Recently the McCulloch Block pictured below was listed on eBay.
I have only seen a few McCulloch engines & have much to learn. I have yet to run across one with the (5) port design shown below. I would like to learn about the various port designs & how they evolved or came to be. Any links to informative articles or information here will be greatly appreciated.
What is the idea behind these five ports vs. just the upper row of three ports?
What is the reason for what I call "The reach around port" and why is it allowed to operate independent of the reed valve?
Does anyone know if the engines perform better if they are fed straight on from the crankcase with a stuffer mounted carb set-up & close the side up with a plate, or does the side feed perform better?
Thank you
McCulloch Blocks & Port Design?
Moderator: Rob Voska
-
John Miller
- Posts: 72
- Joined: Mon Feb 02, 2009 8:35 pm
-
John Miller
- Posts: 72
- Joined: Mon Feb 02, 2009 8:35 pm
-
Jeff Campbell
- Site Admin
- Posts: 581
- Joined: Tue Jun 12, 2007 7:52 pm
- Vintage Karting items owned: 1961 Fox Go-Boy MC20's
Robron Chaparral dual MC101
Margay Cheetah MKIII - Location: West Bloomfield, MI
- Contact:
Re: McCulloch Blocks & Port Design?
John,
That is a big question(s) to answer fully, I'll make it brief. The most of the early macs had 3 round intake ports on each side of the cylinder, with 3 round exhaust ports, plus the so called 3rd-port (your reach around port). The 3rd port when used with the stock flat 2 reed plate was reported to boast power by some 15%, it acts as a piston port induction, basically it's like combining a piston port motor and a reed motor into one, improved induction at the rpm range where the piston port induction is working well. This porting was based on what was being used in the Mac Chainsaws at the time, some saws had fewer than ports drilled or no 3rd-port at all. Later Mac kart motors went to better reed assemblies (pyramid and V types), which flowed much better and made the 3rd-port a detriment rather than a help, it was eliminated on the kart motors. The later 90-93 series motors had 2 large rectangular exhaust ports, most of the 101 series motors had a single large exhaust port, but all maintained the 3 round intake ports on each side of the cylinder, plus they all had 2 boost ports opposite the exhaust port (a few had one large boost port).
The 5 intake ports you refer to in your photo, are not all intake ports, the top 3 are, the bottom 2 are not. The bottom 2 are a typical modification done by engine builders (not McCulloch), to improve flow from the reed induction into the crankcase, and to better lubricate the piston skirt, sometimes builders cut very large openings here, but usually put in 2 openings.
There were a lot of bottom stuffer reed induction after market parts on the market in the 60's, did they perform better than standard induction on the side of the block? ... It depends what is being compared I guess, if you simply look at what was popular on open class motors, there were many hot motors in the 60's that used both bottom stuffer reed induction and side of the block induction also, with 2-3 small carbs. Later era open motors for many years, mostly used V12 or V16 side block induction with 2 small HL Tilotson carbs or a single large 34mm HR Tilotson. What didn't seem to be overwhelmingly popular on hot motors, for any long length of time, was the use of only stuffer reed induction with a side plate to block off side induction.
Also, beware, there are many hacked up blocks out there, that probably perform worse than a stock motor. Generally, top engine builders didn't open up the intake ports much since there is a lot of intake port in a stock motor, they did play with timing of the intake ports (sometimes dropping in a Quick Time piston that had a raised wrist pin location), and flow the intake port entry (aluminum) edges many times without changing the port size entering the cylinder. Opening up and/or raising of the exhaust port was done on all open motors. In a nutshell, be leary of blocks with heavy intake port modifications, especially if they are unbalanced (it's hard to access the intake ports on one side, inexperienced tuners hacked away at the easy to reach side, and did little work on the opposite side intake ports).
Jeff
That is a big question(s) to answer fully, I'll make it brief. The most of the early macs had 3 round intake ports on each side of the cylinder, with 3 round exhaust ports, plus the so called 3rd-port (your reach around port). The 3rd port when used with the stock flat 2 reed plate was reported to boast power by some 15%, it acts as a piston port induction, basically it's like combining a piston port motor and a reed motor into one, improved induction at the rpm range where the piston port induction is working well. This porting was based on what was being used in the Mac Chainsaws at the time, some saws had fewer than ports drilled or no 3rd-port at all. Later Mac kart motors went to better reed assemblies (pyramid and V types), which flowed much better and made the 3rd-port a detriment rather than a help, it was eliminated on the kart motors. The later 90-93 series motors had 2 large rectangular exhaust ports, most of the 101 series motors had a single large exhaust port, but all maintained the 3 round intake ports on each side of the cylinder, plus they all had 2 boost ports opposite the exhaust port (a few had one large boost port).
The 5 intake ports you refer to in your photo, are not all intake ports, the top 3 are, the bottom 2 are not. The bottom 2 are a typical modification done by engine builders (not McCulloch), to improve flow from the reed induction into the crankcase, and to better lubricate the piston skirt, sometimes builders cut very large openings here, but usually put in 2 openings.
There were a lot of bottom stuffer reed induction after market parts on the market in the 60's, did they perform better than standard induction on the side of the block? ... It depends what is being compared I guess, if you simply look at what was popular on open class motors, there were many hot motors in the 60's that used both bottom stuffer reed induction and side of the block induction also, with 2-3 small carbs. Later era open motors for many years, mostly used V12 or V16 side block induction with 2 small HL Tilotson carbs or a single large 34mm HR Tilotson. What didn't seem to be overwhelmingly popular on hot motors, for any long length of time, was the use of only stuffer reed induction with a side plate to block off side induction.
Also, beware, there are many hacked up blocks out there, that probably perform worse than a stock motor. Generally, top engine builders didn't open up the intake ports much since there is a lot of intake port in a stock motor, they did play with timing of the intake ports (sometimes dropping in a Quick Time piston that had a raised wrist pin location), and flow the intake port entry (aluminum) edges many times without changing the port size entering the cylinder. Opening up and/or raising of the exhaust port was done on all open motors. In a nutshell, be leary of blocks with heavy intake port modifications, especially if they are unbalanced (it's hard to access the intake ports on one side, inexperienced tuners hacked away at the easy to reach side, and did little work on the opposite side intake ports).
Jeff