George Lendich wrote:

Jerry,
I rushed my assessment of the PP timing - I was WRONG!!
However it can be very confusing, your IC ( it would appear) is 79 degrees ABDC and is later than the 75 degrees of the Mazda Factory PP.

Given that Lynn's is 85 degrees, 79 - 80 is my choice also, as it is most probably Lynn has his racing PP right on the edge.

So at this point my novice approach agrees with your professional advice.

Now the IO is another matter, your opens at 76 degrees BTDC and is later than  the Mazda Factory PP of 86 degrees.

So in both instances your port opens later as you alluded advised to, I believe i.e. less overlap.

Now the problem with the 12A is that it needs a little less inlet area and can therefore reduce the overlap further so I might try IC same as yours, and IO of
about 70 - 60 degrees depending on the area needed, so it might end up a wide flat area similar to the exhaust. This is also along the lines Lynn suggests for
the 12A.

Thanks everyone for the information and the opportunity to work through the process!!
George (down under)

 
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