Perfect driving idle rates?

A

alexman

Member
I read someone say recently that driving around 2000rpm (such as third at 30mph) is bad for the engine when you start to accelerate, as the "engine is under load" and will use more fuel etc (similarly of course more fuel if you were driving at 30mph in first gear and running around 4500rpm).

based on this, I can't find a comfortable gear around the 30-35mph range (or maybe I'm thinking about it too much now I have the RPI exhaust noise :oops: ). 2000rpm seems like a good idle speed to me and safe to accelerate from here to say 40rpm in third gear. Does anyone agree/disagree with this and find themselves driving along at 30mph or 40mph zones for a consistent amount of time at higher revs?
 
In a 30 zone, everything switches off, mind, eyes the lot as it is so boring.

I have it in 4th then, but when the 30 ends go back to second for a quick catch up.
 
Ah yes, but is it damaging/very fuel inefficient to even speed up slowly in third from 30-40mph if you're doing around 2000rpm in third. I wouldn't have thought so but someone made all these comments about "wear on the engine" etc at these speeds.

Bad thing about the RPI is that it makes you want to drive at higher revs just to hear the sweet exhaust note :roll:
 
I would use 1st, 2nd and 3rd to accelerate and use 4th, 5th and 6th to cruise when driving thru london traffic. 2000rpm is the minimum for changing up.
 
Petrol engines are typically most efficient at 3/5ths (60-70%) throttle when accellerating. This is due to many things, but mostly the position of the throttle plate being almost wide open allowing free-flowing airflow into the inlet. 2000rpm isnt low enough to labour any Z4 engine.

Id stick to the 1500-2500 band for just chugging along... Makes the occasion of putting your toe down more special :)
 
This is more likely part urban legend and part truth grown up from low powered engines and ineffective carburettors. Take an old car and chug it up a long hill in 4th and the throttle will be wide open and guzzling fuel through a carb most likely operated on manifold vacuum. In those conditions fuel economy and to avoid labouring the engine would both benefit from dropping a gear.

Power to weigh ratio of a Zed is so high I cannot see it matters at all if you're happy to use half throttle and let it build speed up. Flooring it then of course you'd be better to drop some gears.

To confirm the point Ed makes above drive an auto and it will spend almost all it's time in the 1500 to 2500 rev range (oftern less than 2000) only going above if you push the throttle a fair bit more. Put it to the floor and it will drop a gear or more.
 
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