Additional Crankcase Breather

[johno440]

Found some threads on the forum around the crankcase breather, but nothing about performance benefits.

Read TRX850racer blog and he has fitted a crankcase breather tube from the generator and cylinder head to an enclosed container with a filter. Performance hit is revving more freely.

Anyone else done this mod, and is it worth it?

[misterdimwiddy]

I have done the mod but do not have dyno run comparisons before and after; not at £20 a go.

With 878, FCR's and Akra mine revs very quickly to the red line (16/42 gearing) and the geezer who did my dyno runs commented 'Oh you've done the breather mod' and he used to race one at circuits and the Isle of Man.

It's a cheap mod but then the bore of the banjo fitting is so small I wonder whether it can pass enough gas to make a tremendous difference?

[johno440]

Just found this thread below where crankcase breather on the generator side did definitely allow the engine to rev quicker based on back to back dyno runs, so I think I've answered my own question

TRX eligible for Bemsee Thunderbikes in 2010

[johno440]

Sorry one last questions.

Do I a separate oil breather/catchcan for the crankcase and head. I.e. one for each, or just one with two inlets?

Cheers
John

[Mincehead]

You can link the two, it`s more to do with the internal volume of the fittings/hose as to how effective the additional breathers will be.
Catching oil mist can be a simple pan scourer in a screw top plastic container of say 100 ml volume.
Think of a tub with the breather hose entering, venting into the container and a one way or drip loop exit in the lid. If you`re real clever you can engineer a `caught oil` drain in the bottom of the container too.

[lenny]

Were talking about engines that pump their crankcases here (v twins, singles, all parallel twins except 180*, opposed twins etc). Ive read tons of bullshit about breathers on this forum. It usually goes "I put a larger/extra breather on my trx and now it revs faster, gets to redline quicker blah blah blah". One even said he had dyno proof. Would love to see that. THE LESS RESTRICTIVE THE BREATHER SYSTEM, THE MORE ENGINE POWER IT CONSUMES. As a crude example, get your leaf blower or vacuum cleaner and partially or fully block the outlet . The motor revs will increase due to less load. The bigger the breather the greater the mass of air you are pumping, using more power. But someone will sell you a kit. I think the mistake most people make is thinking of this flow as an incompressible fluid instead of as a compressible gas which behaves differently. Large breathers were needed on some oil leaking, seal blowing bikes of the past when ridden hard but it is a myth that they increase power. The human mind is a strange thing. The 270* trx pumps its crankcase exactly the same as a 90* V twin eg Ducati. Ducati has probably done more research on crankcase pumping and breathers than any other manufacturer and its interesting to note the development of their breather setups over the years. They started off with a large breather until they realised it was costing horsepower , then through a few interim versions to the current far superior one way valve semi vacuum system. Vacuum is a very good thing and all serious modern race engines apply a level of vacuum to the crankcases. The advantage of having a pumping crankcase is being able to use that pumping to supply some vacuum by putting a fast acting one way valve in the breather line.

I welded a piece of 12mm tube into the exhaust pipe just to the rear of the footpeg. The pipe is angled away from the exhaust flow so it provides an extractor effect. This is connected by a length of silicon hose to a car brake booster valve (a fast acting one way valve.You will find one on your car in the hose from the inlet manifold to the power brake booster)You can get one from the car wreckers for free or buy a new one for very little money.The valve is connected to the breather hose by another piece of 12mm i.d. hose that plugs into the cut down original breather hose..
How it works----as the two pistons move down the bore, air in the crankcase is forced out the breather through the one way valve into the exhaust pipe. When the pistons rise the one way valve closes and a slight vacuum is formed in the crankcase. Once this first cycle is complete the crankcase is operating under a pulsating low level vacuum that helps remove trapped air in the oil and reduces pumping losses.. Any blowby will reduce the vacuum to the point when the one way valve will open and re establish the vacuum. A little thought will show that this will only work on a single, parallel twin or odd fire twin (motors that "pump" the crankcases). Another good breather solution, works for me.

[Wombat]

Have a set of FCR41s I'm gonna fit. Have a K&N Vent Filter for the cam cover. Is there an additional hose for the crankcase breather and do I need another K&N filter for it?
Gotta order some new rubber inlet stubs as mine are getting old and perished, so while I'm at it I'll order the vent as well.
Piccies of the location of the crankcase breather tube. Thanx in advance.

Bob