372 Pston swap/mod

[Yotaismygame]

Was running the XT carb which has a rather large venturi. Blow down could be it, personally I think its the piston characteristics. I think compression needs to be above 170 to make a 372 with a 268 piston strong. I never run short bars on my saws when i test them because the guys who buy them don't run short bars. Buried with a 28" bar in fresh fir wasnt some thing it liked. The Jred I posted I wouldn't say went through a true test. The two of these I've built with compression above 180 were both all around strong saws. That jred sure does scream more but I'd like to see how it does with a 28" in some harder wood. In another thread trappermike advised me not to raise the transfers on the lazy jug.

Just thinking out loud here. Thanks for the input.

 

[Leafy]

I think if you have a saw that you took the exhaust that much too high it needs a bigger carb than that, it'll need to rev to make any power at all.

 

[old guy]

FYI, I tried to put an oem ring in a hyway 353 piston & it would not compress enough to get the cyl. on.

 

[BoominSVX]

Rather than start a new thread, I want to ask some things in here as it seems there's a ton of knowledge gathered in this one place. Does anyone want to share their experience with port timing that produced a saw that cuts and bucks like it knows the job? I know, the 372 is already a beast, but my 2163 BB Jonsered put her to shame and I found unrealistic squish, so I was going in no matter what. I have my 268/670 Meteor piston. The windows have been de-burred, and the .040 popup machined. I did some checks on both pistons and came up with the following...

Original Piston with NO base gasket:

Squish: .058
Int: 72 - 144 duration
Exh: 101 - 158 duration
Trans: 129 - 102 duration
Case Comp: 57 duration
Blow Down: 28 duration

New Machined Piston with Base Gasket:

Squish: .025
Int: 82 - 164 duration
Exh: 104 - 152 duration
Trans: 130 - 100 duration
Case Comp: 52 duration
Blow Down: 26 duration

I've read this thread. Lots to digest and I get lost in the side stories and different builds. I'm trying to target a good runner with what I have. No port work has been done to the head yet, but that's next. There will be a muffler mod when my "beater muffler" gets here. I'll be case matching, lots of exhaust work, cleaning up the transfers, widening the ports (while leaving a minimum of 2mm around the skirt), Most likely blending the transfers toward intake as well.

There are lots of builds from more members than I can remember in the 128 threads I've bookmarked, but people seldom share their numbers. I may be interested in jumping up to the 395xp carb if the need comes up, but I believe the stock HD-12B should be enough to pump a lighter 50mm with some gumption. Sorry if this is coming off rude or typical, but I've never degree'd a saw let alone to this extent, and if it wasn't in pieces all over the bench, I'd probably not be asking. I've read and read until my wife started telling me to lay down the laptop and my eyes started wiggling. So much trial and error here that I just had to ask. I understand, every one is different, but there's a strong work horse out there somewhere, and I'm trying to find a good set of timing numbers without going back to school. If someone can point me in the right direction, I'd really appreciate it! Thanks, Mike.

 

[Leafy]

The bigger carb is going to make the most gains for the effort with the muffler mod. With the 272 piston for a work saw you'd be safe with like 98* exhaust and like 20ish deg of blow down. And whatever the intake ends up with that piston and a base gasket.

 

[Yotaismygame]

I don’t really understand what you’re jabbering about. Some your numbers are confusing. But what I did get is you have a 2163 with a 52mm big bore top end. Sounds like you took a 272 piston and made a pop up. I’ve never timed a 52mm big bore

Intake at 82 is great. You’ll be able to widen it just a hair or not...

I don’t know what leafy is talking about with a exhaust at 98 being safe. 98 for a work saw is up there. 101-102 is safe and produces good power with the 268 piston. I don’t know what to say about the transfers but I would guess 120 would be fine. Roughly giving you 20 BD. With the 268 by simply raising the exhaust to 101-102 and the intake at 83.5 will make for a snappy strong saw.

If this is what you meant you should start another thread since this one is for the 268 piston swap. Would rather leave this thread as that so people don’t come in here and find them selves reading about something else. I hate it when I’m searching for something and have to read 20 pages of fluff to find what I’m looking for.

 

[BoominSVX]

Aww jeeze, so sorry. I did make that confusing. The saw I'm doing now is a 372xp non-xtorq. I'm using the 268 50mm with machined pop up. Which numbers don't make sense? I'll double check.

Glad to see you guys are still here. I know what you mean about keeping info together, and after my internet-wide searches, I believe this thread was the best source for info as well as the best place to keep the stats and outcome. Ya'll have done a damn nice job with trial and error so far.

 

[wcorey]

Which numbers don't make sense? I'll double check.

Your numbers are ok but it's more about how you present them, not what most are used to seeing, like more info than needed so appears confusing.
Convention is more typically either just durations or openings plus maybe blowdown, closing numbers are rarely mentioned, sort of redundant.

Then there are various formats to the degree wheels, that then affect how the numbers are spelled out. Looks like yours is 360 degrees from tdc while I tend to prefer 180/180 where open and closing numbers come out the same.
Everything doesn't necessarily have to be read from atdc only, can be abdc or whatever.

 

[BoominSVX]

This is easier than typing it. Just re-did the wheel with no base gasket. .012 squish now, but I can do some work on the squish band to fix that. Didn't change it too much but I got a better measurement of the transfers.

Yotaismygame: I follow.
Intake went up to 84 with no BG. Not sure if better or worse. Not much to do there except smooth it out and widen in a manner that won't catch a skirt or ring.
Exhaust is still 103/104 for some reason. Maybe my first measurement was off as I've checked it. Port to 101/102 sounds decent.
Transfers: I'm 129. Giving me 25 blowdown as sits. Taking 2 degrees off exhaust would give me 27. I'd have to raise transfers 7 degrees to reach 20. I'm okay with this, but baby steps. Seems like a lot when everything else needed so little. Transfers are a PITA and I'll be swearing and sweating to pull that much in one shot..... but I like it. It seems I might be better off with the base gasket?? Really awesome to have your input!

Wcorey: You replied while I was typing, but you're right. That pic should fix the trouble. I edited the previous posts to avoid confusion. I like to be thorough. All 6 measurements check out, so now I know I didn't slip the wheel. Newbies...

 

[Yotaismygame]

I see now you read the number off the wheel. Cylinder does 180 degrees max. 100 120 80. Exhaust transfers intake. BD of 20.

This jred has a intake of 83-84 and exhaust at 101. Never touched or measured the transfers. I had been told to leave them alone. Did stretch them a bit. 101 is pretty snappy as you can see. 102 is best I think.

 

[Leafy]

You can probably keep the oem transfers alone but the China ones are pretty low.

 

[Terrence Jefferson]

Are you guys running a unlimited coul in these saws? If so what coil are you using? I'm trying to build a 372xp non x torq and I got a 371 black coil to use in it but I'm not sure it's unlimited. I would like the saw to be a strong fast runner I could use at some woodsman competitions this summer and I'm liking the 268 piston idea but I'm still learning all these porting tricks

 

[huskyboy]

Are you guys running a unlimited coul in these saws? If so what coil are you using? I'm trying to build a 372xp non x torq and I got a 371 black coil to use in it but I'm not sure it's unlimited. I would like the saw to be a strong fast runner I could use at some woodsman competitions this summer and I'm liking the 268 piston idea but I'm still learning all these porting tricks

Black = unlimited

 

[Terrence Jefferson]

On all Husqvarna coils? Thank you

 

[Leafy]

I use the Chinese coils. I thought I had a problem with a bunch of them but as far as I can tell it was all my fuel tank vent.

 

[Terrence Jefferson]

I thought I had the rite one and looks like I do.

 

[Ketchup]

@Yotaismygame
Did you ever pour epoxy to raise your intake? I was thinking the 385 carb may be making the problem worse. I ran mine last night with the filter off and it spits like a 660.

Maybe the 268 popup doesn’t benefit from the 385 carb (or RWJ) like a normal port job?

 

[Leafy]

It still should. A ported 70cc see should have like a 19-21mm venturi carb depending on how aggressive the porting is.

 

[Yotaismygame]

I haven’t yet. I actually found the RWJ carb is a terrible carb and I won’t ever run one again. Had one on a customers 372 with 268 piston and he was having strange running issues. Ended up being the carb. Also I could never get any of the 372s with that carb to four stroke. Been running a zama on my saw and I like it much better. Four strokes, runs consistent, easy to tune.

Here’s two saws I built, both pretty strong. Both have 268 pistons with 040 pop ups. Similar porting except I stretched the uppers a bit and the exhaust is at 101 on the jred. The husky has a exhaust at 102. Personally I think 102 is the best all around number for this piston.

 

[Yotaismygame]

Now that I’m thinking about it, it might be fun to leave the piston alone and cut 050 off the band and take 015 off the base. Should land squish around 018-020. Then epoxy the intake back up to 80 and take the exhaust to 100-101. Blow down 20 or less. See if I could get 200psi comp.