V12 friction power

Thought I would see how much torque it takes to turn over the 5.3L being rebuilt.
It takes 4 kgM, roughly 40Nm or 30ftlb to overcome the friction in the bearings, rings and cams…
There are no accessories on the engine right now.
So at 800RPM you need 4.6HP to overcome friction.
At 6000RPM you need 34.5HP.

I will put an electric coolant pump on the engine.
If you add the alternator, power steering and mechanical pump the HP needed will be higher.
All this HP is needed just to turn over the engine and accessories before you deliver any HP to the transmission and rear wheels.

On top of this the efficiency of turning thermal energy in the fuel into mechanical energy is not brilliant.
One time I read the overall efficiency of a typical gas (petrol) engine is 25%. Diesel does better and modern engines will be better too.

Electric motors are so much more efficient turning battery energy into mechanical energy.
Naturally they loose nothing at idle, and maybe 5% running flat out. Converting 50Hz/60Hz power into battery energy has losses, and coal into electric power is a big loss too. Overall not so good unless you use sun power or wind power, then that is much better.

Is that with or without oil? :wink:

I read on a site the other day that F1 engines are reaching 50% efficiency now.

Well, that’s an interesting exercise, but I seriously doubt its validity. When running, pretty much everything in there is supposed to be riding on a film of oil, greatly reducing the friction.

Seriously doubtful, as they are optimized for power, not efficiency. The cars are hybrids which might help the vehicle efficiency a bit.


F1 has been reducing the amount of fuel allowed for years now, and have a strict limit of fuel flow rate. You also want maximum efficiency to reduce the weight penalty of carrying around excess fuel. Unfortunately, not enough is made of the extreme efficiency of these engines, most people only see them as gas guzzlers. But it will take a while for the technology to become something that is considered for mainstream production cars.

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The engine was put together with a generous amount of oil in the bores, on the bearings and cams.
They are the major source of friction. It has only been turned over 2 or 3 times to set the cams and make sure the chain is running OK.
When running there will be pressurised oil in the bearings but that pressure is not going to make a significant difference. It would if the bearings are dry now, which is not the case.

Chances are electric motors will dominate first. When most 50Hz/60Hz power is from renewables car makers will be under the gun to avoid IC engines. Very eco conscious.
Hope there is no future problem with all the lithium or similar batteries in operation and at end of life.

its been known that the piston rings have the most friction drag of any other parts in a IC engine!

when i did my V12 rebuild , the pistons i used had thinner rings than other factory pistons, and the rings recommended are considered proprirtary low drag rings!
so just playing around it put one piston factory setup, and one piston with the low drag rings , pushed them up and down by hand , and by far the LD rings had much lower force to push up and down!
and no problems with blowby at all!
no doubt tho Electric cars are comin on fast!

I did not know about such low friction rings.
Sounds like it could save some HP.
Do they wear out quicker ?
I did reckon that ring friction would probably be the biggest fraction of all the friction ( is that a line from a song ? ).

[quote=“Richard_Dowling, post:1, topic:383930, full:true”]
Thought I would see how much torque it takes to turn over the 5.3L being rebuilt.
It takes 4 kgM, roughly 40Nm or 30ftlb to overcome the friction in the bearings, rings and cams…

Richard, the only way get a true friction read, is to connect the engine to an electric motor and measure the power draw.

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There’s a whole science to those things. One factor is how much spring there is in the rings, meaning what size circle they form when unrestrained and how thick they are. To minimize friction you want the least contact force between ring and cylinder wall you can get – but you never want the ring to lift off the cylinder wall either, because that’d be bad.

In most ring designs, the pressure of the combustion chamber is supposed to find its way to the ID of the top ring, helping push it against the cylinder wall. Which probably means the contact force could be waaaaay higher than that of the spring of the ring itself.

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That’s like expecting the skimboard you use at the beach to work just fine at standstill because it’s wet.

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The connection with a skimboard is a little obscure. Like I said, lots of oil in the bores and only turned over the engine 2 or 3 times. The bores have just been honed so will retain the oil quite well. If the engine had been turned over 20 times then a good chance most of the oil scraped off.
I only raised the topic as a matter of interest to give an idea how much HP is needed to overcome friction. It was not meant to be a precision measurement.
Like Norm said, you want precision you put the engine on a dynamometer.

No, it’s not. The operation of an oil film is exactly that of a skimboard on seawater. It’s gotta be moving to work. Measuring the friction at standstill is wholly invalid.

OK, maybe you are talking about the difference between static friction and dynamic friction. I understand the difference.
So when I measured the torque I did it with the torque arm resting on a weighing scale, and then I allowed the torque arm to move and the difference in weight was very little. So at low speed there is not much difference between static and dynamic, and I quoted the dynamic one which is the one that matters.
No doubt engine manufacturers will do tests with dynamometers when developing engines to figure out ways of minimising friction. It is an important design consideration.
That information is not usually available.

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No, I’m not. I’m talking about how an oil film bearing works.

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ALL right OK , who really cares much about friction , there is not much we can do about it!

and i have used a simple torque wrench for 50 yrs, long stroke engines have more drag than a short stroke, cylinder numbers equal!

and for interest : my top ring is what is called Barrel faced with Molybdenum coating!