Optimum AFR for a RoW 3.2
 

I just welded in a wideband bung just before the muffler on the passenger side of my RoW 3.2 to monitor my AFR 8n different driving conditions, I made a video recording of idle, WOT and cruise :

https://youtu.be/KkbavUqUMKw

As you can see from the clip, I got 16-17 at idle, 12.5-13 when WOT, and around 15 at cruise speed, what do you think? Shall I richen it a bit? The car is driving great and I cant hear any pinging/knocking if accelerate hard even on a high gear.

Check out this thread..

http://forums.pelicanparts.com/porsche-911-technical-forum/895323-aem-wideband-o2-gauges.html

I don't have a Bentley for the 3.2 (I Have a 3ltr) but I think somewhere in this thread it is mentioned what the idle CO2 should be..

I have some email correspondence with Sal and he states for a 3.2 AFR at Idle should be 14.4 AFR.. and AFR at 3000RPM 3rd gear at WOT, just floor it in 3rd gear and hold the brakes a tad. (11.5 to 12.5)

And it depends what fuel you run; the AFR that results in lambda on E10 fuel is not 14.7 like it is for pure gasoline. A lot of cheap wideband gauges apparently have "14.7" built-in as the value to multiply by the lambda reading - so it would be wise to check/know what yours reads for lambda 1.0

Or use lambda as your tuning value. It's what all narrow/wideband sensors report in terms of anyway.

Lambda (stoichiometric)is the same for E85 and gasoline at 1.0, but that implies an AFR for E85 of around 9.8 versus 14.7 for gasoline.

The point about gauges is valid....an E85 fuel will display lambda 1.0 as 14.7 as that is the multiplier.

Dennis

The point about gauges is valid....an E85 fuel will display lambda 1.0 as 14.7 as that is the multiplier.

Dennis[/QUOTE]

Of course; stoichiometric is lambda is stoichiometric. That's the definition. And it takes different AFRs to produce lambda, depending on fuel.

So why does anyone buy into insisting lambda is an AFR of 14.7? That's like saying that pi is 3.

The sensors read lambda.

I'm running ethanol free 91 octane gas.

So to wrap it up, 12.5-13 @ WOT to 6000 rpm, is it good enough to keep my engine in tact?

I would error on the rich side. ROW has higher compression. High compression + heat + lean mixture = detonation.

Chris

for an old hemi head with outwater jackets, that looks pretty good to me for power...

One thing that I have noticed. The more I go to the lean side, the more stable idle I got and better off idle response. I always read that the 3.2 won't idle right above 14:1 AFR, but mine seems the opposite. Also when I was at 13:1 idle, I couldnt get the idle RPM under 1000 rpm no matter what, otherwise it would hunt and die and sometimes when I drive it and get to a stop traffic it would die if I press the clutch, all fixed with 950 rpm idle after I leaned it out to about 15 AFR.

Quite similar to my experience. My car likes leaner but I really wish it would run richer and smooth. Oh well.

If it’s happy leaner at idle, go for it. It is a low load situation. In fact leaner is better since it means you are conserving fuel. The unfortunate reality is that we often spend a lot of time idling at stop lights, traffic, etc.

The problem people have going leaner is that the engine runs rough or there is a slight hesitation at tip in. In your case, you are not having any of those problems.

You only want it richer when you are pushing for max power.

Also runs cooler too. If you don't believe it, look up "lean of peak egt".

My '83 euro 3.0 w JD Cams/Headers made ALL the power right around 12.7, which it holds steady across the RPMs on WOT, 205whp. Have since put 1500 miles on it and it starts/runs happy and temps are right where they're supposed to be.

It actually made 210whp at 13.0 but for longevity made a little compromise. Lean is mean with these motors...

I'd had it quite a bit fatter 10.8 to 11.0 (just from turning mix screw and tuning out surge) going onto the dyno and first pull it made 182whp...

Those numbers at idle and cruise seem off to me. Just too lean to run without popping and stumbling.
Do you have ability to read your 3.2 narrow band sensor voltage? I'd be curious to know if it is oscillating up and down (which would mean it is very near stoic).

Also, ensure that you don't have any leaks at the welds, bung, flange to cyl heads, or any other exhaust flange connections. A very small leak will cause readings to be quite off for your wideband.