Another Stihl 460 build

[Rich Fife]

After looking at builds and their detailed pictures/posts... I'm almost gunshy to post now. I'm hit and miss with pictures and details, and in my vids I tend to repeat myself or contradict myself...
Anyway, I'm building another 460... this one will be a little hotter than the last one... but, to the defense of the last one, that saw was built from 3 parts saws and they were whooped.
I didn't snap any pics of the case, crank, bearings etc... until I slapped it together.

 

[Rich Fife]

I'm using The Dukes 272xp piston for the finished product... I use an AM 460 piston that mic'd identical to an OEM 460 piston... and seeing how consistent the Dukes pistons are, I know that the difference of intake opening from one to other is approximately 4-5*... in this case, it was closer to 5*... the stihl piston yielded 70* of intake timing while the husky piston yielded 75* of Intake. That's without the base of the cylinder being machined. And it leaves it very close to freeporting... approximately .025" - .030". Which if it did freeport, I'm not too worried about it. I built a 660 with .187" of freeporting... and that sucker ran its nuts off @ 17,640rpm... anyway, an 064 piston would give you more play room with the longer skirts.

Dialing in the 272 piston

 

[Rich Fife]

Next up was the cylinder... and jamming out to CCR.

 

[Rich Fife]

Took .045" from the squish @ 7*. I used my shallow boring bar so I had to take light cuts, .010" - .015" per clip... anything more and tool contact is heavy due to limited relief.

 

[Rich Fife]

Did a basic layout in the cylinder, exhaust, x-fers... the intake sides will be blended as well as slight touch-ups in the lower x-fers.

 

[Rich Fife]

The exhaust will be widened a decent amount. I plan on starting with an exhaust of 102* and eventually work my number down until it's pushing the "limit"...

 

[Rich Fife]

It was 68* out and sunny so I slacked a little on the saw build... I played basketball against my youngest and enjoyed as much of the sun as I could... also ate some t-bones, baked mac-n-cheese and corn-on-the-cob. I'm ready for spring/summer!!!

 

[Rich Fife]

What's everyone's thoughts on a Chamfered squishband? (No, I didn't look to see if this was a topic already covered).
It's my opinion that the tapered squish acts to direct the charge/burn... very similar to what we do with our race motors (V8's). On our heads, just "outside" of the combustion chamber, where it's flat, we taper that area to direct the flow/burn. In doing so, it helps with efficiency as well as reducing hot spots that aid in pre-detonation... in theory, by adding a taper one could have more compression without some of the negative side effects.

 

[thedude74]

Squish Ratios and Angles, Combustion Chamber Volume and Shape

I just made a large rounded cutter to cut the majority of a toroidal chamber at once. That’s a big piece of hss, good idea though.

opeforum.com

This thread discusses tapered squishbands. There's probably dozens more....though I've never had particularly great results with the search function.

 

[Rich Fife]

Squish Ratios and Angles, Combustion Chamber Volume and Shape

I just made a large rounded cutter to cut the majority of a toroidal chamber at once. That’s a big piece of hss, good idea though.

opeforum.com

This thread discusses tapered squishbands. There's probably dozens more....though I've never had particularly great results with the search function.

Ok, I seriously have to start looking *s-word up before I ask. Thank You for that link!

Edit: what a Great fawking thread! I'm liking the discussion and debate of angles, surface %, theory, etc!!!

 

[Rich Fife]

This may not be the prettiest but, everything is roughed to 1* to 1-1/2* away from my goal numbers... just leaving room for clean-up and shaping. I already dislike a couple of things, the upper x-fers being one.

 

[Rich Fife]

Compression readings (cold and dry)
1st 212psi
2nd 215psi
3rd 217psi

Originally I wanted 195-205psi... as this will be a saw that won't be used daily... in retrospect I could've left it alone, ran a larger boot and carb and tweaked a couple things but, I have enough play saws that have 205+ compression...
Instead of chucking up the piston and removing approximately .010" (that would give me .028" on the squish I decided to play around and dimple the top of the piston... like a golf ball.
Current reading now resides at 192psi... (cold and dry). I guess I'll see what kind of chaos this creates... I still might cut the base, if so, I'll re-cut the squish and add equally spaced valley's. The Charge above the piston will be like Richard Prior running down the street on fire... ahahaha

I also advanced the timing 8*.

 

[huskihl]

Compression readings (cold and dry)
1st 212psi
2nd 215psi
3rd 217psi

Originally I wanted 195-205psi... as this will be a saw that won't be used daily... in retrospect I could've left it alone, ran a larger boot and carb and tweaked a couple things but, I have enough play saws that have 205+ compression...
Instead of chucking up the piston and removing approximately .010" (that would give me .028" on the squish I decided to play around and dimple the top of the piston... like a golf ball.
Current reading now resides at 192psi... (cold and dry). I guess I'll see what kind of chaos this creates... I still might cut the base, if so, I'll re-cut the squish and add equally spaced valley's. The Charge above the piston will be like Richard Prior running down the street on fire... ahahaha

Hope it hauls ass. That’s a lot of dicking around without running in between to test the changes.

 

[huskihl]

I always thought the dimples on golf balls were put there to grab onto the air. A golf ball with backspin goes a bunch further than one with top spin. Along with the slice and draw…

 

[Hundred Acre Wood]

I always thought the dimples on golf balls were put there to grab onto the air. A golf ball with backspin goes a bunch further than one with top spin. Along with the slice and draw…

Dimples do grab the air, but the net effect is to reduce drag on the backside of the ball. The trapped air reduces turbulence by creating a cushion of air allowing a more laminar flow over the ball.

Dimples on the front of the ball do almost nothing. On a piston? Probably worthless.

 

[cus_deluxe]

my first thought was all the sharp edges…but ive also never tried it so im glad rich is doin the research haha.

 

[huskihl]

my first thought was all the sharp edges…but ive also never tried it so im glad rich is doin the research haha.

True. I’ve never done it to a piston

 

[Rich Fife]

Hope it hauls ass.

Me too man.

That’s a lot of dicking around without running in between to test the changes.

Last year, I did a dimpled/golf ball piston in a 372xp... never thought about anything as I wanted to see how it would run... it ran good, but, being new to building/porting saws I honestly didn't know wth I was doing with the porting numbers.... .... I still don't-ish... .

I've built a few 460s with these same numbers or relatively very close numbers, plus or minusa degree here and there... so, id like to say that I have a relatively good idea of how the saw should run, and any noticeable difference I could in theory contribute it to the dimpled golf ball piston.

Than again, after reading the article about tapered squish etc... if what I am understanding the slightest change in surface could potentially change the results.

So, for what it's worth, I'll document the piss out of this saw with various tests. I'll swap a tapered piston without dimples... test and document. Then I'll do a smooth flat top, run it through its paces, document and then I'll do a dimpled flat top and repeat the process. I should be able to get some info... whether it's good, bad or indifferent... it doesn't matter to me. I'm a caveman, I learn better by trial and error.

 

[Rich Fife]

Dimples do grab the air, but the net effect is to reduce drag on the backside of the ball. The trapped air reduces turbulence by creating a cushion of air allowing a more laminar flow over the ball.

Dimples on the front of the ball do almost nothing. On a piston? Probably worthless.

I originally thought the same thing... then I went into the rabbit hole... I figured with the tapered squishband and piston it would speed the charge up and as the charge passes over the dimples it would create a cushion or help to keep the charge suspended. In doing so I want to say it'll help with a better burn...
I know I'm not thinking complete picture... but, I like to tinker with stuff. Even if I take 2 or 3 steps back in doing so.

 

[Rich Fife]

I did a stihl 400 with equal peaks and valley's cut in the tapered squishband... and I can say this... that saw has a much deeper, throaty sound and it feels like it has more grunt... the sound difference from one to the next was noticeably different... does it have more grunt??? Idk to be honest... maybe with a different sound I convinced myself it has more grunt ??? But, I do know the guys love that little 400. It was a new saw and I told the guy that I wanted to do a saw with a tapered grooved squish and he offered up his 400... man, I was fawking beyond nervous... as I didn't want to fawk up a dudes saw.

Has anybody tried doing the peaks and valley's in a tapered squishband?