McCulloch 125 with piston ported intake?

[Chainsaw Jim]

Has anyone ever modified the reed valve into a piston port intake?

 

[Stump Shot]

 

[cus_deluxe]

For conversations sake, is there an advantage to going that route jim, or limitation of parts availability make it “necessary”?

 

[Chainsaw Jim]

I'm not trying to stir up bad memories of getting rapped across the knuckles with a cane. I noticed it's possible without a bunch of insane work, so it stirred my curiosity about whether anyone has ever done it for a race build.

 

[mgr1]

A reed engine is faster and stonger than piston ported. When you can work out a powervalve in the exhaust, then you have a monster of an engine.

 

[Al Smith]

It's debatable if reeds are actually any faster .They do seem to allow a longer intake though .There must be something to them because they still use them on high end two cycle trail bikes and snowmobiles .
The only power valve exhaust set up I ever saw was on a high dollar off road bike my neighbor had .That thing was under 150-200 cc and produced like 28-32 HP .I tinkered with a valve thing and got it to work for him .Had to Google it to figure out what it was supposed to do .Have since forgotten .

 

[mgr1]

Over here a 70cc air cooled scooter gives a output of 18hp. This is a reed valve engine without powervalve.

The ktm sx125 reed valve engine with powervalve gives on the bench 43hp, this mx raced the european championship.

Piston ported: cheap and easy to manufactured

Reed valve: wider powerband

Rotating intake valve: highest power output and a very narrow powerband.

Reed valve with powervalve almost the same power as a rotating intake valve.

The key to power is cooling the cylinder enough.

 

[Al Smith]

Since you mentioned I think that bike was a KTM .I'd never heard of one before that one .Being an old red neck my ride of choice was Harley-Davidson .That aside I somehow don't think a power valve would be the thing to do on a chainsaw engine reed or no reed .I also might mention horse power ratings can vary so widely it's hard to determine exactly what you have without using the same set standard .

 

[Lee H]

A reed engine is faster and stonger than piston ported. When you can work out a powervalve in the exhaust, then you have a monster of an engine.

Rotax has been doing it for years as well as few others. I have never seen
a snowmobile with a piston ported motor. Both my SkiDoo RT1000's
have reed valve motors and putting out a mere 175 horse in stock form.
Fastest production sled in there day from 06 to 07.

 

[Chainsaw Jim]

Rotax has been doing it for years as well as few others. I have never seen
a snowmobile with a piston ported motor. Both my SkiDoo RT1000's
have reed valve motors and putting out a mere 175 horse in stock form.
Fastest production sled in there day from 06 to 07.

I have this Yamaha 250cc piston ported motor from a snowmobile. It's a quad port design very similar to the 372xp. I'm planning a future hotsaw build with it.

 

[p61 western]

I have this Yamaha 250cc piston ported motor from a snowmobile. It's a quad port design very similar to the 372xp. I'm planning a future hotsaw build with it.

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Oh wow that's going to be a cool project for sure.

 

[Al Smith]

Speaking of Yamaha ,in my drunken young sailor days in Key West I had a 250 twin flip me over backwards at about 40 miles per hour .Being an old Harley rider I had no idea how an expansion chamber pipe worked but I found out .Asphalt fever .

 

[Adirondackstihl]

80’s & 90’s , Rotax used a rotary valve.
One of the first sleds I rebuilt was a 89’ Formula MX with a 467 twin - rotary valve.
Not a top end motor, but 0-50 would rip yer mittens off.

 

[Sleeper]

As for rotary valve two strokes, the Ski-Doo Rotax 583 and 670 are considered some of the greatest ever produced, my 670 will haul my 300 lb ass well over 125-135 mph in a very short distance. Cornfield that was destalked, about 1/2 mile length, yes we can hit 120 in that span. 583 will push 110-120.

Then the reliability, knock on wood. Pump primer three times, pull her over. Starts right up 95% of the time. Yet they still, with power valves in the exhaust, have a wide enough powerband for cruising, and have that all out power at WOT.

Clutches engage at roughly 4000-4500 rpm. Power all the way to a whopping 8500-9000 rpm. Pretty high for a twin of that era. These sleds were so well tuned from the factory that it is hard to get any more out of them without major work like porting and twin pipes with rejetting.

As for piston ported, we had a Polaris Indy 500 with a Fuji twin at one time... definitely not stock. Would scream at 10,000+ rpm (needle would be up against stopper pin at 10,000 on the tach) and haul me at well over 110 mph. Yet would start on first to third pull every time.

I miss that old 500 sometimes, she was a good sled. Cheap, and still fast as a bat out of h-e-double toothpicks. Sure, suspension was crappy, but if you wanted to go fast on a flat field of ice, it was definitely the best choice for that. Light and studded track, hooked right up and about blew you off the back of the sled when you pinned the throttle lever from a dead stop.

 

[Adirondackstihl]

*cough*

 

[Lee H]

My first new sled was a 96 Mach 1 with the 670 and twin pipes. It would literally
smoke any 700cc sled in it's class stock for stock. It took a few 800's as well.
Then in 97 Skidoo came out with the 700 triple with reed valves. Had to have
that one too.

 

[hseII]

*cough*

Go On, spit it out.

 

[Adirondackstihl]

Go On, spit it out.

 

[Adirondackstihl]

Had me a 96’ 583....

 

[hseII]

Had me a 96’ 583....
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How fast was that thang Mang?