Back in 1961 when my dad was racing, a buddy of his had connections to a chainsaw dealer and supplied a large amout of Macs to local racers. Being cheap and always looking for an edge, he was buying certian chainsaw blocks without all of the ports drilled to replace the Mc5/6. Then he would add the ports to his liking. Most of these did not have the third port induction added. So he first started adding two large squared ports instead of the three small ones equipped on kart blocks. Later he started adding one large round booster port in back like they had been having great success on the Power Products AH-61. One motor I remember seeing had two boosters that were drilled thru the block just like the other intakes. Then the passages were opened up and welded over. He said they ran good but took too much trouble. Then he was just plunging three small boosters like was becomming a popular mod to the actual kart blocks. I asked why he didnt plunge down two large boosters on the saw blocks without third port induction added like the newer 91 motors. He said they never thought of that at the time. Something else he did make use of was taking advantage of the blocks with just the two outer exhaust ports drilled. He said some guys were already doing this on a few resleeved blocks and where he got the idea. Well after digging thru a bunch of junk I found the end mill that had been ground to fit exhaust ports on the early motors. So I just had to try it out for myself. One pic is a stock 1-45 with only the two outer ports drilled. The center port is undrilled and just clean aluminum. The other is one I just opened up the exhaust ports like they started doing back then. I also have a rotary table set up on the mill to drill the other intakes that are blank and plunge two large boosters on the back side that never had the third port induction added. Adding boosters to one of these saw blocks really steps up the power. Installing a Mc7-91 crank really brings one of these motors to life. Hope this is helpful to some of you. If so I will follow up with more info and pics.
![Image](http://carphotos.cardomain.com/ride_images/3/1006/4309/27514654003_large.jpg)
![Image](http://carphotos.cardomain.com/ride_images/3/1006/4309/27514654002_large.jpg)