Chainsaw Porting Theory

[wigglesworth]

I must interject.....

How can cutting the base decrease case volume?

The piston will still be traveling the same height, so where is the decease?

Teach me.

You talking volume or piston displacement?

The volume will decrease minutely. The lower trans are always part of case volume, as they are always open to the case. By cutting the base, you lower the uppers, which are tied to the lowers, which are open to the case, therefore, you have decreased the total volume of the case.

Now if u raise the trans, it's all a wash. Which I usually do anyhow....

 

[paragonbuilder]

That's what I was getting at, sorry if I wasn't too clear. Makes me think back to school where we were taught that things want to go from areas of lower volume to higher volume. Or higher pressure to lower pressure. So in order to overcome a having a lower combustion area volume we would need to have higher pressure in the crankcase. I could be completely talking out of my butt here but it makes sense in my head.

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This is true except that the higher pressure in the combustion chamber doesn't happen until transfers and exhaust are closed. So its not overcoming higher pressures. I think.


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[tree monkey]

Right. If U raise the trans back up, the tiny bit you lost on volume is gained back.

soooo, what story are you going to read us at 11.00? how long is nap time?

I gotta go potty

 

[wigglesworth]

soooo, what story are you going to read us at 11.00? how long is nap time?

I gotta go potty

I got some jack and Jill jokes. Maybe an old mother Hubbard or two.

Just use your britches like u always do...

 

[idiotwithasaw]

This is true except that the higher pressure in the combustion chamber doesn't happen until transfers and exhaust are closed. Do its not overcoming higher pressures. I think.


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Yeah you are right, but the total volume is less. How this affects things I don't know.

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[jmssaws]

I had a accident,need fresh underwear and pants. I'm also a glue eater

 

[tree monkey]

it's after 11 here and still no story. wtf

 

[jmssaws]

11.11 here,so sleepy.

 

[tree monkey]

teach is gone, spit balls are flying, my pants are soiled, and no story

 

[Stihlbro]

My abdullah obligato is hurting, I need to go see the nurse. @tree monkey , can I borrow your blanket?

 

[huskihl]

The whole "cutting the base vs case compression" thing....look at like this. Like MM said about bottom fed vs side fed transfers. If when you cut the base, you're removing area that normally has fuel flowing through it, you decrease case volume. If all you cut was aluminum, nothing changed. Makes sense to me like that

 

[tree monkey]

pics of the nurse

 

[jmssaws]

pics of the nurse

She has a mustache but still pretty hot.

So transfers in the 120s is what I'm going for?

288 piston keeps them low correct?

 

[czar800]

I just wish we had this kind of class when I was in school.....

 

[tree monkey]

I would start at about 115 dur

 

[XP_Slinger]

Thinking on a few things so here goes...

Displacement isnt gained or lost in decreasing or increasing crank case volume. Displacement is found by multiplying Bore (squared) x Stroke x .7854. So unless you change the bore diameter or change the stroke of the crank the displacement will remain constant.

I agree that the decrease in crank volume associated with a gasket delete or cutting the base would be present but negligible. I believe this would however increase crank case pressure to the same largely undetectable level without the right equipment to test it. And as mentioned, any volume lost could easily be recovered by raising the transfers back up or even opening up the lower transfers in my mind.

Hard to catch up to you guys after 3 hours! Good thread!

 

[wigglesworth]

teach is gone, spit balls are flying, my pants are soiled, and no story

Here's a story...



If that ain't our government in a nutshell, I dunno what is...

 

[tree monkey]

is she hot if I put a bag over her head? maybe one on my head incase hers falls off?

 

[jmssaws]

is she hot if I put a bag over her head? maybe one on my head incase hers falls off?

Thanks for the transfer numbers and always use 2 bags

 

[tree monkey]

I would cut .040 from the squish band, set squish to .020 and run it with no port work to set a base line. go from there.

I don't think you can get the transfers down to 115 on a 066. but I think that's about where they will need to be.