Porting a 360 H7 cylinder

[jurado]

This is a post explaining the porting done on my 360 h7 cylinder, with cappra 414 piston.  Sorry it is it Spanish, but pictures are self-explanatory.

Work basically included:

- polishing and widening intake manifold and intake cylinder ports
- polishing and widening transfers ports facing crank and cylinder
- opening and slightly raising exhaust port
- polishing and widening exhaust manifold

Result is a motor with significantly improved response throughout all the rpm range.

Regards,

http://www.tumotoverde.com/index.php?option=com_fireboard&Itemid=124&func=view&id=133482&catid=6&limit=30&limitstart=0

[Lozza]

Where is you get the right angle air grinder?
Sorry but 'polished' surfaces do not flow as well as a rough surface.

[cappra]

The only surface we polish is the exhaust port. I leave the intake and transfers rough,
only matching the ports with the liner. We learned years ago that a rough surface flows
better than a smooth. Race car guy's have known this for a long time.

[jurado]

I´ve seen people in favour of and against polishing (i.e. leaving it rough), reading all sort of theories. I guess the only way to right know is to analyse the cylinder in a flow chamber and see flow pattern. The other way would be to do a power test and get the power curve with and without the polishing.

But in my case, I have experience a significant improvement in motor response which, at the end, is the real proof

Regards,

[ChrisACT]

I´ve seen people in favour of and against polishing (i.e. leaving it rough), reading all sort of theories. I guess the only way to right know is to analyse the cylinder in a flow chamber and see flow pattern. The other way would be to do a power test and get the power curve with and without the polishing.

But in my case, I have experience a significant improvement in motor response which, at the end, is the real proof

Regards,

Even with the dyno readout, does that prove the cause of the change in power?
As I understand it, polishing does improve flow but reduces turbulence and therefore atomisation of the fuel.  So polishing transfer ports might decrease power due to a less efficient burn of the mixture but that doesn't necessarily mean it has decreased flow.

[Lozza]

I´ve seen people in favour of and against polishing (i.e. leaving it rough), reading all sort of theories. I guess the only way to right know is to analyse the cylinder in a flow chamber and see flow pattern. The other way would be to do a power test and get the power curve with and without the polishing.

But in my case, I have experience a significant improvement in motor response which, at the end, is the real proof

Regards,

Dyno or drag strip is the only way to gauge an unbiased result of modifications to an engine
Trust me leaving it rough works best here's why. If I sat 2 sheets of glass on top of one another  then attempted to push the top sheet of glass would that move easily? Would move but it would take considerable force to over come the friction, if you introduced oil between the glass it would move a lot easier but you have to overcome viscous friction. Last if I tipped a some beach sand between the glass you would find the glass moved very easily as the sheets are held apart and it can 'roll' on the grains of sand. The principal is the same with airflow , the rough surface energies the boudry layer.

http://en.wikipedia.org/wiki/Cylinder_head_porting

[maico police]

Just enjoy your bike Jurado  . If you get into any drag races and your not winning just tip some sand down the barrel.....

[ChrisACT]

I´ve seen people in favour of and against polishing (i.e. leaving it rough), reading all sort of theories. I guess the only way to right know is to analyse the cylinder in a flow chamber and see flow pattern. The other way would be to do a power test and get the power curve with and without the polishing.

But in my case, I have experience a significant improvement in motor response which, at the end, is the real proof

Regards,

Dyno or drag strip is the only way to gauge an unbiased result of modifications to an engine
Trust me leaving it rough works best here's why. If I sat 2 sheets of glass on top of one another  then attempted to push the top sheet of glass would that move easily? Would move but it would take considerable force to over come the friction, if you introduced oil between the glass it would move a lot easier but you have to overcome viscous friction. Last if I tipped a some beach sand between the glass you would find the glass moved very easily as the sheets are held apart and it can 'roll' on the grains of sand. The principal is the same with airflow , the rough surface energies the boudry layer.

http://en.wikipedia.org/wiki/Cylinder_head_porting

Sorta like the golf ball dimple effect?

[jurado]

Thank you all guys for sharing your views. We also had long time ago these discussions when preparing race cars here in Spain.

In any case, in my view there are many other aspects in our old Montesas with significantly more influence on engine power and response (i.e. carb tuning, ignition timing, exhaust pipe, etc) that polishing or not polishing intakes and transfer tunnels. Definitely, there is clear consensus on the exhaust port.

Regards,