Next project: crankcase pressure reduction?

[mik_str]

Now that I am kind of running out of options with the mods, I am turning to the less obvious areas. In that light, and in the knowledge that four-strokes suffer from significant pumping losses (to the point that mfrs have begun to address the issue in recent sportbikes, for example through the use of larger inter-cylinder vent holes and an actual vacuum pump in the new Ducati Panigale), I have began thinking about figuring out a way to do something similar to my VTR engine.

I had a look at the NAG valve offered by Rising Sun Cycles (http://www.rscycles.com/images/nag_cont ... valves.htm) but the price is absolutely ridiculous for what is obviously just a bleed valve. So, I will be looking at fashioning something similar "on the cheap".... The main thing now is deciding whether to use one or two valves (one per valve cover or link them as the NAG set-up does). Also, have to see about calibrating the said valve(s) to get about 0.5 atm vacuum (that should do the trick).

Comments?

[tony.mon]

You might find that the existing seals (clutch pushrod, for example) aren't designed to work with anything other than positive pressure.
The water pump seal is another example, although that's easily remedied by using an electric pump, a mod I've been meaning to get around to for a while).

There's gains to be had from machining additional ports/port area between the crankcase cylinders, to allow easy transition of air between the underside of each cylinder on the downward strokes.
An externally routed pipe could have the same effect.

The uneven firing cycle of a vee twin leads to higher pumping posses than a normally- arranged crank il4, as with a 4 (or a parallel twin, for that matter) one upwards stroke occurs as there is a corresponding downward stroke in another cylinder.

Bit more tricky with the firing order in Storms.

Something to think about, though.

Good subject to raise......

[lumpyv]

im watching spartacus.

[benny hedges]

I have began thinking.....

Comments?

yeh similar to the vacuum relief valves i have on mine... theyre on the inlets on mine and set to -100Mb as the carbs require -80Mb to work the slides...
they are calibrated by adding or removing copper shims on the spring side of the valve to get the required vacuum.
any reduction in crankcase pressure would have a positive effect imo as the cushion of air leaving the crankcase obviously reduces the downward force of the piston and reduces power.
routing any crankcase pulsing away from the airbox as part of the normal emmission control should also have the benefit of smoothing airflow in the airbox (if you have one...)

i would imagine you could get good effect using a 2 stroke reed valve block slotted in a suitably machined recess... the resistance of the petals can be altered by using different materials from carbon steel to carbon, and they would give almost inhindered airflow out of the engine, possibly chanelled down a pipe with a k&n on the end.
would look trick too

interesting idea from you as usual mik

btw tony

higher pumping posse ......

if i ever decide to re enter the world of popular music, that is my new band name lol

[tony.mon]

Damn that spell-checker and its auto-correct!

I blame it on the Ghost of Christmas Pissed

Could have been worse......

[mik_str]

I just came up with a varaition of sorts of my original idea. I have a spare oil filler cap (made from billet) and will drill it out and press a 14mm fitting into it. I will then route a hose from it to the airbox (where PAIR valve air pick-up was formerly). This should help reduce crankcase pressure somewhat (facilitate bleeding off excess pressure) without necessarily putting added stress on the various seals as would perhaps running below atmospheric pressure in the sump.

The cost of this experiment will be very minimal. Will keep you posted.

[mik_str]

Here is yet another possibility I stumbled across while doing some research for ways to drop the crankcase pressure (to reduce the engine's pumping losses), referred to as the "PAIR sucker mod":

- route the crankcase vents (in valve covers) into the PAIR air inlet ports
- the vacuum created by the exiting exhaust gases acts to draw air from the crankcase vents, thereby creating a partial vacuum in the sump, and reducing pumping losses.

The concept seems logical (and promising).

Comments?

[Phimosis]

Im trying to follow this but the words are going blurred as Im reading them..... I saw a little fitting for the oil filler cap, a little vent/filter which replaces the cap, what does this do.....

[tony.mon]

Mik, it shouldn't be difficult to run a vacuum pump on that fitting, while it's on a dyno, to see what difference it makes.

You can easily vary the vacuum and get meaningful figures.

I've already routed the (non PAIR) cam cover vents on mine to a small external filter, which frees up space in the airbox, the side effect being that it allows crankcase pressure to vent to atmosphere, without disturbing airflow and pressures in the airbox.

However, people following me tell me they can smell the oil vapour, and it drinks a little more oil, although with the standard non-pair arrangement it would just burn it in the cylinder instead, so it shouldn't use any more.

But I'm aware that the front cylinder is quite worn, so I'll be swapping engine internals to a better crankcase set in the next couple of weeks, to get compression right back up again.
It is likely that the won cylinder is allowing oil past the rings.

I might add a further crankcase breather while I'm there, from the oil filler cap as you suggest, but I'll also be looking at crankcase web mods, if I can see places in the cases where additional lightness (holes) can be added.....

I noticed on last year's new ZXR1000 that they changed the crankcase web casting ports from round to a more angular shape, for precisely this reason, and gained 2 bhp with no other mods

[mik_str]

Still looking for info on the working of the NAG valve and found this:

http://zaidantj.hiho.jp/ron/19ron/ron_19_04.pdf

Have a look at figure 4 on page 2. This is pretty well how I imagined it to be (a one-way valve which works off the difference between the crankcase and airbox pressure). Simple and straightforward. In essence, the weight of the floating piston is what sets the vacuum setting in the crankcase (instead of a spring).

[tony.mon]

Ram-air would be a problem.....increases in airbox pressure with speed.
And could it cope with the fluctuating differences in pressure both sides of the valve without a decent damper both sides?

Lastly, is there a likelihood of any leakage past the coolant pump seal being drawn into the engine, rather than out of the vent?

[rob...]

i'm probably missing something here, but, wouldn't any gains made by creating a slight vacuum in the cases be negated by the piston 'sucking' against the vacuum on the next compression/exhaust stroke????
surely the best answer is to have neither vacuum or pressure, but make the air in the crankcases move in the easiest way poss around the cases as the pistons do their thang?

[mik_str]

i'm probably missing something here, but, wouldn't any gains made by creating a slight vacuum in the cases be negated by the piston 'sucking' against the vacuum on the next compression/exhaust stroke????
surely the best answer is to have neither vacuum or pressure, but make the air in the crankcases move in the easiest way poss around the cases as the pistons do their thang?

I understand where you're coming from, having wondered the same thing myself. However, there are various examples of high performance four-strokes resorting to partial vacuum in the sump to improve performance. Drag racers (auto) have been doing it for ages (resorting to mechanical vacuum pumps), apparently all the MotoGP bikes do it, the new Duc 1199 does it,.... While it doesn't totally remedy the pumping loss problem of four-strokes, it does reduce it significantly (at least enough to make it worthwhile).

[tony.mon]

It's the same principle in operation as using a cycle tyre pump, with your finger over the air outlet.

The first part of the stroke is at low pressure, and so it's easy to move the pump.
As you compress the gas more and more, the pump requires more and more energy to close it.

But if you start with the pump halfway closed, THEN put your finger over the hole, then pumping it in is easier.

The volume of air in the closed chamber is the same, but as there's lower pressure difference between pistons up and pistons down it requires less engine work to rotate the engine through it's full four stroke cycle.

[benny hedges]

an easier way to do this would be to drill a large hole in the piston crown.