262xp R&D

[jmssaws]

A friend of mine once told me that I was the reason 340s were so rare these days.

I campaigned one in a 69 Dart for several years.

Then I discovered the Fox body Mustang.......and stuffed it full of SBC. lol

A friend of mine is why darts are hard to find. He's wrecked most of them.

 

[Chainsaw Jim]

Take a looks at the tunnels in the decomp vs. non decomp jug Dan.

Also, if the uppers are equal on both sides with a ring.

Most of the 262's I've seen do NOT have equal upper timing. Very odd. I wonder why they did that and I doubt it's a mistake. IIRC, the flywheel side has the indent on it and I believe that they set that transfer higher because it flowed slightly less.

Jug design is simply excellent for performance. The lowers are right up against the piston skirts. Huge tunnels compared to an 036 Stihl.

The intake tract sucks balls though. Even with the 87 carb, it ain't enough to feed this beast. We need to find another way. @Chainsaw Jim, any ideas on this?

At least for me, the 262 doesn't want to Rev. the fastest I've done so far was happy at 13,800 to be safe. A comparable Stihl 036 will piss rev 4 stroking 1000 rpm higher. I blame the intake tract fo this, I believe it's the limiting step.

I'm comparing a 262 decomp jug side by side to an 036 decomp jug and they share the exact same port locations. I'm not sure where the intake timing is exactly with the piston skirt difference. The 262 jug has perfectly even transfers with no stagger. Two differences immediately stand out which have been mentioned about the extra upper transfer teacup handle bulge, and the tiny intake.
I'm seeing a few possibilities with this... I would use an 036 piston and raise the intake roof up to the bottom of the skirt at tdc. The intake size on the 262 is larger on the outside but smaller inside than the 036.
I still need to peek at the pins to see if there is a conflict there. I'm thinking the 262 might be 12mm? There's other pistons like the 48mm 266 that might be a candidate.
Basically I'm thinking you gotta get rid of that center pin ring piston to fix the intake.

 

[paragonbuilder]

I'm comparing a 262 decomp jug side by side to an 036 decomp jug and they share the exact same port locations. I'm not sure where the intake timing is exactly with the piston skirt difference. The 262 jug has perfectly even transfers with no stagger. Two differences immediately stand out which have been mentioned about the extra upper transfer teacup handle bulge, and the tiny intake.
I'm seeing a few possibilities with this... I would use an 036 piston and raise the intake roof up to the bottom of the skirt at tdc. The intake size on the 262 is larger on the outside but smaller inside than the 036.
I still need to peek at the pins to see if there is a conflict there. I'm thinking the 262 might be 12mm? There's other pistons like the 48mm 266 that might be a candidate.
Basically I'm thinking you gotta get rid of that center pin ring piston to fix the intake.

It's 12mm Jim. I just checked.
Glad you are joining in on this!

 

[jmssaws]

I was going to use a 262 piston in the 034 yesterday but didn't come up with a good way to get around the pin size.

 

[drf256]

Center pin is good Jim. It stays well above the intake roof.

Edit. See what u were thinking .

 

[Mastermind]

Someone get a crayon and draw me a picture.

 

[jmssaws]

Someone get a crayon and draw me a picture.

I just ate all of them

 

[drf256]

Should be porting a 262 jug later today. I'll snap some pics of the jug and especially the piston in both ports at TDC and BDC.

Most of the 262 jugs I've played with have had assymettric uppers when marking for cutting with a ring. Maybe some are equal, but I can confirm on the Christmas 262, one side was 2-3* higher than the other.

I see where @Chainsaw Jim is going with his idea. Besides the pin diameter dilemma, I'm not sure raising the intake roof would do that much. This saw has a very tight small case for sure. With too much area, I'm worried charge inertia would slow down and more spitback might occur. Plus, after widening the intake, I'm already bigger in area than the square inlet to the port.

Does anyone know if an 038 is a 10mm or 12mm wrist pin?

 

[jmssaws]

I've only ported one but liked it.

 

[Chainsaw Jim]

Should be porting a 262 jug later today. I'll snap some pics of the jug and especially the piston in both ports at TDC and BDC.

Most of the 262 jugs I've played with have had assymettric uppers when marking for cutting with a ring. Maybe some are equal, but I can confirm on the Christmas 262, one side was 2-3* higher than the other.

I see where @Chainsaw Jim is going with his idea. Besides the pin diameter dilemma, I'm not sure raising the intake roof would do that much. This saw has a very tight small case for sure. With too much area, I'm worried charge inertia would slow down and more spitback might occur. Plus, after widening the intake, I'm already bigger in area than the square inlet to the port.

Does anyone know if an 038 is a 10mm or 12mm wrist pin?

The uppers on my decomp style 262 jug are as equal in height as two can get.
Raising the intake roof can only help here and it won't have any affect on the volume. How can the tiniest amount of volume be that important while another debate exists over whether the 357/359 runs better with or without crank stuffer cups?

I'm pretty sure the 038 is 12mm.

 

[drf256]

You were correct about the intake roof Jim.

I did the best to measure, but there appears to be at least .150 of space between the lower ring edge and the intake roof at BDC. At TDC, the skirt is way above it. So raising the roof should add area without affecting timing.

I didn't raise my roof. Not my saw I'm working on right now and didn't want to experiment on someone else's. Interested in your results Jim. Maybe a before and after with all things being the same except for the roof?

Another note on this model. Be careful widening the intake port too much and getting into the intake block threads. It's quite easy to do.

Edit:

Just double checked with a meteor piston. Although there is a bunch of room above the roof to the lower ring edge, there's only around .060 to the skirt bottom with the piston at TDC. So there's still potential for an area increase. Just not as much as I thought.

 

[drf256]

Here's the piston at BDC in the exhaust port and lines of the intake floor and roof at BDC. Lines best I could do, not much room to fit marker in there.

I cut .022 off this base and .025 out of the chamber on this mint KS non decomp jug.

 

[drf256]

The fat upper line is the correct roof location.

BTW, the stock piston is .006 longer in length from crown to skirt than a meteor.

Don't have time right now to measure which way that is. My builder case has the OEM piston on it. My last build came in .003 looser in squish with the meteor vs. how it measured on my OEM builder piston.

 

[stihl_head1982]

I've only ported one but liked it.

another pull from the dark side. The more I hear about the 262 the more I'm feeling the pull from the dark side.

 

[paragonbuilder]

You were correct about the intake roof Jim.

I did the best to measure, but there appears to be at least .150 of space between the lower ring edge and the intake roof at BDC. At TDC, the skirt is way above it. So raising the roof should add area without affecting timing.

I didn't raise my roof. Not my saw I'm working on right now and didn't want to experiment on someone else's. Interested in your results Jim. Maybe a before and after with all things being the same except for the roof?

Another note on this model. Be careful widening the intake port too much and getting into the intake block threads. It's quite easy to do.

Edit:

Just double checked with a meteor piston. Although there is a bunch of room above the roof to the lower ring edge, there's only around .060 to the skirt bottom with the piston at TDC. So there's still potential for an area increase. Just not as much as I thought.

Just thinking out loud here. Would it be worth trimming the skirt on the intake side to maximize the top of port to the ring edge, since we have been adding intake timing anyways? Or is it just shifting opening? I can't get a clear pic in my head, and in not near any saws at the moment.

 

[drf256]

Thought about that. Just shifting it Dan.

Plus there is flow geometry to consider. Opens at the bottom and flows downward.

Not sure bud.

I prefer porting that can just accept a stock piston if the need ever arises.

 

[jmssaws]

I like to think about the intake closing so case compression can build.

I'm not sure what raising the roof will gain other than making it impossible to lower the cylinder anymore.

I'm interested in the results for certain.

 

[David Young]

I like to think about the intake closing so case compression can build.

I'm not sure what raising the roof will gain other than making it impossible to lower the cylinder anymore.

I'm interested in the results for certain.

I guess im not following on the not able to lower the cylinder any more comment?

 

[paragonbuilder]

I guess im not following on the not able to lower the cylinder any more comment?

If you raise the roof till just before the ring shows you wouldn't be able to drop the jug anymore. Not sure why you would want to drop it again though?

 

[David Young]

If you raise the roof till just before the ring shows you wouldn't be able to drop the jug anymore. Not sure why you would want to drop it again though?

But if you drop it more the ring moves up more. you couldn't raise the jug back up.