shanec

I see 10.9 @ WOT up to 4,000 rpm (don't have plugs I need to hammer it hard yet)

...and I see 13.9-14.2 on level ground with the cruise control set on 70mph

Vapour Trails

Sounds about right. I get to ~ 11.0 @ WOT with the FRPP tune. I haven't paid attention to my A/F during a highway cruise.

dkersten

11-11.8 is usually the range people see at WOT.. I get 11.3 with my KB, but I think it is a little fat and plan to lean it up a hair.. I think my 91 octane fuel can handle it..

When off WOT, the engine will attempt to go Stoichometric, which is approximately 14.8:1. Here is the thing though - aftermarket O2 sensors can be off by as much as .5, so as long as you are close, you are probably fine.

It is FAR better to be running a little rich than to be running a little lean. You might be a few horsepower shy of your potential, but it's better than a rod sticking out the side of the engine..

BTW, if you datalog, look at Short Term Fuel Trim at WOT.. multiply it by Stoich (approx 14.8) and that is the target AF ratio at WOT for your tune.. Right now my tune has a STFT of .75 at WOT, so it is targeting about 11:1..

Vapour Trails

I am at 14.7 on a highway cruise, just checked this afternoon.

modaddict

Just an FYI: the a/f only matters at WOT and idle. Every other time, the numbers don't mean squat.

shanec

I wonder how the A/F affects MPG - such as me getting 14.2 instead of 14.8 on the highway.

I will say my car has always gotten less mpg than most people say the get in their cars. A long 70mph cruise control highway trip = 22-23 mpg for me instead of 28+ that a lot of people say they get.

modaddict

It's pretty simple if you think about. The a/f is 'measured' in terms of 'rich' and 'lean'. 'Rich' is obviously more fuel and 'lean' is obviously less. Good tuners try t find the 'sweet spot' which is basically a balance between the two.

So a car running 'richer' than another would see a decrease in mpg over a car with a 'leaner' tune. When guys start going up in injector size, that is the biggest factor cause the bigger the injector, the more fuel being pushed through and the worst the mpg. Guys who go up in injectors are always going to drop mpg - just the nature of the beast. Takes fuel to make power and the more power - the more fuel is required.

Hell, my car gets about 6 mpg...lol

shanec

How about a car with 450 rwhp. Doesn't really need 60 lb injectors, but has them anyway. I'm speculating that when that car is tuned for a certain A/F it doesn't matter if he's running 41lb injector or 60lb because either ways its putting out the same amount of fuel. Its just that the 60lb'ers don't get pulsed as often, right...

shanec

My question more along the lines of...how much mpg am I losing by cruising the highway at 14.2 instead of 14.8

modaddict

Equal tunes? - about 0