time is actually shorter than the injector energization time that is used for these calculations. Therefore the engine volumetric efficiency is probably not as good as the table above would indicate. However as the injection times listed are all within 10% of the mean injection time, the introduced error from an energization time offset in these values would not be appreciable.

The torque/VE claim would actually be higher if actual injection time were used as this would decrease the implied VE without modifying the measured torque.

The drivetrain efficiency would have to be 90% (which few people would accept as valid) before the torque numbers would fall into the piston engine domain.


Oh yeah, I need to compute what this engine should make for power if it didn't have ignition issues. No, actually I will need the VE curve for 8,000-9,000 rpm to do that (which I do not have). At 8,000 it is pretty simple 141 Wlb-ft/VE * 109% VE * 8000 rpm / 5252 gives 234 WHp (Probably a little higher at a higher rpm).

What should I use for ignition?