Husqvarna 372 Port and Pop up help ?

[simonUK]

Hi guys Iam pretty sure you guys can help me on this

I am pondering the idea of building my first modded saw. The saw of choice I have picked is a 372/371.

The general conception from porting I have got from reading threads is that.

Widen the exhaust/muffler port leaving 1.5mm each side of the skirts.

Do the same on the intake side (or nothing ? )

Clean up transfers but dont lower them ?

Window the piston

Also for a pop up when machining the Piston how do i determine the squish band do like the outside diameter of the piston that needs machined off.

The pop up in a 372 would be .25 thou off top piston leave at least .100 above top ring machine equal amount off cylinder .

If you guys could help that would be great
I dont know if any ideas are hush hush because of the GTG worksaw build off but any basic ideas would be appreciated.

Also a guy on US ebay is selling a 346 ported pop up the work and he says he can install ceramic bearings is this a recognized mod ?

Sorry for such a book of a thread Thanks again Simon

 

[komatsuvarna]

Hi guys Iam pretty sure you guys can help me on this

I am pondering the idea of building my first modded saw. The saw of choice I have picked is a 372/371.

The general conception from porting I have got from reading threads is that.

Widen the exhaust/muffler port leaving 1.5mm each side of the skirts.

Do the same on the intake side (or nothing ? )

Clean up transfers but dont lower them ?

Window the piston

Also for a pop up when machining the Piston how do i determine the squish band do like the outside diameter of the piston that needs machined off.

The pop up in a 372 would be .25 thou off top piston leave at least .100 above top ring machine equal amount off cylinder .

If you guys could help that would be great
I dont know if any ideas are hush hush because of the GTG worksaw build off but any basic ideas would be appreciated.

Also a guy on US ebay is selling a 346 ported pop up the work and he says he can install ceramic bearings is this a recognized mod ?

Sorry for such a book of a thread Thanks again Simon

On widening the ports shoot to leave 2mm, then by the time you re-bevel the port it will be close to right. You don't want to get to wide....don't ask me how I know lol.

Windowing the piston don't do much unless you raise up the cylinder walls on the lower transfers. Most go even with the base of the cylinder here.

 

[simonUK]

ok thats cool thanks. Also do you raise or lower the exhaust port any ?

 

[komatsuvarna]

ok thats cool thanks. Also do you raise or lower the exhaust port any ?

I wouldn't raise or lower any of the ports with out degreeing it.

 

[gink595]

ok thats cool thanks. Also do you raise or lower the exhaust port any ?

Lowering the exhaust won't do anything except make it free port, and you don't want that. The roof of the exhaust is the business end of it. Depends on what you are wanting will determine if you raise it. Keep in mind if you raise it you will lose compression. With the intake lowering it will give you more duration, once again that depends on what you are wanting to achieve.

SO to recap...

You raise the exhaust, not lower.

You lower the intake not raise.

You raise the transfers not lower!

Hope this helps!

 

[blsnelling]

The 372 will allow you to go as wide as you want on port width. Don't just go by the skirts. Measure as a percentage of bore size.

Always widen the intake as well as the exhaust.

Do not alter any of the port timing at this point. The exhaust is as high as you want on a work saw. Don't lower the intake without degreeing it first. You can go too far an lose throttle response.

A popup is not a standard or a required part of a woods port, but is often done. I recommend you simply tighten the squish for starters. The 372 comes from the factory with a lot.

Don't forget about the transfers. If at all possible, widen them towards the intake.

I'm on my cell phone and that's all I can think of for now.

 

[Boleclimber]

This all depends on factory port timing numbers:

My work saws have the exhaust port raised on average .020 to .030. Intake lowered about the same. Transfers raised .020 or more depending on degree wheel measurement.

Pop- up can vary from .015 to .030, depending on amount of compression I want.

Intake and exhaust are widened to near skirt width (not beyond). Transfers are widened towards intake. If I can find a one ring 371 piston, I use it. The ring pin location lets me not worry about ring ends and transfer openings.

.030 is a lot of compression. At times, on 93 octane, a 372 will not shut down with a .030 pop up. Meaning you can hit the kill switch but the saw will continue to auto ignite. Sometimes I can start the saw with the kill switch off. On start up it wont run long though. Works best when the cylinder is hot.

Timing numbers:
Good 372 numbers I have found are 170 degree exhaust duration. 160 degree intake duration. 124-126 transfer duration. .020-.025 pop up.

At the cylinder bottom, I remove about an 1/8th inch from the lip at the transfer extending into the jug. I re-work (thin) the radius and the transfer divider.

Above has me running 8 pin 3/8ths rims with a 20" bar.

I think that is about un-tight lipped of anything you are going to find.

 

[blsnelling]

Intake and exhaust are widened to near skirt width (not beyond). Transfers are widened towards intake. If I can find a one ring 371 piston, I use it. The ring pin location lets me not worry about ring ends and transfer openings.

A non-EPA 372 piston only has one ring as well.

.030 is a lot of compression. At times, on 93 octane, a 372 will not shut down with a .030 pop up. Meaning you can hit the kill switch but the saw will continue to auto ignite. Sometimes I can start the saw with the kill switch off. On start up it wont run long though. Works best when the cylinder is hot.

I'm running a bigger popup than that and have never experienced anything like that. That's with pump gas as well. No issues at all.

 

[Boleclimber]

Are you welding the piston crown?

How are you going more than .030 with out crown thickness issues above the top ring?

 

[blsnelling]

Rules are made to be broken

 

[simonUK]

Thanks for all the info guys looks like iam going to have to do some thinking on what going to be best. Also on the muffler mod side of things iam in europe so there's a side exit pipe instead of on top of the muffler would it be preferable to enlarge that pipe to something bigger like parrisw did ? Or get a 288 deflector and screw that into the top.
This also might sound like a really dumb question bu how do I degree a saw I've seen a lot of people stick degree wheels on the flywheel and a copper wire pointed but I need some guidance if some has a thread they could link me too that would be great.

Also does anybody have an old 372 top cover lying around they'd be willing to sell to me and ship to the UK I know its a big ask but you never know ?!

Anyway thanks guys gonna be busy iam sure in these coming weeks

 

[mdavlee]

The best way I've seen is to use a drill chuck on the clutch side. Just take the spricket and drum off. That way is easier to do than something on the flywheel. I need a bigger one than I've got but it's 8" and works pretty good. Tzed250 has some good pictures in a thread for degreeing a saw.

The muffler mod a 288 deflector will be easier if you don't want to have to weld or braze a new piece of pipe into the muffler.

I've windowed the piston in the 372 and didn't in the 2171. I think you will be surprised how much tightening the squish and a muffler mod will get you.

 

[Boleclimber]

Rules are made to be broken

You imply you use husqvarna 372 pistons with your non epa 372 piston post. Added to using a large pop-up, you have to lower the jug causing increased intake duration. You said to leave the transfer and exhuast port height alone (widen only). Thus, Leaving exhaust and transfer duration untouched causes lower durations there.

The end result makes for mis-matched (un-synchronized) port timing durations and less out put of a saw.

Simon,

I would use a muffler with the exhaust on top. I add a muffler opening to the right muffler side, like others. Rather than buy a 288 deflector, I cut a 5/8" opening, place stainless mesh over the hole and weld a 1" diameter pipe cut on a 45 to 50 degree angle.
The 288 deflector is nice but when screwed in place the holes can oblong and come loose under everyday use.

Your pop up: if you go that route, you want to remove .375" of material at desired depth from the crown edge. Not sure if you have read that information anywhere.