casting a 2 stroke engine, and question about small superchargers

 Sorry if this is a partial repost, I was wondering if anyone can offer
general tips on casting aluminum engines, of the 2-stroke variety?

I've seen a website of a gentleman who builds Indian-brand motorcycle
parts, and that's very good, but I would like to read more details about
similar, but different projects.

I'm also interested in how a motorcycle turbocharger or supercharger can
be used together with a tuned exhaust system.

Why can't the tuned exhaust pipe size be dynamically changed, by using
helical metal leaves that wrap around each other?  That way the aperture
could be selectively altered to accommodate different RPM ranges, which,
as I understand, are pretty tightly tuned.

Let me know if you know anything about this, thanks.

 

A supercharger overpowers a tuned exhaust system. You can read about
the DKW 250cc grand prix racers of the late 1930's. They had one
larger piston supercharging a smaller piston that operated on the same
crankshaft.

The engine used a wide open megaphone exhaust system that could be
heard 40 miles away. It produced 40 horsepower at only 3700 rpm.

Compare that to a conventional 2-stroke that has to turn 11,000 RPM to
make 40 horsepower.

Do a patent search and if it comes up negative, patent your idea.

2-stroke exhaust tuning is usually done by means of a power valve in
the exhaust port which restricts flow at lower RPM.

 
I know just enough to be dangerous. My free advise is worth less than you
are paying for it.

While one could sand cast parts like the older (pre-70s) Brit bikes one
would have to accept their level of performance (40HP +/-) because their
porous cases would be beat out by any more power.  Modern casting is a
science in itself and prolly beyond the home shop.

Never heard of combining a tuned exhaust with a turbocharger - IMHO getting
the gasses into the turbo as hot as possible (most energy) negates the
possibility.  OTOH dragsters have used tuned exhausts with roots blowers
since before god was born.

I suppose one could dynamically change the length of a tuned exhaust but I
suspect the gains wouldn't be worth the complexity.  Outside NASCAR, race
engine tuning is extremely competative but I never heard of anybody doing
it.

 On Mon, 4 May 2009 21:07:01 -0600, "Bob Myers"


Yeah. One wonders if he's trolling, but if so, he's very subtle. He
wants to build it from scratch, pouring the heads, crankshaft, etc,
then machining all of it, but he doesn't know where to start? That's
years of skill to learn, thousands of dollars, countless wasted
efforts...  It's one thing to be able to assemble an engine from
scratch, quite another to machine the parts, but to cast them, too?
Nice hobby. If he pulls it off, I'll be impressed.

I'd start by enrolling in a basic foundry class at a junior college.

--
Turby the Turbosurfer

 

Like I said, my info is worth what you paid for it <g>.

I helped a foundry write production spec's for the gummymint. I was amazed
at how complicated casting even gun projectiles is.  It was mostly automated
from turning scrap and ore into useable metal but pouring molds was all done
by hand.  Seems that after centuries it's still a black art that must be
learned.  I learned there were many kinds of sand - some imported from
exotic places - and each mix needed particular resins.  Some metals had to
be innoculated just before pouring.  For example, iron was poured over a bag
of magnesium then immediately poured into a mold because that made the
casting mucho stronger but the magnesium evaporated at iron's pouring temps.

You prolly know all this and more but I found it daunting.  I doubt the
typical home mechanic could cast airtight cases for a 2-stroke when H-D had
problems with oil moving between the primary and crankcase via pourous
castings.  I applaud those who can.