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Boxer & Rotary Engines AFR?

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I'm new with Boxer and Rotary engines and I would like to know what AFR would you recommend for these cars at idle, cruise and full load? because I have a few customers with Mazda and Subaru and I'm new tuning these kind of engines. I know that rotary engines need to run a little bit richer than an usual engine because it helps its internal lubrication and I know boxer engines are really knock sensitive but I think 0.72 lambda is pretty rich even for them (attached you will find the pictures for both engines that I did on my dyno).

Also, I'm in Mexico city at 2,400 meters above sea level so air density and oxygen decrease a lot from what I was used to so cars get a little bit hotter than usual, Mazda RX-7 customer told me that his car needs to be always below 85ºC even at high loads which I find a little low for any engine and at this altitude.

Thanks guys.

Attached Files

Hi Victor,

I have tuned a few Roary engine in my time and still got a lot out of these webinars. Ignition timing is very different in the rotary too.

I have tuned a fairly large number of boxer engines and I treat these the same as an inline or v configuration engine with regard to AFR. I can't give you a specific AFR as it will depend on your fuel and your boost level but I have never run a boxer engine as rich as 0.72 lambda. I'd more likely be in the range of 0.78-0.82 with the other factors I mentioned above kept in mind. You will find that in stock form a lot of Subaru engines do run excessively rich and leaning this out to a more reasonable level is actually one way to pick up some power.

Rotary engines do tend to run richer than a piston engine, however if it's a street car I'd still be targeting 1.00 lambda at cruise for good fuel economy. It's common for a rotary engine to run as rich as 0.70-0.74 on pump gas depending on boost.

If you don't already own the Understanding AFR course then this may be worthwhile for you.

Hi guys,

Matt, thanks for the webinar links they'll be very helpful.

Andre, thanks for the comments and I know that the specific AFR it's up to me I just wanted to know if these engines have anything special or different recommendations than with the inline engines. And yes, actually I've already got all the courses.

Thanks again.

A few things to consider:

1) Boxer engines -- depends if it's an EJ series or an FA series. EJ is going to be like an older 90s port injected turbo engine that doesn't make much low end boost. A lot of EJ powered cars had to run really rich under boost to protect the cat in the up pipe (collector pipe before turbo), if equipped. The FA series engine are much more like a modern turbo direct injected engine and might not need to be so rich (depends on all the factors).

2) rotary engines -- Generally you can keep it around 0.78-0.80 under full boost. At part load, it depends if you have an older rotary (pre Rx-8) with the air injection pump still running. If the pump is still running, it will read leaner at idle and low load cruising.

Hi Arghx7, excellent tips.

What about the operating coolant temperature of the rotary engines? because this one has a big intercooler just in front of the radiator (Mishimoto) and I think is the radiator fans can't do so much.


Stock Thermostat opens at 82C and is fully open at 95C. Radiator fans come on at 97C depending on what model you are talking about (105C for 1992-1995 Rx-7 but Mazda went back to 97C after that).

Cooler is better but anything under 108C isn't going to damage anything. 108C is the temperature of highest fan speed on factory ECU. Definitely do not run this hot if you can avoid it.