Accelerating in high gear+low revs considered bad?

[Zane Kaminski]

Hi everyone. First post here, with a question. I’ve got a 2008 Acura TSX with the 6-speed. As I understand, revving high wastes gas, but so too do pumping losses caused by partial-throttle operation. On this basis, I have concluded that full-throttle acceleration in the highest gear possible is the most fuel-efficient.

Therefore, when I accelerate up to speed on a 45+ mph road, I start in 1st, do a little more in 2nd, and then select 5th or 6th as soon as possible to finish the job of getting up to speed, at which point I go full-throttle, which is pretty mild in high gear. I never shift such that the revs are below 1200 in 5th or 6th.

Is this a bad idea? I get pretty good fuel economy doing it. The manual says not to allow the revs to drop below 1000, or else the engine may knock. However, it also says that under “normal acceleration,” you should shift to 5th at 45 mph and 6th at 56 mph, so I am doing it quite a bit early by that standard. I always put in premium gas, have never detected any knocking, and I never put myself in a position where the car is losing speed despite the pedal being down, such as going up a steep hill in 6th. Am I asking for trouble, or is this a valid technique?

Topic

[Mike]

Pumping losses are include such things as effort required to pump oil and coolant, and effort required to operate the valvetrain and move the pistons up and down in their bores. These losses are not affected by throttle angle. The valves, for instance, take the same amount of pressure from the camshaft to open whether at fill throttle or closed throttle. The amount of pumping loss is increased by RPM, in the sense that the valves need to be opened more times per second the higher the RPM.

There’s nothing wrong with the way you’re driving I guess. It certainly won’t hurt anything, although it could produce harmless knocking/pinging in a lesser engine than yours. I don’t drive like that, but I also have cars that can’t get fuel economy bad enough for me to care, no matter how aggressively I drive them.

[James O’Hara]

So long as you are not lugging the engine it does not matter. IE starting out in 3rd gear and mashing the gas to power through. The lower the rpms the better the fuel economy so long as you do not lugg the engine. With that being said running your rpms fully through each gear helps prevent buildups from deposits this is very apparent in diesels less so in gas engines. If you have a turbo you want to be 200rpms past where boost kicks in and when you shift you want it to not drop below that point. This prolongs the life of the turbo and gives you much better fuel economy.

Basically just drive the thing don’t lug it, Don’t pass redline in gear, Don’t under spool your turbo ( if you have one). Other then that the vehicle is not going to give a crap. Higher rpms tend to help blow and clean things out so…

Also try not to engage the clutch at too low of rpm that is bad for the clutch and engine.

[Author]

Replies