Q's on gearing, especially 9&10t, on modded worksaw 660's

[Cerberus]

tl;dr -- Going-up to 8t sprockets worked, but I found the chain-tensioner's range was significantly limited when using my 25" Roll-o bar (but not so bad on the other unit w/ the 32" Oregon) so I'm kinda worried about getting the (9/10)tooth unit only to find it doesn't work/fit!! I should be clear that, if the sole thing one needs to do is grind/carve the rear of the bar itself, to make it fit, I'm plenty OK with that

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Is there any "most-common" worksaw gearing for 660's? Or "ported/built 660's"? I found the 8-pin to work better on both of my units:
#1: 99cc big bore, built for torque, 25" setup and:
#2: 91cc pop-up 32" built for chainspeed,
my 'felling & bucking' units, respectively....both benefitted, w/o doubt, from going-up to the 8pin....I lost the other 8-pin I'd ordered so right now only the 25" big bore has an 8T and I'm about to order, at minimimum, 1 more 8T...but I cannot stop thinking that 9t, maybe even 10t, would be better -- and I'm happy to experiment myself but hate relying-upon that as 'final word' -- so am just gonna be honest that I'm not even sure, if I'm holding an 8t & 9t sprocket, am not even sure which of my 2 units would be 'more appropriate' (for instance, sure, 'bucking saw' is built for higher speed, but is pushing 50% more DL's....and sure, 'felling saw' is built for torque, but on both units I can't help thinking "They're similar-enough output, similar-enough dimensions&orientation of the total units, they're likely to be optimized at the same tooth-count" because, sure, finer gearing would see them wanting different optimums but when the options are simply 7t, 8t and 9t then I'm betting there is a 'best', so am here hoping for insight )

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Thanks a ton for any insight, don't wanna order more random parts I won't use (like a 10t sprocket if it's dumb ) so yeah please be gentle I promise I thought a lot about this before posting, read about it, even keep trying to think of gearing relative-to bikes & vehicles, and -for my saws- keep coming to conclusion that it's likely a specific tooth-count is gonna be the optimum for both of my worksaws despite "different build intents"!

 

[srcarr52]

You can usually get away running a 9T on a standard bar by grinding the tail a little so you can roll the chain on. They become easy to throw a chain because the chain is out of the bar groove at the tail. Some bars with a wider bar pad area work better.

With a 10T it's best to cut down a longer bar mill/drill new bar slot, oiler and adjuster holes in so you can have a wider bar pad area to avoid throwing chains.

With a 10T most people are on a 20" chain or shorter as it's probably going to be for a 10"x10" cant.

 

[Thumper88]

I run an 8 tooth on my 064. Its a tree monkey saw and is pretty hot. Ported, 3 port muff, thinned carb shafts, etc. Almost a 10hp saw. I have a video of it running a 9 tooth 36" in 30" of oak. Itll do it but you cant be heavy handed. I much prefer an 8 tooth with an aggressive full chisel chain in our local hardwoods. A 10 tooth is to much for a work saw in my Opinion, your gonna rob the saw of torque and struggle to keep the rpm with any bar length over 20" in hardwoods, or maybe even soft.

This is the saw I own, but its not my video. 9 pin with a 36" bar.

 

[Homemade]

can you add a driver or two to the chain when going that big on a drive sprocket


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[Dolkitafreak]

can you add a driver or two to the chain when going that big on a drive sprocket


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You can, but that doesn't fix the problem of throwing chains because the bar tail is just too narrow so drivers are out of the groove.

 

[srcarr52]

Here is a custom bar I made for a 10t sprocket vs a standard bar with a 10t.

I’ve tried to run a 10t on the bottom bar, it will make the down cut and throw the chain when the cookie comes loose.

 

[Homemade]

You can, but that doesn't fix the problem of throwing chains because the bar tail is just too narrow so drivers are out of the groove.

Makes sense. 10t is two more then I ever ran so I’m outta my league. I though it was just an issue of running out of tension adjuster.


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