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372XP X-Torq Modding

Started by XP_Slinger, December 28, 2015, 08:16:01 AM

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XP_Slinger

Your cylinder is looking good.  Brainstorming is the fun part of all of this in my opinion.  Having guys like Ed that are willing to guide us through our learning experience from theory to application is immeasurably valuable.  Can't wait to hear your saw run!
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

XP_Slinger

I've never heard of anyone shaping the piston to more closely match the curve of the exhaust port, although I'm sure there's someone that has tried it.  Makes perfect sense because the quicker you can open the exhaust the more efficient the port will be.  A common practice I've seen to achieve this is making the top of the exhaust port more flat.  But with this method comes risk, if the flat area is too wide you'll snag a ring.  This is where experimentation comes in but all my saws are ported now so I don't have any cylinders to play with...lol
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

EvilRoySlade

So, as it stands now I've really only worked on transfers.
Totally stock:             After machining:
Tr 116                       121
Ex 99                        102
In 74                         76
Sq .030"                    .019"

Both with gasket.

Strato is gutted minus the divider in carb, I can see benefits in leaving it with learnings from the dirt bike carb world. I have not raised the roof of intake to bottom of piston at TDC yet but will. I've not yet decided to increase intake duration yet either, but maybe just enough to match strato ports for now.
Unfortunately I have not taken Ed's advice and CC'd the engine. I know how useful it is when traveling this road but...I really have no excuse other than it's not easy.
I've raised transfers to 114 and widened them towards the exhaust to the edge of the strato cut out on the piston. It seems a better visual than measurements. I am starting measurements of the transfers to decide if I want to go towards the intake, it's a bit more finesse.
No matter what I'll be widening the exhaust. As for raising it, I have chosen to take the approach of compression. I'm not sure it's right but if I understand correctly the relationship of transfers to exhaust dictates compression. I have no plan to go higher on transfers so now a goal of 180psi will dictate my exhaust height. Unless it's unreasonable. I did remove .020" from the squish. Worst case I can remove some material from combustion for more volume up top.

Any insight is welcome as I travel this new road.

XP_Slinger

When I raised my exhaust 3* I only lost 5psi of compression if I recall correctly.  My squish is at .024 which gave me 180psi before raising the exhaust.  Being that you're at .019 I don't think you'll have any problems achieveing your goal of 180psi.  I'd be willing to bet that you'll be at 190 or maybe even a touch more with your exhaust as low as it is now.  If you have the room in compression to raise the exhaust I definitely would.  When I built my Saw raising the exhaust really woke the up.  While raising and widening ports, don't forget about your ring locator pins.  You don't want ring ends dropping into a port as it will likey snag. 
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

EvilRoySlade

Thanks, I have avoided anything near ring ends. I'm easily clear of rings at the top of intake while getting full open at TDC. I didn't touch the strato ports because they are near something at just about every position.

XP_Slinger

I assumed you were aware of being cautious of the ring ends, never hurts to bring it up.  Especially with other folks reading along.  When do you think you'll be running your saw?
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

EvilRoySlade

I understand completely about the ring comment, it never hurts to bring things like that up.
Next steps is bevel the ports, then drop the cylinder on with rings to check compression. I'm only doing this to learn. I'll be getting a baseline after cylinder machining and raising/widening the transfers. After that I'll pull again to widen and move exhaust to around 100, then check PSI again. If needed I'll raise exhaust some more but not beyond 98 for now. I'd be happier removing some combustion chamber to reduce compression at that point. Maybe even raise transfers another degree.

CJBrown

What kind of rotary tools are you guys using to do your own porting?

XP_Slinger

I used a dremel with long shank burrs.  Not ideal but it worked well enough.  Saws such as the XT with removable transfer covers make it pretty easy to get by with a dremel. 
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

EvilRoySlade

I have a Fordom knockoff from HF with some Chinese hand pieces. The hand pieces are quite well built for the price.

I have a question about grinding on the piston. I'm hoping @ehp will help out because he mentioned working it over pretty good. I'm touching up any areas on the piston just to drop any bit of weight I can. I know the intake skirt takes majority of side force abuses from the rod, so I wondered about removing some skirt from the exhaust side. I have 1/2" before freeport occurs, I would think I could remove 1/4" safely. In my opinion removing weight (smartly) from the piston will help lower end lifespan and possibly reduce wear on the intake skirt. It's heavy and has got to be stressful and energy sucking to stop and start.

Anyone have experience with this idea. I know it will change front to back balance. I've not seen much wear on the bottom of any saw exhaust skirt. The stress on intake seems to occur both up stroke and down. Up is Rod driving towards the exhaust which rocks the piston that direction forcing the intake skirt against the wall. Then down is the piston driving Rod down which the angle is using the intake wall as a sliding surface. Less piston weight means less force to change direction, less force= easier rotational momentum.

XP_Slinger

I think removing that much material from the exhaust skirt could cause it to get too hot.  Less metal to absorb heat causing premature aluminum transfer to the cylinder wall.  Just a hypothesis, not based on any experience on this subject.  Very interesting thought.  You're right about the XT piston being heavy.  I actually weighed one and it came in 10gr heavier than a 75cc XPW piston.  Not a huge difference, but the fact that it is heavier than the big bore piston says a lot.
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

EvilRoySlade

I started thinking about other pistons I've seen that aren't symmetrical, like the ms261, 562. I'm sure there are others. I wish I had piston and cylinder of those in my hands to investigate. Well I do have a brand new 562 but don't feel like pulling the cylinder, yet...

XP_Slinger

Got a feeling you're gonna be investigating that 562 sooner rather than later...lol. 
I've never seen a piston that wasn't symmetrical or very close to it.  As you said, you could shed some serious weight if it's a viable option to shave the exhaust skirt.
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

ehp

Lots of guys cut the skirts on pistons , I am not one of those type of people . I never cut skirts ever, seen way to many pistons crack or break from that, I lighten piston doing the casting flaws, and work the inside over pretty good . Also guys you have to remember a port can only pass as much air/fuel at the smallest area of the port, I see lots of guys put huge transfer ports in the cylinder but channel of the port is no where even  close to being able to pass that amount of charge so measure what your grinding , In a lot of times doing those huge transfers but not a lot else hurts the power of the saw , Everything has to work together , modding the transfer ports hard but not the ext port does not work either

EvilRoySlade

Ed, thank you for the insight. I'll leave the skirt alone. I have been working over the piston pretty good elsewhere though, inside and out. I have heard you say ports can only flow the smallest area before and I try to approach grinding like that. I've also heard from many people that these single transfers need to be opened a lot.

I've measured my ports as best I know how.
Transfer bottom   188mm^2
Transfer tunnel at turn   159mm^2
Transfer opening to cylinder minus the top edge of piston that is in the way at BDC   178mm^2

Intake still at 76 degrees   275mm^2
Strato ports together untouched   137mm^2

Just looking at those I see I need to open the tunnel more. The intake I am just guessing at but I'm sure with knowing crankcase volume and compression duration it can be figured out. However I have never done volume and barely understand how. From a post long ago Ed said to block intake and exhaust ports and fill the whole engine up to the spark plug threads with ATF I thought. To me, anything non foaming with a surfactant would work. Measure that volume of liquid, subtract the given engine CC and you have crankcase CC. Is that correct?  Then you would use a formula that I do not know to determine your intake needed, transfer volume, blowdown and compression.

So for now, I need to go find T/A reading.  Then maybe I can determine if I at least have close numbers. Or I set the exhaust and run it, see what it does.



ehp

No, you put engine at TDC and it has to be TDC perfect, fill combustion chamber to second thread on sparkplug hole , measure how much volume of oil you used , next role piston down to BDC fill to second thread on sparkplug hole , measure oil volume used , now you got to have the ports closed off but you already knew this and you would already know the cc volume of the engine . I have a computer program that I put the number in and it can tell me pretty much everything I need  now I can make changes to my ports like transfers that will add cc volume to the crankcase and see how that affects the engine , I also have a engine dyno on computer that I can take a engine numbers and port and the dyno will tell me if they work or if the port numbers are wrong mainly thou on if your over porting a port the computer will tell you that will not work. But I honestly cannot remember the last time I used any of that stuff , Had so many different motors apart I pretty much just look and can tell what I want to do

XP_Slinger

Interesting stuff.  I've never measured Case volume, seems like a more precise way to determine what changes should be made to ports. 
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

ehp

crankcase volume plays a huge roll in how a motor runs and mainly torque , you can make top end horsepower playing with making the volume larger but at some point it will become a very top couple hundred rpms will be any good to you. But on average most chainsaw motors are to tight and can use a larger crankcase volume and they will make more horsepower but the down side is the engine will also require more fuel and that amount of fuel depends on the amount you increase the cc volume of the crankcase and also with more power you will produce more engine heat which is not a good thing

XP_Slinger

Yes sir.  It's that delicate balance that we're all looking to achieve.  It's the difference between a DIY woods port and a pro such as yourself.  I really enjoy learning about this stuff. 
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

EvilRoySlade

Which is were the whole BMEP comes into play correct?  It would be fun to see the simulations on the software to help understand what affects what. Watch what happens when fat lazy transfers are ground and such.

CJBrown

If a larger crankcase volume is desirable when trying to produce more HP, what role do crank stuffers play in some of the production saws? Is it to keep the charge above the spinning crank and out of the bottom of the crankcase? Reduce bottom end turbulence? And how do they affect bottom end lubrication?

XP_Slinger

The way I understand crank stuffers is they increase charge velocity and pressure.  Which in turn gives the Saw more torque at higher rpm.  I think...
346XP/NE
357XP...ported by MeDremel
372XP/XT...ported by A. Burr
Homelite (Solo) 340

I'd rather be in the woods than on this computer.

ehp

Bmep is a ratio that can help BUT you still have to use common sense cause you can design a engine that has a super high Bmep number that looks on paper or computer screen to be super but in real world terms the engine could never run at that Bmep ratio . Just like most computer software you still need to think , same as building 2 stroke pipes . You need to tell the program what you want to do,

CJBrown

BMEP - I had to look that one up.

SierraMtns

Great thread.  I am currently porting my 365 x-torq.  This is the first time I have ported a saw.  I am a little nervous so I am and going slow. 

I am hoping to post pictures soon. 
Cut the tree not the wood.

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