Suppose I run a wideband, haltech and other goodies on the car I'm putting together. For tuning safety, what would be the effects on the O2 readings if I threw in some race gas or some other addative. I am fully aware that running leaded gas is not good for the O2 sensor (I only want to run it to tune) but is it going to change the readings I get? I would just like to not have to worry as much about leaning out too much as I tune the car. Thanks -Zach-

 

octane doesn't affect your a/f ratio, unless the lead clogs the sensor, which it shouldn't that quickly. the only thing it does is give you a larger margin of error against detonation

 

When I switched over to aviation fuel my afr's were a little richer than my pump gas setup.

 

How much richer Radkins? Are you running pure aviation gas or just a little extra in each tank?

 

Most race gas also has a different specific density than normal pump gas, so you may run a little richer at the same pulsewidth than you would on normal pump, though it is not because of the extra octane.

 

So I'm guessing that it would be in my best interest to just tune with what I plan to run it on every day?

 

Ralph Friend said to tune it with what you're going to run it with. So, thats what I do. CJ

 

Fair enough.

 

I am running full aviation gas and noticed it ran richer by about 1 full point across the board, say from 10.5 to 9.5. I got several rich stumbles under light acceleration I had to tune out.

 

race gas will show up richer on a tune, However i will probably tune my car with some 94 octane with a little bit of vp red mixed in. nothing leaded though.

As far as leaded race gas with a wideband goes, It will last a long time, just not AS long as nonleaded gasolene.

 

I think you can go up to 104octane rating with race gas before they start to put lead in it. But yes my advice would be to tune your car with the same fuel you are going to use to race it with.

 

I disagree, any margin of safety you can add while tuning is desirable. I have never(knock on wood) popped an engine while tuning, check the boards, plenty of guys have lost their motors tuning. There is no downside, only safety to be gained. So, if you plan on running pump, I would tune with 100 unleaded. The AFRs can vary by about a half a point(vs pump), but if your tuning for daily driving on the street you ought to be a full point away from your danger zone(>12:1 IMHO) on a turbo motor. Can anyone speak to why you would not want that extra safety margin??? Anyway, it's your motor . Carl Byck

 

Most companies publish the density of their fuels at STP, just find something with more octan thats close to the same density as your normal fuel and tune it safe and you will be fine.