Port timing numbers

[Mike Berg]

Hello Bob,

I used to build a lot of Mc's, in the Mc 90 era engines we did the following:
a. raised exhaust to reach 23 to 25 degree blowdown timing
b. eyebrow the exhaust ports, do not narrow the center rib but square off inside top corners with .125"
radius
c. I don't recall the cylinder head cc's but I machined about .040 " off head at a angle so not to enter spark
plug hole
d. general note NO square corners on any port every corner MUST be radiused
e. on the intakes I squared the following corners going from the port closet to exhaust to the furthest
from the exhaust square the right top corner ONLY adding a .125" radius then blend a gentle radius
on the entry edge of the ports don't change the entry angles
f. we set the squish at .028"
g. polished the bore after honing with torque plates set ignition at 24 25 degrees, NO maverick spark lotsa
point tension 26 ounces
That's about it, we did use expansion chambers then, home built with gentle angles, also used HL293 carbs with GEM v12. If you have a good pipe for stock Mc with correct length for stock Mc just add 1.5" to stock length we also used burco clutches 4 shoes with extra weigths, ring, and x 15 oil.

Hope that helps. I am currently building some 3 MC 70's, 1 MC 8, and 6 MC 6's which will have similar mods.
I need .030 over 101 pistons and .040 91 piston and stock 91 pistons all w/rings.
Almost forgot we used methanol with 10 ounces of castor per gallon with autolite pluge AE901x or A203.

Best regards,

Mike Berg
1964 Caretta enduro open MC 8 Margay gearbox

[mcbob]

Again interesting reading Mike ................. McBob.