590 woods-porting, some last-second Q's (and hopes-for suggestions!)

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arborjunky
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Couldn't find a 620 (heck my 590 was a floor model) so am very aware that upgrading to its carb and/or coil may be worthwhile here, I'm going to do a "tinman style" porting job (if anyone's familiar w/ his recent 590 project) but have also read most of the old threads here and on *** and feel confident going forth, have some finer points I want to ask about though!!

Intake: Tinman says it's already high so don't touch it, am seeing Iron Horse not raising many intakes as well.... Will not be touching ceiling height, but will be "heavily scoring/roughing-up" the ceiling, "Iron Horse style". However, since this area is the only way to affect intake duration (read: fuel for next stroke, right?), I'd have thought that if you're not gonna be increasing "flow capacity" by altering the port's ceiling that you'd either lower its floor or, more likely (in my amateur opinion!) simply grind-off some of the bottom of the piston's lower skirting on the intake side, bam now you've got increased "fuel entry capacity" without having altered your #'s! I want to do this, but can't w/o knowing it's OK, certainly not doing it "on the 1st pass"!

Exhaust: Tinman raises the exhaust roof 8 or 10*, I'm a bit stuck on this as I want speed more than anything but worry about compression, and no matter how many times I watch these videos or read the threads I'm still stuck understanding the interplay between compression, speed, and exhaust-ceiling (also uncertain whether total exhaust port surface-area is a factor here, for instance only touching the ceiling height affects timing and increases blowdown, but widening the port or simply making it less oval/more square would increase flow w/o alteration of your #'s, I'm surprised I don't see this more often!

Transfers: I'd been confused why grinding the bottom/case-portion of the transfers wasn't seen "as requisite" if you're doing the piston-portion of the lower-transfers, thankfully I found an Iron Horse video where he talks of doing just that, so while I was hesitant on my transfers-approach before I'm now pretty confident am just going to copy Tinman's "internal widening" of the lowers but continue that into the case's portion so the whole of the lower-transfers are ported, not just the piston portion!)

Well that's about it, I have a handful of minutiae Q's I'll post below but ^that's basically my intention this afternoon, am about to go buy some last second gear/equipment and get rockin'!!! This is my 1st true porting, although I did do some practice on a dead cylinder (IE I couldn't test results, just grinding technique), but with Tinman's videos I basically have a cookie-cutter instructional, would not be ready for this if I had to pick my own #'s from the start!
 

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arborjunky
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I found my 6A die grinder was fine for doing my test porting.....I was gonna get a variable-speed setup for it (it's fixed 25k), but then saw how cheap the Dremel kits were...

Would you guys consider a 1.5A dremel suitable for this stuff? Would it be powerful enough to drive the "right type" of bits, the carbide burrs with deep grooves for aluminum? I was able to port using 25k rpm and sanding stones, and metal rasps, and diamond rotary bits, with my 6A, so am now in a pickle choosing whether to go grab the dimmer/variable-speed unit for my 6A grinder, or just get the 1.5A dremel!
 

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arborjunky
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I know I alluded to it but want to be clear on my misunderstanding here in hopes of learning: I still cannot figure out why there's so little, sometimes zero, widening of the ports? Is it that they're typically already coming spec'd as wide as the piston allows? Even if that were the context, there's still "flow"(total port surface-area) to be gained by "squaring" the ovalesque ports so common on husq & echo pistons, I'm confused by (a perceived) lack of people porting this way, I mean I get how important it is to alter the port-timings, and that in doing this the ports themselves now flow more, but it's hard to imagine that the increased flow just happens to be optimal, would've thought 'more is better' would be a good guideline in this case so long as it's not causing problems and squaring-off an oval port doesn't cause any problems I can see, yet I don't see people commonly doing this :p
 

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arborjunky
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Oh also......I cannot figure out something-- is it considered dangerous / too-close-to-edge to do a "keyway ignition timing advance" in addition to the porting? Watching some of mweba1 's youtubes on his 7310 ports and he's still adding a degree or two via the flywheel....hrrrmmm
 

lostone

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First off you need to know what your ignition timing is before just changing it some of the Echo models are already where you want to be and pushing it will only give it to much timing advance.
Secondly widening ports isn't always an option the shape of the piston and where the ring ends are will be an issue some times so they have to be taken into consideration, squaring off to much without an arch to help the rings isn't advised. Chamfer, Chamfer and Chamfer, when you think you have it right check it again, this is why I used AM cylinders to learn on and it took me awhile to get them right.
Thirdly Lower transfers, I tend to blend the divider to try to give a bit more towards the intake side but I believe it's more important to worry about the timing, shape and direction of the upper transfers in the end that make the difference, YMMV. Removing stock from the lower to the uppers can affect velocity also.
Lastly I have ported several saws with just a dremel, yes it's a pain to get into places but it can be done. I now use a dental tool with a Contra head to help and while it allows me to get into places I could not get with the dremel it is a bit of a pain in itself since shortening the bur's is a pain because of the way they are retained by the hand piece.
 

Ronie

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A few suggestions,
The first one is the most important one, stop taking advice from Iron Horse.
Keep the carb, remove the limiters and change out the main jet to a 199 jet.
Just widen the exhaust to 65% of the bore.
A 620 coil would make it easier to tune.
I think in another one of your threads you said you did a muffler mod.
Base gasket delete. if you can.
Put it back together and see what you think.
Practice on some older used saws.
 
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