SHOVELHEAD
Super OPE Member
Drilled & tapped 8mm for clutch side, 5/16" for Degree wheel side.
CASE VOLUME DISPLACEMENT ? / Introduction
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SHOVELHEAD
Super OPE Member
YUP !
SHOVELHEAD
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Going under the knife in a couple of hours, so it will be sometime before the Build can proceed.
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Good luck pal
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Best of luck with the surgery!
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SHOVELHEAD
Super OPE Member
Just wanted to say thank you to you all.
Well I'm still on this side of the Dirt !
I'll be resting for a while now, Till I'm able to move around.
Hoping to have some time in the shop to resume the Builds & start fitment of P&Cs.
I have lots of Ideas! (Thanks Al) 066 piston ! (I have another 2156, maybe 36 stroke)
But still rethinking the carburetor Boot?
I do however want to keep the stock appearance & linkage.
SHOVELHEAD
Super OPE Member
Playing with some #s this morning.
1st is the Displacement of whats currently being Built 72.206 CCs
With & With Out Crank Stuffers.
2nd using 36mm Crank from a 2171 & 272xp Cylinder 76.453 CCs
This is a easy Build & looks like it could be a Hell of a Performer in a Mid weight saw.
Finally #3
$$$ The Money Pit $$$
Using the same 272xp Bored and plated to 54mm would come in @ 82.447CCs
1st is the Displacement of whats currently being Built 72.206 CCs
With & With Out Crank Stuffers.
2nd using 36mm Crank from a 2171 & 272xp Cylinder 76.453 CCs
This is a easy Build & looks like it could be a Hell of a Performer in a Mid weight saw.
Finally #3
$$$ The Money Pit $$$
Using the same 272xp Bored and plated to 54mm would come in @ 82.447CCs
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Terry Syd
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I love this kind of dirty talk. A 60cc engine taken out to 72cc is a 20% increase in displacement. My 365 BB only took the displacement out from 65cc to 77cc, for a 18% increase - heaps more power when everything is feeding it.
So a 60cc engine taken out to 76.5cc is a 27.5% increase. A 60cc engine taken out to 82.5cc is a 37.5% increase.
My best on boring and stroking was taking a 49cc engine out to 104cc, for a 112% increase in displacement. HOWEVER, you have to be able to feed the displacement. The head work (homemade valves, etc) to get that engine to breath was more work than the boring and stroking.
On two-strokes, the size of the transfers becomes the restriction. If you shift the bore out and neglect (let alone restrict) the transfer area, the power will suffer - been there, done that.
I'd go for the 82.5cc engine and work the transfers to feed it.
If you blow it up, consider it a sacrifice to the 'God of Speed'.
So a 60cc engine taken out to 76.5cc is a 27.5% increase. A 60cc engine taken out to 82.5cc is a 37.5% increase.
My best on boring and stroking was taking a 49cc engine out to 104cc, for a 112% increase in displacement. HOWEVER, you have to be able to feed the displacement. The head work (homemade valves, etc) to get that engine to breath was more work than the boring and stroking.
On two-strokes, the size of the transfers becomes the restriction. If you shift the bore out and neglect (let alone restrict) the transfer area, the power will suffer - been there, done that.
I'd go for the 82.5cc engine and work the transfers to feed it.
If you blow it up, consider it a sacrifice to the 'God of Speed'.
MustangMike
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For a lot of "big bores", smaller case volume also becomes problematic, resulting in high RPMs, but reduced torque. There is often more to it than just increasing displacement and the corresponding transfers.
This dilemma is common on the 440/460 big bores.
As for Lee's big bore, that saw is an animal, I have run it at GTGs. I also believe he said he did not do any port work to it, truly impressive! (Must be the 880 piston ... Ha, Ha, Ha).
This dilemma is common on the 440/460 big bores.
As for Lee's big bore, that saw is an animal, I have run it at GTGs. I also believe he said he did not do any port work to it, truly impressive! (Must be the 880 piston ... Ha, Ha, Ha).
Terry Syd
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Here's my two cents. The area inside the tunnels will have to be increased. The best way is to WIDEN the tunnels. The reason to widen the tunnels is you can widen the transfer port openings.
Widening the transfer openings is a proportional increase in time/area of the ports. If you widen the ports 10%, you increase the time/area by 10%. (you also do not decrease the INDUCTION STROKE, which occurs from transfer closing to TDC)
If you increase the displacement by 37%, then widening the ports by 37% will keep the time/area of the transfers in the ballpark. However, I'd go smaller to begin with.
Now there is gonna be a problem with high crankcase compression which will push the powerband up and narrow it. Perhaps an open sided piston (windowed) is available.
With the windowed piston you can eliminate much of the side cylinder wall which will increase the case volume. It will also make porting this beast easier.
To help with the porting, I recommend you drill a 1mm hole between all the fins in the port so you can monitor how close you are getting to breaking through. You can watch your progress, when you get about 1mm of wall thickness, then stop and patch up the holes with some GB Weld. You can use a bit of extra GB Weld to help strengthen the cylinder.
Widening the transfer openings is a proportional increase in time/area of the ports. If you widen the ports 10%, you increase the time/area by 10%. (you also do not decrease the INDUCTION STROKE, which occurs from transfer closing to TDC)
If you increase the displacement by 37%, then widening the ports by 37% will keep the time/area of the transfers in the ballpark. However, I'd go smaller to begin with.
Now there is gonna be a problem with high crankcase compression which will push the powerband up and narrow it. Perhaps an open sided piston (windowed) is available.
With the windowed piston you can eliminate much of the side cylinder wall which will increase the case volume. It will also make porting this beast easier.
To help with the porting, I recommend you drill a 1mm hole between all the fins in the port so you can monitor how close you are getting to breaking through. You can watch your progress, when you get about 1mm of wall thickness, then stop and patch up the holes with some GB Weld. You can use a bit of extra GB Weld to help strengthen the cylinder.
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