Friction Losses - some questions.

[Arragonis]

Hi,

Friction losses isn't something I know too much about - as in I know the basic idea, the more moving parts and bearings the greater the energy required to move those parts. But I don't follow everything involved from an engineer's standpoint and probably wouldn't understand. However I started thinking about this today.

The reason this came up in my thoughts was an article in this month's Motor Sport magazine (it covers a lot of historical racing from pre WW1 to the modern era) about the Ilmore Indycar engine of 1994.

It was built to exploit a rule about engines with an OHV / Pushrod / 2 valves per cylinder layout being allowed to run more boost than race spec engines, i.e. ones with DOHC and 4 valves per cylinder. The rule itself was made to encourage more teams to compete with essentially road going engines - i.e. the Buick V6 I think.

It (the Buick) a lot of power compared to other engines because of this rule - the extra boost, but wouldn't normally last a race. The Ilmore engine had more power again purely because of the pure race design, and was reliable enough to last a full race.

The thing that caught my eye though was the explanation for the engine also being very good on fuel - the Penske cars also maintained their lead by not having to stop as often as the competition - a little like why the Audi TDI Le Mans thing wins too. The fuel efficiency was put down to the lower friction losses, partly down to the OHV layout (single cam-in-block design) and the use of roller bearings in a few places.

I know BMW is banging on about Efficient Dynamics at the moment which seems a similar kind of effort - reduce the energy wasted by the engine in just keeping itself going.

So a number of questions. Firstly apart from BMW are there accessible engines which exploit this which we can all benefit from ? I know older Honda sports cars (S600 and S800) used roller bearing cranks but not many others in mass production. Or this just down to choosing 'engineered' cars like BMW or perhaps Honda, rather than 'produced' cars lik GM, VW and so on.

Secondly are there things we can use to promote this - for example I've seen posts on people using different oils to reduce friction in engines. Does this make a big, measurable difference ?

And finally are we (outside the US perhaps) kind of wrong to giggle when people still make OHV engines in modern cars ? Are SOHC units better ?

Or am I putting 2 and 2 together and getting 22 ?

[user removed]

Efficiency and valve trains can be less connected than you might think.

Delage racing engines in the 1920s and early 1930s had 60 ball and roller bearings and the engine block and heads were cast in the same unit to eliminate head gasket failures.

The stock block Indy engines were allowed significant displacement advantages over the turbocharged specialty engines.

One example I remember was the Alfa 8c engine developed in the 1930s. In the early post WW2 era in grand prix racing trim they produced 390 HP out of 90 cubic inches at 2 miles per gallon.

Since best mileage is achieved at lower speeds and many times with higher rates of EGR, it may be we actually go back to smaller valves, and less effective cylinder scavenging, with higher turbulence at lower RPM.

It would be interesting to take some of the older designs of many decades ago and use modern fuel delivery and ignition technology to see what could be done.

My old 37 Ford with the original Flathead V8 would idle at 350 RPM and glide down the road in high gear at 7 MPH idling. Max revs were 3800 RPM.

The engine weighed 525 pounds. The whole car was lighter than a Toyota Corolla.

regards
Mech

[Patrick]

Originally Posted by Arragonis

Secondly are there things we can use to promote this - for example I've seen posts on people using different oils to reduce friction in engines. Does this make a big, measurable difference ?

And finally are we (outside the US perhaps) kind of wrong to giggle when people still make OHV engines in modern cars ? Are SOHC units better ?

WRT oil, yes, using an eco oil can reduce friction and improve economy. The 2010 Prius uses 0W-20 oil and supposedly loses 1-2 mpg if you switch to a heavier weight.

Millions (billions?) of OHV pushrod engines have been made. They are proven and reliable. The limitations show up when you try to get maximum power from them. They typically have 2 valves per cylinder, which limits the flow, and the mass of the valvetrain limits how much you can rev the engine before the valves float. The valve springs have to push all the mass of the valvetrain back into position and at a certain RPM they can't do it fast enough. Heavier valve springs help, but there's a limit to high you can go here. Lightweight pushrods and rocker arms have been used too. OHVs usually use hydraulic followers (lifters)and oil-bath timing chains so no maintenance is needed.

OHC engines remove the pushrods and rocker arms (in some cases), reducing the reciprocating mass and allowing higher maximum revs to be achieved. It's also easier to add more valves per cylinder, improving volumetric efficiency. But they are more expensive to make. They also increase the overall height of the engine, so if your engine is upright or nearly so, it might compromise your aero efforts. OHCs usually use a timing belt that has to be replace periodically and some use cam followers that have to be fitted by hand and/or adjusted peridically, increasing the maintenance cost.

There are roller rocker and roller cam follower kits available to reduce friction in some of the OHV engines. The roller followers require a special camshaft because the contact point with the camshaft is on the same spot instead of constantly changing as with the flat followers.

[Arragonis]

Mech - interesting read. I've looked at the between-war and postwar racing engines quite a bit. Always been impressed with the high outputs and low sizes of some of those supercharged engines and more impressed they survived being lubricated by the poor oils of the time. One question, wouldn't smaller valves encourage more pumping losses instead ?

The stock block requirement was dropped for 94 which allowed Ilmore to exploit the loophole and make a specific race engine.

The FE thing is confusing. My 1.9 TDi makes less FE with 130 HP in a small hatchback than my wife's 2.0 TDi (with 16v mind) does in a Jetta sized estate.

Time to look more at that nut behind the wheel again I suppose.

[Laurentiu]

Originally Posted by Old Mechanic

My old 37 Ford with the original Flathead V8 would idle at 350 RPM and glide down the road in high gear at 7 MPH idling. Max revs were 3800 RPM.

The engine weighed 525 pounds. The whole car was lighter than a Toyota Corolla.

regards
Mech

Wow, that's the lowest idle RPM i've ever heard of. Did it have a muffler or just a straight pipe exhaust ?

[Laurentiu]

Originally Posted by Arragonis

The FE thing is confusing. My 1.9 TDi makes less FE with 130 HP in a small hatchback than my wife's 2.0 TDi (with 16v mind) does in a Jetta sized estate.

Time to look more at that nut behind the wheel again I suppose.

You are comparing THIS engine with THIS engine, right ?


Well, first of all like you mention the 8v vs. 16v makes a difference straight away when it comes to efficiency as well as 5spd vs. 6spd (The Octavia has 6 speed transmission ?)

The weight/output ratio is practically identical but those differences as well as a Cx of 0.30 for the Octavia vs. 0.33 for the Fabia bring that extra FE capability.

I see also the stock tires on the Octavia are narrower (195/65 R15) vs. 205/45 R16

The factory numbers are pretty the same (5.5l/100km vs. 5.6l/100km) but the way they measure that is not by ecomodding...

BTW, what do you think of the new 1.6TDI's in the new Fabia's ? Pretty sweet FE rated at 4.2 combined (56MPG US) :drooling: