CASE VOLUME DISPLACEMENT ? / Introduction

[XP_Slinger]

View attachment 114375
6.75 hours later......

Can I come hang with you? I’m jealous!

Is that a 181/281/288 with a 920 laying behind it front and almost center????

 

[SHOVELHEAD]

Loading up

 

[SHOVELHEAD]

Some more Pics.

 

[XP_Slinger]

View attachment 114381 View attachment 114382 Some more Pics.

Nice Haul!!! Heaven.........

 

[SHOVELHEAD]

 

[SHOVELHEAD]

I think I have CAD

 

[drf256]

Great work!

 

[Deets066]

Hory chit!

 

[drf256]

Any Donations ??

If you want AM 066 slugs for mock-up, I can help ya out.

 

[SHOVELHEAD]

If you want AM 066 slugs for mock-up, I can help ya out.

I need to get though these 2 BUILDS 1st
If You want to donate one however,
I do have a clapped out Cylinder that @srcarr52 Donated.

 

[SHOVELHEAD]

So after CC,ing the three different case volumes.
Can anyone tell me what the different performance benefits will be, using the same 272xp 52mm cylinder on the
2156 @ 75cc Volume
VS
2159 @ 97cc Volume

That's a 22cc difference.
& the 272xp @ 110.4cc

All using the same 34mm stroke with 52mm bore.

This build is slightly over Square.

 

[Red97]

So after CC,ing the three different case volumes.
Can anyone tell me what the different performance benefits will be, using the same 272xp 52mm cylinder on the
2156 @ 75cc Volume
VS
2159 @ 97cc Volume

That's a 22cc difference.
& the 272xp @ 110.4cc

All using the same 34mm stroke with 52mm bore.

This build is slightly over Square.

2156 ought to be really snappy, may get a bit peaky compared to the 2159.

Little one may be a spitter out of both ends if it gets plenty of fuel...

 

[mgr1]

Less case capacity, hp at higher rpm.
More case capacity, more torque on al rpm's. Just a guess....

 

[SHOVELHEAD]

Less case capacity, hp at higher rpm.
More case capacity, more torque on al rpm's. Just a guess....

While I'm Building one of each,
I would like to run 24" bars and Build for torque if possible.

 

[Red97]

While I'm Building one of each,
I would like to run 24" bars and Build for torque if possible.

Imo

Exhaust down, transfers up.

Turn all the case pressure into "flow"

Will mellow things right out.

My echo hybrid had a ton of pull with abnormal numbers. But it also has almost 4mm more stroke than you are working with.

 

[SHOVELHEAD]

Imo

Exhaust down, transfers up.

Turn all the case pressure into "flow"

Will mellow things right out.

My echo hybrid had a ton of pull with abnormal numbers. But it also has almost 4mm more stroke than you are working with.

While I'm not a saw guru, can you explain this in more depth?
Thanks

 

[Red97]

While I'm not a saw guru, can you explain this in more depth?
Thanks

https://www.google.com/url?sa=t&sou...FjAAegQIBhAB&usg=AOvVaw2rYimfamsi4kiSxZX-6yip

Even with all the banter/derails. This has a lot of pertinent info for your project.

If you raise the transfers it will start flowing sooner. Not letting the case build the full pressure before the exhaust opens.

You can open the transfers sooner and still have the same "pressure" as the larger cased saw.

The lower exhaust allows a longer power stroke.

With the extra pressure in the transfers they should force more out the exhaust with less blow down than a "normal" saw.

 

[Lightning Performance]

While I'm Building one of each,
I would like to run 24" bars and Build for torque if possible.

Middle of the road. Medium case imo. He said a target build or 24" bar assuming 3/8 full comp 8pin for bucking. Correct?
32"+ 7pin for milling, large case, low rpm, high volume.

 

[drf256]

I personally think different rules apply here. You’re building a one off, so the numbers that work best may suprise everyone and defy common theory.

I’d say lower exhaust roof as well, but you’re gonna have a harder time filling that swept volume column with the smaller case. I’d say 102-103 range.

On the transfers, I’d keep them lower personally. I’d go 122-124ish. You’re gonna have the same volume change between TDC and BDC as on a stock 272 case, but it’s occurring in a case that’s smaller, so you’ll generate more pressure. In general, when you make a case smaller and you get more pressure, the transfers can overscavenge if they are set too high in the bore. If you read Blair, he talks about this concept happening in the 70’s in motorcycle engines. The OEM’s figured out that as they made cases smaller they had to physically lower the transfers. In general, you want them to open after the exhaust pressure drops (so there’s no backflow) and early enough to fill The entire swept volume.

Intake is anyone’s guess, but I’d guess the old reliable 78-80.

 

[SHOVELHEAD]

I personally think different rules apply here. You’re building a one off, so the numbers that work best may suprise everyone and defy common theory.

I’d say lower exhaust roof as well, but you’re gonna have a harder time filling that swept volume column with the smaller case. I’d say 102-103 range.

On the transfers, I’d keep them lower personally. I’d go 122-124ish. You’re gonna have the same volume change between TDC and BDC as on a stock 272 case, but it’s occurring in a case that’s smaller, so you’ll generate more pressure. In general, when you make a case smaller and you get more pressure, the transfers can overscavenge if they are set too high in the bore. If you read Blair, he talks about this concept happening in the 70’s in motorcycle engines. The OEM’s figured out that as they made cases smaller they had to physically lower the transfers. In general, you want them to open after the exhaust pressure drops (so there’s no backflow) and early enough to fill The entire swept volume.

Intake is anyone’s guess, but I’d guess the old reliable 78-80.

I'll be taking a 272 cyilynder that @srcarr52 donated to the Build & Milling a window so I can see where the OEM degrees to, & procead from there.