Ported head and low end torque

[DSM]

Those of you that have ported the head on the CG clone.
Did you loose any bottom end torque?

This pushrod engine is no rev master and seems to do well at low rpm in stock form.

[JohnC]

It's pretty hard to tell. I had about 900 miles when I did my head and have put about 300 on since then. Seat of the pants says there is definitely an improvement. I also did the 4 degree advance key at the same time, so I expect that contributes as well. I have yet to do anything with the exhaust which I expect to make a big difference. I really don't want it any louder, so we'll see.



John

[TxTaoRider]

I didn't notice any loss, but I didn't really make the ports any larger. I blended the casting in the bowls, narrowed up the guide area, and smoothed out the short side radius. I left the intake port pretty rough to keep the fuel suspended better and the exhaust I used some sanding rolls on to help keep carbon from building up so quickly. I also left the "ridge" around the intake valve seat in the combustion chamber to help the fuel "shear" as it passes into the chamber and I smoothed that ridge out a little on the exhaust.

Another thing I did, as do many others, is to use a thinner head gasket to give a little more compression and it helps the squish band to work a little better, both aid in boosting power across the board.

So if you're conservative an dont just hog everything out, it should gain across the entire operating range.

Good luck!

BTW: When you're all done don't expect it to become a fire breathing motocross machine.

[Megadan]

I lost nothing on the low end. I only port matched the intake and opened up around the valve guide sides along the roof and blended the bowl. The exhaust side got the most work in terms of actual material removal because it needed it a lot more.

Top end saw a slight improvement, but the power curve of these engines is dictated by the cam far more than the head ports. If the head porting is done properly, especially if you free up the exhaust side and improve the exhaust to intake ratio, the whole power curve should improve. With all of the upgrades I have done, my bike is tractor in the mid RPM range.

[herbie]

Originally Posted by DSM

Those of you that have ported the head on the CG clone.
Did you loose any bottom end torque?

This pushrod engine is no rev master and seems to do well at low rpm in stock form.

I didn’t lose any low end torque and after the exhaust port and polish and head milling, aftermarket exhaust and the PE30 install, I was able to do small power wheelies on low end acceleration. When it was stock it was no where close to doing that. I really feel like it woke the motor up quite a bit.