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Looking good as long as the boost port sits lower than the exhaust Port it will work

If you have a degree wheel you can set it up and figure out your duration and adjust the port height accordingly
 

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There are some good tips and techniques that we can apply to our engines
 

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Chrisi is correct about the boost port direction, it should be aimed toward the spark plug. Also boost port height should be the same as main transfers. There is some debates that boost port should be slightly higher so it would help to start the scavenge loop upwards.
The main transferports in stock shape are also terrible in this respect. If you look at it, they have an abrupt angle which seems to be about 90*. They should be pointing slightly upward, following the curvature of piston dome. But it is hard to fix this by grinding because the transfer port roof cannot be raised, it will rise the duration too much. One way is to fill the corners with epoxy.

Edit: some more ranting... about the exhaust port. Enlarging the exhaust duct and making the pipe side outlet larger is a mistake. This will enlarge exhaust duct volume and rob energy from the initial exhaust pulse. (although this matters only when using a tuned exhaust pipe).
It will also slow down the flow when the area is made larger. I'm not saying exhaust port shouldn't be enlarged. But it is the cylinder side port only that should be enlarged, not the duct and exit port at the flange. I think an exit port with a 20mm diameter is quite sufficient for a 40cc engine. This should be of course converted to an oval port with the same area. I haven't calculated it yet so I'm not sure whether the stock outlet is already larger than this but I'm pretty sure that the exhaust duct could benefit from actually filling the bottom side.
 

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Blata quadard. 2 xhinese copy quads. 3 lucky 7's. 1 lucky 7 trike. 1 cag.
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Discussion Starter #25
Thanks for the input above guys, I've watched a fair few of that chaps videos, all very good info.
I will give this exhaust a try as is, ive got a few other heads Im going to work on so I will try another with the port widened but no material removed from behind and compare.
Would would be a side effect of opening up the port like this, just a decrease in power?

Took the bike and quad to the yard this morning for a spin. Both ran brilliantly. Slight blip when the quad started loosing power and then cut out right at the end of the video. Turns out some idiot in their excitement forgot to retorque the head bolts and they were all loose. So quick tighten and she was popping again. Took another video with my brother still riding to show the accelation. Bear in mind if not really set the tuning yet and he is 15 and a half stone. Its definitely got the legs on the gokart round this track only thing slowing it down is our skill.

https://flic.kr/p/2jYZWUi
https://flic.kr/p/2jZ1aSh
 

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Awesome video that thing is really moving!!!

Like everything with these engines there is a careful balance too big on the exhaust port and some of your fuel charge may leave too small and some of the uncombustible exhaust gases get trapped

 

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The quad really looks like it has some oomph. Especially considering extra weight of the quad. Are you using the stock pipe and any modifications on it? Do you use the 44mm cylinder with separate head? Would be interesting to know the final drive ratio, tyre diameter and top speed to be able to compare.

With the opened up exhaust outlet, it will probably just lose some power and high rpm capability but the difference will not be big. Hard to do a good comparison without a dyno. Acceleration tests with a timer are also a good comparison tool.
 

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Blata quadard. 2 xhinese copy quads. 3 lucky 7's. 1 lucky 7 trike. 1 cag.
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Discussion Starter #28
Quad is running a standard blata 2.5 exhaust i think that came on it.
Its running a 44mm 2piece big bore kit with two boost ports. FCC. Very enthusiastic armature blueprinting of case and head skirt. Very slightly widened exh port and opened up back of port like above, also matched it to gasket and exhaust. 15mm pumper carb with fitting kit. New 3 shoe aluminium clutch. Stock flywheel, no key and wound forward to maybe 5degree of advance. Stock electrics and cheap chinese plug that came with kit. 6tooth front and 74 rear(stock on quadard).
Not sure on tyre size.

158215


Need to grab some new plugs as the one in it is hanging in oil from breaking in engine. Its way faster than the bike which is the same gearing. Wheels are obviously bigger and its just got a stock 44mm 1piece head and no blueprinting just a bit of cleaning up of the exhasut port. Bike now needs stripping down and going over. And so it continues, lol.
 

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Blata quadard. 2 xhinese copy quads. 3 lucky 7's. 1 lucky 7 trike. 1 cag.
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Discussion Starter #29
That gold head is not on right, the flat spot is to clear the coil, if that clears your coil its ok.
Oops, I used it to clear the exhasut had to file the left corner very slightly to get the exhasut to fit. Everything else fitted alright, was tight but no issues? Shouldn't cause an issue m should it? Thanks for spotting anyway.

Max
 

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Chrisi is correct about the boost port direction, it should be aimed toward the spark plug. Also boost port height should be the same as main transfers. There is some debates that boost port should be slightly higher so it would help to start the scavenge loop upwards.
The main transferports in stock shape are also terrible in this respect. If you look at it, they have an abrupt angle which seems to be about 90*. They should be pointing slightly upward, following the curvature of piston dome. But it is hard to fix this by grinding because the transfer port roof cannot be raised, it will rise the duration too much. One way is to fill the corners with epoxy.

Edit: some more ranting... about the exhaust port. Enlarging the exhaust duct and making the pipe side outlet larger is a mistake. This will enlarge exhaust duct volume and rob energy from the initial exhaust pulse. (although this matters only when using a tuned exhaust pipe).
It will also slow down the flow when the area is made larger. I'm not saying exhaust port shouldn't be enlarged. But it is the cylinder side port only that should be enlarged, not the duct and exit port at the flange. I think an exit port with a 20mm diameter is quite sufficient for a 40cc engine. This should be of course converted to an oval port with the same area. I haven't calculated it yet so I'm not sure whether the stock outlet is already larger than this but I'm pretty sure that the exhaust duct could benefit from actually filling the bottom side.
So explain your theory on NOT posting the exhaust??? You are not making any sense, considering others on this forum have proven some of the things I perceive you are saying.
 

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Here is the theory. It's pretty simple to understand. With a higher exhaust duct floor, there is less step between the piston edge and exhaust duct, which should improve exhaust blowdown flow.


blowdown_ex_duct_floor.png


There is also other benefit which comes from less exhaust duct volume. A tuned pipe can pull fresh charge into the exhaust duct and back to the cylinder more efficiently when the volume is smaller. That helps the pipe to create larger pressure fluctuations.

I bet that no one has done a documented comparison about the exhaust duct and exit port enlargement, without including any other modifications in the comparison. So I don't regard it as a proven modification. I of course want to try this and see for myself, if I manage to do it I will post the results.
 

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Here is the theory. It's pretty simple to understand. With a higher exhaust duct floor, there is less step between the piston edge and exhaust duct, which should improve exhaust blowdown flow.


View attachment 158241

There is also other benefit which comes from less exhaust duct volume. A tuned pipe can pull fresh charge into the exhaust duct and back to the cylinder more efficiently when the volume is smaller. That helps the pipe to create larger pressure fluctuations.

I bet that no one has done a documented comparison about the exhaust duct and exit port enlargement, without including any other modifications in the comparison. So I don't regard it as a proven modification. I of course want to try this and see for myself, if I manage to do it I will post the results.
This theory is simple wrong, you shouldn't make a smaller exhaust to get less step, you should setup your cylinder in the right position to the piston. At bdc the top of the piston should be in one line with the bottom of the exhaust port, there should be no step.
It is not for nothing that multi-part outlets are used for racing cylinders in order to obtain a larger blowdown area. 3-part outlets are often as large as 90% of the bore.

In the picture I added you can see a cylinder with 40mm bore.
158242
 

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But my picture isn't referring to a point where the piston is at BDC. It refers to a point where the exhaust port is about half open. The most exhaust flow will be at this first half of the exhaust port opening. That is why this reduction of the step of piston and exhaust duct can improve blowdown flow.

Making the exhaust port wider or adding auxiliary exhaust ports is a different thing. Of course you want to gain blowdown area by these methods. But the point is that the lower half of the exhaust duct isn't so important and grinding the unimportant part larger should be avoided.

If you want you can read about this theory (and many more) from kiwibiker.co.nz topic called 'ESE's works engine tuner'. From there you can read some amazing two stroke tuning info and experiments by some very experienced and knowledgeable people. Although it can be quite time consuming as the thread is over 2000 pages...
 

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So basically that was a whole lot of words for exaclty the same porting CAM2 showed us how to do.
Inside by the piston upper is massaged and lower outside by the exhaust header. For basically a straight line for the exhaust out when the piston is halfway down.
If you need a picture there are plenty in his threads or I can give you a picture.
 

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Maybe the original point of not enlarging the pipe side outlet got a bit mixed up when I started talking about the idea of increasing the duct floor height. So yes, that is done correctly if the piston side port is not ground from bottom side. But the exhaust header side should still not be enlarged for the same reasons that I described (the volume and blowdown flow slowing down). Now one might ask what to do for the step between the round header and oval exhaust port if the exhaust port should not be ground. Well the ideal solution is to make an oval to round transition adapter which retains the same cross sectional area and does not make it any larger.
 

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Yes the right side cylinder is ported too much.
The header modification is ok, that's how the oval shape should be converted to round, or then using an adapter piece. The only problem is that the header is too large to begin with.

Challenge accepted to prove it wrong :unsure:
 

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Blata quadard. 2 xhinese copy quads. 3 lucky 7's. 1 lucky 7 trike. 1 cag.
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Discussion Starter #38
When I did the exhausts on both the bike and the quad I opened up the exhaust side much like my picture above, more so on the quad and I did the most on the latest engine pictured above. It will be interesting to compare the engines as they are both stock 44mm engines. The first of mild exhaust port matching, no boost port or any engine blueprinting.
This engine is stock beside a very rough boost port and matching window in cylinder and the heavy exhaust porting and again rough engine blueprinting. One will be a bike and the other a quad so not an ideal comparison, but it should at least tell us the rough characteristics of each engine. That's as close as ill be bothered to get to a direct comparison. Ill run them on the same exhaust for parity sake before I fit the polini. That will again be interesting to see the difference if any.
 

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Yes the right side cylinder is ported too much.
The header modification is ok, that's how the oval shape should be converted to round, or then using an adapter piece. The only problem is that the header is too large to begin with.

Challenge accepted to prove it wrong :unsure:
Not sure how you will prove it. Face to face hesd to head build would really be the only way. What dimensions are you looking at or do you even know the principals of a TOOL BASED engine in general?
If an engine with a custom CDI can't rev past 12k and yet here we have and can get 13,5 on a regular coil.
It might be the way of thinking on porting a TOOL BASED engine....An engine designed retarded to promote lowend max torque be user friendly for the tool operator.

Checkout mexicanos thread on how people who treat TOOL BASED 2 strokes like MX or eurobike 2 stroke engines never get favorable results but those skilled in the art of modifying chainsaw engines into racekart engines DO!
Check out these engines pictured, CAM2 SPECIALS, it would take a lot to top these.
Then hit up the 2 stroke boat threads and tell everyone with a 60mph 18cc weedeater engine they did it all wrong too.
Just a thought.
 

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