346 porting (first time)

[paragonbuilder]

Blowdown is transfer minus exhaust height so 18.85 correct?


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[Red97]

Nice work

Should run well,

I say put it together and try it out.
Curious to see what the comp ends up at. With the exhaust that low, should have some good pull for a lil saw.

 

[paragonbuilder]

Should run well,

I say put it together and try it out.
Curious to see what the comp ends up at. With the exhaust that low, should have some good pull for a lil saw.

So lower exhaust for more torque?


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[Red97]

From what I understand,

Lower the exhaust height, traps more compression, therefore more torque, to a point.

Raise it up, will pick up some rpm lose some compression.


But as I said, you may really like it the way she sits now. If not you can always grind more.

 

[mdavlee]

The exhaust is about perfect. The transfers could be a little higher for less blowdown. It helps for higher rpm. I think I went 14-15 on the last one.

 

[paragonbuilder]

Thanks Mike!
So here is the really cool part.
Take 105.81 which is where my exhaust is and add 14 and input it and get this.

Or add 15 and get this

Now I add .5mm (the squish measurement that I subtracted) to the blowdown I choose and raise transfers to that measurement from the squish band.


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[paragonbuilder]

So I need to raise them between .5 and 1 mm to get to Mike's numbers.


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[paragonbuilder]

So doing it this way you could use Randy's @Mastermind method of cutting card stock the height you need and put it in the cylinder. Than grind to the card stock.
And all you need to get the measurements is your squish measurement and the timing numbers you want to use. Plug them into this program and you know how high to cut your card stock.


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[huskihl]

How are you measuring port heights?

 

[paragonbuilder]

Intake was trickier because you are measuring the bottom of the port. So I set the caliper on the cylinder extension and measured the port from there. Then I zeroed the caliper. Then I measured from the cylinder extension to the squish and it read the difference.
Hopefully that's clear enough.


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[paragonbuilder]

Now that I think about it since you need to deduct piston height for the intake, I could have dropped the piston in first and just measured from the skirt.


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[huskihl]

Now that I think about it since you need to deduct piston height for the intake, I could have dropped the piston in first and just measured from the skirt.


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That's what I was thinking. I've always used a degree wheel, but that seems simple enough for sure.

 

[drf256]

I'd still use a degree wheel Dan.

I'm intrigued by David's post. I certainly may use it to calculate and cut card stock, but I'd still double check it with a wheel.

The relationship is so non-linear that I don't think I'd trust it without double checking it.

Who knows, it may prove to be just as exact.

 

[mdavlee]

That program is taking into account rod angle so it should be pretty well on the money.

 

[paragonbuilder]

The exhaust is about perfect. The transfers could be a little higher for less blowdown. It helps for higher rpm. I think I went 14-15 on the last one.

So I'm curious. If raising the transfers will help rpm, will it hurt torque?


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[paragonbuilder]

Here is the link to the program
http://torqsoft.net/piston-position.html


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[mdavlee]

So I'm curious. If raising the transfers will help rpm, will it hurt torque?


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Not usually. If the blowdown is too long you lose power all around. You can try it where it's at first then raise them and see the difference.

 

[jrsdws]

 

[Ironworker]

Really digging this, not to derail this thread but how do I go about finding rod lengths on other saws.

 

[mdavlee]

Some are out there in google searches but most will have to be measured. Which ones you want to know? I used to have a bunch of them measured out and wrote down. Not sure which pad it was on though.