The topic of breathers comes up from time to time. The truth is, for most people who motor about gently its not as much of a problem but truth is the stock breathers are woefully inadequate and contribute greatly to oil leaks. This can be tested on any engine easily enough, But the Norton people seem to take the obsession to the next level. However real results have proven that improved breather systems, especially with a check valve does improve performance as well as eliminating oil leakage.
Especially on a long stroke vertical twin, Uncorking it and then measuring the sheer volume of air going in and out, will show this. There is also a correlation between pressure and volume, as in, the greater the capacity, the less the pressure exerts force. Triumph, and late BSA engines tried to exploit this by sharing crank case pressure into the primary and then venting with a much larger pipe.
Ideally, the best system was developed by a clever fellow in Wisconsin named Erik Buell. Other designs have since followed suit, But this can work on a British Vertical twin as well Although on some models the passage to the crank case is constricted via the pushrod chamber, But the attch picture shows the concept,
Used to be much press on a design called the BUNN BREATHER, and the ideas have evolved, what was relevant was if its possible (And proper check valves can make that happen) going from positive, to neutral and then ideally to negative pressure can really benefit any motor, especially long rod twins. (lots of huffing and puffing)
So what are the benefits?
A) Oil leakages will almost be eliminated
B) Slight boost in power
C) less oil fouling and contamination, as the rings seal better under a negative pressure.
Now,,, a modern Automotive LS motor is a total universe removed from these old engine, the benefits are measurable and demonstrable. However, percentage wise may not seem worth it.
Horses for courses.
However this article, which just came out demonstrates this concept quite well. Many of the guys running vintage race bikes are using these same techniques, and guys like Herb Becker, and Alp are proving it at the track while racing 1950s and 60s vintage Britt Iron.
See:
https://www.enginelabs.com/news/efi-university-finds-out-how-much-power-a-dry-sump-system-is-worth/?utm_source=rss&utm_medium=rss&utm_campaign=efi-university-finds-out-how-much-power-a-dry-sump-system-is-worth" “From 3,000 rpm to 6,000 rpm, on average, the engine made 17 lb-ft more torque and 14 horsepower more… Everywhere. Some places made more than that, some made a little less, but there was an increase everywhere.”
In addition to power, Strader also recorded crankcase pressure on the dyno pulls to be able to illustrate how hard the scavenge pumps are working. “We had no pan vacuum with the wet-sump system all the way across [the RPM range],” says Strader. “With the dry-sump, we had about 6.5 inches of vacuum at 3,000 rpm, and by the time we got to 6,000 rpm, we had almost 10 inches of crankcase vacuum in the engine. That improves the ring seal and helps with the windage, and that’s where that extra power came from.”
