Husqvarna 576xp port work

[blsnelling]

This first video is with the 13,300 blue limited coil.



This second video is with the black unlimited coil.

Is it my imagination or is it holding RPMs in the cut better with the limited coil? Either way, it definitely sounds stronger than the one ported 576 I've run. I've never done one myself. Sounds great. nice work.

 

[Chris-PA]

if i can fit an unlimited coil on an AT saw to do the work i do i will be tickled absolutely ****'n pink. raw pink actually! will have to pull it off the hill in a day or so to try it. even if only to rid myself of that limiter hammering while limbing. even if it's realy not that bad.

That doesn't sound like a good idea. With a traditional carb the terminally rich mixture determines that max no load rpm. With a feedback carb that keeps the mixture correct - or even just less than puking rich - then something else will limit the max rpm. That something might be when parts fly apart.

This is actually the entire reason the limiting coils have come into use.

 

[Chainsaw Jim]

That doesn't sound like a good idea. With a traditional carb the terminally rich mixture determines that max no load rpm. With a feedback carb that keeps the mixture correct - or even just less than puking rich - then something else will limit the max rpm. That something might be when parts fly apart.

This is actually the entire reason the limiting coils have come into use.

Do you really think the engineers are going to leave it that close? I don't. There's no way they'll have a saw blow up at a certain rpm and then limit it just barely below that.

 

[Chainsaw Jim]

Is it my imagination or is it holding RPMs in the cut better with the limited coil? Either way, it definitely sounds stronger than the one ported 576 I've run. I've never done one myself. Sounds great. nice work.

I can't really tell, but I have it tuned way leaner than in the limited video. I'm still going to record a few runs with the ignition bumped all the way versus stock.

 

[Big_Wood]

Do you really think the engineers are going to leave it that close? I don't. There's no way they'll have a saw blow up at a certain rpm and then limit it just barely below that.

it's not about blowing up at a certain RPM. it's about blowing up after a certain amount of time doing a certain RPM.

 

[Big_Wood]

the fact that the AT coil parts number is the same as the non AT 570 coil says something. i'm gonna try it anyways and if the coil is in fact a feedback coil i'm sure i will know right away it ain't gonna work. probably run the saw with the 13,300 coil anyways though. where else would i use that coil? it is likely better for the saw to not turn over 13.3k with a big old heavy turd of an XT piston.

 

[Chainsaw Jim]

it's not about blowing up at a certain RPM. it's about blowing up after a certain amount of time doing a certain RPM.

That's kind of the same thing in my opinion. It's still max rpm failure. McCulloch scrapped the BP-1 due to being too scared it would grenade, but as far as I have heard, it never did.
It would be a huge liability for the engineers to leave tolerances that close.

 

[Big_Wood]

That's kind of the same thing in my opinion. It's still max rpm failure. McCulloch scrapped the BP-1 due to being too scared it would grenade, but as far as I have heard, it never did.
It would be a huge liability for the engineers to leave tolerances that close.

ya i hear ya and agree. do they run one at a certain RPM til it grenades? no. they likely just know saws starting coming apart at about this speed and just making them limited base on that. while limbing my 576 would sing way past the limiter though i'm sure. it hammers it constantly. not the end of the world though. still a very usable saw with that coil. it really doesn't need to turn any faster. would be nice to know if other coils would work on that old AT system though because i can't say i'm gonna wanna go out of my way to get that coil just cause it's for the AT saw when i have a pile of other coils from other saws that would bolt up.

 

[Chainsaw Jim]

ya i hear ya and agree. do they run one at a certain RPM til it grenades? no. they likely just know saws starting coming apart at about this speed and just making them limited base on that. while limbing my 576 would sing way past the limiter though i'm sure. it hammers it constantly. not the end of the world though. still a very usable saw with that coil. it really doesn't need to turn any faster.

Easy solution...use a 14,100 limit blue coil from the 346xp.

 

[Big_Wood]

Easy solution...use a 14,100 limit blue coil from the 346xp.

somebody has had to have tried this before? if i had to tune this saw by ear i would care alot more about which coil is on it but because AT does all that it doesn't bother me all that much. about the only thing i'll gain from it is it will sound cooler limbing lol.

 

[Chainsaw Jim]

I'm no expert with auto tune, in fact I know nothing about it.
A saw running the proper tune will only reach a certain rpm level unless you lean it out. Wouldn't an auto tune on a saw that large max the rpm between 13,500 and 14,000 anyways?

 

[Big_Wood]

I'm no expert with auto tune, in fact I know nothing about it.
A saw running the proper tune will only reach a certain rpm level unless you lean it out. Wouldn't an auto tune on a saw that large max the rpm between 13,500 and 14,000 anyways?

that's the thing, nice when you can tune it and leave it but what if you want to leave it but AT thinks otherwise? mine hammers off the limiter so hard while limbing i would not be surprised to see it exceed 14k or more if there was nothing holding it back. i don't think there would be any benefit on an AT saw. only reason i run a higher limit is ease of tuning but AT does that for that saw anyways.

 

[Chainsaw Jim]

that's the thing, nice when you can tune it and leave it but what if you want to leave it but AT thinks otherwise? mine hammers off the limiter so hard while limbing i would not be surprised to see it exceed 14k or more if there was nothing holding it back. i don't think there would be any benefit on an AT saw. only reason i run a higher limit is ease of tuning but AT does that for that saw anyways.

This really is a great saw to begin with, but I think they should use a higher rpm limited coil than 13300. I don't see why it shouldn't have something closer to 13,800. The 372xp has a max of 13,500 and many push those saws to 14,000.
If I had an auto tune version of this saw I would definitely test the unlimited versus the 14,100.

 

[BGE541]

When it was still rich for break in. @rattler362 built 371XP

 

[Big_Wood]

This really is a great saw to begin with, but I think they should use a higher rpm limited coil than 13300. I don't see why it shouldn't have something closer to 13,800. The 372xp has a max of 13,500 and many push those saws to 14,000.
If I had an auto tune version of this saw I would definitely test the unlimited versus the 14,100.

yep, when i get it off the hill i will give it a try. i will likely swap back to the 13,300 though as the saw works good with it. if this was a non AT saw i would have no problems running a higher limit coil. i would actually want to for ease of tuning.

 

[Big_Wood]

When it was still rich for break in. @rattler362 built 371XP

View attachment 476486

i would have no problem running a 371 that high. my old ported OE easily tuned that high as well. i would not even consider allowing an XT to turn that fast though.

 

[Chris-PA]

Do you really think the engineers are going to leave it that close? I don't. There's no way they'll have a saw blow up at a certain rpm and then limit it just barely below that.

Well of course it isn't going to blow up the first time you exceed a certain rpm, and there will be some safety margin, but there are still limits. And the discussion was in removing the limiter - but for what purpose? Your saw seems to be holding some good rpm in the cut, but nowhere near the rpms where the limiter kicks in. What is the point of increasing the max speed when it is so far above where the saw runs under load? Increasing the limit does nothing for performance at lower rpm.

I'm no expert with auto tune, in fact I know nothing about it.
A saw running the proper tune will only reach a certain rpm level unless you lean it out. Wouldn't an auto tune on a saw that large max the rpm between 13,500 and 14,000 anyways?

No. A properly tuned saw with a conventional carb will only reach a certain rpm because as the rpm goes up from max load the mixture gets increasingly richer. First it misfires ("4-strokes") and ultimately it can't rev any faster. But while it's doing all that it's pumping raw fuel out the exhaust, which is a major waste and a lot of pollution.

The whole purpose of a feedback carb is to fix this major mixture problem, so it does not 4-stroke and it does not limit the max rpm with a rich mixture. That's why they needed to limit the max rpm through the ignition module, as the mixture is now correct and won't do it.

 

[Big_Wood]

Well of course it isn't going to blow up the first time you exceed a certain rpm, and there will be some safety margin, but there are still limits. And the discussion was in removing the limiter - but for what purpose? Your saw seems to be holding some good rpm in the cut, but nowhere near the rpms where the limiter kicks in. What is the point of increasing the max speed when it is so far above where the saw runs under load? Increasing the limit does nothing for performance at lower rpm.
No. A properly tuned saw with a conventional carb will only reach a certain rpm because as the rpm goes up from max load the mixture gets increasingly richer. First it misfires ("4-strokes") and ultimately it can't rev any faster. But while it's doing all that it's pumping raw fuel out the exhaust, which is a major waste and a lot of pollution.

The whole purpose of a feedback carb is to fix this major mixture problem, so it does not 4-stroke and it does not limit the max rpm with a rich mixture. That's why they needed to limit the max rpm through the ignition module, as the mixture is now correct and won't do it.

that's what i thought. the thing sounds like it would easily reach 14k limbing without that limiter. i would not be surprised to see it go higher then that even.

 

[Chainsaw Jim]

The whole purpose of a feedback carb is to fix this major mixture problem, so it does not 4-stroke and it does not limit the max rpm with a rich mixture. That's why they needed to limit the max rpm through the ignition module, as the mixture is now correct and won't do it.

They should limit it a little higher than they are.

 

[Chris-PA]

They should limit it a little higher than they are.

But why? Is there any purpose to running up there?