why not get rid of the gasket to lower the squish to an ideal range, use a thin layer of yamabond, and index the piston to the bottom of the exhaust floor ??
From my experience with these bikes, high squish sucks at every part of the power range. My low squish setup totally rapes the same setup with .3mm higher squish on all accounts(.45mm and .71mm).
thats odd...since I lowered my squish, my bike just revs much higher gives a nice kick in the beginning of my powerband....it was obviously better than what my bike was when it had a squish of .67mm.
I guess it varies from different bikes/engines. Doesn't lower squish (not too low..) = lower compression = more revs/ power output?
If you look inside your cylinder and see how big the combustion chamber is you will realize that it is a miracle that these things run with that low of compression. Get your squish down first, compression is power all across the power band, no compression no power no matter what the ports are doing. You can also index your piston, I do that with the midbike engines and it works great. Go 1mm in and 1mm down on the side at a 45^ angle and you will see huge improvements without touching the transfers as you would have effectively increased their duration. Also, look into buying a C1 H2O piston, it fits the cags and is much lighter and a single ring.
What is all this piston indexing? Surely removing any matal from the piston crown will lower the compression ratio, and therefore power?
On another note, while googling piston indexing I came across spark plug indexing! - its using a copper washer under the plug to get the gap to point into the chamber when its done up tight. Seems its a good thing to do,although results may vary it won't do any harm. Every little counts, especially when tuning these cags
If i drop the gasket, the squish will get better(.5 to .6mm) but, wont the timming being off cancel any effect the squish had?!?!
DK
If i was you DK i would keep the gasket (it is really needed to seal right) but stick the barrel up on the lathe and face off half a mm off the base to get your squish. Then take the exhaust up by a few(3) mm and leave the transfers alone cos they'd be about right.
thats odd...since I lowered my squish, my bike just revs much higher gives a nice kick in the beginning of my powerband....it was obviously better than what my bike was when it had a squish of .67mm.
I guess it varies from different bikes/engines. Doesn't lower squish (not too low..) = lower compression = more revs/ power output?
What I meant is that my low squish setup really rapes the high squish setup, which is what I think you said. Lower squish would make more compression becasue the piston is moving closer to the head.
Ooh i'm on a roll tonight...
In answer to my original question about working out the port areas, I was talking a bit of bull about a general guide never being given in tuning literature. A technique for working out a good start point is there in black and white in The 2-Stroke Tuners Hand Book. Cheers Bartw . Just gotta do some mathes now. I'll post when i've got some numbers
What I meant is that my low squish setup really rapes the high squish setup, which is what I think you said. Lower squish would make more compression becasue the piston is moving closer to the head.
I think what is more likely is that by increasing the squish JDQuikSIR has actually bought the ports into a better position giving the impression that the engine runs better for a larger squish but really its due to the better port timing now.
~You can also index your piston, I do that with the midbike engines and it works great. Go 1mm in and 1mm down on the side at a 45^ angle and you will see huge improvements without touching the transfers as you would have effectively increased their duration. ~
But at the expence of Blowdown time? Given that these engines look like they usually don't have enough to start with that probably is last thing you'd want to do.
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Ohh hang on this is all wrong innit! indexing would increase blowdown not decrease it. but the exhaust opens sooner, increasing the exhast duration.
to index the piston to the exhaust port you would look through exh. port with the piston at BDC and if it (piston) is siting higher than the port floor just scribe it and grind a 45 degree chamfer from the top of the piston to the mark so it sits flush with the port at bdc, thus eliminating the "step" and allowing the gas to flow smoothly..as for plug indexing, my current ngk bm7a plug gap already faces down toward the piston/intake port:
if you indexed the piston to the exhaust port, wouldnt the exhaust duration time be closer to what it is supposed to be in the original spec since all you have done was brought the port opening/closing to the original distance now that the piston is not blocking the port opening, although i guess it would be opening sooner with the chamfer but also allowing more gas to flow smoother??? hmmmm where is blah when ya need him??? how much of a change in blowdown time would this cause & where can ya make up for it if it is really an issue??
Quote:
Originally Posted by Mr_Cag
But at the expence of Blowdown time? Given that these engines look like they usually don't have enough to start with that probably is last thing you'd want to do.
if you indexed the piston to the exhaust port, wouldnt the exhaust duration time be closer to what it is supposed to be in the original spec since all you have done was brought the port opening/closing to the original distance now that the piston is not blocking the port opening, although i guess it would be opening sooner with the chamfer but also allowing more gas to flow smoother??? hmmmm where is blah when ya need him??? how much of a change in blowdown time would this cause & where can ya make up for it if it is really an issue??
Yeah you're right, I'm wrong. i was editing that post as you posted that
Quote:
Originally Posted by cagaroni
~..as for plug indexing, my current ngk bm7a plug gap already faces down toward the piston/intake port~
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Try it in different positions to see what if any difference it makes? e.g. at 90 and 180 degress to it's current position.
What I meant is that my low squish setup really rapes the high squish setup, which is what I think you said. Lower squish would make more compression becasue the piston is moving closer to the head.
ok.. I guess it was just a bunch of miscommunication.. it's all good man!
Also, look into buying a C1 H2O piston, it fits the cags and is much lighter and a single ring.[/quote]
I think you'll find the water cooled pistons are only 37mm diameter. The air cooled pistons are 40 and 44mm.
to index the piston to the exhaust port you would look through exh. port with the piston at BDC and if it (piston) is siting higher than the port floor just scribe it and grind a 45 degree chamfer from the top of the piston to the mark so it sits flush with the port at bdc, thus eliminating the "step" and allowing the gas to flow smoothly..as for plug indexing, my current ngk bm7a plug gap already faces down toward the piston/intake port:
you COULD do that...but the real proper way would be to raise the floor and remove from the top of the exhaust port. You would basically have to add material to the lower floor so it sits flush at BDC...and remove from the top of the exhaust port. Any material you remove has to be compensated somewhere else...JB weld will work but will eventually burn off...I would weld material and grind-to-match. This goes for anyone that has a FCSC/stroker crank...since it raises the piston a few mm's..
I was told this is the most proper way of doing it....and kind of makes more sense....
I have a balanced FCSC to be put in and have started to work on my cylinder head....hopefully the result will be positive....lots of grinding and re & re...
i like that idea of adding to the floor and raising the roof, however i dont have a milling machine or a welder but i may look into that option of having someone weld material on the floor and maybe try dremmeling the roof although it looks tight to get in there evenly.. i have a fcsc & bbk on the way too and am not looking forward to all the work needed to be done to get it tuned properly..i was hoping to get away with just indexing the piston but im not sure exactly what i'm going to do at this time, i know i need to widen the ports & possibly raise the roof
