Each grinder has their own "theories" on engine operation that are the basis for their designs. Typically a better designed camshaft will require less flycut depth than a camshaft with a poor design and slow ramp rates. Due to this fact, it is important to flycut the depth the manufacturer of your camshaft calls for unless you are wanting to go a bit bigger to make room for any changes or upgrades you might want to make in the future. Most of our bigger cams will be covered by .060-.080" flycuts and .120" on our biggest pulling cams.
There are several factors to think about when there has been contact. The first is piston protrusion, which will be altered if there has ever been a rebuild where the block was decked or a non-factory piston has been used. Another factor is the valve face depth. I usually look for .040" +/- on the 24v's and
.55" minimum on the 12v's. Although you may not have ever rebuilt your engine or have had any head work in the past, that doesn't mean that the dealer might not have done warranty work or something might not have been done prior to you owning the truck. For this reason, we put in our instructions that it is up to the customer to verify clearances.
Lastly is installed centerline. Time and position of everything in your engine is super important. This is especially true when talking about injection events or camshaft timing. As was stated earlier, when the gear starts to walk off of the camshaft, this affects camshaft timing and can cause clearance issues. A bolt on retainer for p-pump applications will easily solve this.
Beyond that instance, cam timing can easily vary one or two degrees from engine to engine due to wear or the allowed "variance" in any manufacturing process. Typically this is due to the fact that centerlines easily vary a couple degrees in either direction for oe geartrain.
For this reason if you are running a radical performance camshaft, or have mixed components in your build. It is very important to degree or verify your installed centerlines.
I deal with a lot of builds and am privy to a lot of information from different engine builders. I recently helped a guy out that could not get his performance to the level he wanted. After everything was gone through it was found that his installed centerline was off 9 degrees retarded. BINGO. Especially when mixing parts from different engines, the gears can be off quite a bit. I bet there a more than a few people on here that are not seeing the performance their friends are with the same setup due to variances in cam timing.
THis is why I harp on the fact that camshaft makers need to disclose a lot about the cams events. If you blindly install a camshaft "straight up" how much power are you giving up? Could be a hell of a lot, or it might be only 10 or so, but you might never know.
Sorry for the long winded response, Yoshi I have a few new guys we are working with that will get you where you want to be with only .045" extra clearance. I would just get some .080" cuts to give you room to grow or play with installed centerlines.
Goodluck with your build.
Zach
