E: Engine Not another breather thread!

[vibrac]

Enough has been written about breathers certainly I thought all aspects had been done to death .
In my mind I had long ago settled for a ball or reed valve system from exhaust or inlet (or both on a twin) top spring cap leading to a racing regulation catch tank thats always worked for me and the racers. and enterprising experimenters with french letters had proved to me that after a start up the air flow became almost zero and negative pressure ruled in the crankcase. and that of course ment less resistance on the power stroke, all good stuff

And then today I read in a 1989 article in classic bike about a drag racer with a sophisticated breather valve system he had introduced on his Norton because "a negative pressure in the crankcase works against the upward movement of the piston", Of course it does! why has that never been mentioned? have I been wrong all this time? should I go back to timed breathers? crisis! no no not another breather thread

 

[Dave61]

In my ignorance I'd always thought a Breather was to vent pressure, only with my interest in Vinnies did I discover that negative pressure is allegedly desirable.
Going to fit the PCV valve you recommended & possibly the modified cap I got from Young John as well & see how things go.
Cheers
Dave

 

[erik]

the negative pressure helps the Piston to go down.so it doesn`t matter in the Balance of Energie.

 

[len.c]

I was browsing through an old MPH and a BBB breather was mentioned ,has anybody any useful info , on this item ,, what is the latest , best course of action to minimise c/c pressure,, thanks len.c

 

[stu spalding]

I remember reading somewhere that NASCAR engines are fitted with pumps to keep crankcase pressure down. Is there anything in this and if so, why? Cheers, Stu.

 

[Flo]

I remember reading somewhere that NASCAR engines are fitted with pumps to keep crankcase pressure down. Is there anything in this and if so, why? Cheers, Stu.

Engines with four or more cylinders are highly likely to have a constant crankcase volume hence breathing deals with blow-by in the first instance.

 

[davidd]

Rex Bunn did a lot of work on motorcycle engine breathing. I do not have his book, but I think some of his articles are on line. I think Martyn has some experience with his breathers.

There appears to be a huge focus on breathers in the VOC. I just assume that 11 out of 10 breather problems are due to poor rings. It is so much easier to add breathers than fix the rings.

I often thought that an evacuation pump would be a better addition to the timing chest than an oil pump for most Vincent owners. The good pumps remove air and also allow an air bleeder to pull air in from an outside source if the crankcase pressure goes to far negative.

Alcohol and nitro engines have much less vacuum to worry about. The volume of fuel is very high and usually liquid when it hits the rings. The rings hydroplane over the fuel on the cylinder wall. This is why there is so much oil contamination with alcohol and nitro. Many dragsters use two oil tanks so they do not circulate the contaminated oil.

Part of the reason low crankcase pressures in racing are desirable is that you can then lower the ring pressures. I think that piston and ring friction is still 75% of the friction in the engine and that reductions of friction are good at making BHP.

David

 

[greg brillus]

The Goodwood racer the Horner's built has a vacuum pump under the seat, looks like an in line injection pump.

 

[Cyborg]

I believe caution should be used with vacuum pumps. When you are sucking out pressure, you can also suck out some of the oil mist that is helping to keep things glued together. I stand to be corrected, but I think the pumps started with the drag racing fraternity. Originally they would just tap into the header and let the exhaust pull pressure out of the engines. When the "people against everything" started complaining, they had to reduce exhaust noise and this reduced their vacuum source, They then turned to pumps and then to pumps with relief valves so they wouldn't create too much vacuum.

Our friends with airplanes are afflicted as well https://www.aircraftspruce.ca/catal...bvSAn8jE1MU7uDV4P7VmOzt3Idorb8GxoCo3kQAvD_BwE

 

[Chris Launders]

I remember seeing dragsters in the late 60s with pipes from the block into exhaust headers. Also the rotary Norton race bikes used the same venturi effect to draw cool air through the rotors.