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Wolframore

Joined Jan 21, 2019
2,609
Porting for 2 strokes is completely different than 4 strokes. The porting is done on the piston and cylinders since there are no cams or valves. Timing and duration is changed with port placement And piston shape. It’s taken a while to understand it.
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shortbus

Joined Sep 30, 2009
10,045
Porting for 2 strokes is completely different than 4 strokes
Back in my day, both the exhaust and intakes ports in the cylinder were changed from a round hole to one that was more "D" shaped and some times also raised to change timing. Transfer chambers were polished to aid flow. Piston port engines were few and far between. Most were reed valve engines, and we used "stuffers" in the crankcase to raise the primary compression. This was on gokarts and mini bikes, most using either a McCullough or Power Products engine.
 

Wolframore

Joined Jan 21, 2019
2,609
Ah, I see what you’re getting at. The D ports would raise velocity. The cylinder ports are best as ovals or rounded squares, biggest concern being Ring life. Exhaust, combustion and transfer ports are polished. Intake ports are rippled. Exhaust ports are designed for velocity but transfer ports should slow the flow so less is lost. Transfer port angle and expansion chamber have large impact. Everything is checked with a degree wheel as the exhaust duration changes where the power band lies.

Window pistons have to be used with reeds.
 

Wolframore

Joined Jan 21, 2019
2,609
Were the D ports in the cylinder walls? If so with the curve on top? It is one way to increase duration and give the rings a gentle close. Too much duration and the power band shifts losing low end torque. I like Suzuki’s method of having an adjustable port which changes with RPM. Its an ingenious way to keep low end power while opening up at higher RPM. I believe it changed from 178-204 degrees.

Some Stihl saws have reed valves, they might be so small they’re easy to miss. I like the windowed pistons as it helps cool the engine, but if you don’t have a reed it will push fuel back to carb.
 

shortbus

Joined Sep 30, 2009
10,045
Were the D ports in the cylinder walls? If so with the curve on top? It is one way to increase duration and give the rings a gentle close. Too much duration and the power band shifts losing low end torque. I like Suzuki’s method of having an adjustable port which changes with RPM. Its an ingenious way to keep low end power while opening up at higher RPM. I believe it changed from 178-204 degrees.

Some Stihl saws have reed valves, they might be so small they’re easy to miss. I like the windowed pistons as it helps cool the engine, but if you don’t have a reed it will push fuel back to carb.
Yes in the cylinder wall, with the flat side toward the head. When I say flat ,they did have a radius in the corners. The rings were kept from rotating in even stock engines back then by a pin in the gap.

I have 3 Sthil saws left now from my fire wood cutting days, had 5 at one time. All of them use piston ports for the intake without reeds. As the piston goes up and down it covers and uncovers the intake port with the piston, so no reeds needed.
 

Wolframore

Joined Jan 21, 2019
2,609
Cool that’s a new one for me. The windows pull in from the carb and allow a better charge, the reed is used so the power stroke doesn’t push back through carb. The windows mean the intake stays open almost the full duration. I would love to see those engines.
 

Wolframore

Joined Jan 21, 2019
2,609
Stihl has some very cool design. Some get rid of transfer ports in the cylinders and add them to the pistons. You would need to stuff the heck out of the crankcase to run that top end.
 

shortbus

Joined Sep 30, 2009
10,045
Stihl has some very cool design. Some get rid of transfer ports in the cylinders and add them to the pistons. You would need to stuff the heck out of the crankcase to run that top end.
I don't know about that. Before I went to the Stihl's I had Mac's, Poulan's and Craftsman's(most made by Poulan). Besides not having the same amount of power they didn't make as high of RPMs as the Sthils. This was on saws with similar or the same CC's displacement. I always thought the Stihl name was pure "hype" advertising, but after using one that a friend had I was a believer.

They are much easier to start too. I was buying an new saw or two every year with the other ones but the Stihls just keep running.
 

Reloadron

Joined Jan 15, 2015
7,501

Reloadron

Joined Jan 15, 2015
7,501
I don't know unless it figured into acceleration? I was surprised at the numbers. When chatter first began on the Live Wire I also wondered about the range on a battery charge. My old '92 with a 5 gallon tank gets me about 200 miles. Tell you what, if I were looking to buy a new bike off the showroom floor today I would be hard pressed to decide which way to go. I would like to ride one.

I may be deciding something soon as yesterday's ride I had a noise starting again in 4th gear which does not sound good. I just changed the transmission oil a month ago and lately it makes noises in 4th gear which do not sound good. :)

Ron
 

Thread Starter

killivolt

Joined Jan 10, 2010
835
My Harley Dealer here in Orem have a training track for people who want to learn and get a Drivers License. I’ll bet they would let me ride one on the Track.

kv
 

Reloadron

Joined Jan 15, 2015
7,501
My Harley Dealer here in Orem have a training track for people who want to learn and get a Drivers License. I’ll bet they would let me ride one on the Track.

kv
My local dealership also has try it days. Not sure if they have a new Live Wire for us to check out up close and personal. My next HOG chapter meeting is Friday the 4th so if I remember I'll ask the dealership.

Ron
 

Wolframore

Joined Jan 21, 2019
2,609
Top speed of the new Chargers are 149 mph. The bike is traveling roughly 3 miles a minute or a mile in 20 seconds. It would be out of sight in no time.
 
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