Decking/Porting questions

[petervp14]

I apologize if this has been discussed somewhere already. I'm new to the forum also.

I have a 45cc saw I put a 58cc top end on. The squish was horrendous, so I did a DIY deck that's been very successful in the past for resurfacing.

I got my squish down from .0855 to .0340 and I'm not sure if I should go further.? I still have room at the bottom of the skirt so I wouldn't be losing my charge out the exhaust port.

I took measurements before and after (New to using degree wheel)

Ex. opens @ 103 ATDC
Duration was 158 (I may have screwed that up I have 58 written down but I think I just forgot the 1)
Blowdown 12
Intake @103
duration 162

After decking

ex. opens at 108
duration 149
Blowdown 20
Intake opens at 109.? (I had 80 wrote down and that didn't seem right, so I measured again and got 109) Does that mean my duiration is off
duration 167

Take these with a grain of salt. I'm very meticulous but new to official port timing.

I'm looking for a aggressive badass porting. This is a cheap learning saw and does not need to run for hours etc.

Do I justr raise the intake and exhaust ports 5 degrees to go back to stock.? I've widened ports that worked great. Like I said I'm looking to make it crazy aggressive but I'm asking that just for the sake of understanding IF I wanted to get back to stock timing after decking.

Thanks so much sorry it's long.

 

[thompsoncustom]

What do you want with the saw more RPM or more torque? If your numbers are 108/128/80 I bet it will run really strong think more torque less rpm but taking the exhaust down to say 105 and transfers to 125 will gain some rpms I would run it and see what you think first before modding it anymore.

How are you measuring squish is it .0340 all the way around the piston perfectly or close to it? If so I would lower it, .020 is safe but if it's true I would have no problems going to .015. What's you compression measure currently?

 

[srcarr52]

On a 50cc saw you can run the squish as tight as 0.016" and be ok. Usually everyone sticks with 0.020" which is safe for even large saws until you start spinning stupid high rpm.

Cutting the base and effectively dropping all the ports will decrease exhaust and transfer duration, and increase intake duration. It will not effect your blowdown (exhaust opening to transfer opening) much at all.

So, I think you've got something mixed up with your numbers.

Exhaust opening at 103° would be 154° duration. (180-103)*2=154

After your machine work you have it opening at 108° which is 144° duration. This is direction of change we would expect from the machine work although it seems a little large for only 0.051" change.

Your large change in blowdown I suspect is from your error in the exhaust numbers. You should keep track of the transfer opening/duration as most people will discuss those numbers and not blowdown.

Intake opening at 109° would be a duration of 218°, this is huge! Which this very well could be the case as you've put a 58cc top end onto a 45cc bottom end and most likely destroked the 58cc top end by 4mm or more. You'll probably have to fill the bottom of the intake port to get the timing into a more reasonable range.

 

[Junk Meister]

On a 50cc saw you can run the squish as tight as 0.016" and be ok. Usually everyone sticks with 0.020" which is safe for even large saws until you start spinning stupid high rpm.

Cutting the base and effectively dropping all the ports will decrease exhaust and transfer duration, and increase intake duration. It will not effect your blowdown (exhaust opening to transfer opening) much at all.

So, I think you've got something mixed up with your numbers.

Exhaust opening at 103° would be 154° duration. (180-103)*2=154

After your machine work you have it opening at 108° which is 144° duration. This is direction of change we would expect from the machine work although it seems a little large for only 0.051" change.

Your large change in blowdown I suspect is from your error in the exhaust numbers. You should keep track of the transfer opening/duration as most people will discuss those numbers and not blowdown.

Intake opening at 109° would be a duration of 218°, this is huge! Which this very well could be the case as you've put a 58cc top end onto a 45cc bottom end and most likely destroked the 58cc top end by 4mm or more. You'll probably have to fill the bottom of the intake port to get the timing into a more reasonable range.

Not a project that cuts any slack for a dyslexia prone person like me. You (PORTING) guys have a way of dissecting each degree of rotation that makes for good reading. Thanks

 

[Motorka]

I apologize if this has been discussed somewhere already. I'm new to the forum also.

I have a 45cc saw I put a 58cc top end on. The squish was horrendous, so I did a DIY deck that's been very successful in the past for resurfacing.

I got my squish down from .0855 to .0340 and I'm not sure if I should go further.? I still have room at the bottom of the skirt so I wouldn't be losing my charge out the exhaust port.

I took measurements before and after (New to using degree wheel)

Ex. opens @ 103 ATDC
Duration was 158 (I may have screwed that up I have 58 written down but I think I just forgot the 1)
Blowdown 12
Intake @103
duration 162

After decking

ex. opens at 108
duration 149
Blowdown 20
Intake opens at 109.? (I had 80 wrote down and that didn't seem right, so I measured again and got 109) Does that mean my duiration is off
duration 167

Take these with a grain of salt. I'm very meticulous but new to official port timing.

I'm looking for a aggressive badass porting. This is a cheap learning saw and does not need to run for hours etc.

Do I justr raise the intake and exhaust ports 5 degrees to go back to stock.? I've widened ports that worked great. Like I said I'm looking to make it crazy aggressive but I'm asking that just for the sake of understanding IF I wanted to get back to stock timing after decking.

Thanks so much sorry it's long.

Is this china clone ?

 

[petervp14]

What do you want with the saw more RPM or more torque? If your numbers are 108/128/80 I bet it will run really strong think more torque less rpm but taking the exhaust down to say 105 and transfers to 125 will gain some rpms I would run it and see what you think first before modding it anymore.

How are you measuring squish is it .0340 all the way around the piston perfectly or close to it? If so I would lower it, .020 is safe but if it's true I would have no problems going to .015. What's you compression measure currently?

So with this saw with that top end just slapped on. It had terrible throttle response almost like turbo lag. Then it would scream and soon as it got into the cut just no power. I want to just make this thing a high-power saw just to learn on a total test mule doesn't need to be used for work I have many others for that. It's cheap if I wreck a cylinder and a cheap saw overall. I'm in all this to learn porting. I've been a 2 stroke guy my whole life. That's the main thing with this saw.

The saw did run good with those numbers, and you are 100% correct the rpm is not very high.
Squish I'm measuring solder, and it is 305-315 all around.

Cold compression I'm at 170psi

 

[petervp14]

On a 50cc saw you can run the squish as tight as 0.016" and be ok. Usually everyone sticks with 0.020" which is safe for even large saws until you start spinning stupid high rpm.

Cutting the base and effectively dropping all the ports will decrease exhaust and transfer duration, and increase intake duration. It will not effect your blowdown (exhaust opening to transfer opening) much at all.

So, I think you've got something mixed up with your numbers.

Exhaust opening at 103° would be 154° duration. (180-103)*2=154

After your machine work you have it opening at 108° which is 144° duration. This is direction of change we would expect from the machine work although it seems a little large for only 0.051" change.

Your large change in blowdown I suspect is from your error in the exhaust numbers. You should keep track of the transfer opening/duration as most people will discuss those numbers and not blowdown.

Intake opening at 109° would be a duration of 218°, this is huge! Which this very well could be the case as you've put a 58cc top end onto a 45cc bottom end and most likely destroked the 58cc top end by 4mm or more. You'll probably have to fill the bottom of the intake port to get the timing into a more reasonable range.

Thank you so much. Very helpful info. This all may be stupid to some people but I'm doing this to learn things and see what is possible etc. I will cut some with it and report back and put the wheel back on to confirm my numbers. I guarantee i messed some up haha.

 

[petervp14]

Is this china clone ?

Yes, it is. I have Husqvarna but didn't want to screw up my 1k saw. $200 cylinder vs a $20 cylinder lol. Plus, a cheap small saw that isn't a clamshell is perfect to learn, I think. Maybe a bigger saw would be easier but I don't want to ruin the 660 yet. I just widened those ports and cleaned them up.

 

[thompsoncustom]

Yea getting you numbers measured right is a good place to start. If your intake is opening at 109 I would think you would have a ton of air and fuel spitting out the carb. Next time your out running it take the air filter off and at WOT and see if it's spitting fuel back at you through the carb.

Like Scar said your gonna need to fill the intake (jb weld) but after you take the squish down more I'd like you see you with higher compression numbers.

Also I assume you are using the carb off the 58cc top end and not the 45cc right?

 

[Motorka]

Yes, it is. I have Husqvarna but didn't want to screw up my 1k saw. $200 cylinder vs a $20 cylinder lol. Plus, a cheap small saw that isn't a clamshell is perfect to learn, I think. Maybe a bigger saw would be easier but I don't want to ruin the 660 yet. I just widened those ports and cleaned them up.

Shorter crankcase ?