Thinking about this Howard’s cam

Here are the timing numbers I get.

Howard’s:

EVO: 67 BTDC
ECL: 110 BTDC
EVC: 27 ATDC
IVO: 32 BTDC
ICL: 102 ATDC
IVC: 56 ABDC

268/274 106/102

My numbers:

EVO: 75 BBDC
EVL: 112 BTDC
EVC: 31 ATDC
IVO: 29 BTDC
ICL: 106 ATDC
IVC: 61 ABDC

270/286 109/106

Looking at the numbers, and like I see a lot most of the extra 12 degrees of exhaust duration of which went to Exhaust Valve Opening. So it opens the exhaust valve 8 degrees sooner. That’s 75% of the extra duration added to the opening side.

That is because (my opinion or better yet my WAG) with the geometry you have the engine wants to reduce pumping losses with that earlier opening.

Without the extra exhaust duration if you tried to open the exhaust valve 8 degrees sooner you’d also close it earlier and that hurts overlap.

Equally interesting is with only two more degrees of intake duration it opens the intake valve 3 degrees later but closes the valve 5 degrees later.

Crap I forgot to calculate overlap. I’ll do that next.

Also interesting is the Howard’s cam with its 4 degrees of advance doesn’t center the overlap triangle.

My numbers with 3 degrees advance centers the overlap triangle.

I’ll run the overlap numbers.