Forum » General Tuning Discussion » rotary ign

rotary ign

General Tuning Discussion

Discuss all things tuning in this section. News, products, problems and results. 


Page 1
Author
1632 Views

Hi i have over 10 years of experience with tuning piston engines but lately im digging into rotary and i have a bit of a concern especially were it comes ignition split. im building a motor for drag to work on M1 with semi PP and im using link ecu for this.how do you advise me to approach ign timing and especially split.thanks

My advice is to tread carefully! Rotary engines are VERY intolerant of knock so I always start with very conservative timing. If you're using M1 then you have a little less to worry about as the fuel is much better than pump gas.

As far as the ignition split goes, generally I will have around 15 degrees split at idle and low load. Under high rpm/boost you can reduce the split to around 7-8 degrees. Reducing the split is the same as advancing the timing so you do need to be careful how far you go. I have never really seen much change in power from reducing the split further anyway.

As far as specific timing goes, this will depend on the engine and turbo as well as the boost pressure. If you are used to tuning piston engines, the amount of advance a rotary will take is quite a lot less. It's not uncommon for example to only run 10-12 degrees advance with 30 psi boost and perhaps 6-8 degrees advance with 40-50. My 4G63 for example was still running advance in the low 20's at 50 + psi.

Unlike a piston engine, you will generally find that the rotary engine isn't as sensitive to timing and once I stop seeing the power improve or the gains slow down, I'll tend to leave the ignition advance where it is. My personal opinion with a rotary is that you're always better to use a little more boost and a little less timing.

One last thing - Make sure you use plenty of fuel. Rotary engines love to run very rich.

What Lamba do you aim for under boost Andre? 15-20psi for example

the target lambda depends on the fuel. On pump gas (which I'm guessing is what you're interested in), I would be in the vicinity of 0.73-0.75 lambda. On methanol you would want to be closer to 0.65 though.

thanks andre for the input.

on m1 0.65 lambda is for high bosted applications?

thanks

0.65 or richer to be honest.

On a high boost methanol rotary drag engine you need a LOT of fuel going in. Most of the rotary engines I've tuned for drag applications run Motec hundred series with the Bosch LSU onboard wideband option. These tend to 'bottom out' at 0.64-0.65 lambda. I use this along with EGT to aid the tuning.

Andre

what egt`s you should see at that kind of fuel quantity?

thanks

Methanol or petrol? Either way the EGT will still be boost dependent as well as dependent on how far from the exhaust port the sensor is mounted.

As a rough guide on methanol I like to see the EGT at about 800 deg C or below. On petrol you can easily see EGT's reach 900+

Good info there andre o have been dealing mostly with piston engine. But there will be more rotary engine on the island .thanks for info to understand the way to tune a rotary engine.

You're welcome Bellotech :)

About to start a Rotary conversion on a customers car... Are we a ways off from a Rotary Webinar or even better a course? Or could you maybe explain rotary split on here? I understand its the degree's between the leading and trailing spark plug firing, But how do you tune/select the correct split?

We are a little way off both sorry @Viper. I'm happy to explain here though.

As you correctly mention, rotary split is the difference between the leading and trailing spark angle. The trailing spark is there to aid complete combustion and reduce emissions primarily, although it can show a small effect on power too. To put it in perspective, many ECUs in years gone by did not offer any trailing split and simply fired the leading and trailing together - This isn't ideal though as I'll explain.

Advancing the trailing timing (reducing trailing split) has the same net effect as advancing the timing and hence this makes detonation more likely. This is one of the reasons why firing the leading and trailing together isn't ideal.

The trailing split values I listed earlier in this thread are a reasonable starting place. You will normally find that more trailing split tends to result in a smoother idle quality. It's easy to try adjusting the split on the dyno and then seeing for yourself the result.

Thanks Andre, I noticed the S4 13B supplied for this conversion has a Knock sensor fitted.. What frequency do you use in your knock software (seeing as there is no piston bore to calculate from!)

Is Knock monitoring still recommended or is it really a case of if you have knocked then its all too late.

What sort of timing numbers would you start out with in your timing map as safe timing? (at various load levels)

I noticed in the Haltech basemap there is also injection angle split, Whats the function of this? and how would you tune it to the optimum

I'm not sure how the knock sensor was dealt with by the stock ECU. I have never personally used knock control on a rotary. Purposely inducing knock to calibrate the knock control system is often enough to cause damage. While a rotary can withstand light detonation for a short period I certainly wouldn't be recommending it!

A conservative approach to ignition timing is the name of the game with rotary tuning.