262XP Day

[Sepia]

What if it was the other way around, they changed the porting and needed less carb?

most of the time changes are made for the betterment of emissions.

The porting changes came some time after the carb change, but still could be related to emissions. However, I would think that longer durations would result in more spit back through the carb, and more raw fuel exiting the exhaust port.

 

[David Young]

The porting changes came some time after the carb change, but still could be related to emissions. However, I would think that longer durations would result in more spit back through the carb, and more raw fuel exiting the exhaust port.

spit back happens when the base is full. so a smaller carb requires more time to deliver the same quantity.
Also remember the formula for figuring the area of a circle (venturi) is dependent on the square of the radius. The increase is not linear.

It is odd that the blowdown was shortened but may be due to a change in case compression. more often you will see a increase in blowdown but the muffler opening/ restriction plays a role as well.

 

[Sepia]

I will have to have a look inside the two mufflers to see if the hole in the baffle under the deflector changed in size. It could be that the newer saw has a more restrictive muffler.

I also have 1990 and a 1991 saws that will be coming apart at some point, and I am curious to see if the KS cylinders are different than the first Mahle cylinders.

 

[David Young]

Dr Al,
has some other photos from various 262's, maybe we can summon him.
@drf255

Im looking forward to seeing what you find out.

 

[El Moobs]

Who is this Mastermind guy and where did he go?

 

[Sepia]

I heard he loaded up the truck and moved to Tennessee

 

[El Moobs]

I heard he loaded up the truck and moved to Tennessee

Hrumph........flippin slacker.

 

[Sepia]

Maybe if you unlock the door to his shop, he can get back in and get back to work!

Just an idea...

 

[David Young]

Who is this Mastermind guy and where did he go?

You will know him if you see him. He looks like a potato with platinum fuzz all over and two legs that look like toothpicks.

 

[Sepia]

You will know him if you see him. He looks like a potato with platinum fuzz all over and two legs that look like toothpicks.

I'm thinking you two are either best friends or worst enemies lol

 

[MustangMike]

most of the time changes are made for the betterment of emissions.

Exactly what I was going to say.

 

[Sepia]

I checked the mufflers and they are identical. Maybe this Fall I can compare a stock 1990 with the 87 carb and KS cylinder, to the 1993 with the Mahle cylinder that has the large transfers, and to the 1998 with the Mahle cylinder and narrow transfers - all with the same bar/chain and see if there is any performance differences.

 

[El Moobs]

You will know him if you see him. He looks like a potato with platinum fuzz all over and two legs that look like toothpicks.

Mmmm platinum......

 

[drf255]

I thought I would resurrect this thread as there is a lot of good info in it, and also because I have a couple 262XP cylinders sitting on my desk. One is a non-decomp Mahle from a 1993 saw, and the other is a decomp Mahle from a 1998 saw, and there are notable differences in the two. The 1993 cylinder has much wider transfer tunnels than the 1998. The 1998 has noticeably taller/bigger upper transfer ports. Lowers are the same size on both. The intake port is shorter and wider on the 1998 cylinder, and is located lower in the cylinder, indicating more duration on the newer cylinder. The exhaust port is taller and is higher in the 1998 cylinder, indicating more duration there as well. The transfers on the 1998 are much higher, indicating a shorter blowdown compared to the 1993 cylinder.

Now the question here is; why were these changes made? !993 was the first year for the smaller venturi carb (HDA120 vs. HDA87). Did the Husqvarna engineers discover they needed more duration and shorter blowdown to get the same performance from the smaller HDA120 equipped saw as the previous HDA87 equipped saws?

Did you time the ports or are these just visual observations? It would be interesting to know the results.

I've only ported maybe 10 262. Moobs would know more.

As for the intake port, I'd say it's tough for it to be wider because the threaded holes for the carb mounts are in the same place. Easy to grind through for sure. I've measured the intake port and found that's there is no need to widen it at all, I just drop the floor a bit. There is already more area to the inner port opening than the outer port opening or the 87 Venturi. The floor always winds up around 73-74 after the machine work on every jug I've done. Stock, all have been 71, no gasket.

Exhaust port, I've never noticed a difference. The piston has skirts a mile long. I can't remember if the piston crown drops below the exhaust port at BDC right now. I'm pretty sure it doesn't, because one could lower the floor if it did and I never was tempted to do so.

Everyone says that the KS transfers are wider and bigger than the Mahle. I'm not so sure if it's actually true or not. The KS jugs I've been around (all model including Stihl) are a harder and brighter/less staining aluminum alloy. Many times it looks like the ports are bigger, but the brightness of the alloy created an illusion for me. They were the same. The KS just stain less.

The only 262 I've been around that has very wide external transfer tunnels was the Mahle Decomp that I used in the Christmas saw. It needed to be clearanced externally to miss the flywheel.

Wish I had more for you guys. Pretty sure I have a Mahle decomp and a KS here that I can take pics of.

 

[Sepia]

Here is a pic of the transfers. The 1993 cyl is on the left, the 1998 on the right. The flash makes it hard to see the difference in the tunnel widths, but the 1998 is about 1/8" narrower. You can also see the 1998 upper transfer ports are much larger than the 1993.


All my observations were made by measuring ports and port placement with calipers. Multiple measurements were made to ensure accuracy, then recorded. Intake and exhaust port measurements were taken at both the cyl wall, and the external faces. I also measured the cylinder depth at multiple locations on the 2 cylinders, with the variance between the 2 cylinders being .004" (2.796" vs. 2.800") The squish band-to-base measurement was consistent on both cylinders regardless of where measured.

Exhaust ports on both cylinders were within .010" in both height and width at the exit. The 1998 cylinder was .017" narrower and .021" taller at the cylinder wall.

The intake port on the 1998 was .018" narrower and .020" shorter at the inlet. It was .072" wider and .010" shorter at the cyl wall.

I am going to be away for close to 2 weeks but when I get back I will bolt these cylinders on and set the squish by shimming so they are both the same, then get some timing numbers. I am sure that will mean more to porting guys than my measurements.

 

[drf255]

Awesome work buddy.

I'm not some sure bigger tunnels make more power.

Very confusing

 

[drf255]

Here is a pic of the transfers. The 1993 cyl is on the left, the 1998 on the right. The flash makes it hard to see the difference in the tunnel widths, but the 1998 is about 1/8" narrower. You can also see the 1998 upper transfer ports are much larger than the 1993.
View attachment 587741

All my observations were made by measuring ports and port placement with calipers. Multiple measurements were made to ensure accuracy, then recorded. Intake and exhaust port measurements were taken at both the cyl wall, and the external faces. I also measured the cylinder depth at multiple locations on the 2 cylinders, with the variance between the 2 cylinders being .004" (2.796" vs. 2.800") The squish band-to-base measurement was consistent on both cylinders regardless of where measured.

Exhaust ports on both cylinders were within .010" in both height and width at the exit. The 1998 cylinder was .017" narrower and .021" taller at the cylinder wall.

The intake port on the 1998 was .018" narrower and .020" shorter at the inlet. It was .072" wider and .010" shorter at the cyl wall.

I am going to be away for close to 2 weeks but when I get back I will bolt these cylinders on and set the squish by shimming so they are both the same, then get some timing numbers. I am sure that will mean more to porting guys than my measurements.

Timing numbers would be interesting, thanks for taking the time.

One question, did you measure the lower transfer opening, the tunnel, or both?

 

[Sepia]

I did measure the lower transfer opening on both cylinders and they are identical. Another observation is when looking at the external casting of the two cylinders, the 1998 is .070" wider when measuring the overall width at the transfer bulges. Also, the transfer bulges extend higher on the cylinder on the 1998 version, which matches the taller upper transfers of that cylinder. So while the transfers are narrower on the 1998, they make a wider, larger radius loop to the exit at the uppers.

I think it would be fun to swap between these two cylinders on the same saw and measure the results on a dyno to see what the engineers accomplished with these changes. I bet there is a difference in the torque curve.

 

[drf255]

Highly cool stuff...

I'm diggin it.

 

[Paragon Builder]

I need to compare the 4 cylinders I have at home.


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