A/F Ratios for street performance
 

I ordered an Innovate MTX wideband O2 sensor/gauge and I wanted to see what A/F Ratios I should be aiming for. I know different cars like slightly different levels, but I'm just looking for what others have found work well. I searched but most of the info I found was from FD owners. Not sure how close my NA carbed motor should be to a turboed, FI ECU-controlled car. What seems to be typical for a stockish FD is-
Idle - 11:1
Cruise - close to stoicroic 14.7:1
WOT - 10:1

Does anyone have an A/F meter on a good running carbed FB? What kind of #'s are you reading?

u didn't look that hard.... your car wil fall on its face at 10a/f.. 12 to 12.8 open..... at cruise and 12 anything in between 13..... idle whatever your engine seems to like.... like to kno whats goin on on both rotors https://www.fuelairspark.com/gasolin...al-sensor.html

That's a nice looking setup but too rich for my blood. Yeah the #'s above were just what an FD driver posted his car was running. I figured that setup wouldn't work for me; it was just an example of what I'm looking for.

The last time I was bitching about my Holley 465 you asked if I had tried adjusting the jets. At that time - no, I hadn't. RB told me it was way over-jetted at 55 primaries (that's how it came to me) but it was obviously too lean. I fully cleaned and rebuilt it, which fixed the air leaks around the throttle shafts, but the setup was still too lean. Better, but not good. Since ranting about that I swapped in 57 jets and it was better, only needing the choke wired 1/2 way shut to run okay.

*RB uses 49 primary jets, and mine is running better as I get into the high 50's. This is why I'm not asking for jetting advice. I'm looking for target A/F ratios. I don't know if a previous owner hogged out the air bleeds or what, but there are no vac leaks anywhere below the carb.

I got a secondary jet conversion plate so once I get the primaries right I can dial in the secondaries. The 4160 style carbs come with a metering plate rather than jets. And these plates are $30 each, vs $6 for a pair of jets, so it will be more affordable (and cooler :) ) to fine tune the secondaries when I get there. And I got the A/F meter to know just how the changes are affecting it.

When I was younger and playing with carbs I had a nice 1/8 mile section of abandoned road with an empty lot at each end, right near my house. When I was tuning my truck I could make an adjustment, stage myself, and launch WOT all day until I found the best setup for whatever part I had changed. I don't have that luxury where I live now. Or the time. I live in a nice residential district with kids and soccer moms all over the streets and sidewalks, so I want to get it "in the ballpark" in my driveway, then fine tune based on out-of-town driving tests. So far this Holley hasn't even been in the ballparks's parking lot. And as a Holley, it's a messy PITD to re-jet, so I'm hoping the A/F meter will help me get it dialed in faster.

I wouldn't aim for anything in particular, just tune by feel. As lean as it likes running at idle and cruise, basically, which is not a number you can really shoot for because it might idle at 13:1 or 15:1 or 12:1 depending on your ignition timing.

Under cruise, as the load increases the engine will be happier with leaner mixtures. For example it might not like running leaner than 13:1 at 50kpa (7" of vacuum) but as you feed in load it might be just fine running at 16:1 at 85kpa.

At WOT you more or less can't hurt the engine with lean mixtures, one of the advantages of the rotary is that you can run them lean of stoich at full load and not have to worry about melting a piston or exhaust valve, and the high mixture motion and heavy quenching at the corners of the chambers makes detonation almost impossible, so somewhere between 10:1 and 14:1 is okay. Obviously richer is more wasteful and results in more oil dilution, and leaner will result in higher plug temps but this is not something you are going to have a problem with on the street until the speed limits are raised to 130mph or so. If you need a hard number, then somewhere in the 12.5-13.5 range is fine. There's remarkably little difference in power at different air fuel ratios, just spark plug temps.

This all assumies NO CONVERTER. If you have a converter, make it run 14.7:1 during the part of the drive cycle where the car gets tested on the rollers, and 10:1 everywhere else to keep from melting the converter. That is the way Mazda did it and for that reason. Since rotaries generally don't like to idle at 14.7:1 without lean misfiring, they had an air pump that added air to the exhaust at idle so the "final product" was 14.7.

Stock Nikki, stock porting, still with rats nest aside from deleted air pump and valve, using Racing Beat long primary exhaust yields the following readings from an Innovate Motorsports DLG1/LC2 dual wideband.

Readings from front rotor at the end of the header:
Cold start w/ choke 12.5
Warm idle 13.7
Warm cruising 14.7
Warm light throttle 13.7-14.0
Warm open throttle midrange 12.5-13.0
Warm open throttle high rpm 13.0-14.0

Readings from rear rotor at the end of the header:
Same as above except about 0.5 leaner.

I never saw anything over 15 or under 12.5 at any point other than when the shutter valve closed the rear rotor under decel and it jumped to 22 as expected.

Thank you to everyone, I appreciate the knowledge and experience. Thank you to chuyler1 in particular - that's the type of data I was looking for.

Na 6 port. I tune for the following for track use

12.5 idle,. Car idles smoother and stinks less
13.5 cruise and part throttle
12.5 85kpa-wot, for extra premix oil and cooling vs 13 or leaner.

Gas mileage is terrible.

Turbos commonly run really rich for safety any time they reach boost.