Is compression king?

[A.E.E.llc]

Is high cranking compression an indicator that a saw will perform excellent in the woods?

In the case of 2 saws of identical model - Can the saw with significantly lower cranking compression (example 175 psi) perform better than the saw with high cranking compression (say 215 psi)?

Justify your answer.

Compression test have been done with timing not changed. No, compression is not king. Yes, less compression can out perform higher compression.

 

[RI Chevy]

Ahh. OK. I was equating high compression to automotive. High compression ratio in a car motor, 13:1, 14:1. You usually need high octane race fuel to get detonation. 105 to 110 octane fuel.

 

[jmssaws]

That's why a alcohol race car is 15 to 17:1 alcohol is 160 or so octane

 

[exSW]

Nope. Not king. Two 262 XP's,same compression,same squish ,same carb,same muffler,same builder(me),different jug. One runs good. But the other one runs better .

 

[Termitebuffet]

Nope. Not king. Two 262 XP's,same compression ,same carb,same muffler,same builder(me),different jug. One runs good. But the other one runs better .

Which ones sets closer to the 2186 .....[emoji200]

Zoo City Sawz

 

[Jon1212]

So how does my altitude effect my overall saw performance? My little 5105 that @Termitebuffet built for me is pushing 183psi at 4700', but my stock 395 only pushes 152psi.

 

[exSW]

Which ones sets closer to the 2186 .....[emoji200]

Zoo City Sawz

They flank it,one on each side. Luckiest redhead around.

 

[exSW]

So how does my altitude effect my overall saw performance? My little 5105 that @Termitebuffet built for me is pushing 183psi at 4700', but my stock 395 only pushes 152psi.

That's one I've wondered about. Do certain combinations perform better at altitude? Is there a design reason mile high Bill likes 262's so much?

 

[junkman]

So how does my altitude effect my overall saw performance? My little 5105 that @Termitebuffet built for me is pushing 183psi at 4700', but my stock 395 only pushes 152psi.

From what i was taught ,denser air closer to sea level will always make more power than up in the sky .

 

[jmssaws]

Here's the only 262 I've done.
Not high compression

 

[Termitebuffet]

So how does my altitude effect my overall saw performance? My little 5105 that @Termitebuffet built for me is pushing 183psi at 4700', but my stock 395 only pushes 152psi.

Ok 5105 -395 =4710 and your at 4700 ft ....coincidence. ..I think not ....[emoji200]

Zoo City Sawz

 

[drf256]

There's some parasitic loss at a certain point. So at that point, the increase in power will be negated by the extra work needed to compress the charge. The extra heat will start to cause other issues, like less charge density, etc...

I used to like very high comp, but I'm learning.

Also depends on intended usage. A saw with more comp won't feel as "free" and rev happy as one with less. But the higher comp saw will have more low end grunt, all things being equal.

 

[Red97]

That's one I've wondered about. Do certain combinations perform better at altitude? Is there a design reason mile high Bill likes 262's so much?

Exactly.

Take both scenario saws from sea level to 8,000 ft then which one is better?

If 215 is the slower saw at sea level, will it still be slower in thin air? Don't know the exact equation, but guess it wold be in the 170-80 range at elevation.

 

[mdavlee]

You lose performance with thinner air. I don't know if it's the same loss as the compression shows per 1k feet. I do know guys that live at higher elevations I do try to give them higher compression than I would for me at a lower elevation.

 

[exSW]

From what i was taught ,denser air closer to sea level will always make more power than up in the sky .

Dense,cool,dry air.

 

[Red97]

Here's the only 262 I've done.
Not high compression

Hooray Sally saw

I hear ya made a pretty nice 346 too..

 

[Termitebuffet]

Moderate compression on this one

Zoo City Sawz

 

[Termitebuffet]

Dense,cool,dry air.

How about hot humid sticky air ?

Zoo City Sawz

 

[RI Chevy]

That 262 was nice Jason. Not very angry, but very smooth

 

[Termitebuffet]

There's some parasitic loss at a certain point. So at that point, the increase in power will be negated by the extra work needed to compress the charge. The extra heat will start to cause other issues, like less charge density, etc...

I used to like very high comp, but I'm learning.

Also depends on intended usage. A saw with more comp won't feel as "free" and rev happy as one with less. But the higher comp saw will have more low end grunt, all things being equal.

I agree here , but I want to believe little Sawz like the compression. ..[emoji2]

Zoo City Sawz