My aux ports, running with a camden. And just for fun a pic of an aux plate I found on the net I call "The Abomination". This is where someone got real creative!

 

Your 12a engines had a 75* BBDC open timing which is even earlier opening then current 13b (all of them for that matter) and is street port-ish being its a whole 5* earlier. MAZDA made the port timing more retarded for the later engines in an effort for better emissions and gas mileage, not a move for more power as this was made up for by the extra dissplacement of the 13b over 12a. And for those 757, 767 and 787 mufflers, they were 4" and 5" INSIDE DIAMETER STRAIGHT THROUGH style mufflers LOL, so you can give that a rest as theres very little restriction. Anywho, I'm not going to try convincing only 1 guy now who still insist in using MAZDA as examples but in the end MAZDA shows more support for the opposite side of the aurgument/disscussion. This thread is pretty far off topic now lol, sorry.

~Mike..............

 

It might've taken me a few months to find this, but I read your entire post. It might not've been the easiest to follow, but it sure was entertaining! I'm so confused now-not because of exhaust port timing-but because I've got yet another thing to try and figure out for my project. I thought a simple template for the exhaust ports might suffice before, but I'm thinking differently now...

BTW-thanks for all the great info-all you guys! I had to post here to save this in my thread subscriptions for the valuable info and links I'll be needing soon...