Low Gear or Hi Gear
Discussion
Something Mike said at Austec the other week got me thinking - fizzix and all that.
When you're driving about - not ragging the arse off it or anything - but just driving about - staying in a lower gear should cause less engine wear (even though the revs are higher) as the amount of work being done per rev is lower. Your not labouring the engine by leaving the change up late.
Does anyone know what this means in terms of fuel consumption ? Traveling at a steady speed, would you use more or less fuel in a lower gear than a higher one ? (Or about the same
)
When you're driving about - not ragging the arse off it or anything - but just driving about - staying in a lower gear should cause less engine wear (even though the revs are higher) as the amount of work being done per rev is lower. Your not labouring the engine by leaving the change up late.
Does anyone know what this means in terms of fuel consumption ? Traveling at a steady speed, would you use more or less fuel in a lower gear than a higher one ? (Or about the same
)Swings and roundabouts as far as the efficiency is concerned, dropping the revs might improve the efficiency slightly but not enough to matter in the scheme of things. In terms of wear and tear it is well worth keeping away from the upper and lower limits of the rev range, some of the highest loads occur when you labour the engine. This is one reason auto transmission improves the engine life, it stops you from labouring the engine.
Agree with the labouring the engine sentiment. AFAIK beddng in of a new Cam on the RV8 is done at between 2-2.5Krpm to reduce pressures on the lobe's, so using that as a yard stick I tend to keep it above 2K, or around 2K when really cold. Wereas the Omegod gets driven everywhere at 0.5-1.5Krpm, judge which one I care about 
.
Harry
. Harry
Most recent evidence points to lower revs / larger throttle openings helping fuel efficiency .. as long as the car is still operating in lambda control then torque ouput for any given airflow will be slightly lower than at righer mixtures, so you increase throttle opening therefore increasing compression pressures .. it's the combination of advanced ignition, higher compression pressures and lambda control that contributes to the better economy ..
as regards engine loads, well piston /rod forces increase as the square of engine revs so high revs certainly put enormous stresses on bearings, and at low revs it's difficult to build hydrodynamic wedge of oil between bearing and journal which is responsible for keeping the two apart. As HarryW says also cams spin at half engine speed so they are particualrly prone to damage at low revs ..
best advice is probably to just drive the car normally
as regards engine loads, well piston /rod forces increase as the square of engine revs so high revs certainly put enormous stresses on bearings, and at low revs it's difficult to build hydrodynamic wedge of oil between bearing and journal which is responsible for keeping the two apart. As HarryW says also cams spin at half engine speed so they are particualrly prone to damage at low revs ..
best advice is probably to just drive the car normally
Okay. Thanks guys.
So what you're saying is, provide enough revs to keep the engine well coated in oil (and thus keep wear low) - but not so many revs as to wear your bearings out.
Presumably staying within the 2-4K rev range would be a good starting point then (apart from when you're sat at the lights
)
And with regard to fuel enconomy. I ain't gonna notice much difference regardless of how I drive.
Cheers,
WG
So what you're saying is, provide enough revs to keep the engine well coated in oil (and thus keep wear low) - but not so many revs as to wear your bearings out.
Presumably staying within the 2-4K rev range would be a good starting point then (apart from when you're sat at the lights
) And with regard to fuel enconomy. I ain't gonna notice much difference regardless of how I drive.
Cheers,
WG
Gassing Station | S Series | Top of Page | What's New | My Stuff