A Tale of Three Saws

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Ms660

Here's a detailed build of a 660 woods port that starts at 150 psi and ends up at 170. Timed cuts were done at several steps along the way.
Timberwolf's 660 build

If I remember correctly, even TW once said that in some cases, dropping the jug to raise compression may actually slow the saw down, unless port timing is adjusted to compensate.

Since we are talking about the 660, which has excessive exhaust duration, its exhaust port timing may actually benefit from dropping the jug.

It's ultimately up to the customer whether he wants a pop-up. If he wants a 145 psi 660, that's his call.

No argument about the quality of recent Stihl jugs. If only Stihl would make better jugs, with sane timing and a healthy compression ratio ...... :confused: As it is, they're getting spanked by the competition.
The MS660 is a touchy subject, an 066 is a different story. I've seen what a well tuned, non-ported 066 is capable of and it is nothing like a stock MS660. Personally as a work saw I'm satisfied with my MS660 just the way came from Stihl, I've added the DP muffler covers and retuned but anything else? nah, not when 372's gain soooo much better when ported(and you can still buy a new 372, the 440's are looooooong gone). Besides as soon as you hit your pride and joy 660 with a grinder, the resale value more than likely is lowered.
I kinda question those pop up set ups as far as reliability. They great in 5 seconds of video, but what about a days work of milling?
 
The MS660 is a touchy subject, an 066 is a different story. I've seen what a well tuned, non-ported 066 is capable of and it is nothing like a stock MS660. Personally as a work saw I'm satisfied with my MS660 just the way came from Stihl, I've added the DP muffler covers and retuned but anything else? nah, not when 372's gain soooo much better when ported(and you can still buy a new 372, the 440's are looooooong gone). Besides as soon as you hit your pride and joy 660 with a grinder, the resale value more than likely is lowered.
I kinda question those pop up set ups as far as reliability. They great in 5 seconds of video, but what about a days work of milling?

I don't see any reason why it wouldn't be reliable with a popup, as long as you have enough crown thickness left.
 
I realize most are probably more interested in seeing the 660/390 comparison. But it's cool to see the next size smaller saw compared to it's bigger brothers.

Once ported, I plan to test with 32" bars in Oak.

Dont port yet...I would like to see the stock 660/390 with 36" bars in big oak!!

No offense, but I would never use my 660 with 24" bar, thats what my 440 is for....660 with big bar, for big oak....this would be a fair comparison bro.
 
Last edited:
Thanks!

The only thing I wonder about having a popup in a 2 stroke is the flow across the piston and what it does to it?

A 028 super sports a factory popup, as most of you guys already know.

I can't see any reason a popup piston would make a saw less dependable, unless as Brad mentioned the area above the rings was cut too thin.
 
A 028 super sports a factory popup, as most of you guys already know.

I can't see any reason a popup piston would make a saw less dependable, unless as Brad mentioned the area above the rings was cut too thin.

That's a domed piston, rather than a popup. It has a smooth convex radius all the way from the edge of the piston.
 
That's a domed piston, rather than a popup. It has a smooth convex radius all the way from the edge of the piston.

It is just raised in the center on the 028 super, on the early 028 AVs it was a dome.

44105.jpg
 
Hey just a tech question Brad.
Is doing a popup just to gain compression only? If so by taking out the base gasket on my older 7900 and cracking 200psi compression does this mean, providing the porting is the same, that it would have the same power as a saw with a popup providing the compression is also 200psi?
Reason I ask is because my old saw has more compression than the 7901 you built but has nowhere near that amount of grunt :cheers:
 
Is doing a popup just to gain compression only? If so by taking out the base gasket on my older 7900 and cracking 200psi compression does this mean, providing the porting is the same, that it would have the same power as a saw with a popup providing the compression is also 200psi?

Yes. The only reason I do it is for added compression.
 
i thought Pop-ups were done to increase comp. and also decrease the CC size. now i know decreasing the CC will net more comp, but isnt there something else going on with a reduced CC????

Serg
 
The MS660 has been measured and is apart. Here are some specs on it.

Compression - 158
Squish - .019"

Exhaust - 95° ATDC - 170° Duration
Transfers - 120° ATDC - 120° Duration
Intake - 80° BTDC - 160° Duration
Blowdown - 25°

I've got a lot of pics of the P&C coming up.


878125357_CHGdG-M.jpg


878122891_VgMko-M.jpg
 
Last edited:
The MS660 has been measured and is apart. Here are some specs on it.

Compression - 158
Squish - .019"

Exhaust - 95° ATDC - 170° Duration
Transfers - 120° ATDC - 120° Duration
Intake - 80° BTDC - 160° Duration
Blowdown - 25°

I've got a lot of pics of the P&C coming up.

Good stuff mate - interesting. Aren't you meant to be sleeping or something? :D
 
Back
Top