The holes in my breather bolts are app .305" (just under 5/16") on the engine side.
I believe this to be a loose fit (through hole) pre-tap size for the 5/16"x24 threads that are tapped into the A/C side.
Anybody know what those threads are for?
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg


My theory is yes they do alter overall crankcase pressure.
Any restriction for the pressure to leave the engine should back up pressure inside to an extent.
To what extent can only be determined thru testing.
With the horseshoe or a Y connector, you are taking two individual normally exhaled vents and tying them together farther down the path and forcing each to accommodate the other.
So it should be a restriction, to an extent.
But the restriction should increase CC pressure which by default increases scavenging, to some extent.

We just gotta think harder that's all.

That'd be interesting if you could tell any difference while testing CC pressure at the same time.
Aaron has done a lot of testing with the breathers but I think his criteria was for any HP increase (which he couldn't find any extra ponies).
The big advertising gimmicks of course are the HP increase with (our latest and greatest).
I don't remember reading that he was testing for CC pressure level though.
He added an extra vent at the timing hole plug with no check valve leaving the factory breathers in place.
Therefore, the crankcase was being allowed to pull in air as the pistons go up.

You'd have to ask him more about this rig.
http://xlforum.net/forums/showthread...1946516&page=4

http://sportsterpedia.com/lib/exe/fe..._aswracing.jpg

But here are the charts.
His observations:
When a motor is started with nothing screwed into the timing plug, there's a massive inhalation and exhalation evident.
But apparently, necking it down to a 3/8” hole and connecting 2 feet of hose adds a pretty significant restriction.

10 best pulls from the stock configuration.
http://sportsterpedia.com/lib/exe/fe..._aswracing.gif

10 best pulls from timing plug vent configuration.
http://sportsterpedia.com/lib/exe/fe..._aswracing.gif


Best stock pull and the best timing plug vent pull.
http://sportsterpedia.com/lib/exe/fe..._aswracing.gif

As you can see, the difference is within the repeatability of the measurement.
If a person *had* to declare a winner, the results with the stock setup would seem to have a little edge.
(both in the “best” results and just looking at the average of the 10 best results)
But I'd be careful doing that, you could be looking at normal variation.

I don't think the restriction of the horseshoe or tubing length is significant, there is so little flow. Tubing length only matters when you don't have an umbrella, for anti-reversion.

Oh, and don't forget about this post:
http://xlforum.net/forums/showpost.p...4&postcount=22

So perhaps not coincidentally the breather bolts changed in 2004 and the Hi Scavenge oil pump went into service in 2007 ?

Well, that's kind of the point.
I'd like to be able to prove instead of theorize.

Yeah, I saw that post.
So where is the point of those two extremes?
That is the question.

Don't think it was coincidence at all.
I've read the MoCo sold out to the EPA til I'm blue in the face.
But upon following the progress, it is obvious what they were doing.
Each little change did make a difference.
Why it took up to 3 years to change the pump, who knows.
There may have been other intermittent changes undiscovered to us yet.
But one of the goals was to get a handle on wet sumping and at the same time cooling the pistons more than previous years.
Rubbermounts are heavier than rigids.
That extra load may have transferred to extra heat to the engine.
As dieselvette mentioned, changing one thing may be detrimental to the other.

do you think hd has change much over the decades?
hd never throws away parts. every retooling costs $$$$ so it stands to reason.
r&d takes time and is not instant in application.
now for the kicker, do you think they are concerned with all of this?? hummm, perhaps but the machine functions as is and for the majority of owners is of no importance. if you want to take it to the next level, it is your r&d unless you are buying their race models.
before this thread, i paid no mind as when i twist it, it goes and i have no issues with all of this. now my 1974 xh did make territory but only when setup for weeks at a time while at work. with the addition of the pump seal, knocked it down 98%, still will weep a little after sitting for months.

Not exactly scientific as I did make jetting changes too but in my case it's obvious that excessive cc pressure is detrimental to performance. Especially above 5000rpm. Only stands to reason when the pistons are fighting it on the downstroke. My motor revs noticeably easier now.

I have seen what you're saying about reusing tooling and parts.
For instance, the L84-85 and 86-90 oil filter mount.
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg


The first was a simple in/out to a filter off the return side of the system.
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg

In 86, they added an oil pressure relief and moved the oil pressure switch to the filter pad instead of off the oil pump.
Then plumbing it into the feed side.
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg

Same pattern for both, they just popped a couple more holes in it.

You have to remember that while HD may be doing specific things to pass EPA, sometimes they will discreetly leave an "out" - a way for a person to "undo" the EPA requirement. (mopar and others have been known to do this too). One example would be the bosses in the SE air cleaner which just happens to line up with the rubber breather hoses, should you happen to want to vent that outside.

The small breather holes could be to lessen peak bad-air or oil flow into the combustion, only for the purpose of EPA regs - on the other hand, it could be strictly to manage CC pressure.

So I think it's important to keep these things in mind, and not make assumptions as to why HD made xyz changes to any part of the system (although some changes may be obvious).

I think you had more than one thing going on at the same time.
You haven't installed smaller pistons so the fact that you still have a higher volume of pressure isn't affecting you now.
I think you improved the balance.
That goes back against the fact that the practice of engine upgrades screws up CC pressure.
According to the XLF poll, that is a changing factor of problems.
So it wasn't necessarily the upgrade that mucked the mix, but the end combination of things that did. ;)

+1

So when they changed the pump in 07 they went back to less restrictive bolts? Any other changes?
If not, then it seems to me HD is struggling to find the right balance themselves.