Head breathers?

[VernDiesel]

At least one (long time respected performance Harley) company makes an aftermarket head breather to replace the factory breather in the rocker box. This is in addition to or aside from the EGR. As I understand it the M8's build some HP robbing resistance pressure in both the bottom end crankcase/oil tank and in the heads outside of the combustion chamber. Best I understand it controlling or relieving pressure in the top of the motor is somewhat similar to relieving or controlling pressure in the bottom end. Or allowing them to breath. 

From what I read my understanding is making sure this pressure somehow separate from combustion pressure only goes one direction with enough room and vent for it helping to relieve or minimise blow by. Though I don't fully understand how. Not to be a cure for poor ring seal but that if you have a motor that has through increased compression, more rpm, bigger bores, or even just wear seeing or unseen experiencing some power escaping through blow by. That maybe it could be a worthwhile investment for some motors.

So I follow the theory but I have not seen anybody show say before and after dyno results or any other type validation. Their breathers are not cheap or I would just buy it and try it. Thoughts engine builders? 

How do you contend with this or do you just chalk any such losses as un avoidable or un capturable or insignificant or not worth the cost & effort even if its a 12-1 or 7k rpm motor? I mean maybe its snake oil but MoCo put the breathers in there for some reason. A machinist might say fresh professional machine work new rings etc but is there a case for this product?

[Tail Ridr]

Aren't the Harley valves more like a PCV than EGR?

[VernDiesel]

Yeah I think you are right but don't they share a common compartment in the process? I believe you could say that he is saying Harely's "PCV" is insufficient. 

[cheech]

At least one (long time respected performance Harley) company makes an aftermarket head breather to replace the factory breather in the rocker box. This is in addition to or aside from the EGR.

My guess is you're referring to T-mans breathers for the M8.

Harleys vent crankcase pressure to the airbox.
But they don't have any EGR system as do cars where they are redirecting exhaust gases into the intake tract.

Is the EGR wording yours or from a "long time respected performance Harley company"?

Can you link it if it's the latter?

[hrdtail78]

As for as the oil and breather systems on m8's.  I haven't found that the stock plastic breathers ever being the problem.  With the addition of the oil pump seal.  What really is the purpose of the breather valves in rockers?  Plus the addition that so many then run a breather off oil cap or trans cover that isn't going through a one way of any kind?

I have never backed to back a stock vs Tman breathers.  I do back to back free breather test vs plugged additional breather.  No power difference with any of them.

To stir the rumor mill.  S&S is almost done with their case.  I have heard of some interesting testing that they performed.  From what I am told.  Because they really want to have a fix plus the existing HD patients.  Their design is quit different.

I got a m8 project I am planning on reading crank cavity vs cam cavity pressure over crank degree.  Be interested in comparing these to an S&S case.

[Thermodyne]

Aren't the Harley valves more like a PCV than EGR?

PCV is positive crankcase ventilation.  Or in other terms, manifold vacuum sucks the crankcase gasses out one side and draws fresh air in the other side.  Burning said gasses to save the planet.  It replaced the draft tube that just used air flow under the car to pull air through the engine.  The PCV valves come in a multitude of designs, but have three basic functions.  They prevent intake backfires from detonating the fumes in the crank case.  They meter the flow in the PCV system.  And some of them determine when the system is active based on manifold vacuum.

EGR is exhaust gas recirculation.  That system meters some exhausts back into the intake manifold.  The purpose is to quench combustion.  That lowers the combustion temp, which lessened the amount of NOx produced.  Some brands also used it to increase fuel economy, the recycled exhausts offsetting the Air-fuel mix being drawn into the cylinder.  Making the engine have the fuel demands of a smaller engine.  But that was mostly smoke and mirrors for the EPA.  As the carbs tended to just compensate by adding fuel from the power valve as the manifold vacuum dropped when the EGR was applied.  Ford also used EGR to control detonation.  The quench EGR gave them, allowed for more aggressive spark advance.

The Harley breather is something totally different.  Since 93 its just a one way valve.  It lets the gasses out, but does not let air back in.  As the pistons travel down and decreases crank case volume, they push crank case gasses out of the breather ports.  As the pistons move up and increase the crank case volume, the valves prevent air from being drawn in.  So in a mechanically well sealed engine, it runs at a partial vacuum in the case. There is a mechanism to separate the oil from the crank case gases, a sponge and some bottle necks in the breather assm.  And a little baffle unit on the M8.  Problem is, as the ring seal goes away, so does the breather ability to manage the amount of case pressure needing to be vented. 

[VernDiesel]

Cheech "like EGR" was my best attempt description. Exhaust is not the correct word but their is an oily hot gasses vent from each head that is run back to the throttle body and MoCo does this to meet epa compliance. Sort of like EGR systems in some diesel trucks that I am familiar with.

Yes its T mans. I understand they are site supporters and I don't mean to question the value of his product but would like to see some validation as to helping with blow by. Also asking what other builders thought about this whole confusing thing to me.

https://www.tmanperformance.com/tman-custom-breathing-sytstem/

[VernDiesel]

Thermodyne  "Problem is, as the ring seal goes away, so does the breather ability to manage the amount of case pressure needing to be vented."   So do you think T mans head breathers could help or too little too late?

He seems to be showing it as the 3rd part of three. First oil pan/crank case vent then what he labels as  improved external breathers then the third thing being head breathers which is the part I am inquiring about where he says "can help with blow by" perhaps when ring seal is just starting to compromise ring seal. Such as on a higher rpm, higher compression, big bore or just worn bore/ring motor. Thoughts?