RPM for Everyday Driving

[BobMarley1]

I can definatly state that I have become more knowledgeable by MNBOxster's posts.

Thanks MNBoxster, I enjoy ALL your posts!

Originally Posted by MNBoxster

Hi,

A Car needs a Transmission as a consequence of the characteristics of the Internal Combustion Engine. Engines typically operate over a range of 600 to about 6000 ± revolutions per minute, while the car's wheels rotate between 0 rpm and a maximum of around 2500 rpm.

Happy Motoring!... Jim’99

[shumphries]

I think the shifts seem smoother if done above 3500RPM. Might also indicate I'm concentrating more on the shift if I'm driving it a little harder, though...

[xclusivecar]

Originally Posted by shumphries

I think the shifts seem smoother if done above 3500RPM. Might also indicate I'm concentrating more on the shift if I'm driving it a little harder, though...

I agree. My shifts are a bit clunky unless I shift above 4,000 in 1st and 2nd. If under 4000 I give the gas a little blip as I shift to the next gear. This matches my rpm with the car. I think the car unloads quicker than I can shift and when I do shift I'm not rev matching any longer. Thus the clunk.

[donv]

Great advice above. One other key point to keep in mind is that the biggest risk for over-revving the engine is not really on acceleration but rather deceleration. If you're an engine braker, or otherwise downshift unintentionally and don't match gears properly to your road speed, you can easily blow past redline and stay there (unlike when accelerating). On acceleration, the rev limiter is going to help protect the engine and back you off from redline - there is no rev limiter protection on deceleration, when the wheels are backdriving the engine through the tranny.

[Adam]

For normal driving I just shift between 3-4,000. There is no doubt that for max acceleration you shift fast and hard at the redline to the next gear. The boxster power band(which varies only slightly if you have a base or S) is between the TQ peak of 4,500 and the hp peak of 6,200 rpm. The boxster acceleration drops off slightly from 6,200 to 7,200 rpm because there is less hp and TQ up there. However, you still receive the fastest times by shifting at redline because that keeps the car in the best part of the power band when you shift. The vario-cam sees the biggest switch at around 5,200ish rpm. That when you really start to move and you hear a noticable sound difference at WOT(wide open throttle).

[shumphries]

'01 S gears at redline (7200) at:

1st: 38 mph
2nd: 66 mph
3rd: 96 mph
4th: 119 mph
5th: 143 mph
6th: 160 mph (6650 RPM)

Great point donv re engine speed at deceleration. Had never thought about it. (When I learned to drive a stick (in 1985, in a 1979 Corolla) i was taught to use the engine to slow the car, on account of not wanting to "wear out" the brakes. Boy did I get an earful when tried to pass that advice on at some point. What is the justification for using engine braking, if any?

[donv]

Engine braking is useful if you have no brakes or weak ones. Other than in that situation there's likely little use for it. In the old days there were cars that had stronger engines than brakes - and it may be that today's Big Rigs still fall into this category based on those "No Jake Brake" signs you see in rural areas.

Theoretically you could do a good job of matching the right gear and engine speed when downshifting in a modern car such that brake use is minimal and engine braking would fill the void. In a world of long slow off ramps or other gradual deceleration situations this could be great. In an unpredictable/fast deceleration world then the downshifting to engine brake becomes more difficult or harsh such that clutch wear starts to factor in more (or as mentioned before, over-revving and engine wear), not to mention the possibility of unbalancing the car by overloading the drive wheels' friction patch.

For me, bottom line is if I have to choose between a clutch job and a brake job, it is always going to be the brakes - so I minimize engine braking's use to long slow gradual hills etc.

BTW - nice color choice on that 2001!