Tech Post - Breather Check Valves

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With permission from and thanks to: NRHS Performance

Back when I was writing tech articles for Battle2win magazine, I did an article on these breather check valves you see advertised for HD motors. Sold under the names "Krank Vent" "Krank Vent Plus", "Power Vent", and various other names, they either promise or in some cases highly suggest that using them will add power to your motor.   I understand where they're coming from. An HD motor has a variable volume crankcase. Unlike most car motors, which have a piston going down for every piston going up, the volume of the HD crankcase changes due to the 45 degree common crankpin design. It stands to reason that check valve on the crankcase vent could cause a vacuum to get pulled on the upstroke of the pistons, potentially helping ring seal. Dry sump oil pumps that can pull a vacuum when used in conjunction with low tension oil rings are a well known technology in the circle track car racing world.   What I couldn't understand was how these things could bring anything to the party considering the bikes already have a check valve in line with the breathers (the umbrella valves). Unless of course those valves were defective. But then it seemed like the marketing around these check valves must be based on the notion that the valve you already have is defective? That didn't make much sense.   So anyway, I went off to dyno test these things and see if I could substantiate any of the claims, blatant or subtle as they might be. Spent hours messing with the Hayden and Spyke brand devices. Here's what I came up with:   Open is just that, vented to the atmosphere with no additional valves, other than the factory umbrella valves which were in place at all times.   "Kuryakyn" refers to the little Kuryakyn adapter I used to route the blow-by back into the carb.   "Spyke" and "Hayden" are the best pulls with these respective devices in place. Just for kicks, I blocked the vents and did some pulls, "closed" is the best of those results.   As you can see, the only thing that really mattered was whether or not the blow-by was being recycled back into the engine. Recycling the blow-by, the way the factory does, costed a little power over a wide range. Other than that, the motor largely ignored what I was doing with the breathers, at least from a power point of view.   When this result was published in Battle2win, I got quite the reaction from ET products, makers of the Spyke device. A dialogue ensued and I tried to pin him down on my basic question, i.e. how does putting a check valve downstream from the factory check valve change a thing? But I never got a real answer. He did claim though that the Spyke device was effective at improving power, even though he never explained how.   Anyway, in the interest of fairness, and just because I really wanted to be sure of myself, I did a whole bunch more testing of the Spyke device in particular on other bikes. Here are the results of that testing.   Dyno's are not a 100% repeatable measurement tool, you instead get a range of results in any given configuration. So I'm showing the range rather than a specific result for each:   1999 Buell M2 Here are all the baseline pulls on my '99 M2, no breather check valve in place other than the factory umbrella valves, and vented to the atmosphere. The power varies from 84.3 to 85.4. Here are all the pulls I did on the same bike, same day, with the Spyke device in place. The power varies from 83.5 up to 84.8. Blue: With Spyke Device Red: Without Spyke device And of course, this the best pull from each configuration, overlaid onto the same chart. Yeah, I know, it *looks* like the bike ran a tad better without the device, but it didn't, this is normal variation. I guarantee you if I did enough pulls with the device, and played the heat soak just right, I could've equaled the other results. This is a tie. 1996 Buell S2 Here are all the baseline pulls on my '96 S2. The power varies from 85.9 up to 87.1

Here are all the pulls I did on the same bike, same day, with the Spyke device in place. The power varies from 84.7 up to 87.4. Blue: With Spyke device Red: Without Spyke device This the best pull from each configuration, overlaid onto the same chart. Again, it's a dead heat. 1996 Buell S1 Here are all the baseline pulls on my '96 S1. The power varies from 92.6 up to 95.3. Here are all the pulls I did on the same bike, same day, with the Spyke device in place. Pulls 38 and 43 are omitted, because the tach pickup screwed up and if I put those on the chart, I can't show rpm and torque. They were not as good as pull # 42. The power varies from 93.7 up to 95.1. Blue: Without Spyke Device Red: With Spyke device (sorry for the color inversion vs. the other results) This the best pull from each configuration, overlaid onto the same chart. Again, it's a dead heat. I didn't actually use the "best" baseline pull, this one has a tad less peak hp but a little nicer curve. 1990 HD FXRS Here are all the baseline pulls on my '90 FXR. This is a little different animal from a Buell, in that it breathes off the lower end using a timed breather gear. There are only 3 "baseline" pulls because this was a tune-up, and I did all my tuning that day with the device in place. Only towards the end, when I had it all tuned up, did I remove the Spyke device for comparison purposes. As you can see, the power varies from 85.7 to 86.9. Here are all the pulls I did on the same bike, same day, in the final tuning configuration, with the Spyke device in place. The power varies from 86.2 up to 86.6. Blue: With Spyke Device Red: Without Spyke device This the best pull from each configuration, overlaid onto the same chart. Again, it's a dead heat. Bottom line here, folks, I tried my damndest, I can't find power with these devices. I know that pisses some people off. All I have to say is "show me". Don't just show me a result, either, anyone can skew procedures or pick and choose among the full range of results to support what he's trying to say. Show me procedures and ranges of results.