Here's the deal. In the upcoming months I plan on getting an SAFC-II to tune my 88 RX-7 N/A. I've got a few questions regarding the tuning.

I've got access to a 4 gas analyzer and scan tools, but all I've ever really heard about tuning with an SAFC-II involves a wideband O2 sensor. I know when reading voltages of a regular O2 sensor, the lower the voltage (between 0-.3v) is lean, and when it goes higher (.6-.9v) that is rich, with four and five being closer to stoichiometric.

I was talking to one of my professors, and he said that I could tune my car just by using the readings that the O2 sensor puts out. How accurate would that be? I'm assuming a wideband would be just that, a wider and more detailed range of voltages to use, which would make for a more detailed tune?

I'm aware that running an RX-7 too lean will lead to detonation, and a rebuild. That's something I plan on straying away from.

If anyone has any reccomendations for good A/F ratios I'd be interested to hear. I would like to lean out the current stock mixture once the 5/6 ports open at around 4K RPM. Not too much, maybe to around a 13.5-14.0:1...I feel like the stock computer has it running more rich than this? Would that be safe?

I'm pretty new to this tuning world, but I've been doing a lot of reading, and I know about when running rich the combustion chamber runs cooler, due to all the air being used up, therefore there is less chance of detonation. Rich is safe, right?

I'd just like a little more insight into the use of widebands and what the good tuners out there do. I'm very interested in this aspect of making power.

Thanks in advance.
James

 

Widebands are a far more linear sensor as opposed to a narroband. If you looked at their voltage vs AFR plot, the wideband is a upward sloping line, while the narroband is an "s" shaped curve. Why is that important? Because narrowbands are accurate at stoich levels, and increasingly lose accuracy as you stray further from stoich.

If you want to make the most of your SAFC, the wideband is your tool of choice.

 

By an "s" shaped curve do you mean an analog voltage signal? They go up and down in a range with varying frequencies.

The Wideband sensor would just be an upward slope.... which could be seen with an oscilloscope, correct?

I didn't know that a narrowband sensor increasingly lost accuracy the farther you strayed away from stoichiometric.

Fatty_FC3S, thanks for a quick and detailed response.

If anyone has any more information, please feel free.

Thanks in advance,
James

 

i have the same set-up (88..N/A).. have no SAFC-2 yet ..and plan on doin it... so ya ..any more info guys?.. and you can satisfy 2 people with one post!