when you raise too much on the exhaust timing you loose bottom end torque! did you use a degree wheel to know how much degrees you raised on exhaust duration?
Yeah i was definitely expecting a loss in low end power. Na i didnt bother putting a degree wheel on it, i know from experience that 90° opening on exhuast works well, so easy way todo that is make the exhaust port height half your stroke
Yep, but if you go too aggressive you'll loose power, the higher the ports are the more duration you have but dynamic compression drops. Its a balancing act
OH and as a climber I've been trying, w/o success, to find the answer to this & suspect you may know... What general #'s are considered "woods port", "hot woods" and then "hot"? I'm asking in a gas-only (eth free of course) / no methanol, no pipes context, work saws, anyway as a climber I realized that I'm usually just doing a cut or two then repositionoing/roping whatever's next, and that I could easily "go hotter" --- if I'm currently defaulting to like 99-101 exhaust, 125 transfers(always 25deg blowdown minimum) and about 80deg intake with "strong" but not crazy compression.. Would love thoughts on "semi hot" numbers, honestly have no idea if you just increase exhaust AND intake durations simultaneously/proportionately, how you work the transfers in etc (on that note, I'd like your thoughts on something I find myself doing: I port, 1st & foremost, based on port-timing, but *then* I measure port surface-area and compare it to the OEM ratio, for instance if it was "intake port is 5% larger volume than exhaust"(regardless of its timing) then I'd widen & shape my ports seeking to maintain that "OEM relationship"..) But for a hot-saw, or "hot work-saw" that is, something running eth-free pump gas, I'm very eager to hear how you'd port (and, for context, what you consider "regular/woods port") Thanks again for such awesome content whether you can offer insight to my Q's here or not!!
Your asking the wrong person about the woods port and stuff. I based my timing of 50cc 2 stroke mini bikes i use to race, if i remeber right they would run the exhaust at 90* and transfer at 112-116*. I didnt even put a degree wheel on this saw i just made the exhaust port hight half the stroke (ruffly 90*) and left the transfers alone. Everyone tells me its wrong or too aggressive, but it works. You can actually fell it come "on band" as you play with the throttle. At the end of the day its a toy, i dont cut for a living or compete in competition, its for fun
It could be your crank seals... They often will seal fine for a little while after you start it, but as you use it and it gets up to operating temperature, they leak air into the case, then into the combustion chamber...
GREAT thought! May I ask-- HOW do you do this, specifically I mean is *my* method OK? I: - seal everything properly (ie a 3-times+ approach to diagonal bolt-tightening pattern on jugs, proper tension & loctite on fixture bolts, etc, and then do post-assembly, post-break-in retightening of everything from cylinder back) - Use gasket sealant appropriately (including spark plug's base, decomp plug's base etc, am even anal about muffler//exhaust flange tighteness) - When I suspect a potential problem, I grab "brake clean" or "carb & intake clean" sprays, and use quick short blasts at possible leak-areas, UNDER THE IMPRESSION that, on a running saw, ANY&ALL vacuum leaks would intake the potent spray and give SOME audible indication of the leak!) I know that a knee-jerk intuition is "this would only uncover vacuum/suction issues, not 'leaks'", but I would argue then that the inherent "suction/pulsing" nature of our 2-strokes means that, basically, EVERY hole/orifice in that system is BOTH intake&exhaust, all holes 'go both ways' I mean we try minimizing this by, say, the angles of the intake or exhaust ports when porting a cyilnder, but at the end of the day I'd bet even an untouched, pro-level OEM off-shelf still sees all ports experiencing *both* suction&vacuum (even if it's predominately one or the other, kinda like how the exhaust flange is an outlet, it's THE outlet in a sense, and even there *vacuum* is seen when muffler pressure > cylinder pressure sometime during blowdown's finishing) Would love your thoughts on this, or @Reds Projects thoughts, am so reluctant buying pressure/vacuum gear because *1* I only work on my own work-saws and am "mostly done" at this point, and *2* I already got a compression-gauge from auto zone, same model shown in another video, and turned out to give wildly varied readings, and they all seemed incredibly low like barely 120psi IIRC when testing a brand new cs590... so I simply returned it & considered it pointless (yes I had a perfect seal at spark plug hole, and yes I pulled that cord a million times / "max'd out" the PSI reading, could not break ~125psi-ish, was so disappointed--- yet that saw, today, is a total thumper in fact i have a skip-tooth 36" setup for it, set aside exclusively for spur-cutting large stuff, anyway yeah it's ported and all and it's not cutting fast with that bar but it works & doesn't feel like you're pushing a sawzall through a 1' Oak log LOL) Great video, blown away at the playing you guys w/ CNC/fabrication gear can do, I literally bolt muffler deflectors on my gear for metal-work is limited to my grinders' new metal-attachments (long-time wood carver, just had to go from rasps to 1/8 and 1/4 'tungsten double cuts' to start working alum like I worked wood, was blown away how good mine came/come out compared to professional work and am literally basing that on a pro's ported cylinder I happen to have in-hand ;D )
("How good they come out" am referring to my craftwork/skill w/ grinder, not porting-theory...I basically copy others' known recipes and/or default to a tendency of ~100/125/80 squishing under 25 better if 20)
If it ran rich when cold, it's not too low flowing to run right when hot. Aggressive porting like you did lowers torque, so at the same RPM, it will be lower power. Keep the RPM high.
Ok thats interesting, it didnt seem much difference cold to hot, i just assumed ive tillted the power curve (less bottom more top) so the fuel curve needed to change. Also i guessed the fuel demand was higher and the carby was running dry with sustained high rpm running. I tryed fixing in in the next episode, i also try running it on methonal
Amazed & inspired by your ingenuity here, thanks for posting!! Just a hunch but you may really dig poster "John's Custom Saws" he does modern 46*'s & 500's but has a very "outside of box" approach I rarely see. You piped a chainsaw...lol are you competing or is it strictly fun experimentation? I only work on my own work-saws, therefore pipes have zero interest to me as they aren't practical (ergo they have same appeal as, say, a saw that can only run 10sec, or requires methanol, etc) Would LOVE seeing how far a box-type exhaust system can be pushed....Dominant's "grunt gasket" is effectively a header tube, Stihl's change to exhaust port from the 084 to the 880 shows they're increasing divergence of the port so if you added a properly matched grunt-gasket that was "smooth trumpet" or had at least 2 distinct, increasing angles/lvels of divergence then you'd be greatly increasing the "suck-outta" effect created by the exhaust pulse (as, w/o a pipe's length & proper tuning of it, there's no "divergence wave's return to suck-out some charge, before baffle/convergence's wave comes to 'cram' the exhaust-flange & prevent charge spill-out") SO I have begun having a lotta fun working the box/square style muffler, because instead of "wave pulses" & acoustics you're basically stuck with an optimum being (IMO/IME!!) one wherein the exhaust charge is creating a 'cyclone'/swirling in the muffler, for instance a 660 muffler with all holes closed *except* the biggest primary exit beside the flange, in that configuration the pulse hits front of muffler, "blooms"/expands as it rolls-back and heads to the exhaust-flange *en route* to the exit....repeated pulses (operation of machine!) should simply create&speed-up 'the cyclone' here, which is both pushing & pulling if, respectively, you've: - got it so the exit forces strong exhaust gas pressure against the flange (and this does *not* require restrictions to the muffler's final exit surface area, which *is* the usual choke-point of an OEM), and: - the exhaust stream is positioned such that an active expulsion-stream is right-to-the-side of exhaust-flange, this would mean that whenever an exhaust pulse is not creating high-pressure, there's inherently a beyond-low(vacuum)pressure of said gas trying to escape. Kinda "2 birds / 1 stone" having it swirl/cyclone, so long as things are positioned properly....I love the 880 muffler's layout (would enlarge the final exit hole though), just wish the "exit tubing"'s intake were not dead in-line with the bounceback exhaust pulse, woulda been nice to have a flat baffle-wall a half inch in front of it so the air only gets there by "pressure bleed-off" and not "because it's aimed that way" (which, sadly, makes me think even more that stuff like "bark box" and "egan straight shot" products are actually inferior to the cheap, simply OEM's they replace....OEM's that only needed the muff's final exit opened up 20-40% over OEM spec and nothing more...) Thanks so much for such a great vid am gonna check your library, darnit I have *real* saw work (recoil spring, new chains, air filters etc) to do and just wanna geek-out on my project saws now ROFL ;D
Im glad you like what ive done. It was more of a fun toy then anything practical, it is a small saw. I have taken it out with the other saws to get fire wood. I just love the sound and the smell of e85 mixed with castor oil. I havnt played much with box mufflers, my back ground with 2 strokes is bikes and they all have expansion chambers so box mufflers have seemed backwards to me. The box muffler does have its place, my saw with the expansion chamber is a pain and im always burning my self on it.
The ex duration must me at least more than 180 degree for making the pipe resonate properly with the divergent cone working ,all about back wave. Beetween 185-190 the best effect. Than if you are still less and don t want port again just make a alluminium gasket forma rise up ex to 180 and also all the other port. In this case chek inlet duration must ne around 155-160 degree. Than you will already fly.
Thanks for the tips. I didnt want to go too aggressive on the port timing so 90 atdc (180) total was conservative. The pocket bike that the expansion chamber came off had similar port timing but much better bridged exhaust port and 5 transfer ports. I dont think this little motor can make fuel use of this pipe so i opted to be conservative with timing.
The problem is the timing is all out of wake. You didn't time the ports before you started, so you don't have a clue what the timing was on the exhaust, intake or the transfers. Then you ported the snot out of the exhaust then raised the cylinder so yeah its not going to run right plus the squish is way to low ,it should be around .20 not .50 thousandths.
Nah, 0.4mm clearance is for 98 gasoline, 0.7 is for 95 gasoline, 0.2 should be for something with even higher octane, it's hard to find fuel wuth octane higher than 98 at any gas station, and if you run 0.4 squish with 95 gasoline it will end up with hole in piston
I didnt do any "head work". Why would i do that? Wouldn't that be like asking a camshaft grinder to give me stock intake lobes and big as lobes on the exhaust side
@@ar2043 so your saying i should have given it heaps of exhaust duration only? Ill admit i didn't bother putting a degree wheel on this one, but the timing/port hight ive aimed for is very similar to other motors ive built with great success.
@@ar2043 that expansion chamber came off a motor that has around 90° atdc for exhaust and 118° on transfer. They make power from 8k to 15k. So i was was trying to give it a lot of duration to work with pipe and move power in the top end of the rev range
@@RedsProjects Isn't there a drive gear in this that you could adjust. Once you start messing with moving around the power you need to change the gearing to follow. You have to find the best balance of torque and rpm to extract the most hp for your application.
I use to aim for .5 with the bike motors i built back in the day. i guess i probably could have gone tighter on something this small. what would you set it at?
@@damnthiccassboye7138 this is a quote from a 2 stroke performance book. "Increased port width, to a point, is always a good thing. Locate your ring ends to be sure they will not fall into and snag a opening. On the exhaust side do not go beyond 65-70% of cylinder bore and do not go beyond piston skirt width."
15% alcohol is ok for automotive with fuel injection, probably not for carburetor. Open the jets a little for E85 and more for 100% alky. I'm not convinced that raising the ex port too much is worth it, since it throws away more of the expanding gases instead of producing power. The expansion tube probably forces some of the waste back in, but at what RPM? Don't you need some low end torque while cutting the wood? It's not a motocross bike. I appreciate your efforts at any rate.
Running the saw on e85 and methanol was just for fun, honesty i dont thing it would make much difference besides it running cooler on methanol. As far as the port hight, i setup the port timing like i use todo on small cc motorbike motors. The expansion chamber on the saw is off a 40cc motor that has a lot more aggressive port timing then i used on the saw.
@RedsProjects I started my career repairing small engines. I had one of those McCulloch MC-101 cart engines; only 100cc pushing 10 HP on gas. The compression was so high I had to use a 3/4" breaker-bar extension with a wire rope to start it, since a regular cord and handle would break the fingers. In reality, the pulley was designed for a car starter motor and v-belt. Back in that day, the Komet rotary valve on nitro was the ticket. A cart book said it pushed 40 HP but didn't say for how long. Anyway, just recently (as a graybeard) I've been watching these porting/timing videos and see, with these engines, the various timings are critical. It looks to me that even a crude dynamometer would be quite helpful in these endeavors. I also like the piston mods, especially the drilled port holes that cool the exhaust port area. The other one is the grooves at the piston crown the push the ring tighter against the wall, and also cools and lubricates the piston a little.
@@RedsProjects maybe earn some extra cash doing it.. I have a pain in the arse Mini Dirtbike keeps cutting out I've done all the checks ect and it's still cutting off ticks over soon as it hits half throttle it dies out then starts up and does the same again I'm thinking it's the cheap carb on it
@@dannythomas8296 theres not much money to be made with mini bikes. i worked in a couple motorbike shops and sometimes people would bring in china minibikes/pit bikes. we would do a service on them, fit a new tyre and maybee a new chain or pads as requested by the customer. Then when they pick the bike up they would be upset because the bill was a couple hundred bucks and they could have gone a bought a brand new bike for the same cash.
Sounds like the carb is borderline able to supply the engine under no load, then when under load when the saw is trying to hit powerband it is not getting enough air/fuel, just slap a bigger carb on it that will be able to support the needed CFM for when the engine hits power band. Run high octane if you can Or try methanol Nice build 👌👌
Check out my other videos, i mod the carby for more fuel flow and run it on e85 and methanol. Its not perfect but at the end of the day its just a fun toy
