Jmssaws ms460

[paragonbuilder]

There must be an optimal transfer velocity that changes based on duration. With a longer transfer duration, to get the velocity high enough when they crack open, intake needs to close sooner to start compressing. With shorter duration however could the velocity be too high? And so the added intake duration lowers that velocity? Of course at some point spit back becomes an issue...



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[drf256]

I've been wondering this as well?

How did Marcello's 262 run Dan?

We broke some rules there, didn't we?

 

[paragonbuilder]

Yeah... And it seemed to run as good or better than the other two. It was torquier and didn't seem to lack any speed...


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[drf256]

Yeah.

I think the answer isn't easy. It's predicated on case volume, intake boot size, exhaust roof arc, muffler outlet, transfer cross sectional area, etc..

What works on one model won't on another. But the basic theory should get you close.

Case in point was my MS360 at the GTG. I added an 038 boot, which was 100%+ larger in opening than the stock boot. The saw was a dog with an 84* intake. The smaller boot must have increased velocity and overcame the big intake duration. I'm betting that raising the intake to 78* with epoxy and adding the 038 boot gains.

You remember what the saw did on the Dyno with no filter Dan.

 

[mdavlee]

This one has low exhaust and low transfers with a ton of compression. Its fighting itself and a 562 is faster in this wood right now with the same chain.

 

[drf256]

How much compression?

How low are your transfers?

 

[drf256]

Isn't the 562 a strato?

So you've got massive intake and transfer area. 6 ports on the intake side. And a huge wide exhaust.

Do you have another 372 to compare? You should be able to Lower compression and leave everything else alone easier than anyone Mike. What have you found with this?

 

[paragonbuilder]

Yeah.

I think the answer isn't easy. It's predicated on case volume, intake boot size, exhaust roof arc, muffler outlet, transfer cross sectional area, etc..

What works on one model won't on another. But the basic theory should get you close.

Case in point was my MS360 at the GTG. I added an 038 boot, which was 100%+ larger in opening than the stock boot. The saw was a dog with an 84* intake. The smaller boot must have increased velocity and overcame the big intake duration. I'm betting that raising the intake to 78* with epoxy and adding the 038 boot gains.

You remember what the saw did on the Dyno with no filter Dan.

So many variables...and we don't even really know what we are looking for. What really are we doing when we change them?

 

[drf256]

The factory gave us the clue. We are trading one variable (i.e. Fuel Econ, emissions) for another.

The engine has to be thought of as one, not as intake/transfer/exhaust.

I think it's the puzzle that intrigues us all.

 

[drf256]

So many variables...and we don't even really know what we are looking for. What really are we doing when we change them?

In some cases, we are making them run worse.

Case in point, Matt's 350. All that work and a stock muff mod saw was right there with it.

 

[paragonbuilder]

In some cases, we are making them run worse.

Case in point, Matt's 350. All that work and a stock muff mod saw was right there with it.

Right. But one more small change might make the difference...

 

[mdavlee]

How much compression?

How low are your transfers?

235 lbs warm. Somewhere in the 125 range. Exhaust is between 112 and 103. It's the one I broke the base on and never finished raising the exhaust. I was in the middle of that when I broke that ear. I'll tear it apart and raise the exhaust and transfers maybe today. I need to get into the 665 here and see what it will gain.

562 is a strato with 2 strato ports and the 2 transfer ports. The exhaust isn't real wide on this either. It was a work saw that ended up getting a head since I couldn't seal the base any other way.

 

[drf256]

On those big guys, I think there is faster burn with wider bore.

Probably why they like more exhaust duration?

Not sure why they like it.

 

[mdavlee]

They need more area to evacuate the exhaust. End goal on this one is probably going to be methanol only any way for this cylinder. The compression is a touch high and just need to tailor the timing now. I could build another head and see what it would do with lower compression. I think I have 2 more blanks here.

 

[drf256]

I can talk theory all day.

Likely because I talk from both my mouth and my ass.

Less back pressure, like a dual port muffler.

 

[mdavlee]

I can talk theory all day.

Likely because I talk from both my mouth and my ass.

Less back pressure, like a dual port muffler.

The quicker it gets out of the cylinder the better. Stihl on the 660 runs a high exhaust and tiny muffler outlet. Like 40cc husky size outlet on them before the 661 replaced it. Must have been to trap heat in the muffler to try to burn some of the unburnt charge that escaped the chamber.

 

[Mastermind]

I'm still finding out things that work for one model, and kill another. I wish there was a way to check case volume, and predetermine what numbers would be best....

 

[mdavlee]

I'm still finding out things that work for one model, and kill another. I wish there was a way to check case volume, and predetermine what numbers would be best....

There is that program. You do have to know case capacity and rod length.

 

[jmssaws]

The last 3 064's I've built have different exhaust,transfers, intake but all run the same. It's only a few degrees different but still different.

If a saw is very strong at 98 123 83
It can also be very strong at 96 121 81
Or 100 125 84. There's no set number

 

[jmssaws]

Two saws with the same numbers can run very different.