ronT2
ArboristSite Guru
I'm kinda thinkin 
Question for the "porters"
- Thread starter motomedik
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gink595
Addicted to ArboristSite
ALot
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ronT2
ArboristSite Guru
Very Nice!!! Love the roost on the up cut.
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A new 346XP only has about 17° of blowdown. Not every saw needs 25° of BD. As a rule, I would not raise the exhaust on a worksaw. For example, my hot 346 has less than 20, and my 261 has 20. The 261 only had 18 stock, and has tons of torqeu. The exhaust was low, so I bought myself a couple more degrees.
I'd shoot for 75-80° BTDC on the intake. You really need to put a degree wheel on it. You will not weaken a piston by shortening the skirt a little. I use both approaches depending on the saw, and how much I want to change intake timing.
I'd shoot for 75-80° BTDC on the intake. You really need to put a degree wheel on it. You will not weaken a piston by shortening the skirt a little. I use both approaches depending on the saw, and how much I want to change intake timing.
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Blowncrewcab
ArboristSite Guru
Do you motor guys use a regular automotive degree wheel (like an 8"-10") or do you have smaller ones?
gink595
Addicted to ArboristSite
I use a big one, bigger one is more accurate.
gink595
Addicted to ArboristSite
Why wouldn't you raise the exhaust but you would the transfers?
Metals406
Granfodder Runningsaw
Save this picture, size it to print out to the size of a cd. Glue it to the cd, and you'll have your degree wheel.
I'm not sure I follow you. I didn't mention the transfers. If the exhaust is lower than 100° and BD is <20°, I might raise it to buy more BD. If the BD is >20°, I might raise them on some models.
gink595
Addicted to ArboristSite
I remember talking with you at a gtg about a saw you ported and you said you raised the transfers like 8* maybe you raised the ex. as well, but when you said you don't raise the ex. I wondered why you would want less BD like that.
I'm speaking in generalities here. There are exceptions to every rule. I'm not sure what saw you're referring to, and don't save the specs for every saw, so I can't say for sure.
gink595
Addicted to ArboristSite
Thats cool, I understand now, I think I just misunderstood something with that.
parrisw
Tree Freak
Ya, that's what I was getting at with my first post. I agree with the way you do things Brad.
Usually on my saws I end up raising the exhaust most times, to get it where I want it. I'm doing a 372bb now and raised the ex a fair amount, just trying something different, I think its ending up at 164°dur, 98°atdc.
parrisw
Tree Freak
Blowncrewcab
ArboristSite Guru
motomedik
ArboristSite Operative
Save this picture, size it to print out to the size of a cd. Glue it to the cd, and you'll have your degree wheel.
That's what I did, doesn't last forever, but it's cheap and easy!
motomedik
ArboristSite Operative
Brad and Parrisw I agree with you as far as not raising the exhaust to get the 25 degrees blowdown. Rather make compression/torque.
It occurs to me that like any engine build, you need to decide what you want, can't have it all, and do things that support your goal. It all works together.
Reason for the question is discussion of the relationships between all the ports and other things like base volume, intake length, muff volume, stroke, etc. If I can get a grasp of how all these things work together, I'll be MUCH better at building a powerful and usable powerband.
Thanks for all the great info, gents!!
It occurs to me that like any engine build, you need to decide what you want, can't have it all, and do things that support your goal. It all works together.
Reason for the question is discussion of the relationships between all the ports and other things like base volume, intake length, muff volume, stroke, etc. If I can get a grasp of how all these things work together, I'll be MUCH better at building a powerful and usable powerband.
Thanks for all the great info, gents!!
Tzed250
Addicted to ArboristSite
just wondering what you guys look for when tuning a ported saw im very familiar with 4 stroke engines and can see why you would never want to raise the exhuast as it would just lower your compression ratio but, that being said you cant usually lower the intake much, if at all, how about lowering the exhuast or raising the intake both would increase duration and rpm whats your limits as per rpm seing how torque is just math technically you would gain both hp and torque with the higher rpm so if a stock saw is set at lets say 13000 rpm when tuned correctly how do you go about tuning your ported saws that may need to considerably higher rpm above stock to take advantage of the porting, are you still just doing it by ear or tach only?
Dan_IN_MN
Addicted to ArboristSite
Sense this thread is about modding saws, anyone know were there is a good tuned pipe program that's free?
Thanks!
Thanks!
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