Fuel Air Mixture

A head of hair to a louse is a head of hair.  but as to air fuel mixture as far as I know  atmospheric pressure makes a difference on it hence elevation changes cause issues and why FI has an ability to self adjust itself as you go up and down the mountain.  For carb owners, those living on higher ground,  they have to adjust their carburator jetting to compensate.    That is all I know, but others on here with higher wisdom can comment and make this clearer for you.

@R Thorpe posted:

As far as fuel air mixture is concerned does an engine know the difference between 3000 RPM sitting your garage and 3000 RPM out on the road?

Yes, the difference to the engine in terms of what A/F mixture is needed has to do with how hard the engine is working.

When the car is sitting in the garage, the engine is only using the amount of fuel needed to overcome the friction in the engine (not much). On the road, to get to 3000 rpm, more fuel is needed to overcome drive train losses, air resistance, tire rolling resistance, uphill/downhill resistance or assistance, etc.

The amount of fuel drawn in by the carburetor's jets is controlled by the manifold vacuum and RPM (traveling air volume) which is a good measure for how much load is on the engine. Fuel injection uses a combination of manifold pressure and RPM to approximate the engine load/need for fuel. It's basically the same thing.

Many of us have a whole stack of carburetor jets to adjust the amount of fuel drawn into the carbs at different times, speeds and loads.

Great question, by the way.

Thank you. It makes sense. I have this air/fuel mixture measuring system from Innovate Motorsports I purchased it years ago to tune the fuel injection in my BMW 2002tii, it has a sensor fixture that goes in the tailpipe and can connect to a computer.  The thought of going down the road with this setup is not appealing. I guess I should look for a dyno. Cheers.

@R Thorpe posted:

Thank you. It makes sense. I have this air/fuel mixture measuring system from Innovate Motorsports I purchased it years ago to tune the fuel injection in my BMW 2002tii, it has a sensor fixture that goes in the tailpipe and can connect to a computer.  The thought of going down the road with this setup is not appealing. I guess I should look for a dyno. Cheers.

While not perfect, you could use it to ballpark your setup. My mechanic buddy used his, normally used for setting up racing motorcycles, to check mine. Checked at idle, checked at 2500 rpm. The jets/vents Dave set me up with were perfect, as was his “ear and unisyn” preliminary settings.

The hardest part is holding your engine at 2500rpm in the garage. It seemed like cruel and unusual punishment to the poor engine.

@R Thorpe posted:

Thank you. It makes sense. I have this air/fuel mixture measuring system from Innovate Motorsports I purchased it years ago to tune the fuel injection in my BMW 2002tii, it has a sensor fixture that goes in the tailpipe and can connect to a computer.  The thought of going down the road with this setup is not appealing. I guess I should look for a dyno. Cheers.

A dyno guy can give you info on your A/F under many different speeds and loads. Good idea.

Yes of course, load is a important factor...duh!

I have that tailpipe set up. Honestly it works quite well. Aside from it wanting to fall out.. be sure to put a safety wire if some sort on it as the clamp is know to come loose. As for using it to tune. I got the same results using the rpm and Wideband going down the road as I did on a fancy high end chassis dyno. It was instrument in settings up the jets on my IDFs.

Just drill a hole in your exhaust and weld a bung in. After you're done tuning, install a plug in the hole(use Neverseize). You'll never worry about the sniffer tube coming out.

Tip: Always install O2 sensors between 10 and 2 o'clock, prevents moisture buildup in the sensor for permanent installs.

Danny that’s the plan next time I have the exhaust off the car.

@DannyP wrote: "weld a bung in. After you're done tuning, install a plug in the hole(use Neverseize)."

That's what I did for the O² sensor for my A/F gauge, which I just decided I don't need anymore.  TOTALLY forgot that part about the Never-seize, though.  

Like Jim, I get reminded of something cool (usually something I forgot) every time I visit this site!

If you ever need to take it out, use a propane torch(Mapp gas is HOTTER) and heat the bung orange/red. It will come right out. That's how I get out those OE O2 sensors that fail after 150-200K.