Get XiED(tm)! Performance Parts

Don't let the Harley heat monster ruin your riding.
Reduce  Engine Surging
Improve Throttle Response
Reduce Engine Ping


HD 2007/2008 Engines

High Heat on 2007/08 HD engines

HD 2007/08 Performance Recommendations

Cool your exhaust temperature with the Wide Band O2 upgrade for 2007/08 HD

Harley Camshaft Specification Tables

HD Twin Cam Engine Builds
TC 128 HP 95 CID
TC 100HP Street Engine

The basics of Fuel Injection explained

Rammer Performance Air Cleaners
TC Performance Heads 100+HP

Pro Tuning on a Shade Tree Budget


Do Crank Vents work?

This is a common question to Nightrider's Motorcycle Performance Guide technical support line. We attempt to provide an answer this question. 
Update: January 2002

Nightrider was contacted by the supplier of the "Krank Vent", ET Performance. They have asked Nightrider to "retest" their products under closely controlled conditions on our two test bikes (80 CID and 97 CID EVO engines). We have attempted to meet the proper installation conditions as defined by Krank Vent. Two of the primary installation requirements listed by the company are a completely air tight engine and removal of the umbrella valves in the rocker boxes. Although Nightrider has been unable to ensure that both these conditions have been met on the test bikes some dyno testing was conducted.
To date, dyno testing has been inconclusive with no differences in dyno runs we have conducted. In support of the Krank Vent we have been unable to create a tightly sealed engine on the 97CID engine and did not remove the umbrella valves from the 80 CID engine. We do find it disturbing that a simple "bolt on" approach does not seem to apply to these products. To ET Performances credit, they have not pressured Nightrider to publish anything other than information that we are comfortable with. They have also been helpful in offering assistance and suggestions on letting the Krank Vent work as advertised. We find it difficult to fault their attitude and belief in the product.
At this point in time, Nightrider can only state that it finds the Krank Vent an effective way to reduce blown rocker box gaskets and the associated oil leaks this problem leads to. Nightrider will continue to report on new dyno results as they come available.

Hayden Enterprises told Motorcycle Consumer News (MCN) in August 2001 that their crank vent is to prevent blown rocker box gaskets on EVO engines. There is no benefit to Twin Cam engines. MCN simply states "The Krank Vent is a waste of money"

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.

Crank Vent Dyno Testing by Aaron Wilson

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 ...

M2 Dynos

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).

M2 Spykes

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.

M2 Spyke result

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.

S2 Dynos

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.

S2 Spykes

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.

S2 Spyke result

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.

S1 Dynos

Here are all the baseline pulls on my '96 S1. The power varies from 92.6 up to 95.3.

S1 Spykes

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.

S1 Spyke result

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.

FXR Dynos

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.

FXR Spykes

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.

FXR Spyke result

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.

By Permission, Copyright 2001 Aaron Wilson

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.


Table of Contents
Search the site 
Nightrider COPYRIGHT

Ask us a Question

Modification, Installation, Maintenance and Tuning Index  will help you find most of the information you want on one page.

How to get Professional Tuning Results at home
Testing the Innovate Motorsport LM-1 portable air fuel meter

Profession Tuning on a Shade Tree Budget

Veypor VR2 Data Logger and Instrument Panel
Video Installation and Demo
Purchase VR2

Engine Performance
How to Build a
TC96 2007 Engines
TC88 70HP Stage1  
TC95 128HP Stage 3
TC95 100HP Street
TC96 2007 Stage 1/2
EVO 64 HP Stage 1
EVO 74 HP Stage 2
EVO 82 HP Stage 3
EVO 95 HP Stage 3
883 to 1200 Upgrade
Shovelhead Modifications

New EFI for EVO and TC

Performance Gallery
Horsepower Gallery
Evolution 80
Twin Cam 88/95
Evolution Unlimited
Sportster Unlimited
Drag Strip Gallery
Land Speed Racing Gallery
CV Carburetor
Modifying the CV carb
Tuning a CV carb
Selecting a cam
Install a TC 88/95 cam
Install a Big Twin cam
Install Sportster cams

Camshaft Specifications
Twin Cam

Exhaust Systems
EVO Exhaust Testing
TC Exhaust Testing
Khrome Werks AR100 test
Making Drag Pipes Work

Shop Manual
Carburetor Troubleshooting
Finding Manifold Leaks
Cylinder Heads
Pistons and Cylinders
Belt Drive
Shop Manual Appendix
$20 Bike Lift
Plug Wires
Spark Plugs
Engine Tuning
Nitrous Oxide
Motor Oil
Stutter Box
General Information
WEB Links
Buy Books and Manuals
Performance Calculations
Estimate Horsepower
Estimate 1/4 Mile Time
Estimate Top Speed

Engine Displacement
Exhaust Length
Gear Ratios
Air Density

The Nightrider Diaries
The ramblings of a genius a, a madman and something in between.

Where is Sifton Cams?

Autocom Active-7 tested

Harley-Davidson EFI
-EFI basics explained
-EFI modifications explained

183 HP, 2 carbs, 2680cc

Copyright 1997-2006  Stephen Mullen, Oldsmar, FL -+-