Revs v fuel consumption.

[JockoT]

I was out for a run this afternoon and I observed that it was sometimes more fuel efficient to run in 4th gear at 2200 rpm than it was running at 1800 rpm in 5th. Both gave me a similar speed. And carrying on from there it was better to run in 5th at 50 mph at 2200 than in 5th at 1800 rpm and 40 mph. It is amazing the information I can glean from my ScanGauge.

[R.I.D.E.]

80% load is supposed to be ideal as a general rule. If 5th gear won't accelerate well then you might be at 100% load and still not doing the job, then you need a lower gear.

[herektir]

Depends on engine torque / hp curves for best rpm to engine load for your specific engine. Example is n my case ka24de engine has a flat torque curve over 1900 rpm so I cruise at the whatever gear keeps me at or a little above.

[JockoT]

I don't really find that I am on load at these speeds. It is when I am on a very light throttle. I'll try setting up a custom display using mpg and load and see what my load figures are. What I can tell you is if I open the throttle very much in any gear the fuel figures tumble. Going up the gears at about three quarter throttle returns about 10 - 15 mpg!

[trollbait]

I've noticed the same when climbing the steep hills here. 6th will be at 2000rpm, but the fuel economy will be slightly better using 5th at around 2500rpm. I had suspected the computer is using less turbo boost with the lower gear. Being a slight increase, I tend to not bother putting the automatic into manual mode. So haven't checked other parameters during the climb.

[luv2spd]

Can the ScanGauge provide information such as the air-fuel mixture? Can it calculate instantaneous horsepower and torque used like in some modern cars?

I love driving my car on the highway, it has so much torque that regardless of how steep the hill is, the cruise control never shifts down, it stays in 5th gear around 1,900rpm. Just chugs along quietly. It also helps that it is very aerodynamic, keeps the wind noise to a minimum.

[JockoT]

It can only display what OBM2 provides.

[R.I.D.E.]

Look at a Brake Specific Fuel Consumption Chart. The most efficient point is the smallest circle in the chart, usually in the upper left center of the graph.

This tells you the precise RPM and Load where the conversion of fuel into work is at it's peak. The lowest amount of fuel producing the greatest amount of work. If you are in a gear that loads your engine too highly (there is always some load, even at idle)then you need to go a gear lower to keep the power production in that narrow range of highest efficiency.

As I posted before 80% is a good GENERAL rule for best power for least fuel. The reason most of those who get really great mileage out of their cars is they "pulse" at that load, then "coast", either with the engine shut off or idling.

When I do that in my Mirage (coast), engine idling, I can see mileage over 400MPG at higher speeds. When I shut the engine off the mileage is INFINITE since the vehicle is moving and no fuel is being consumed.

That is the essence of pulse and glide, using that 80% load to gain some inertia, then bleeding off that inertia with little (engine on) or no (engine off) fuel consumption.

My guess would be you were climbing a grade that gave you better efficiency at a lower gear. Maybe check that next time you are in that exact situation.

[R.I.D.E.]

Long ago I saw a dyno test on a GM 4 cylinder engine. At a 20 HP load the engine consumed 1 unit of fuel.
Increasing the load to 50 HP (same RPM) the fuel consumption increased by 50% or 1.5 units of fuel.
That additional .5 unit of fuel produced 30 additional HP, compared to TWICE that fuel amount producing 20HP in the first test run.
The secret to pulse and glide is to use the higher load to ADD energy to the vehicle's inertial state, then kill the engine and use that higher inertial state to get INFINITE mileage for that period of time when you coast.
I can get 50 MPG AVERAGE in my car within 2 miles of my trip, even with the engine sill not near normal operating temperature. 30MPG in less than 3 tenths of a mile.

[trollbait]

Originally Posted by luv2spd

Can the ScanGauge provide information such as the air-fuel mixture? Can it calculate instantaneous horsepower and torque used like in some modern cars?

I love driving my car on the highway, it has so much torque that regardless of how steep the hill is, the cruise control never shifts down, it stays in 5th gear around 1,900rpm. Just chugs along quietly. It also helps that it is very aerodynamic, keeps the wind noise to a minimum.

The Scangauge II can so give horsepower. Air-fuel mix might be possible through the Xgauge function.