Nightrider's Motorcycle Performance Guide can not state that the use of any Crank Vent will enhance the performance of an engine although we have strong subjective evidence that the devices are effective in reducing blown rocker box gaskets. We can state that these devices will not hurt performance.

Dyno testing described below by Aaron Wilson of Team Elves Racing does seem to supports this position. Claims of improved performance by the various manufacturers of the crank vents have been difficult to substantiate by testing. Counter claims by manufacturers of  crank vents that testing was not properly conducted have also been leveled.

Are these devices anything more than expensive PCV valves? Probably not, but this does not mean that the "one way" valve principle used in these devices is wrong. Racers do use vacuum pumps to reduce crankcase pressure in engines. Does this racing trick translate to street power? Nightrider will continue to investigate and report its findings.

The first time I did this was on my S1 only, Don Casto and I spent several hours testing both the Hayden and Spyke brand devices. The results were published in Battle2win awhile back. We also did some other things trying to influence the power of the bike with the breathers, like plugging them, and connecting a vacuum pump. Bottom line, the only thing that really gave a result was the act of pulling them out of the intake stream. That gave a nice 1 to 2hp gain over a wide rpm range. Nothing else seemed to matter at all.

That article generated quite a response from one of the manufacturers, ET Performance, who apparently makes the Spyke device. They really took exception to it. So in the interest of fairness, I retested the Spyke device on 4 bikes. Here are the results of that testing.

It's very important to understand that dyno results are not 100% repeatable. The temperature of the motor, and the "heat soak" effect, can really play hell with the repeatability. When you're looking for potentially very small differences, the only solution I've found is lots and lots of pulls, playing the heat soak rhythm. That's a whole other discussion, though. Here I'll post enough sheets that you can see the range of results in each configuration. One of the nice things about putting the results here, versus Battle2win, is I can post a whole lot more data.

Something else I'd like to point out, too, is that you have to pay attention and be careful when you're doing this kind of testing to keep from being fooled. For example, I had a guy write to me and tell me how he got 1-2hp with a crank vent device. When I queried him about his testing procedures, it turned out he had done some baseline pulls, then pulled the breather from the air cleaner and attached the Spyke device and did some more pulls. So he inadvertently changed 3 things: he removed the blow-by from the intake, left the hole in the air cleaner thereby allowing more air into the air box, and attached the device. He had no idea which of the 3 things changed his power, yet he was crediting the vent device!

One last note and then we're on to the results. Several people have tried to make the claim that even though it doesn't show up on the dyno, their engine revs up quicker with the device. That is total BS, folks. A Dynojet like this one literally measures how long it takes to spin up the drum. If it spins up faster, it'll show more torque and hp, period.

Okay, enough background, here are the results ...



Here are all the baseline pulls on my '99 M2, no breather check valve in place other than the factory umbrella valves. The peak power ranges from 84.1 up to 85.4. Mikuni and a Bullett muffler and an air cleaner, that's it (not bad for a near-stock M2, eh? It's done a lot of dyno time).




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.



Here are all the baseline pulls on my '96 S2. The power varies from 85.9 up to 87.1. Pretty fair for an S2 ... this bike has Brian's stage 1 work on the stock Sportster heads, a set of N4 (Lightning) cams, a race kit module, and a V&H muffler. Stock CV carb.



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.



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.



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. I don't believe there's actually a check valve in place. 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. This is a classic "heat soak" set, too ... notice how the first one is the best, then they fall off. Let it cool for 7-8 minutes and do this again, and once again the first one will be far and away the best.

Torquey somebitch, huh? Has Brian's stage 1 work with a Crane 316 & Mikuni.

I've learned a few tricks for generating legible dyno sheets from Winpep, too.



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, show me procedures and ranges of results.

Aaron Wilson is an Electrical Engineer from Berthoud, Colorado. He's been riding motorcycles for over 30 years. He is currently the Crew Chief for Team Elves Racing. Team Elves currently holds several Land Speed Records at Bonneville on their Buell. Other competition experience is primarily sports car racing, having competed in SCCA Solo 1, Solo 2, GT-1, and Trans-Am over a period of 17 years, and he has dabbled in drag racing several times as well. He holds the GT-1 course records at two hill climbs and one Colorado region track.