M8 Cam Timing

[WhipLash96]

How is reading cam specs differ than that of a Twin Cam? Looking at a few different aftermarket cam manufacturers and they all say that it's different. But why?

Duration is Duration, lift is lift, valve close is valve close. No?

[Tail Ridr]

My take is with dual valve on each side, valve lift and duration doesn't need to be as much as you are getting the flow through the valves with less, more swirl in the chamber and all cane be done with smaller valves keeping velocity up.
If I'm responding as you're asking...

[rigidthumper]

Only thing that I can think of is advertised duration specs on TC cams were taken @ .053" lift, M8 cams are taken at .050" lift.

[WhipLash96]

Right. These sites are pretty vague. I completely understand why the valve lifts are less than those of a Twin Cam but they make it sound like everything a person knows about cam timing no longer applies to the M8.

[wfolarry]

What they are alluding to is the different size lobes & the offset of the lifter bores.

[rigidthumper]

Look at stock Rushmore cams- 213° intake/233° exhaust duration @ .535 lift, VS stock M8 cams- 188/227 duration at .350 lift.
Stock 107 M8 is only 1/16" bigger piston ( less than 4%) than the TC, but beats it by 10% on the drum with smaller cams. Has to be the heads, right?

[Don D]

Heck yes its the heads. By the way there is about +2.8° difference between checking duration at .050 and .053

[WhipLash96]

Heck yes its the heads. By the way there is about +2.8° difference between checking duration at .050 and .053

Yes but it is only relative to the M8 design. The information that the cam card provides doesn't mysteriously change because of this. If the MoCo is measuring @.050" so is everyone else. So an M8 cam that reads it has an intake closing event at 27 is still a closing event at 27. No?

[WhipLash96]

What they are alluding to is the different size lobes & the offset of the lifter bores.

Thanks Larry!