Detonation rotary engine on methanol

Hi all,

we have had a broken front iron and opened the engine. The first rotor has a little dent which is a sign of pre-ignition, detonation ....

We are running 8° degrees ignition @ 2.4 bar of boost, 12° degrees split and a lambda of 0.61. Average EGT was 630°.

I can not imagine that 8° is to much advance. Is lambda 0.61 to lean?

We ran 12° advance @2.2 bar of boost with a lambda of 0.74 on E85 and never had a problem with that.

Any input is appreciated as i am not sure what to do now.

engine specs: 13b, large streetports, 8 x bosch 210 lb/h injectors, CAS, 4x aem smart coils, semi p-port, borg warner s475, castor oil premix ratio 1:80

Your timing is probably about right given the boost pressure you're running, however you're running way too much split. Generally I'll run perhaps 12-15 degrees split in the off boost areas but as you come up into boost you narrow the split down. At 2.2 bar with 8 degrees leading, I'd likely be running around 6 degrees split. Your lambda target is also about right. I've had some rotary engines that needed to run much richer than this but given your EGT I'd say you're just fine.

Thank you Andre, i never thought of running that little split. Is it a common value or is it because of our 8° timing?

And a second question, just to be sure that we are doing it correctly.

We are running the racing beat pulley that has timing marks at +10, 0, -10 and -20°. When we set the timing we lock the ecu at -20°, set the timing light at 2-stroke mode and start with 2000 rpm. As the original CAS tends to be off at higher rpms we check the timing at 6000 rpm as well. Is that correct?

I attached the timing and split table. Does it look ok for you for the start?

ps: I just noticed that i switched colums. At 0.5bar it should be 10° and at 1bar it should be 9°

Your split reads correctly off the crank pulley with timing light with negative values in the table? Most ecus are positive table values for trailing firing after leading and vice varsa (some people and mazda used neg split in vacuum). Yours appears to be the reverse but I'm not familiar with those ecus. If it isn't that could be the cause of your detonation.

Yes it reads negative values.

You are not the first asking that :-)

Can we get some more background on the project?

What engine did this start life as? Is it a 13B-REW? Is it a 2nd gen engine (series 4 or series 5)? The older engines (before the Cosmo and FD Rx-7) had weaker irons, especially if it's pre 1989. Over the years Mazda strengthened the castings.

What ECU is this running? What is the crank angle sensor? It sounds like this is a 2nd gen engine with the drop in crank angle sensor. Why did you get rid of the original pulley?

When you say methanol, does that mean you are running pure M100 methanol? If so, why did you switch from E85 to M100? Or are you running some other fuel with methanol injection? What plugs are you running? Alcohol fuels (methanol or ethanol) are more sensitive to preignition and need really cold plugs. I would run at least an NGK "10" heat range in the leading and trailing for your application.

As for the split, speaking respectfully I think Andre and I have a different philosophy. I increase split with boost, he reduces it. That's its own debate.

Hey Raymond,

thank you for your interest. Some more infos for you:

The car is only build for drag racing

- It is a 13B-REW with 9.0:1 rotors and semi p-port housings.

- We are using a 12A front cover with the drop in CAS because of the engine mount.

- The ECU is a Fueltech FT500 with 3 lambda controllers ( R1, R2 and O2 general )

- We bought the racing beat pulley on a recommendation of Fueltech when we switched from the R-tech to the Fueltech ECU.

- Yes we are running pure Methanol ( VP M1 )

- We switched from E85 to methanol as you can not buy it here in germany anymore at gas stations. We talked to some fast rotary guys and all of them said " switch to methanol and you will have less problems " ( we hope that they are right :-) )

- We are running the NGK BR10ES spark plugs for both leading and trailing. But we are thinking about the NGK R6725-105

Interesting with the split. Maybe we could debate it a bit more as it seems to be a problem in our tune.

With the trailing split I will generally keep the trailing firing at or pretty close to TDC, where as you would be firing it 4 deg ATDC. I don't necessarily say that's your issue since it's not like it's going to be firing on the next chamber, but this did jump out to me. As Raymond has mentioned, obviously our philosophies differ here - This is just how I approached the tuning on the high boost methanol drag engines that I've tuned and I've had good results and reliability. His experience may well be different to mine. It's important to note that reducing the split does have the same affect as advancing the timing overall so some care is required. A number of years back it was common for ECUs to not offer the control we now have and many ECUs fired the leading and trailing together (essentially zero split). This is definitely NOT recommended.

Almost without fail all of the methanol high boost drag engines I've tuned use the R6725-115 plug which is a lot colder than the 10's you're running. Again I can't say that this is your issue, however I'd move to the colder plugs for the future. They are outrageously expensive unfortunately.

I'm not a fan of the distributor-style CAS sensors in the older rotary engines. They have lots of downsides including:

1. The pre-1992 pickup sensors send a weaker signal than the ones from the 1992+ FD3S front cover. Weaker signals are more susceptible to interference.

2. The pickup sensors inside the CAS are mounted physically near each other which can result in cross-talk between the two signals.

3. The CAS module itself is mounted relatively near the spark plugs, which are a source of interference.

4. The slop in the CAS drive gears is not helpful in terms or measuring eccentric shaft position accurately.

If you are unlucky, your ECU may have received interference or bad signals on the 'crank' or 'cam' wires, which can sometimes result in coils firing far too early or far too late depending how the ECU handles signal errors. Best case scenario is the ECU will respond by disabling the fuel & spark outputs which will just sound like a misfire or rev limiter. If you have datalogs from the problematic run, check for signal errors or odd measurements in RPM or indicated 'cam' angle if the ECU keeps track of that. All those things are symptoms that suggest the ECU may have received bad signals for engine position.

If the FD front cover is not an option, look into the Full-Function Engineering crank-mounted trigger kits. Check that your ECU will work with that pattern on a rotary engine, it's different than the original 13B trigger pattern.

I've got no experience regarding what lambda to run on a methanol rotary engine, but be aware that O2 sensors don't always measure extremely rich mixtures accurately. Any aftermarket wideband controller trying to measure that rich is working outside of what the Bosch or NTK sensor was designed to do. Teams with very high budgets might test the sensors using calibration gas, but at sportsman budgets we usually just try low-boost pulls with 10% or 20% more fuel than our usual lambda target to double-check that engine responds as expected to the richer mixture.

(sorry for weird text formatting, some of this is was copied/pasted from old emails)

@andre: Thank you for your input. As you said reducing the split is advancing the timing. Does it make sense to start with, lets say 6° ignition advance and then slowly advance it more and let the split at 6° under high boost? I asked a lot of dyno owners but no one has agreed to let us on his dyno. Many are afraid of the methanol which I can not understand at all.

I have ordered the R6725-115. Yes they are pretty expensive but it costs more to rebuild the engine :-). And if it only makes it a little bit more reliable it was worth the costs.

@Scott: Very interesting what you say about the CAS. We thought about what to do for a long time, we also thought about the FFE Kit. We've " investigated " a lot what the real fast Rotary guys are doing and many of them are running the CAS we use. I attached some screenshots of the log of the run before the engine damage. To me it looks good so far (have marked the affected areas yellow).

RPM cam sync sensor is almost the same as the engine speed ( 3 rpm difference at 7500 rpm ) and the cam sync angle is 0.2° of the rpm signal setup. To me it was always ok when i saw values like this. But i am here to learn and i am glad about every hint or tip that i can get.

You are right with the O2 sensors. The Bosch LSU 4.2 does only read from 0.65, not richer. But the O2 alcohol conditioner from Fueltech costs almost 1000$ and the NTK sensor is at 700$. That is way too much for us at the moment. My goal is to read 0.60 in the datalog, lean it out a bit to 0.65 and than add 10 to 15% fuel to the whole map. I dont know if this is the correct way but it is the easiest regarding our equipment at the moment. As you said the budget is limited and it is almost impossible to find sponsors here for this sport :-(

@andre: Thank you for your input. As you said reducing the split is advancing the timing. Does it make sense to start with, lets say 6° ignition advance and then slowly advance it more and let the split at 6° under high boost? I asked a lot of dyno owners but no one has agreed to let us on his dyno. Many are afraid of the methanol which I can not understand at all.

I have ordered the R6725-115. Yes they are pretty expensive but it costs more to rebuild the engine :-). And if it only makes it a little bit more reliable it was worth the costs.

@Scott: Very interesting what you say about the CAS. We thought about what to do for a long time, we also thought about the FFE Kit. We've " investigated " a lot what the real fast Rotary guys are doing and many of them are running the CAS we use. I attached some screenshots of the log of the run before the engine damage. To me it looks good so far (have marked the affected areas yellow).

RPM cam sync sensor is almost the same as the engine speed ( 3 rpm difference at 7500 rpm ) and the cam sync angle is 0.2° of the rpm signal setup. To me it was always ok when i saw values like this. But i am here to learn and i am glad about every hint or tip that i can get.

You are right with the O2 sensors. The Bosch LSU 4.2 does only read from 0.65, not richer. But the O2 alcohol conditioner from Fueltech costs almost 1000$ and the NTK sensor is at 700$. That is way too much for us at the moment. My goal is to read 0.60 in the datalog, lean it out a bit to 0.65 and than add 10 to 15% fuel to the whole map. I dont know if this is the correct way but it is the easiest regarding our equipment at the moment. As you said the budget is limited and it is almost impossible to find sponsors here for this sport :-(

First, the wideband. Does your ECU control the sensor directly or are you running an external unit? The LSU 4.2 is a very old sensor, it was in production almost 20 years ago. I am attaching specification sheets for LSU 4.2, 4.9, and LSU ADV. If you can look at the "nominal characteristic line" You can see that the newer sensors read at a richer range. They also warm up faster, but that's not a big concern for your application. As emission standards tightened over the years they improved the wideband sensors. A richer detection range allows better control over CO emissions under heavy acceleration and a faster light off time reduces hydrocarbons on cold start. If you can get a system that uses the LSU ADV you will be better off, at least the 4.9 . It's probably way easier and cheaper to get Bosch sensors in Germany too.

For the crank angle signal, well I'm not sure how good your ECU is in electrical noise filtering and signal processing for the crank sensor. The old Haltech E6K for example was notorious for not working so well with that sensor, and my old Megasquirt 1 on my 2nd gen didn't like it either. But I've never had a problem with a stock ECU or a Power FC.

For the ignition split, I base it on the stock maps and Mazda research. I dig up as many stock spark maps I could find. Basically they are available for 2nd gen and Rx-8 but not FD or Cosmo. See attached. "Stock T2" is series 4 turbo (8.5:1 compression), N374 is series 5 (9.0:1 compression, a bit higher boost) turbo, and Rx-8 is series I Rx-8. You can see split is roughly 15-16 degrees in most of these areas. Keep in mind that these are airflow based control systems, so the load axis is based on the flap type (similar to old Bosch L Jetronic) airflow meter signal where more air at a given rpm is higher load. I posted a pic from a Mazda study on where knock occurs in the rotary engine. It is primarily associated with the trailing combustion chamber, but keep in mind that the study was done at low rpm. I've never tuned a methanol powered rotary drag car, so your results may vary.

We are using 3 Fueltech Slim WB-O2 meter http://files.fueltech.com.br/manual/Portugues/WB-O2_Slim_v25.pdf which are connected via can bus to our FT500 ECU. And we followed the recommendation of Fueltech using the LSU 4.2. I just had a look at the LSU ADV and it reads 0.65 and leaner as well. What would be my advantage of using this one? I am not familiar with all the differences of the O2 sensors .....

About the crank angle signal i dont know how good it is in filtering. I have no comparison to others since this is the first ECU i deal with.

Unfortunately there are no attachments? It is very interesting to me.

let me try again with the attachments

Thank you Raymond, interesting to see your attachments.

Just in short for those who want to know.

We switched to Andres recommended spark plugs and we dont have any problem yet. We also advanced the timing by 3 degrees and reduced the split by 1 to 2 degrees. I am pretty happy with the EGTs and lambda and it shows me that i am on the right way now. A 5.86@188km/h on the 1/8 mile is ok for the 8th run on methanol. But still a lot to do.

On the next test i will advance it a bit more, turn on the boost and let it rev some rpm higher.

That is excellent news Marc!

Hey Jesus my friend ! Didnt know that you are here

Glad to hear you're seeing some success now!