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Actually, there are reasons you want negative pressure in the crank cases. Not a lot, but negative pressure none the less. There is actual horsepower to be had there. But that is not very feasible with a V11, and I am not sure it is worth the effort. On a big V8 it can be a fairly significant amount of horsepower. But on a V11 I doubt you would be able to feel the difference.

 

Running slightly negative pressure in the crankcases improves ring sealing and reduces pumping losses.

 

It's a fine line. Too much negative pressure and you could have oil going where you don't want it or not going where you need it.

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The subject of crankcase pressure has the same voodoo about it as balancing v-twins, quench clearances, and oxygenated fuels.  Every engine design is different, so each requires a particular vent lay

You can see the effect of the reed valve on my Norton. On this model there is a vent off the back of the crankcase, then a very short hose, reed valve and then a long hose back to the oil tank. I dril

Its  a drain back hose from the frame spine. The crankcase breathes into the spine and from there into the airbox. Any oil that accumulates in the spine can drain back into the cases. No check valve i

 

 

I did once try a valve in the breather of my Daytona (same basic system) and it caused issues with the return line. I put the one way valve on the line from the crank case to the spine. That dropped the pressure in the cases which caused air to be pulled down the return line, aerating the oil in the cases like a fish tank bubbler. Then I tried moving the one way valve to the atmospheric vent for the spine. That resulted in oil being sucked up from the sump in the return line.

I did try it without a return line, and it worked. But I thought the return line was more important than the negative pressure. So I re-installed the return line.

At that point I gave up on the one way valve and creating a negative pressure in the cases. Perhaps it is do-able, but I got tired of trying. I decided it was more trouble than it was worth.

You actually don’t want negative pressure because of that. Ideally you shoot for neutral pressure.

 

 

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Actually, there are reasons you want negative pressure in the crank cases. Not a lot, but negative pressure none the less. There is actual horsepower to be had there. But that is not very feasible with a V11, and I am not sure it is worth the effort. On a big V8 it can be a fairly significant amount of horsepower. But on a V11 I doubt you would be able to feel the difference.

Running slightly negative pressure in the crankcases improves ring sealing and reduces pumping losses.

 

Ducati think its worth the effort on the Panagale engine. It employs a gear driven vacuum pump to pull the crankcase pressure down which helps with oil leaks and pumping losses.

 

Ciao

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Actually, there are reasons you want negative pressure in the crank cases. Not a lot, but negative pressure none the less. There is actual horsepower to be had there. But that is not very feasible with a V11, and I am not sure it is worth the effort. On a big V8 it can be a fairly significant amount of horsepower. But on a V11 I doubt you would be able to feel the difference.

 

Running slightly negative pressure in the crankcases improves ring sealing and reduces pumping losses.

 

It's a fine line. Too much negative pressure and you could have oil going where you don't want it or not going where you need it.

 

There are two questions here, really. One is how much negative pressure would yield the maximum benefit? The answer there is probably more negative pressure than you would think. On our old air cooled two valve Ducati 750 racebikes we would run a reed valve on the crank case breather to create a small amount of negative pressure in the crank cases. But other engines go much further, like the new Ducati motor that Phil mentions. Even back in the day there were performance tuners creating negative pressure in the cases by things like vacuum pumps, using either intake vacuum or exhaust velocity to create much larger amounts of negative pressure in the crank cases. There was one classic story of a NASCAR tuner who was testing such a system, it was working great until the driver slammed the throttle closed at high rpm. The sudden spike of negative pressure / vacuum in the crank cases sucked the oil pan in around the crank. How much of that is true, how much is exaggeration I don't know as I was not there. But the main point is negative pressure in the crank cases is a good thing. There is a point where too much is too much. But that point is probably a lot higher than you think.

The other question is how much negative pressure can you run in a V11 motor? Sadly, my experience is that the V11 does not like much, if any, negative pressure in the crank cases as it messes with the oiling and breathing systems. But with some work it is possible that those hurdles could be over come. And if you manage that you should see an increase in power and possibly in reliability / longevity.

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I think we’re on the same page about the pressure. But coming back to the V11, an engine that was designed for more traditional breathing I’d stay away from negative pressure without a ton of engineering and testing. The simple answer is low to no pressure would be ideal for a typical owner with modest resources.

 

 

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The core of the thread was keeping oil from escaping the breather. Negative pressure is really just a potential side benefit of changing the breather arrangement to better control oil transport.

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The core of the thread was keeping oil from escaping the breather. Negative pressure is really just a potential side benefit of changing the breather arrangement to better control oil transport.

Biggest breather tank you can fit in the space ( with an oil seperator if possible ) available with a drain back line and the tank vented via a tube out the back of the bike.

 

Ciao

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The core of the thread was keeping oil from escaping the breather. Negative pressure is really just a potential side benefit of changing the breather arrangement to better control oil transport.

Biggest breather tank you can fit in the space ( with an oil seperator if possible ) available with a drain back line and the tank vented via a tube out the back of the bike.

 

Ciao

 

+1

Just make sure oil return is below the level of the oil

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The core of the thread was keeping oil from escaping the breather. Negative pressure is really just a potential side benefit of changing the breather arrangement to better control oil transport.

Biggest breather tank you can fit in the space ( with an oil seperator if possible ) available with a drain back line and the tank vented via a tube out the back of the bike.

 

Ciao

 

+1

Just make sure oil return is below the level of the oil

 

Yeah, I always hear this, but what is the physics behind it?

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I mounted a Agostini breatherbox at my LM2(950cc) and LM3.

http://hmb-guzzi.de/Oil-separator-Agostini-LM-1-T3-1000-SP-etc

That works fine, even without the valve, although I am not sure if the box has a valve installed after all.

Every now and then I clean the inside of the box with diesel or petrol in order to solve the clotery.

 

The problem that I could not fix before the Agostini was the pumping of oil after ca 10-15 minutes of constant 5500-6000 rpm (165-180 km/h). I never tried it at a higher speed, because maintaining  200km/h with a more or less standard LM2 or 3 is difficult.

When using the throttle a lot, f ex on a twisty road, I never had a breather problem with the old little breather box, but that also needed serious cleaning to work nicely.

 

I would estimate the total crankcase at a minimum of 10liters. The delta in the volume will not be more than 600ml, so the pressure will be 6% below the outside pressure. That is higher than the vacuum in the manifold when shutting the throttle. Maybe even higher than with open throttle.

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The core of the thread was keeping oil from escaping the breather. Negative pressure is really just a potential side benefit of changing the breather arrangement to better control oil transport.

Biggest breather tank you can fit in the space ( with an oil seperator if possible ) available with a drain back line and the tank vented via a tube out the back of the bike.

 

Ciao

 

+1

Just make sure oil return is below the level of the oil

 

Yeah, I always hear this, but what is the physics behind it?

 

Then the oil mist/pressure can't be blown out the oil return pipe (against traffic so to speak :)

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I would estimate the total crankcase at a minimum of 10liters. The delta in the volume will not be more than 600ml, so the pressure will be 6% below the outside pressure. That is higher than the vacuum in the manifold when shutting the throttle. Maybe even higher than with open throttle.

 

10 liters sounds excessive with the crankshaft and all the other bits. Maybe when it's empty.

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  • 5 months later...

Still at IT !

 

Sorry I have been AWOL for a while but life just gets in the way. 

 

Was first off doing a MERA (Motorcycle Endurance Riders Assoc.) event out of Salt Lake City.  Don't ask how I did there; 36 hours with the temp. in triple digests and I bailed out and headed to a hotel with AC.

 

We did race at Willow Springs and did OK for it being a new motorbike found and fixed some teething problems.

 

Last weekend (Labor Day) we raced Utah Motorsport and got a third (not really a big deal and there were only 4 bikes) but did shave over 14 seconds off our times.  Bike is running good but now we seem to be running out of gas.  We think it might be the size of the Guzzi fuel valve outlet.  As we are using a standard petcock X 2 but the fuel bowls seem to be going dry.

 

We are still sorting the scooter out and are planning to head to Barber next month.  Barber will be our last chance before the bikes get loaded for OZ in January.

 

Anyhow hope you all had a great summer.

 

Cheers

Rich   

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