Mac extra porting !!!

[Rob Voska]

That's not only cool. It's REAR legal

[mcbob]

Here's the intake or reed block i modded to fit the underside of the Mac cylinders







Now i would only have to get it welded on.

Mc Bob.

[ted johnson]

Hey, McBob...It's a good idea to do a hone job and check all the gasket surfaces for flat after welding. Sounds logical, but I've known guys who neglected to do so after welding, with the expected result! Ted

[Bill Johnson]

Just Epoxy it on with Hysol 1C from Loctite to keep from distorting it so bad from HeliARC welding. The Epoxy will hold it if you do it right. Put a little Chrome Paint over the epoxy and it will look like a Heliarc weld. Is that a 101 block you are working with?? Do you have enought Reed Cage Tip Clearance??

Your are having fun...but you could have tried this out on a WB820 to see how it would react since that would have been all bolt on.

[mcbob]

Gday Bill, i have the latest Copperhead and i have two Tilly's i can bolt on in pairs both in upper and under locations plus i will have when there available another copperhead induction manifold so i can run two boysen reed assy's with 2 tilly HR's ........ these will be for future development and testing i'm afraid.

As to which engine i do the Mac conversion to ....... maybe a Mac 92 as i have enough spares to get it running plus i don't have a spare 101 block to spare the cylinder i'm messing with is off a SP125C which has no boost ports and a fixed head this engine was knackered to start with so boring holes in it is no big drama.

If i fit the manifold mod i may just get it tacked on at the corners and seal the rest of the join with some type of bonding epoxy this may save a bit on the distortion side of things.

The reed assy clears the crankcase stuffer but tomorrow i'll remeasure things as i remember Steve talking about reeds fraying when the reed block was to short ...........

Mc Bob

[mcbob]

Well fellas had a bit more luck today as i found the fella who helped build Chris's engine and he said he'd take some photo's of it ... not sure when but they will arrive some day soon he reakons.

When i asked if the engine was available he said he'd ask on my behalf but it's a bit soon after losing Chris but who knows ? Chris passed away last July. But his wife still owns the Mac engines.

From the conversation we had it sounds as if we are on the same path only 10 or so years apart with my ideas and method very similier ..... man i can't wait for the pic's to see how close our ideas really are to eash other.

Mc Bob.

[mcbob]

Once the reed block is tack welded into place the reason for tacking is to stop distortion i'll fill the surrounding area with some form of epoxy to seal the joint ...... at this stage i have modded a Mac 92 block and once this job is done i'll get it rebored as it will need it as the bore has been needled.

Mc Bob.

[Gordon Duax]

Bob,

Why don't you supercharge it with a real supercharger?
I have several 300cc/rev roots style superchargers that would lend themselves to a saw.
I sold one to a guy who now holds the 125cc bike record at El Mirage (102 mph),
and at Bonneville (88.858 mph).

Instead of McBob, we would have to call you Mc Super Bob !

E-mail me for pictures if you get the itch...........

[steveohara]

Gordon,

Please post the pics and be sure you show the exhaust pipe. Super charging a typical two cycle engine would seem to be of minimal benefit since you can't trap any more pressure in the cylinder than the exhaust will allow out. It seems that to make supercharging a typical transfer port type 2 cycle useful the exhaust system would have to be designed to run at a much higher average pressure than the typical expansion chamber. If run with an open header the supercharger will just blow the intake charge right out the exhaust until the transfers are covered by the piston on the way up. Once they are covered the cylinder will have time to normalize to near atmospheric pressure and there would be nothing gained other than perhaps a very clean charge with no residual exhaust gases. With a typical pipe the design is intended to reverse flow fresh charge back to the cylinder after the transfers close and that reverse flow is dependent on the pressure differential between the pipe and the cylinder.... again, the supercharger can't have much effect unless it has pumped the pipe up to a higher pressure with a larger fresh charge than would have occured by normal scavenging.... which seems possible to some degree.
It's a subject I've been curious about for a long time but never bothered to explore since karting has (almost) always ruled it out.
Regards,
Steve O'Hara

[Gordon Duax]

Sorry, no pictures of what pipe the guy ran on his bike.
I'll try to get some of the little blowers transferred over to photobucket.
Forums have turned into such a pain in the a$$ to post pictures on......
Most likely I will have one listed on eRip within the next 24 hours or so, seeing they are having a 50 cents listing day.

One way to approach supercharging a 2-stroke would be to run very tall transfer ports (or very low exhaust ports).
McCulloch had a supercharged engine at one point.
They used 2 pistons, one larger than the other.
The large one was just to supercharge the smaller one.

I am looking at bolting one of the mini blowers to an 820, and not running any reeds (they shouldn't be nessesary).
Then scallop the piston to give much more transfer duration.
If I were to get serious about it, I would go for a re-sleeved block so that I could lower the exhaust way down.

The benifit of supercharging would be a very flat torque curve.

I am thinking that a strait exhaust pipe would work just fine.