Widening the intake port at the bottom

I went on vacation with my bike this summer. My mother in law and wife were both nice enough to allow me to use their baggage limit so I could bring my bike on a plane for free. They had 10 kg of carry on anyway, so I'm not a tyrant ;-)

While I was on vacation, I was able to spend more time figuring out how to tune my Kheihin 22mm carb that's on my Chinagurl 66cc engine. At one point I was getting mega results, power just became intense and the high end opened up and let me out of the bottlekneck of sputtering at high end that had plaugued me always before. I like to do clutch slips, while barely squeezing the clutch, I rev it out to high rpm's and accelerate fast. Well now I had gotten it to where it accelerated so fast that I got worried about getting used to the new power. The high end got at least 20% faster. Later I was plaugued by unknown problems. Finally I discovered the black wire to my ignition coil was severed, but it was holding on by a piece of insulation. Sometimes I had good spark, then it was bad, and then it was not. So since I had already torn down the engine looking for the problem, I decided to do one mod. I realized that I could widen the intake port at the bottom where it is actually open when the piston skirt comes up. The upper part of the port never being open at all. The small diamond dust file did a pretty good job and I was able to widen it out to under the transfers. The piston ring pins not coming down that far. When I got it all back together, the power boost from the mod was really noticeable. It seemed definitely more responsive at lower RPM's.

I had the bike where it was almost popping wheelies, though I didn't want that. I had to be careful giving it gas too fast on dirt or gravel because it would spin out and drift which posed a danger of laying it down at times. All the locals in vacationland were really pleased with the way it wold take off fast, and I had my new stainless steel gas tank on which had people waving me down all the time. Up in the steep mountain roads, it had more pull than I could use due to the curvy and dangerous roads.

whatever works, go with it.
Is the intake the only port you modified?

wow...REALLY widened it


wider is always better than raising. until you run out of cylinder wall...

get yourself some dental tools if you plan on doing this more...

90 and 45 degree heads are really good for getting right into those transfers.

failing that, rather than remove material from the outer wall that then needs epoxy bog, remove the inner wall of the cylinder... it serves no purpose.

then you can REALLY get into them transfers and alter their shape.

keeping in mind that the air needs to be directed in certain directions, smoothly, with no turbulence, no bypassing straight out the exhaust, etc etc. really hard to make both sides identical yet opposite to each other...


also...make a port map BEFORE playing with your ports.... sheet of stiff paper, rolled up into cylinder, port locations pencil etched in.

then a bit of transferring of info to graph paper, combined with a degree wheel chart... and you get your open area times, and know what to modify.



then you know where youre starting, and where youre heading with subsequent cylinders.



www.amrca.com/tech/tuners.pdf

lazylightning@mail.r said:

was able to widen it out to under the transfers. The piston ring pins not coming down that far.

Click to expand...

ah.... question answered.

"remove the inner wall of the cylinder... it serves no purpose. "
NOT!
Both I and butre tried it and didn't like the results.
I think letting the piston (which is coming down) be exposed to the fuel/air mixture which is traveling upwards in the transfers causes excess turbulence which interferes with its flow.

whatever works, go with it.
Is the intake the only port you modified?

jaguar said:

"remove the inner wall of the cylinder... it serves no purpose. "
NOT!
Both I and butre tried it and didn't like the results.
I think letting the piston (which is coming down) be exposed to the fuel/air mixture which is traveling upwards in the transfers causes excess turbulence which interferes with its flow.

Click to expand...

you must link this reference to butre...

all i can find in relation to transfer walls is this

http://www.motoredbikes.com/showthr...ect-from-these-port-specs&p=399568#post399568

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I've actually cut out the transfer walls entirely before. it does really nasty things to your intake velocity but can make for one hell of a top RPM screamer


doesnt say he doesnt like the results, now, does it? maybe there was a PM i missed or its on another site altogether?

link, please.

remove the lil bit of cylinder wall and gain easy unrestricted access, increase flow, lose some velocity OR gouge out the transfers with no real idea of how theyre shaping up internally other than an eyeballed guess, and having no real control over directionality, meanwhile, also increasing flow and losing velocity, and have to bog up the exterior surface to ensure enough gasket contact area...




each to their own. it was stated plainly. do what works for you

hopefully he will see this and let us know in more detail of his results.
When I did it there was a notable power loss all thru the rpm range. a complete waste of a good cylinder.
Have you ever seen any production engine with this feature??? I haven't.
hmm, maybe there's a good reason- like it is completely counter-productive.
NO it does not increase flow, it decreases it due to the turbulence.

oops













90% of chainsaws....

but then, chainsaws cant be used in motorized bikes...

and of course, chainsaws dont run very well either so why would you bother?

compared to a ht, a chainsaw is an anchor, right?

agreed

better tell anyone using a zenoah about this cus at least one of them is a zenoah...


or maybe none of these are production cylinders perhaps? homemade?

Actually I had widened the transfers forward as far as possible with about 2mm before the start of the ring pin path. I corrected the transfers by widening the inside back far enough to give it the angle for the proper forward mix projection. As far as removing the cylinder/transfer dividing wall, I want to make it thicker on the contrary. I will be able to do this only when I cnc machine out a custom cylinder and or cast it with really wide transfer passages. The thicker cylinder/transfer dividing wall is so that it can be made to have a curve, or hump/mound on it. This is to make the flow of mix curve around for aerodynamic effect. I did round the top edges of the transfer/cylinder dividing wall on my current setup though. The thing is that the piston top doesn't even come down close to the bottom edges of the transfers. Thus I can only increase flow volume by extending the transfer forward towards the intake, which I did, and also perhaps move it back a tad towards the exhaust, considering that the inside form of the transfers have been widened so much towards the back that the flow shoots forward towards the intake. I've studied performance moped cylinders and these multi port systems have bridges to prevent the rings from snagging up anywhere. The problem with these bicycle engines in that respect is that the head bolt pattern is only 45mm. This is so close to the cylinder that it kind of prevents one from desiegning a cylinder with lots of port space since the bolt holes take up space close to the cylinder and prevent making transfer ports closer to the exhaust but with an angle cut even farther back to send the mix forwad towards the intake side. Or a wider exhaust with a bridge down the middle. This will add some restriction on expanding the cc's of this engine via stroker crank with +12mm stroke. The Honda Lead 90 for example has a 50mm stroke and a 47mm piston like ours. There is even an overbore that gives a 51mm bore and something like 103cc's. The Lead however has a 48 mm bolt pattern. Though such a setup as the Honda Lead may be inhibiting in flow area if one is trying to use the largest rated carb per cc's for maximum output. I need to study this more. Obviously the manifolds mating surfaces will have to be bigger, and perhaps a slightly larger intake and exhaust bolt pattern will be needed. I barely managed to fit up an intake tube with a 22mm inner diameter(squared it at the flange end to match the outer mating surface passage of the cylinder). By widening the intake at the bottom, I was able to utilize this large volume carb better. Obviously it had been restrictive if it became better after widening it.

So I have been imagining what I will have to do to make an improved bottom end with a 48 mm head bolt pattern and of course with the intake side carter bolt being moved back considerably so as to fit a good deep and wide third transfer(with a bridge) path up from the carter and much more metal for widening the side transfer passages to fit a high performance Lead 90 cylinder straight up. At this point it would be just good sense to go ahead and deseign in the passage and reed valve mating surface right into the carters between the new bolt position and the clutch shaft chamber. The same general area on which Arrow adapts a carter fed reed setup. I wouldn't want to have the carb connected to the carter just under the exhaust pipe like on some machines.

Actually I'm planning to do up a new(Chinese made) cylinder for a reed setup on this old lower end because the Yamaha conrod I put on it is still really nice and tight. I was thinking of a whole new engine for putting on a hybrid hydrofoil board for sea adventures. For a bicycle, I'm getting great power as it is now and a stroker with whaterever breathability that I can manage around these head bolt holes would probably be quite enough. The bicycle is great for losts of terrains and city driving, but once you get on those really steep mountain roads(adventure vacation) and off roads, and really mucked up asphalt pothole farms, or sand then one needs something a little beefier and some gears. I came to accept this on my last trip with the bicycle. My next wheel transport will be a bicycle with ATV wheels, a 125 - 200cc engine(gears for sure) with a small homemade roots blower(electromagnetic coupling on pulley) and proper internals for the engine (and race coatings). With an electric motor on the front fork for the front wheel and one on the back swing arm so I'll have 2x2 drive for really steep inclines. A small generator that will be driven by the engine and a small coupling that will allow me to connect the engine to the jackshaft at will so as to not risk my bicycle status on asphalt roads. A few batteries too. And decent lights and signals.

One of the problems with these Chinese made cylinders is the thin walls around the transfers that limit one's ability to widen them and bring the transfers forward. I managed to poke holes through on both transfers and ahve jbweld from both sides to keep those holes plugged. Not nice for the subconsciouss! I tried to add some aluminum via TIG but there was no way that I could get down between those fins. I was only able to add to the manifolds mating surfaces, which is good since the manifold passages have to be widened alot to fit a 25mm inner diameter header and a 22mm diameter flow area within a square between the two intake bolts. I was also able to add alot of aluminum to the outside of the carter at the transfers. The walls were like only one mm thin before I did that and thus a narrow mating/sealing surface. Cranks are stuffed to make up for widening passages and stuff.

My exhaust is widened to about 29 - 30mm which is just under the 70% diameter of cylinder rule. I once broke a ring on the lower edge of the exhaust port, so I really rounded it since it was already rounded quite a bit when it snagged. Maybe my piston has a little play because I trimmed the skits so that it be used with the shorter conrod (80mm). The cylinder has 5mm lathed off of the bottom to make up for the shorter rod.

Somebody around here will hook me up with a shop that plates cylinders with a type 3 anodizing like coating that they do only for aluminum cylinders. It's not a bad choice, but there may be other more advanced ones. That one is supposed to be done so it's better than a nikasil plating.