Mac extra porting !!!

[Tom Smith]

McBob, the Super Pro 125 exhaust port bottom opening is a V shape. This reduces the noise level and helps with ring wear. When you raise the top of the exhaust port which is a D shape it's a good ideal to leave a small triangle of the original port material in the center of the port to help deflect the rings back into the bore. This ain't nothing new here, Konig used large raised D ports in the 60s!
The Nazis had a good handle on supercharged combustion chambers and ports back in the 40s.
Maybe that's why Offenhauser copied the split D exhaust port and combustion chamber from a Diamler V-12 ME-109 fighter plane powerplant when they turbocharged their Indy Car motors in the early 70s.

[Tom Smith]

McBob, I had a nice story written up for you last night about a few prototype Mccullochs I know about when my kitten trotted across the delete button on the damn keyboard. I had all the Super Pro 101 stuff described, like the 2 transfer windows on the bottom transfer passage etc.
Here's another story instead, Bob Mcculloch was interested in high pressure direct gas injection like the Mercedes Benz race cars used in the early 50s. Mcculloch had a prototype aircooled 5 cylinder radial engine they were trying to perfect direct gas injection on. They could not get the injectors to not bleed off pressure after the motor ran and this caused raw gas to drip into the cylinders which could then hydraulic or catch fire the next time the motor was started. It was concluded that the US did not possess the machinery necessary to grind the injectors precise enough to overcome the leak down problem with hot injectors etc. (a friend of mine was the machine shop foreman at Mcculloch and I have heard some interesting tidbits about all the wild/wet dream projects he worked on at Mcculloch like the Novi Indy Car superchargers) as it turns out, Mercedes Benz had the same problem with their Bosch direct gas racing injection at the time so it would seem like Mccullochs findings were accurate.
I don't know if you ever saw Mcculloch Motors on Century Blvd. in LA or not, but it had 500,000 square feet of offices and workshops on 62 acres of land. It took them about 6 weeks a year to produce all the kart motors.
Today it would be a piece of cake to build a direct injected 5 cycle multi cylinder engine. In fact it's being done on the East Coast.
A screwcharger seems like the best way to supercharge crap these days. Tom

[mcbob]

McBob, I had a nice story written up for you last night about a few prototype Mccullochs I know about when my kitten trotted across the delete button on the damn keyboard. I had all the Super Pro 101 stuff described, like the 2 transfer windows on the bottom transfer passage etc.

First thing shoot that bloody cat ...............

Now you got my attention young Tom i'd like to hear more so keep that cat in another room.

No all jokes aside it would be more than interesting if you would share what you know about these prototypes with us especially with the improvements to our beloved 101 and whatever came along later.

But it's like what you said their just trying to reinvent the wheel.

Mc Bob.

[Dan Flanders]

Hey Tom-
Is this the old Mac building you were talking about?

[Dave Brillhart]

Before you Mac enthusiasts go overboard, you might want to check out a few facts. That BP-1 owes more than a little to the 1938 DKW SS250 racing bike, that had a huge charge piston feeding a two piston combustion chamber with the exhaust exiting one side(and a lot of the fuel with it. That said it was the first performance racing two-cycle. The japanese took the great leap forward when MZ (East German) factory motocycle racer , Ernst Degner, defected in 1961 taking Walter Kaaden's secrets to Suzuki including the third transfer, and the expansion chamber exhaust. As far as the BP-1 goes, that offset crank must have produced significant vibration on its own due to the rocking couple.

[Gordon Duax]

McBob,
Are worried about vibrtion?

By the way,
You won the Mac catalogue last night on eRip only because
your feedback was 666 (the sign of the devil ),
and I was afraid something nasty would happen to me if I out bid you !

[mcbob]

Gordon i'm siting here with a (censored ) looking at those photo's and admiring that wonderful showroom fantastic. Don't worry ol mate i had that catalogue well and truely covered or protected by the 666 and i'll let you call on over if you wish to read it but you be needing a little shark repellant.

The BP-1 I HAVE IS AS SMOOTH AS SILK very little if any vibration at all.

Gee now what was we talking about ??

Mac's BP Engines http://macbobaust.com/engines.html

Mc Bob.

[Gordon Duax]

I think your dual intake Mac.........
Not obsolete motor bikes that have long fadded away.......

I once converted a Jacobson 2-stroke from reed to piston port by boring a port in the side of the cylinder, and epoxying a manifold to it.
Run fine for about 5 minutes, and the epoxy let go.

[mcbob]

I have a fella at the local tech college who will add 4 tig tack welds to the corners of the reed block this may stop this bit from falling off and i'll epoxy the rest of the joint, hopefully this will seal the joint as this engine will get little use hour wise as it's for a hotsaw plus i'll possibly build a brace that will help take the weight of the carb.

Dan where abouts in LA was the showroom / office located was it the building opposite LAX airport ? When i came to LA in 2006 i want to see the old building is it still there fellas as when i arrived it was late and we had to clear the city so there was no time for driving around sightseeing.

Your right Gordon we need to stay off the dirt and back on the sealed track.

Here's the exhaust port off the SP125 @ 123cc and SP105 @ 103cc neither of these engines had rear boost ports.



Mc Bob.

[Tom Smith]

Dan, ya, and there was one display window, front center of the structure if I remember, that had an R1 kart with dual Mc-30s hanging under nice big spot lights day and night for years. It looked great at night when you drove west on Century Blvd. on your way to LAX.
oh Dan BTW, I finally figured out that the Max-Torque Special steering wheels were H and S products (Hands), Tom