Another way to reduce pumping losses

[300zxrb26dett]

Thought I would share this here since this could benefit this forum as well.

Found this while browsing the internet one day. Its a superbike engine, but I have no idea what kind anymore. Those notches between the companion cylinders are designed to reduce pumping losses by allowing the air to move back and forth between cylinders as they move up and down. There was a Porsche engine that also had this but I cant remember where I found it anymore.

[bandit86]

By increasing the vacuum in the crank case you can do the same. I would no want full vacuum but a 5psi difference to atmospheric pressure would do the same. A lot of single cylinder engines have reed valves that allow air from the crank case to escape and when the piston comes down but not return when the piston goes up. The cummins onan 140h has one, unfortunately it is a wear item like most feed valves. But a manifold ported vacuum would do the same

I was sure pumping losses were meant sucking the air through an intake and pushing through an exhaust. If you are concerned with the inside of an engine you should also knife edge the crank and smooth out anything else like the rods that move a lot

[drmiller100]

just to be clear, this is showing the bottom of the pistons from the crankshaft side.

and with an inline 4 cylinder, typically 1/2 and 3/4 pistons are exactly opposite each other, so as 1 goes up, 2 is going down.

kind of makes sense.

[mwebb]

just to be clear, this is showing the bottom of the pistons from the crankshaft side.

you must be seeing a different photo than i see

[300zxrb26dett]

Yes its cut into the bottom of the cylinder, if it was cut in the top the compression/ AF mixture would get pushed right into the other cylinder and then break the rings when they got caught in it.

Look at the shiny parts of the bores where the rings have been touching, and the dark spots on the bottom where the rings never go.

[drmiller100]

Originally Posted by mwebb

just to be clear, this is showing the bottom of the pistons from the crankshaft side.

you must be seeing a different photo than i see

Kind of why I posted the comment - the pic really is showing the BOTTOM of the cylinders.

On the motorcycles, it is pretty common the cylinders unbolt from the crankcase

[Ed-in-Maine]

I would have to see an ABA test to believe this design would have any benefit. There may be slightly less cylinder mass and slightly less pressure. But I doubt there would be a measurable difference in HP or MPG within the tolerance of identical motors. In fact if this is superbike stuff I suspect it's more about reducing mass where ever oz counts.
Ed

[user removed]

That's to reduce windage in the crankcase. Think that's the right term.

regards
Mech

[Sularus]

You are correct Mech, it is to help reduce windage. By lowering the pressure inside the crankcase below atmospheric you allow the pistons to travel down toward the crankshaft easier. It is a minimal gain on a street car, especially in an instance where you are running lower RPMs, such as driving conservatively. It is highly effective on high horsepower race engines though. Those engines spin at high rpm with tons of pressure inside the top end of the engine. Reducing pressure in the crankcases allows them to work more efficiently and use more of the power the engine is capable of making.

[oil pan 4]

Originally Posted by bandit86

By increasing the vacuum in the crank case you can do the same. I would no want full vacuum but a 5psi difference to atmospheric pressure would do the same.

A high vacuum would be bad. Having about -5psi or 10''Hg is ideal.
Word on the street is a high vacuum pulls oil away from wrist pins. It would also cavitate the oil pump, before pressurized hydraulic oil tanks came along aircraft above 30,000ft could have their hydraulic pumps cavitate do to lack of absolute pressure on the return side.
You might be able to go as high as 15''Hg to 20''Hg on a non racing application. Monkeying with your oiling system is playing with fire, I took a risk by running low tention oil rings on my diesel and it seems my reasoning for needing standard or high tension oil rings was sound. (diesels dont need them because they don't draw much vacuum)