Decoding & Breaking Down the 1ZZ-FE Engine BSFC

[jeff88]

Can somebody help me with the BSFC map for my 2001 Toyota Corolla?

Do I have this right?:

The best BSFC engine speed is around 3100-3200 RPMs. The engine puts out the most torque around 4500 RPMs. The top chart shows the least power at 1000 RPM and the most at around 5500, tapering off after that. Is that power (in kW) the engine uses or the power it outputs?

At 60, the engine speed is around 2000-2100 RPMs, but the best (least) pollution is at 3100-3200. Is there any way to make the 'g/kWh' the least at a lower RPM?



Thanks for the help! I'm hoping with this information, I can *properly* drive the car!

[bestclimb]

The BSFC curve is only valid when the engine is making the torque in the other curve, IE when heavily loaded during acceleration. I really do prefer graphs of BSFC plotted against torque as apposed to with or BSFC plots at different levels of load.

Looking at that torque curve you get up to speed fastest (least time spent accelerating) around 3800-4200 rpm with a nice little secondary dip in BSFC. I tend to prefer a quickish acceleration (If there is not much of a fuel economy hit).

As for steady state cruising (lightly loaded) some sort of instant fuel economy info will give you better data than a graph depicting a fairly heavily loaded engine.

One thing that may help is a cam reground for low end torque but the cost would likely eat fuel savings.

[Occasionally6]

Those are curves, not a map. They are developed at a single throttle opening i.e. wide open, meaning the inlet manifold pressure is very close to atmospheric. That's the maximum the engine will do at a given rpm. The single curves are not a whole lot of use because you don't (usually) drive with WOT.

What is needed for a BSFC map is the BSFC figures corresponding to power outputs at a range of manifold pressures and rpm. You might generate that by holding the inlet manifold pressure constant, at a number of different pressures, and generating similar curves to those above for each pressure. They can be then be displayed together in the form of 3D maps; manifold pressure vs rpm vs BSFC and manifold pressure vs rpm vs torque. Power is, simplistically, torque X rpm.

Because a given power output can be obtained at more than one combination of manifold pressure (~ throttle opening) and rpm, that map allows you to pick the most efficient combination from the load vs rpm points at which the power you want/need can be generated.

[jeff88]

Originally Posted by bestclimb

Looking at that torque curve you get up to speed fastest (least time spent accelerating) around 3800-4200 rpm with a nice little secondary dip in BSFC. I tend to prefer a quickish acceleration (If there is not much of a fuel economy hit).

As for steady state cruising (lightly loaded) some sort of instant fuel economy info will give you better data than a graph depicting a fairly heavily loaded engine.

One thing that may help is a cam reground for low end torque but the cost would likely eat fuel savings.

So basically when accelerating, I should try to accelerate at around 4k RPMs. This has two benefits: best BSFC as well as get up to speed faster so I can than cruise. My question though is the BSFC is in g/kWh, not necessarily MPG, so the engine may pollute the least at 4k, but not necessarily be the most efficient in fuel used?

If one was to research a cam reground for economy use rather than street racing use, what would one be looking for?

Originally Posted by Occasionally6

What is needed for a BSFC map is the BSFC figures corresponding to power outputs at a range of manifold pressures and rpm. You might generate that by holding the inlet manifold pressure constant, at a number of different pressures, and generating similar curves to those above for each pressure. They can be then be displayed together in the form of 3D maps; manifold pressure vs rpm vs BSFC and manifold pressure vs rpm vs torque. Power is, simplistically, torque X rpm.

Because a given power output can be obtained at more than one combination of manifold pressure (~ throttle opening) and rpm, that map allows you to pick the most efficient combination from the load vs rpm points at which the power you want/need can be generated.

Could this be done with an Arduino and tapping into the ECM?

[Occasionally6]

Originally Posted by jeff88

So basically when accelerating, I should try to accelerate at around 4k RPMs. This has two benefits: best BSFC as well as get up to speed faster so I can than cruise. My question though is the BSFC is in g/kWh, not necessarily MPG, so the engine may pollute the least at 4k, but not necessarily be the most efficient in fuel used?

Given the condition of WOT, yes it is the most efficient use of fuel to operate in the range of 3-4K rpm. Accelerating in that rpm range is still more energy efficient because the energy released from the fuel is stored as kinetic or potential energy, not lost.

At WOT the engine management will be adding fuel to protect (cool) engine and catalytic converter so just less than WOT will be more efficient than WOT. To detect if that is occurring look for an indication of open loop on your Ultragauge.

The curves for inlet manifold pressures near WOT will be close enough that the rpm range for greatest efficiency will be similar to that for WOT. The 'dip' will be deeper and the rpm of lowest BSFC will be lower as inlet manifold pressure decreases.

If you can get a display of MAP pressure on the gauge then you want that either in the range of 0.6-0.8 bar (when accelerating) or the engine off (or at least idling). Higher, short of going into open loop, is better.

The reason is that, literally, half the engine (4-stroke) is acting as a vacuum pump, pumping from inlet manifold pressure up to exhaust manifold pressure (actually cylinder pressure on the inlet and exhaust strokes but close enough).

You can appreciate that if the engine wasn't an engine but motored as a vacuum pump it would take power to do that. Opening the throttle and increasing the inlet manifold pressure reduces that pumping work.

If you cruise along in gear at light load the engine is still pulling the vacuum. Higher rpm increases the amount of work being done so idling (with the engine disconnected from the wheels) reduces the pumping work. If you could arrange for the engine to be off (as well as disconnected) it would be even better.

The other effect that reduces efficiency is friction. That is proportional to the square or cube of engine speed (depending on the source). That is why the efficiency falls as rpm increases.

Could this be done with an Arduino and tapping into the ECM?

Normally that would be done on an engine dynamometer but yes. Without modelling it won't be possible to separate out road and aero drag or transmission losses from internal engine losses though. With a fuel consumption rate and kinetic and potential energy measurements it will be possible to determine the equivalent of BSFC based on the power used to drive the car. In the real world that is what matters anyway. Maybe call it Road (Power) Specific Fuel Consumption?

[bestclimb]

Originally Posted by jeff88

So basically when accelerating, I should try to accelerate at around 4k RPMs. This has two benefits: best BSFC as well as get up to speed faster so I can than cruise. My question though is the BSFC is in g/kWh, not necessarily MPG, so the engine may pollute the least at 4k, but not necessarily be the most efficient in fuel used?

If one was to research a cam reground for economy use rather than street racing use, what would one be looking for?



Could this be done with an Arduino and tapping into the ECM?

AT WOT, at less than WOT slightly lower RPM is likely what is called for. At very high loads the computer is likely fueling via the fuel map which is less effcient than consulting the O2 sensor. An MPguino or ultra/scan gauge will tell you what is more efficient.

Quicker acceleration at a high GPH will get you up to cruise speed and high MPG sooner. Where the most efficient balance between quick (high GPH for short time) and slower (low GPH for a long time) acceleration is best evaluated with some sort of instantaneous fuel consumption display.

4000 very likely not an efficient cruise RPM due to it being efficient at lower power settings and being at a speed that is high drag. it is probably close to a decent shift RPM for getting up to speed fairly efficiently and quickly, but without a BSFC map, and/or observing some instant data.

Efficient and polluting are two different things. one is using the fuel smartly the other is not burning it enough (hydrocarbons in the exaust), or too much and creating NOx. your catalytic converter and computer should be taking care of that.

[serialk11r]

1ZZ owner here, let's clear up a few things.

No, fuel enrichment does not happen on this engine at 4k. It kicks in at something like 4500, before that it's stoichiometric closed loop.

3000rpm is highest efficiency at max load but the way it typically works out is that at lower loads you're better off at slightly lower rpms since friction is more correlated to rpm than load. I wouldn't be too concerned with acceleration on this engine because it doesn't enrich the mix at low rpm, just give the pedal a solid push and you'll be at a good load level to be using the engine efficiently and focus on everything else.

Also if you want an all out economy cam grind, you can have a high duration low lift intake cam at the expense of torque. Cost is 200 bucks from delta cam, not really worth it unless you drive an insane amount of miles or you're looking for more top end power or something.

[mrmojo]

I have this engine and I had the same questions on the map (or curve). Doesn't seem too helpful. The posts are a little confusing, too, at least for me, so ease excuse my ignorance.
Re: watching the UG/SC for what is more efficient driving technique for best operation of the engine, other than instantaneous mpg, what other parameters should be monitored? Load, TPS, vacuum (I think this might be Intake Manifold Absolute Pressure, but as there is no MAP sensor on this engine, not available)?

[topcat]

I also have the 1ZZ-FE engine. At Wide Open Throttle (WOT), my scangauge indicates open loop at all RPMs, even as low as 1.4k RPM. This means it will enter fuel enrichment WHENEVER I floor it. So I don't floor it unless absolutely necessary!

Personally, I find the best MPG using the technique of hard acceleration in as high a gear as possible (preferably 6th gear) at around ~80% load on the scangauge (roughly 80% accelerator pedal deflection). Once up to speed I then stay in top gear with a steady speed or very slight deceleration, during this period my scangauge indicates 12-15 miles/litre (54-68 MPG imperial). I've seen others describe this high MPG period as "hang time".
The transmission changes tone to a slight whine during this "hang time" period.

BTW, if my rpms are too low during the hard acceleration I get rattle from what I'm led to believe is the timing-chain. In that case I of course back off the throttle until things sound better or change down a gear. Busting the engine will negate any MPG savings!

With this technique, my best 20 mile commute was 58 MPG (imperial). A tank fill up of ~48 litre (55litre tank) gets me over 500 miles in the summer. However the roads I use rarely go over 50MPH. I'm very happy with that.

[mrmojo]

Originally Posted by topcat

BTW, if my rpms are too low during the hard acceleration I get rattle from what I'm led to believe is the timing-chain. In that case I of course back off the throttle until things sound better or change down a gear. Busting the engine will negate any MPG savings!

According to the Haynes manual, checking and adjusting the timing chain appears to be pretty straightforward, even for someone like me. I haven't had the problem you describe, but the, my engine is mated to a wussy 3-speed AT, too, so maybe it's just your engine lugging in low RPMs?
Cheers,
Stephen