How Fast To Accelerate?

[MorningGaser]

I have an automatic 2007 Yaris...I pull out from a stop light at about 1/2 throttle, then back off at 40 mph, and feather the gas peddle from there, and I have fount this gives better MPG then feathering from the start...the gradual increase to speed kills MPG big time...better to get there fast, but doing so too fast will also kill MPG, so you'll need to find a happy medium.

Also, don't make the mistake of equating MPG with RPM...they is often no correlation between the two.

[omgwtfbyobbq]

Originally Posted by MorningGaser

Also, don't make the mistake of equating MPG with RPM...they is often no correlation between the two.

During acceleration, yup. During a steady cruise, not so much. During a steady speed engine speed correlates to engine load, which determines how efficiently an engine operates. Not to be contradictory or anything, but I just wanted to make sure that was clear.

[MorningGaser]

Originally Posted by omgwtfbyobbq

During acceleration, yup. During a steady cruise, not so much. During a steady speed engine speed correlates to engine load, which determines how efficiently an engine operates. Not to be contradictory or anything, but I just wanted to make sure that was clear.

I agree...but there are those that keep the RPM razor small while getting to speed, and this can actually burn more gas then using a higher RPM to get to speed. True once at speed then there is a direct correlation to MPG and RPM, but even then I see exceptions, if minor:

I find that when I drive 34 MPH in 3rd gear, my milage is actually less then driving 40 MPH in 4th gear, and it is even better at 42 when the T/C clicks in...it seems that to overcome body drag, and/or A/C drag on the engine, the car needs to be at a certain speed...I think the tranny gear ratios come into play, of course, as well as the torque converter too.

For this reason, I ignore RPM on the ScanGuage, and judge my MPG performance with these paramters: TPS, GPH, and of course instantaneous MPG. I find RPM to often be useless, and for the reasons I wrote.

The RPM's can lie about MPG....those that drive manual trannys, and short shift keeping the RPM's very low may actually be burning more gas then otherwise.

[trebuchet03]

Just an interesting tidbit to add.... I've been accelerating based on TPS and load. The other day, I compared TPS and Loop on my 2000 Jetta gasser.

While accelerating, I couldn't do anything to get into open loop. Mind you, I wasn't bogging the engine down... But 1500rpm + full throttle was closed loop o.0

[Jim Dunlop]

I'm glad I read this thread. I am currently feathering the gas starting from a dead stop...apparently this is not the best, especially since I start from dead/rolling stops at least a few times during my commute. It really annoys other drivers, too.

I will try the "feather after 40 MPH" technique. Also I have been shifting prior to 2000 RPM, which drops it down to 1000-1200 and it seems like the engine is working a little too hard. I'll try shifting a couple hundred RPM's higher.