Crank case pressure zones

Here pumping loss example in GSX'rs.
The cylinder displacement of the engine remains the same 988 cc but more power and torque and better throttel responce has been achieved by adding four ventilation holes between the cylinders to equalize crankcase pressure beneath the pistons, moving the air intake nearer to the centerline and upgrading the engine management system to a 32-bit CPU that monitors and controls the engine functions, input from the rider and the exhaust tuning valve.
http://www.suzukicycles.org/GSX-R-serie ... 1000.shtml


Here's summary of V8 builder ballpark power benifit via ring sealing and windage.
How much vacuum should you use? You should check with your engine builder as there may be some special issues or firm opinions that they may have. In general GZMS recommends no more than 15" of vacuum in a drag race wet sump application without pressure feeding oil to the wrist pins. In our own in house testing, anything over 12" seemed to offer relatively nominal increases in horsepower (maybe 15% between 10" and 15").
http://www.gzmotorsports.com/vacuum-pump-guide.html

The Cheapest Power You Can Buy
If you can achieve a crankcase vacuum level of at least 8 inches HG, you will very likely realize an immediate power gain of at least 15 HP.
HOW IT WORKS

The reduced pressure ("vacuum") in the crankcase is generated by having a substantial excess of scavenging capacity with respect to the engine's oil flow rate. The "vacuum" increases the pressure differential across the ring package, producing an improved ring seal. The improved ring seal allows the use of a low-tension (reduced friction) ring package, yielding a power increase as well. Further, the reduced crankcase pressure dramatically reduces windage losses at high RPM.

Here are a few observations we have made over the years of developing winning race engines. First of all, in most engines, the expected power gains will occur with 8 to 10 inches HG crankcase vacuum. Beyond that point, more vacuum does not generally produce any measurable power gain until (a) you get more than 20 inches HG of vacuum AND (b) you are operating in excess of approximately 8300 RPM.
http://nutterracingengines.com/racing_o ... facts.html

This technical brief reports expecting ~10% power increase with low case pressure.
Charles Falco predicted this in old vintage cycles and was right on.
http://www.britcycle.com/products/bunnb ... rticle.pdf

Just to belay remarks about 15 hp, duh not in our small sizes but there are also percentage remarks to go by, so can expect 4-5 hp if done well.

Keep in mind that the main horsepower loss in a Norton with an open breather is due to pumping loss- not windage. It takes a lot of power to move air in and back out of the crankcase through the open breather. Jim

Very interesting information---thanks for posting Hobot. I'll have to dig further into this to see just how much engine breathing can have an effect on basic road going machines---cost / benefit that is. For racing purposes---probably good--a few more Hp---for road machines--probably not too noticeable and then there's the effects of altitude to deal with. If not too costly---why not do it--can't hurt, but if several hundreds of dollars---most people will probably say not worth it.

Yes that's what I was told/learned a decade ago so put in 3 half inch holes in TS case to add both volume to tame pressure pulses and ease the pumping in/out of TS case volume. i don't think racers hold WOT over redline longer more often than I have on Peel Combat for the few seasons she was able nor had stuck throttle for hand full of seconds way way beyond red zone, yet breather hose passed white glove test in big clear hose from TS case, not even hint of mist coat detectable! Can't claim it did a thing for power or response but no oil weeps nor Combat wet sump I had in gushers at lower rpm tests prior.

Purpose of my post was to ball park what power gains might be attained. Best reports are 15% mo power but don't know if applies to our twin so only mentioned the more realistic 10% that Falco calculated. Charles used to hang out on Brit Iron and always professor level inputs.

Peel contests with the sports crazies out here averaged 20-40 min long and used up couple gallons before stops to decide next leg or gas station. Ms Peel didn't come on cam to matter until like 6800 for 3rd piston power. More than one way to skin the breathing cat. Next Ms Peel won't use any of these tested ways of Commando to breath in fresh air and out.