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There are techniques to get better mileage, such as coasting in neutral or with the clutch in, drafting, short shifting and staying in higher gears, and just never using any throttle.
Surprisingly, the technique of achieving maximum fuel efficiency actually involves using full throttle (but low revs) because volumetric efficiency is greater at wide throttle openings. BMW did the footwork on this in the 80's and found substantial (if not nearly unbelievable) gains can be had by driving that way but conceded most people would find it difficult to utilize that method as a habit. I've tried it and found them to be right on in every respect.
 

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Surprisingly, the technique of achieving maximum fuel efficiency actually involves using full throttle (but low revs) because volumetric efficiency is greater at wide throttle openings. BMW did the footwork on this in the 80's and found substantial (if not nearly unbelievable) gains can be had by driving that way but conceded most people would find it difficult to utilize that method as a habit. I've tried it and found them to be right on in every respect.
The reason that WOT is especially efficient is not due to volumetric efficiency, but due to pumping losses which are a function of throttling losses. Any time a machine tries to push or pull a gas across a throttle (a restriction), you get significant losses. We measure these losses as Pumping Mean Effective Pressure (PMEP), and are more significant the smaller the throttle opening is and the higher the engine speed. Another way of understanding pumping losses is that when the throttle is closed the engine acts like a big vacuum pump (vacuum in the intake manifold), and it takes energy to create and move air through a vacuum. Think vacuum cleaner. If we could run our engines at WOT without fuel enrichment or knock-limited spark retard, they would be much more efficient. This is one of the main reasons that Diesel engines are very efficient at light to moderate loads; they run unthrottled, lean mixture, and ideal combustion phasing.

DAve
 

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Discussion Starter #43
I got a Prius.

Anyone claiming to get ~40+ mpg in an MR2 Spyder is either wrong, lying, or an incredibly unique confluence of events occurred.
I'll take this as a challenge.
With the next tank of gas I will get over 40 mpg aka less than 5,88 l/100km.
Who is buying this car for fuel economy? Granted, it's probably more fuel efficient than most other 2 seat convertibles on the road.
Fuel economy wasn't my main cocern when I bought the car, but keep in mind fuel is a bit more expensive here in germany at ~1,40€/l wich equals about 6,39$/gallon.
Also had to drive a lot recently and I'mstill in university, so not much money to spend on gas.
I dispute the claim that better mileage comes from driving with the top up or windows up.

I have hard data to prove it, so enjoy your convertible.
During the last drives I often had the top down to transport long parts, it didn't make much of a difference.
However I have noticed a difference in topspeed before, so it does increase drag to a certain degree.
Weather fluctuations over here are too extreme at the moment for me to get accurate data.
The reason that WOT is especially efficient is not due to volumetric efficiency, but due to pumping losses which are a function of throttling losses. Any time a machine tries to push or pull a gas across a throttle (a restriction), you get significant losses. We measure these losses as Pumping Mean Effective Pressure (PMEP), and are more significant the smaller the throttle opening is and the higher the engine speed. Another way of understanding pumping losses is that when the throttle is closed the engine acts like a big vacuum pump (vacuum in the intake manifold), and it takes energy to create and move air through a vacuum. Think vacuum cleaner. If we could run our engines at WOT without fuel enrichment or knock-limited spark retard, they would be much more efficient. This is one of the main reasons that Diesel engines are very efficient at light to moderate loads; they run unthrottled, lean mixture, and ideal combustion phasing.

DAve
You can also often look up charts with brake specific fuel consumption at certain loads/rpms.
Rule of thumb for maximum efficiency is the rev range where your engine produces maximum torque at 50-80% load.
If anyone has found such a chart for the 1ZZ-FED, please post it here.
 

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Discussion Starter #44 (Edited)
I've done a little digging myself and found some info on the BSFC of the 1ZZ engine, sadly it's only at wide open throttle, but the chart does look interesting.
You can see a sharp decline from 1100 rpm to 1500 rpm but none from 1500 rpm to 2000 rpm, so ~1500 rpm are probably the sweetspot for maximum efficiency.
But I don't have a proper BSFC-map for the 1ZZ and this might not be the right 1ZZ-FE, so I might be wrong.
81619

Found some info about the fuel efficiency ratings for our car:
81620

But appearantly my '00 Spyder is FWD, seems like they fixed it in the facelift version...
81621
 

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I often had the top down to transport long parts, it didn't make much of a difference.
However I have noticed a difference in topspeed before
It certainly does affect stability at high speeds. I've noticed that between 90-11x MPH the buffeting is bad, but when you get to 12x MPH it gets smooth again. Or at least that's what this one guy who looks like me said.

Driving that fast would be illegal.
 

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Discussion Starter #46
Driving that fast would be illegal.
I'm german, so it's not illegal to drive that fast here.
Besides,our cars are not exactly known for their high topspeed.
I noticed a difference in high speed stability based on weight in the frunk.
The more weight in the frunk, the better the high speed stability.
 
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