Why no fast acceleration?

[JohnAh]

A completely different proof of concept may be a crazy vehicle class we have here in Sweden, the "A-tractors". An A-tractor is originally a normal passenger car, usually a larger RWD. It can also be a 4x4 pickup or even a big truck. The A-tractors are modified for a maximum speed of 30 km/h (around 20 mph) by adding an extra gearbox. The body must be modified so it can't carry lugguage or more than one passenger. The purpose of an A-tractor is to be a cheap "engine" for towing trailers or agricultural tools. As tractor it's allowed to drive by a 15 year with only a quite simple license. (minimum age for car licence in Sweden is 18 years). -Guess you can see now who the average owner of an A-tractor is? Yes, most A-tractor drivers are 15+ teenage boys who don't like to freeze their ass off on a two-wheel moped in the winters. The standard A-tractor is a Volvo 740/940, modified to look like a pickup.

There's A LOT of cheeting with these A-tractors, not only to make them go faster, but also to save fuel. Maximum speed is limitid by gear ratio with the engine running on MAXIMUM speed! For a 2.3 liter Volvo petrol engine this means 5000 rpm at 30 km/h (aprox 20 mph)! Exept for a crazy fuel consumption you have to replace the engine every month or so... Here we talk about 20-40 litres per 100 km!
You simply can't use a street legal A-tractor unless it's a low rpm diesel.

Most A-tractors are therefor illegal with unrestricted gearbox. Some boys drive way to fast but most of them stay below 50 km/h (30 mph). Still these vehicles consume serious ammounts of fuel, often MORE than they did as normal passenger cars. The reason is that there the low engine load at low speed makes combustion seriously inefficient no matter what gear you use. Going 30-50 km/h instead of 70-100 km/h will make almost any car consume a lot more fuel. Obviously it's not pumping losses and friction that is the main reason, it's entirely about engine load. To go slow, you should have a smaller engine!

Diesels are a lot better for slow vehicles and my guess the reason they perform better at low rpm's is the fact that they inject fuel multiple times during each power stroke. In a petrol engine, the entire charge is set on fire at once, increasing heat transfer losses at low rpm's.

[skrotbil]

Thanks to all who have posted on this thread. As a hypermiling novice, it has been a real eye-opener for me. My car is equipped with MPG gauges (instant and average) and a tachometer, but I was wondering if I could use my ScanGauge2 to help determine the optimum rate of acceleration. For example, from reading this thread, I gather I could use the Loop Status gauge to avoid enrichment during acceleration, but could someone help me understand how to use other parameters to determine optimum acceleration, such as Throttle Position Sensor (TPS) or Engine Loading (LOD)?

[serialk11r]

I would not worry too much about it, just try your best to stay out of open loop, and don't deliberately accelerate slowly. You'll be operating the engine in a relatively efficient way if you do that, and will have gotten most of the possible gains.

[secaturbo]

I have 2005 Insight MT no IMA and need Open Loop clarification.

Example : I noticed if i lift and coast IN GEAR the scan gauge reads Open Loop. It stays in Open Loop till RPM drops Below 1200-1400RPM.
Isn't this the fuel injectors shutting off?

Judging by previous post if I accelerate too hard then the opposite is ture - Open Loop means it is Dumping excessive fuel?

[Ecky]

If you don't have the IMA, there's little reason to coast in-gear unless you're intentionally using the engine to decelerate. Better to drop it in neutral and use a kill switch in most cases.

I suppose that's also "open loop", but the open loop generally refers to those times before the engine is fully warmed up, and near-WOT, where it's not shooting for 14.7:1 AFR and is instead going for a richer and less efficient mixture.

[Fat Charlie]

Originally Posted by skrotbil

... help determine the optimum rate of acceleration.

Optimum is determined after the fact. The car is a closed system, but it operates in the real world. Outside conditions take what the car does and turn that into real numbers, so what is optimum in one place at one time in particular traffic and weather conditions and in a particular gear won't be optimum if you change any of those things.

YMMV, as it were.

Fun, huh?

I tried using load and throttle % back when I started, even instant gph. I ended up settling on instant, short trip and tank mpg. Theoretical efficiency inside the block is moot if it's not being applied well.

[skrotbil]

I have a 2015 Toyota with 6-speed automatic 2AR-FE engine. In addition to Eco Drive mode, it is also equipped with an Eco Driving Indicator. Quoting from the manual: "During Eco-friendly acceleration, Eco Driving Indicator Light will turn on. When acceleration exceeds Zone of Eco driving, the light turns off."

Following suggestions of others in this thread, I started monitoring Engine Load (LOD) on my ScanGauge, trying to accelerate steadily with a target load of around 80%, but each time I do so, the Eco Driving Indicator light goes out, telling me I have exceeded Eco-friendly acceleration. To stay within the so-called Zone of Eco acceleration, I have to accelerate very slowly and gently.

BSFC maps would seem to suggest otherwise, but as I have no specific map for this engine, I've done as Fat Charlie suggested and ditched the LOD and TPS gauges and just monitor the instant MPG on my car's display and try to adjust my driving accordingly. Trying to monitor LOD, TPS, LP, and MPG, I sometimes forget to watch the CAR in front of me.

[user removed]

Don't think I would want to trade miles per gallon for miles per front end sheet metal.

regards
mech

[Fat Charlie]

Ignore what the car tells you, with its Zone Of Stupidity.

Don't even watch the gauges too closely- you're not trying to hit a moving needle, you're trying to get to work. Take each acceleration event as a whole: I gave it this much gas, got to that speed, and it did this to my trip mpg. Instant mpg will be horrible while accelerating hard, but that's okay. What matters is what you do with it overall.

[Mustang Dave]

Originally Posted by Fat Charlie

Ignore what the car tells you, with its Zone Of Stupidity.

Don't even watch the gauges too closely- you're not trying to hit a moving needle, you're trying to get to work. Take each acceleration event as a whole: I gave it this much gas, got to that speed, and it did this to my trip mpg. Instant mpg will be horrible while accelerating hard, but that's okay. What matters is what you do with it overall.

Well stated. Acceleration is bad for fuel economy. Try not to waste too much time accelerating.
When driving home from work, I enter I-40 eastbound on an up-hill on-ramp. I don't drive with an egg on the accelerator; I drive with a deck of cards under it. I push the accelerator to achieve 100% load on my Ultra Gauge without going into open-loop enrichment. I shift at 2500 RPM. Instantaneous MPG is about 6.9 MPG in 3rd gear; 9.9 MPG in 4th gear; and 13 MPG in 5th gear while accelerating to 65 MPH. I set cruise control @ 65 MPH while still on the on-ramp. Driving in town and in rural neighborhoods, I generally shift at 1500-2000 RPM - still accelerating @ 80-100% load. I know I'm doing a few things wrong, but 32+ MPG (6 month average) isn't THAT bad for a 4.0 liter Ford Mustang.