Q. When profiling my Dyno Cam I check my .050 checks and the .020 checks and there off by the .050 and .020 checks that you have posted for that cam on your website. I also check the Centerlines. If my .020, .050 and Centerlines don't exactly match yours do I need to get another block or twist that cam to achieve the most horsepower?

 

A. If you've had experience with various manufacturing processes, then you know that tolerances in precision and quality vary depending on the equipment used and inspection methods performed. Perfection can only be achieved when all factors governing precision are taken into consideration and standards are implemented to produce the precision product. 

Our sport is unique in that the motor we use was developed for a lawnmower! It should be understood that the Briggs 5HP is basically a utility motor. Because of the differences from block to block there can be as much as a 4 degree variation in readings from one block to another. Major contributors to this problem are the tappet angles, but processing imperfections such as burrs on the teeth of the cams can also produce bad readings. When developing a cam we create maximum horsepower by pushing the limits of acceptable tolerances while also maximizing available lift (thus increasing open valve duration). As a result, there are several factors that come into play when dialing in your motor that can cause it to not meet tech requirements.  Let's look at the requirements to meet tech and see what could be done when your cam is not profiling...

WKA sanctioned stock class rules dictate that camshafts meet the following criteria:

"All cam profile readings must be taken with zero valve lash and degree wheel at top dead center (TDC) of compression stroke. Set dial indicator at zero and do not reset during the profile process. Only stock factory camshaft with alignment as shipped from factory is permitted. The camshaft lobes must remain flat and of original width."

The nature of a controlled valve float cam is a cam that meets the above criteria, but only because of it's non-symmetrical design. Every minute area of the lobe surface that can be used to produce horsepower is manipulated to provide maximum horsepower for it's particular application.  It is indeed a science to properly produce this effect.  When dealing with controlled valve float, know that if the cam will pass tech requirements, more than likely it's going to produce horsepower.

It should be noted that the closer you can bring the back side of the cam to the legal checks, the more horsepower you stand to gain. 

In the situation described in the question, you have a block that does not check when read. Let's look at an example to gain a better understanding of what's going on, and how we might be able to fix the problem:

A stock 95-3 cam was pulled from the shelf to be used in our example. Fortunately we now have the benefit of our new Landis 3L CNC camgrinder to verify that the lobes have been ground with precision accuracy (A random comparison of cams ground on this machine from completely separate runs will show less than 3/10 of a thousands variation). So we can attest whole heartedly  that the cam (lobes) are precise. In our example we took this 95-3 cam and read the results of it's profile in four different stock class blocks. Our results where as follows:

 

 

 

 

As you can see, test block #3 is out of profile. But if you'll examine it closely, you'll find that it's really not that far off. In fact, if you could somehow advance the centerline values (timing) of the cam 1 whole degree it would solve the problem. Well, let's do just that... Back to the shelf we go, except this time we'll try a 95-3 Advanced 1 degree, (that's right we stock advanced as well as retarded cams). This is the profile reading from the new cam in the same test block #3...

 

 

There, that's what we we're looking for. And as for test block #4, a 1/2 degree retarded cam would work perfect. Take our word on it. Block inconsistencies can be a nightmare, but when you know what your looking for and moreover how to solve it, you'll be racing without worrying about the profile check, and that may be all you need to perform your best. 

A few notes: 

1. If you were expecting dead on accuracy, unless your lucky, you probably won't see it. A few tenths difference between advertised profile and actual readings are expected.

2. Twisting the cam using a cam twister or other device is not recommended. All of our cams are heat treated to approximately 50 Rockwell. When cast iron is heat treated to this degree it tends to take on properties similar to other stronger metals, hence it's great wear properties. However iron has a very poor grain structure which makes it susceptible to overload breakage or warping, especially when stressed in the manner necessary to change it's lobe timing.

3. The blocks above show typical results, however there are blocks that vary more than these. We've introduced the idea of a variable position woodruff key to the WKA that would allow motor builders to more easily adjust there timing. This would be the best possible solution due to the amount of flexibility in timing adjustment that could be performed. 

Well, that's that.  We hope you've enjoyed this months installment of "The DynoCams Tech Question of the Month".  Join us next month as we delve into other mysteries of Karting issues.