Mac boost ports ..............

[mcbob]

Gordon that first one looks like my girlfriend on a good day and the 91 looks like a wild musheroom ...................

Man i have to get off this xxxx.

Mc Bob.

[Tom Smith]

Ted, yes, block taped, 1/4 20 x 1/4 28 studs used with .125" thick washers and NAS 6 point nuts. One thing you will never have happen again is a 10/24 center lok nut spinning around stuck on a socketcap head bolt down in the nut pocket after the nut retaining clip broke or fell out.
BTW I would never run 15% in one of my Mc-101s. That thing is just something to fool around with.
It was a blank block that needed +.030 to straighten up and I already had everything else except the Wiseco super-pro dykes/single thin ring piston. Tom

[ted johnson]

Tom, thanks for the skinny on the studs - I remember the nut clips breaking, and wedging something into the nut pocket so I could remove the head! TJ

[steveohara]

Guys, No intent to change the subject here but Tom's comment about the nut spinning in the pocket prompted me to offer up this tip for your Mac engines..... remove the locknuts that receive the cylinder head bolts and either replace them with good quality non lock type nuts or run a tap through the nuts you take out so that the "locking" effect is eliminated or reduced to a low level. Those locking nuts can take up to as much as 25 inch pounds of torque just to turn the bolt and there is no way to assure consistent torque levels from one bolt to the other even if you are using a torque wrench. With the non locking nuts you will want to torque the head bolts to 75 inch pounds. I have never had one come loose but there is no harm in using Loctite if you are worried about it. If you have a real strong lock nut you can have as much as one third of the torque going into turning the bolt rather than applying clamping force to the head gasket. After eliminating the lock nuts I never had another head gasket problem even with the flimsy little .016" aluminim gaskets on the 91 series motors.

OK, back to the original subject
Regards,
Steve O'Hara

[jmendoza]

I'm guessing from looking at my MC-91A that you could eliminate the web between the two boost ports, like the later MC-91B/1. This should work on the 101, but I'm not sure it would do anything other than weaken the cylinder.

The way I understand cylinder transfer porting, you have to increase the ability of the crankase to breath more in before it can pump more into the cylinder, and a tuned pipe can really increase the amount of effective charge in the cylinder. It is possible to realize a significant increase in power without altering the ports, if the right tuned pipe is used.

I have several Mac chain saw I have used through out the years cutting big 200 foot+ Ponderosa pines on my property in the San Bernardinos, and they are brutes.
I don't know high in RPM you turn your saw motors, but it would seem to me that torque would be more valued that peak HP for cutting through a log. That way, the saw would bog less as it went through the heartwood and knots. If that is the case, more dissplacement always helps. A tuned pipe can keep more charge in the cylinder, making it's effective disspalcement and torque greater.

On my saws, If I used an Azusa stack in place of the little round muffler with spark arrestor, the saw had less torque and bogged down easier. It seems the back pressure of the muffler helped the saw's torque.