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043 | Rotary Ignition Tuning - Link G4+/ViPEC

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Hello Andre the Rx 7 you been using in the webinar have the factory crank trigger ?? if there is only one timing mark in the trigger wheel and the procedure to chk the static timing will b e the same as on any other piston engine .

Yes the FD RX7 has the stock trigger system. On the S6 engines there is a single timing mark at -20 degrees (20 ATDC). Checking the timing is essentially identical to a piston engine but ensure you're checking the base timing using L1 spark plug.

Just wondering , isn't the -20 degrees supposed to match the T1 spark ?? L1 is supposed to be -5 in mazda's workshop ....

Sorry if my comments may have caused confusion - Just to be clear when setting the base timing in an aftermarket ECU you would be locking the timing to a fixed value and then confirming this with a timing light. Every ECU is different in exactly how this functions. in the Link G4+ when you have the timing set to 'Calibrate', the leading and trailing plugs are fixed to whatever the calibrate angle is so effectively there is no trailing split. In this case you would set the calibrate angle to -20 and adjust the offset to suit. In this example you could actually use the leading or trailing to set the timing since they both fire at the same time.

An alternative way of adjusting the offset since the engine won't run particularly well with the leading and trailing firing at -20 deg is to set your main ignition table to -5 in the idle areas and the split table to 15 and then do as you mention and check the timing mark off the trailing. If you choose to use this technique though you need to ensure there are no trims for ignition timing active.

Generally with a rotary engine I like to confirm both the base timing, as well as which coil is the leading and which is trailing as I've seen the coils wired incorrectly as well as just being connected to the wrong plug. This can easily cause engine damage if the L and T are in the wrong orientation so I like to test both aspects.

Hi Andre

WoIld it be possible while you have the Link Rx7 in the workshop to do a webinar on the effects ignition timing has on EGT.

That's a good idea. I'll see what I can do.

hi andre i noticed on the rotary tuning webinar you had a egt attached to your dyno what thermocouple do you use? i have a new mainline dynolog with the egt module but they didnt supply the probes. and i prominently want to use on diesels what would you recommend?

Any K type sensor can be connected to the Mainline dyno. The sensor we have came with our dyno so you could ask Mainline to supply one. Haltech also supply them or you could buy from here: http://www.exhaustgas.com/

Hi Andre

When tuning rotaries on Ethanol have you found they are still knock limited or can they generally be tuned to MBT.

Depending on the boost you can still run suffer from knock so please don't think you're immune. I still treat E85 with caution and follow the same general rule of being conservative when tuning a rotary.

Bump to an old one, but I've just watched this webinar after I talking to a friend about rotary tuning & ignition timing.

Obviously doing a "hook" test on the timing will allow you to set MBT, but how do you approach finding optimum timing where you are knock limited? Normally with a piston engine you'd keep advancing timing until you encountered knock and then retard to a safe angle but I believe this approach could cause damage or apex seal failure on a rotary - so how do you approach finding optimum timing on a knock limited rotary engine? Also is knock less of an issue on rotary engines on pump fuel due to lower compression ratio?

Thanks

Alex

Knock is definitely an issue with a turbo rotary on pump fuel. Stop adding timing when the gains are minimal and don't justify the increased risk of the extra timing. Especially if the engine will see high load / boost for extended periods. And tune the engine rich with the same principle of sacrificing some power to control combustion temps. Andre covers it all in the webinars.

With boosted piston engines you can still be seeing significant torque gains with more timing right up to the knock limit so the the gains won't necessarily start to drop off before you encounter knock?

As Boostn has mentioned, knock is very much a concern for rotary engines and can damage them very quickly. In general you don't tend to see such a dramatic effect on torque from ignition timing. My personal approach is to start with very retarded timing and begin adding timing as we would with a piston engine. As soon as I see the torque gains slow down or plateau I'll normally stop advancing the timing. This may end up giving away a little power and torque but it's a worthwhile tradeoff to maintain reliability.

Thanks Andre. I understand what you are saying about the approach. What I'm getting at is that the description of adding more timing until torque gains starts to slow down or plateau sounds like the same approach for tuning a piston engine to MBT, but on pump gas you will almost certainly hit the knock limit before reaching MBT - so with a piston engine the torque may not slow down or plateau before this occurs. With a rotary because the engine is less sensitive to timing it will start to see diminishing gains before hitting the knock limit. I've drawn a crude graph to show my understanding; is that broadly the right thinking?

Attached Files

I guess in very crude terms your drawing illustrates the concept. In both piston and rotary engines it is quite possible that you may reach MBT before detonation occurs however, particularly under light load and also with high quality fuels such as race gas or E85. In general though the percentage gains you'll see on a rotary engine from adding timing are much smaller than what we see on a piston engine so it's sensible to be conservative.

Thank you :)

Sorry for waking up such an old thread but it i find it still very hard to get around the term conservative timing. I grabbed some on screen data from the webinar and calculated the %-gain in power per 1° spark advance. As the power dropped off going from 12° to 14° this would mean the engine was not knock limited at given circumstances (boost pressure / fuel quality). As you went back to 10° btdc timing, this would still be only 0.62% power gain per 1° spark advance coming from 5° btdc on the full power run.

First question: what kind of fuel did you run in the test?

Second question: is there a guideline regarding the %-gain per 1° spark advance for rotary engines. With normal pump fuel 98 octane euro spec (= 93 us spec) would it be still considered as safe to stop as the gains fall to around 1% per 1° spark advance or should one stop even earlier?

Greetings from Germany

Markus

Hi, another question concerning the split on rotary, as I see on the window of my software, the split table stop at 7500 rpm, and no possibility to add another case to up it to for example 8500 rpm.

Any advices?

Thanks.

Irvin, if you have a Link ECU you can adjust the trailing split table axes just like any other table. Right click on the table and choose axis set-up, you can then set the RPM columns however you like.

Hi, thanks for you response, I already tryed to add column in this menu, but I can't do nothing.

I have actually 16 columns, I need to add 2 new one, but when I click on the + button, nothing happen.

I attached a picture.

Attached Files

Correct, your max table size for that particular table is 16 x 11. You do not need columns every 500RPM, especially in areas where the VE is changing little. Nor does the axis need to start from 0RPM. Delete some of the columns you dont need.

OK, I'll do like that, thanks!