CG250 Head - A Closer Look.

[JerryHawk250]

Originally Posted by Megadan

For the head only, there is likely just enough room if you can get the head bolts out.

Sorry I haven't gotten around to the bolt spacing yet. I wound up taking all day fixing my Jeep, and then ended up back at work all week. I am going to TRY and get around to it this coming weekend.

Yeah, I think it will be close. Sure would save a lot of time if it does. I wish I would taken all those measurements a few weekend ago when I had the tank off chasing down a bad connection on the fuel gauge. I had the valve cover off too and adjusted them while I had the tank off.

[franque]

Have you guys thought about something like this: https://produto.mercadolivre.com.br/...-preparado-_JM
after the head is ported? I've not really heard anything about people using alternate camshafts in their CG series motors, but it'd definitely be interesting to see what a cam would do to wake it up!

[Weldangrind]

I'd also be interested. Since there is only one lobe, neither valve event can be optimized, but a little extra lift and duration sounds like fun (as long as the valve doesn't kiss the piston). The cam that is referenced in the link is for a 125, so I'd be curious to compare it with the stock 200/230 cam profile.

[Weldangrind]

BTW, that's only $52.18 US plus shipping.

[JerryHawk250]

Originally Posted by Weldangrind

I'd also be interested. Since there is only one lobe, neither valve event can be optimized, but a little extra lift and duration sounds like fun (as long as the valve doesn't kiss the piston). The cam that is referenced in the link is for a 125, so I'd be curious to compare it with the stock 200/230 cam profile.

It looks like the lift will be the same but has a longer duration. Hmmm. could be interesting.

[ben2go]

Originally Posted by Weldangrind

I'd also be interested. Since there is only one lobe, neither valve event can be optimized, but a little extra lift and duration sounds like fun (as long as the valve doesn't kiss the piston). The cam that is referenced in the link is for a 125, so I'd be curious to compare it with the stock 200/230 cam profile.

I'm waiting on Megadan to make up a set of offset rocker arms and spin out a twin lobe cam.

[Megadan]

A small part of me is interested in the cam idea, but my whole goal is to try and simply achieve 20-22 crank hp, or roughly around 17 wheel HP without altering the power curve of the engine more than necessary. If I do this right, I should see hopefully about 4hp over stock, which I know is doable, without shifting the power curve more than a few hundred RPM, if at all.

From my own experience, and learning from the wisdom and mistakes of those before me, anybody can build impressive power numbers, but building a powerful AND useable engine is far more tricky. I have simple goals.

1. Be able to utilize the full rev range of the engine. One of the most annoying things about my Hawk is that past 7500rpm the power falls off sharply. I would like to reduce that sharp drop off into a gentle decline, giving more useable power to redline. As it sits right now, the engine basically has a 1000rpm window it simply can't utilize well, even in the lower gears.

2, Maintain the base reliability of the engine. That is why I only want to bump the compression by about half a point.

3. Not alter the powerband, as I mentioned at the beginning. Since I have relatively tall gearing, and utilize my bike mostly on-road, it is more in my interest to keep as much of that lovely mid range power this engine makes as I can.

If I were building the bike for the goal of, speed and power to go rip it up, and be as fast as a Hawk can be, then yes a Cam, higher compression, and more aggressive head work would be a great idea. The kind of power this engine build would make would be much better suited to shorter gearing, and at a certain point would also need to spin much higher RPM.

My biggest issue with the cams is that both valves share a single lobe. If you increase lift alone, both valves open more, and that on it's own could be a good thing. The issue with increasing the duration of the valve events is that by default you are decreasing lobe separation angle, which means a loss in low speed charge velocity/port vacuum. There is also an increase in wear and strain on the rest of the valvetrain from any change in cam profile, which will affect the reliability aspect to some degree.

Now, if you can find me a set of higher ratio rocker arms... I would probably do that.

[Megadan]

Originally Posted by ben2go

I'm waiting on Megadan to make up a set of offset rocker arms and spin out a twin lobe cam.

At that point I would rather spend my time fitting a different engine lol. For about $1000 I can get a 300cc water cooled 30hp engine that I know will fit the frame.... Sure, I have to figure out the cooling system, and I would probably spend another $500 making it work, but at least the gain would be worth the cost and time. Plus, I would get an extra gear out of it!

[goat67]

What engine are you talking about got a link for it? 70cc an extra gear and water cooled would go along way to really waking up my bike.
What does it have for fuel? EFI? That would be another plus.

Anyway a 300cc bike for 2600.00 (1600.00 + 1000.00) would not be bad. Shoot even add an extra 500.00 for whatever's still makes this something to consider.

[JerryHawk250]

Even the 250cc water cooled engine make 26hp and 5 speed are reasonable . https://www.ebay.com/itm/250cc-Zongs...4383.l4275.c10 and 6 speeds https://www.ebay.com/itm/Shineray-25...97.m4902.l9144 Believe me the thought crossed my mine.

[Megadan]

Been a long time coming, but I took out the valves to try and get a better overall view of the ports. So without further delay...

Exhaust first.
First Picture - A nice dead on view of the exhaust valve guide area in the port. This is by far the worst restriction of the whole head.

Second Picture - I was attempting to show the machine work done at the valve seat area from the factory. This was done to nominalize the port size at the seat, but in many spots on both the valves it created a very sharp turn into the valve and in some places actually turns the flow away from the port wall. This would cause turbulence and low pressure zones right above the valve and reduce flow a bit. Very easy flaw to clean up that can make a difference.

Third picture: Already a familiar shot, but without the valve it helps show the overall port shape much better. You can see that most of the port work will be on the top half of the head for the exhaust side. Otherwise simply smoothing out the port shape to a more consistent "roundness" and matching it to the I.D. of the header pipe is all that is really needed.

[Megadan]

Intake Side.

Picture 1.: Not as good of a picture as the exhaust side, but a dead on view of the valve guide. The intake side is a lot less intrusive into the port, but there is still a lot of material that can be removed and shaped to greatly aid in flow. Much like the exhaust, this is where the largest restriction is.

Pictures 2,3,4, 5, and 6 (4, 5 and 6 on next post): Much like the exhaust, the machine work at the valve seat area has created a ridge between the port wall where it transitions to the valve. In the case of the intake port it is more drastic and some reshaping of this area would be a huge benefit. The worst area is actually on the inside radius of the side of the port where the port crurves slightly around to the right (port is not straight on). Otherwise, some minor work to the outer radius of the valve seat area on both ports can be worked a little as well. In this heads case, the valve seat itself actually sticks out into the port a tiny bit on the inside radius, so I plan on smoothing down that edge. It's not ideal to grind on the valve seat, but it's the back edge and only maybe 1mm of the very edge. I will probably just try and file it down to prevent putting too much heat into it.

[Megadan]

4, 5, and 6...

[Megadan]

Final verdict.

For the goal of trying to improve power without harming the powerband there are two entirely different approaches that have to be taken because of how different each port is.

The intake side mainly needs some minor reshaping around the valve seat in relation to the curvature of the intake tract, a minor bit of smoothing at the intake manifold for proper port matching, and removing and reshaping the material around the valve guide.

The exhaust side is going to require much more extreme reshaping work. If I were to rate the percentage of power gained from each port, then I would say that at least 60-70% of the restriction of this head is on the exhaust side. I might pay the extra money (if it costs anything) to have them do a before and after flow bench test to compare the two.

[ben2go]

There appears to be plenty of meat in there to hog out on both sides for better flow. Do you think there would be any gains in cutting back the guides so more heat is put into the head and increase flow?