Ok i have heard different things from different people so i was wondering if some on could explain it to me that knows what they are talking about.

I have heard that a 12 is rich and i have heard that its lean so im not sure whats what and what the optimum A/F ratio is. I have also heard that the optimum A/f ratio is different for a rotary.

if some one could clear this up for me i would apreciate it. im not planning on tunning my car i just want to be able to keep an eye on it and be able to read what its doing.
thanks

 

Im not a 100% sure either, I like to keep mine in the 12's and no higher than 12.5 under boost. 13 is too lean and 11 is ok, but rich.

 

12 is NOT rich for a turbo-rotary under boost. Go to the PFC sub-forum and run a search for any posts by Chuck (cewrx7r1) on this topic. Here's one thread:

https://www.rx7club.com/showthread.p...ight=boost+afr

You can also read Brian Davies tuning document:

http://www.zeroglabs.com/rx7/singleturbotuning.htm

 

I think sub and low 12's is a little rich for normal boost levels. But there are other variiables (temp, timing...etc.) that come into play. I aim for 12.5 or so, but run only 11-12 lbs. I have yet to see anything alarming from the knock sensor in my logs.

 

There are two contexts at work here:

1. The actual chemical context, in which anything lower than 14.7 is "rich" and anything higher than 14.7 is "lean". At the stoichiometric ratio 14.7:1, air and fuel are available in just the right proportion such that you don't end up with extra air and fuel after a complete burn. (<-- or something like that; this is my layman's understanding)

2. The context of tuning a car, specifically a turbo rotary. In this context, there is no specific proportion that is "right", but something like 12:1 is kind of the center point between what people call "rich" and "lean". 13:1, for instance, is still technically "rich" (see context 1 above), but it is not as rich as you want for a turbo rotary, so we call it "lean", meaning "not as rich as it should be".

Note also that context 2 mainly applies to the mixture under boost. At idle and light load cruising, you don't need (or want) the engine to run that rich, so something more like context 1 applies.

-Max

 

thanks that cleared it up for me alot

 

i've found that rotaries tend to like the number 12.4 but this all depends on each persons setup.

 

Personally I lift if it goes leaner than 11.5...maybe 11.6:1 at full boost on 91 octane. 11.3 is my target AFR.

On a rotary mid-low 11's is quite a bit safer than mid 12's and you really don't take much of a power hit for it.

Anything richer than 10.9 or so won't light very well though. Random misfires occur pretty often with stock design plugs.

 

Just to keep things in perspective, a stock car will run AFRs around 10:1 or less under boost above 4000 rpm.

Anything over 12:1 under boost on our ****-water 91 octane out west would be too lean for me. Trevor's numbers are very reasonable for a car not being tuned for max power but to make good power while lasting longer than 10k miles.

Another thing to consider is that the car will run slightly leaner in real driving as compared to AFRs measured on the dyno.

 

Ah...thanks guys I did not think about lower octane applications. I am surprised by that stock AFR reading. Do you know how those readings were recorded?

 

Yes, with several different wideband setups on several different cars.