365 special / 372 big bore

[minermatt]

hey, new to the forum.

so i've read many of the threads on tuning and porting, now my brain is ready to explode. Here is the scoop....
just picked up two dozen 365 specials/372 for free. (i asked for one, got 24, good deal!) I'm more or less building/modifying as a project, and to prove to a guy that it can be done. What i have right now is a 365 special, with new husky crank, good seals, and a NWP 52mm big bore kit, and a modded muffler with the 288 deflector.
BB kit isn't installed yet, so im wondering what kind of port work i should do before i put her all together. I have a degree wheel, and 90% of the tools to port, a mill and a lathe. I'll open up the muffler ports to 85-90% of the exhaust ports when done, and maybe put a 385 carb on it. The saw will be used for cutting my firewood and felling. Not looking to build a competition saw, just a fun/ "I TOLD YOU SO" saw, and it would be really awesome if it would give my father in-laws 576xp a run for its money!

sorry for the 5000 word write-up, but thanks in advance.

Matt

 

[werewolf]

Last 365 I did before polishing

 

[minermatt]

And how does it run? Did you change port timing, or just open it up? I assembled one BB this weekend with just a little port cleaning, no base gasket and muffler mod. 18"bar with 8 pin sprocket. I goes like a bat outta hell! But I'm sure there is lots more potential.

 

[werewolf]

Just widened the intake and exhaust about 2mm and nice with nice round shape on the sides to keep the rings stress free. No timing changes, just gasket delete and muffler mod. Customers eyes popped out when he ran it, 18" bar ands it screams

 

[werewolf]

If I had many of my own I would push the envelope until a failure to get some guidelines

 

[minermatt]

How did you re-chamfer the port edges to get rid of the sharp edges?

 

[werewolf]

I have some diamond coated grindstones for my dremel, similar to chain Sharpening stones, that I use from the outside through the port, it's long enough to chamfer the edges pretty well, I follow up with emery cloth on my finger from the bore to really smooth it.

 

[minermatt]

Cool, that's what I have too. Gonna put another one together soon. I'll let you know if I find the max limit. Lol!

 

[werewolf]

Please do!

 

[Walter Glover]

Reviving thread
I am currently starting the bigbore for a 365 special. Ordered parts to repair a lean seized engine due to a torn carb boot. This saw belongs to my sil's friend and he gave the go ahead to bigbore it. Hoping to make a real hum dinger for him that will make him smile while milling lol

 

[trappermike]

When you do "the ol' trick" of removing the base gasket you gain a few psi of compression(maybe 20) but you also lower the exhaust and transfer ports by about .5mm,reducing their duration and hurting full power. It is an old myth I'd like to put to bed forever. Unless the motor already has less than desireable compression this mod will lower mid to high rpm power. If the motor has decent compression to start with I would rather raise the cylinder the thickness of the gasket and enjoy much better ex. and transfer duration which will give much more power than extra compression.

 

[Walter Glover]

Would love to see dyno numbers on various configurations
With the 372 kitsaw coming i will try a few. Hope to figure out a good popup piston source that will allow a base gasket and enhanced compression. Btw would you have numbers for the differences? For that engine?

 

[Walter Glover]

Would love to see dyno numbers on various configurations
With the 372 kitsaw coming i will try a few. Hope to figure out a good popup piston source that will allow a base gasket and enhanced compression. Btw would you have numbers for the differences? For that engine?

 

[trappermike]

Well dyno testing isn't easy or cheap. Best find out what is overall agreed numbers for the 2100 and try them, I Will however be releasing a piston swap for 372 that includes high comp.dome and much better flow characteristics and port duration,a huge boost.This combo makes real power.

 

[Walter Glover]

Looking forward to that Mike. Sounds like a good deal.

 

[werewolf]

hey, new to the forum.

so i've read many of the threads on tuning and porting, now my brain is ready to explode. Here is the scoop....
just picked up two dozen 365 specials/372 for free. (i asked for one, got 24, good deal!) I'm more or less building/modifying as a project, and to prove to a guy that it can be done. What i have right now is a 365 special, with new husky crank, good seals, and a NWP 52mm big bore kit, and a modded muffler with the 288 deflector.
BB kit isn't installed yet, so im wondering what kind of port work i should do before i put her all together. I have a degree wheel, and 90% of the tools to port, a mill and a lathe. I'll open up the muffler ports to 85-90% of the exhaust ports when done, and maybe put a 385 carb on it. The saw will be used for cutting my firewood and felling. Not looking to build a competition saw, just a fun/ "I TOLD YOU SO" saw, and it would be really awesome if it would give my father in-laws 576xp a run for its money!

sorry for the 5000 word write-up, but thanks in advance.

Matt

Ok there is limits but I would recommend checking squish with the gasket then cutting the cylinder base mounting flange enough to get your squish to .020, then only raise your ports the amount you cut from the cylinder, you can then use a sharpie through the intake and exhaust to mark the piston by rolling engine over and marking where the port edges are in relation to the piston edges, you can widen your ports but leave at least 3mm of port to cover piston edges or ring ends. You shouldn’t go more than 80% on your muffler or you will lose power, I have used up to a 1” tube in a muffler with great results, I just use different length tubes to “tune” where the power is, 2.5” long seems reliable enough with only 3/4” of tube outside, at a 45 degree to the cylinder face. Those saws love mods so anything you do will usually help, open up the transfers at the base and open the entrance a bit. I’m not a huge fan of advancing the timing on saws I max out compression on but there are guys that will have the numbers for you, a slight filing on the key edge, no more then 20%, will likely give a edge but you will have to run a decent octane fuel, 91 octane minimum and closer to 100 better.

 

[mixxer]

Well dyno testing isn't easy or cheap. Best find out what is overall agreed numbers for the 2100 and try them, I Will however be releasing a piston swap for 372 that includes high comp.dome and much better flow characteristics and port duration,a huge boost.This combo makes real power.

Do you offer a modded 268 50mm pop up for the 372??
VERY much interested in purchasing if you do

 

[Ronie]

Do you offer a modded 268 50mm pop up for the 372??
VERY much interested in purchasing if you do

Hyway sells one for the 372 in 50mm & 52mm, if you can't find someone to make you one.

 

[mixxer]

Hyway sells one for the 372 in 50mm & 52mm, if you can't find someone to make you one.

Thank you...
I have seen the 52mm one, but so far no luck on the 50mm...

 

[Ronie]

Thank you...
I have seen the 52mm one, but so far no luck on the 50mm...

I was wrong about the Hyway 50mm pop up it for the X torq.