Using an AF ratio meter on our Porsches
 

Hi guys. As checking AF ratios follow a good rebuild, I thought this might be a good place to query AF ratios.

I purchased a MoTec PLM (professional lambda meter) today so I can measure AF ratios on my 993tt engine. The MoTec only has one sensor and my engine has two separate, independant exhaust piping. How do I measure each side at the same time?? The easiest way is to purchase TWO MoTecs, but at better than $1,000 each I find it hard to do.

Do Porsche owners usually measure one side at a time? Is there a lamda sensor (accurate) that can take two sensors at a time?

Jaime

Dang, $1000 each, that's steep. I hope it does alot more than measure AFR's.

For a cheaper alternative check out www.tuneyourengine.com

The Innovate LM1 is a good unit.

Wow, Brian.....thanks for the tip!! I'll buy two of the stand alone kits and be more or less at the same price!

Thank you SIR!!

Jaime

I had a company in Sonoma make me a dual a/f gauge for $170. Looks like the gauge in the picture except it has dual a/f meter.
http://www.westach.com/images/showcase/3DC2-1-Dual_EGT.jpg I mounted a 02 sensor at each collector. I paid about $50 ea. for the 02 sensors. I mounted the gauge in a old clock housing and now resides in the clock hole in my race car.
74 rsr w/3.4 twin plug.

'You can't do that with WBO2 sensors. They require pump-circuitry for each sensor. It's not just matter of switching between two voltages.

Re: Using an AF ratio meter on our Porsches
 

Jaime, MoTec PLM is not able to log anything. It's just a display with bus allowing it to be connected to some other device. LM1 has all that PLM has + logging capabilities + inputs for additional channels. For half a price. They both use same WBO2 sensors.

I noticed that www.innovatemotorsports.com now has the LC-1 for under $200 which is flexible enough to even tune individual cylinders by using multiple LC-1 kits (ST-12 Kit). It lacks logging.. but will give you real time data to a laptop and progammable outputs to drive A/F guages.

I just ordered a kit so I can do my bi-annual A/F adjutement on my 930 using my laptop

I'll vouch for the LM-1. I've tuned a few engines with one to set up custom fuel maps for EFI conversions. It's a lifesaver. Same with carbs, but it's not as fun to change jets as it is to hit a few keys.

You guys ROCK!

I was able to get a killer deal at www.titanmotorsports.com I got two for less than I paid for the MoTec. Now, If i could only get educated on what ratios I should be looking for at idle/part accleration/wide open throttle for my Ruf ecu/cams. I think Ruf protects this info, not readily available I suppose.

Jaime

In my personal experience tuning, I found that 13.8:1 was a sweet spot I aimed for, but some engines like 12-12.8:1 at WOT or under or near full 100% loads. If you can run closed loop at say highway conditions, something near stoich is common with OEMS. Just don't try to run closed loop at low rpms, high rpms, or high loads.

Hi,

Just as a tip:

13.8 at WOT sounds a little lean for a turbo car for thermal (not power) reasons. The closer you get to stoich (14.7) the higher the cyl. head and piston crown temps. Therefore also more knock probability. CHTs have a peak at around stoich.
For a street driven car at partial load and idle go for stoich (14.7) for smog reasons. On a race-car at partial load I would go for ~15-16 if possible (avoid lean surge). That makes it run at best BSFC and therefore can lengthen the time between refueling stops.

Regards,
Klaus

Sorry about that- should have clarified that 13.8:1 was N/A, not for a turbo car :-) You're totally right on that.

As Klaus said, it goes without saying that you should monitor head temperatures as well as AFRs for a more accurate picture of true performance. In both cases that I was tuning at 13.8:1 I had quad chts (it was a type 4) and the engine actually ran cooler at 13.8:1 than at 12.8:1. It's about finding what your engine likes and needs.

I want to teach myself the intricacies of a/f ratios as my '83 3.0 engine has been pinging during WOT at full load in very warm weather conditions. Will any of the listed a/f meters in this thread work with CIS?

Thanks.

Yes, you'll need to weld in the o2 sensor bung on your exhaust- the closer to the engine the better, although if you get a heated sensor like what comes with the LM-1, it's not so much of an issue. Most definately do it before the muffler and any cat.

Another option for a WBO2 and data logger:

http://www.zeitronix.com/

I use one to tune and log my 930, works well!

Another option would be SDS's (simple digital systems- Canada co.) wideband (as well as excellent fuel and ingition systems).

Most definitely yes. I'm running an LM-1 on my 81 CIS Lambda engine. With the programmable outputs of the LM-1 it's now running closed loop at WOT at 12.8 AFR. I described that trick in another post a while ago. Mine also pinged in hot weather. Turned out it was running a touch lean (13.4) at the max torque point. Running it in closed loop now makes it run a lot smoother and it feels more responsive. Butt dyno says it makes more power throughout the rev band.

Regards,
Klaus

I took the www.efi101.com class which has good info for tuning without blowing up your engine.

From the course book lambda for high boost should be .80 to .85 and for low/medium boost .82 to .87.

Are these lambda measures for NA engines or turbo engines or does it matter?