The SCARR Husqvarna 592XP build thread.

[Catman]

We can go even further into the math rabbit hole.

I measured the OD of the chamber at 1.550" (39.37mm). Calculating the volume of a cylinder that size and the depth of what we remove from the squishband would be the amount of volume removed from the chamber.

v = pi (d/2)^2

So if we removed 0.050" (1.27mm) from the squish we'd reduce the chamber 1.55cc. Which with stock exhaust timing, squish at 0.020" would be a theoretical compression of 168psi.

I plan on running about 161 degrees of exhaust duration (exhaust height of 1.015") with 0.05" out of the squish the compression would be 163psi. Then with no grinding on the intake the duration will be 158.5 degrees.

View attachment 317481

Ok, so I only know Basic Math, IM OUT!LOL

 

[Maintenance Chief]

Yeah , I was so bad at math in college I had to take theoretical math!

 

[MG2186]

Dam engineers and their fancy number equations! Way over this mechanics head

 

[Duane(Pa)]

My dad was an engineer. I must have been such a disappointment to him...

 

[pbillyi69]

My dad was an engineer. I must have been such a disappointment to him...

my dad was an engineer too. he didnt have the degree from a school but he worked at the bonnivelle power administration he tested power sub stations and worked in the R&D lab at the end of his career. he was an electrical engineer without the school paper. he was really smart and so am i but i never did any good with my smarts so im a blue collar worker and use my body for work and talk *s-word to the ones that do the smart people jobs.... lol

 

[Funky sawman]

Dang..... All those numbers now my head hurts. Time for some advil

 

[pbillyi69]

i know exactly what you mean. im pretty sure i could do a decent job of porting a saw if i had all of the necessary tools but holy crap that was a lot of math that i just dont remember or know at all

 

[Hinerman]

My dad was an engineer. I must have been such a disappointment to him...

my dad was an engineer too. he didnt have the degree from a school but he worked at the bonnivelle power administration he tested power sub stations and worked in the R&D lab at the end of his career. he was an electrical engineer without the school paper. he was really smart and so am i but i never did any good with my smarts so im a blue collar worker and use my body for work and talk *s-word to the ones that do the smart people jobs.... lol

Dang..... All those numbers now my head hurts. Time for some advil

i know exactly what you mean. im pretty sure i could do a decent job of porting a saw if i had all of the necessary tools but holy crap that was a lot of math that i just dont remember or know at all

That is why they make pressure gauges for us less educated folk...

 

[Duane(Pa)]

That is why they make pressure gauges for us less educated folk...

Quite a bit different, but we used to spend time on long flights figuring out "how much closer to home" we were every time that propeller makes a revolution

 

[Redfin]

View attachment 317481

Only one right answer. Eager to run one of these Shaun.

 

[huskyboy]

That is why they make pressure gauges for us less educated folk...

I’ll be curious what the real reading will be with the proper gauge.

 

[Redfin]

No gauge will be more accurate than the math Shaun showed.

I do not recall the difference between his math and the first comp he took with gauge but after machine work Id hazard it will show the same % of difference.

 

[Hinerman]

No gauge will be more accurate than the math Shaun showed.

I do not recall the difference between his math and the first comp he took with gauge but after machine work Id hazard it will show the same % of difference.

^^^^This, the math doesn't lie if the values are entered correctly. The math is used to make sure the gauges are accurate.

 

[pbillyi69]

ok i have a question now. when you cut the squish band and make it bigger, does the compression go up because you made the chamber smaller or because you made the band bigger?

 

[TreeLife]

ok i have a question now. when you cut the squish band and make it bigger, does the compression go up because you made the chamber smaller or because you made the band bigger?

When the squish band is cut, the hemispherical combustion chamber loses volume, increasing compression.

 

[pbillyi69]

thank you thats what i figured was happening but i have a way of overthinking stuff sometimes

 

[TreeLife]

You aren't overthinking, you're right on the money.

 

[Dieselshawn]

I love compression. Compression means power.

 

[TreeLife]

I love compression. Compression means power.

To an extent, when it comes to a 2 cycle engine. At some point, and it's a point that one would consider low, it starts to be counterproductive. The characteristics of these engines require a...freeness for a lack of a better term. Beyond 220psi for engines greater than 50ccs and *some* designs start to be less powerful or create excess heat. Beyond 70ccs I prefer to see them at 200 or less. Especially taking into consideration the starter design etc...now I'm rambling nonsense. Sorry guys.

 

[Funky sawman]

To an extent, when it comes to a 2 cycle engine. At some point, and it's a point that one would consider low, it starts to be counterproductive. The characteristics of these engines require a...freeness for a lack of a better term. Beyond 220psi for engines greater than 50ccs and *some* designs start to be less powerful or create excess heat. Beyond 70ccs I prefer to see them at 200 or less. Especially taking into consideration the starter design etc...now I'm rambling nonsense. Sorry guys.

I ran a buddy's stock like new jonsereds 90 that was 205# of compression. Torque monster for a stocker