Honda PA Engine

Cylinder Porting

There's "free" power to be had by porting. I found some port maps on-line. Some are clear, some not so much. If you don't know how to port, be careful - you may end up with junk! Most important is chamfering!!!

There is about 2mm of the bottom of the transfers that is still blocked by the piston at bottom dead center. Though if you base spacer and deck the cylinder without doing anything else your blowdown(in degrees not distance) will be greatly decreased. If aiming for more than 30 degrees of blowdown your exhaust port will need to be raised significantly, increasing exhaust duration to over 175 degrees.

Now - most cylinder for USA Hobbits are P1 (for PA50I's) or P2 (for PA50II's). The P3 and P4 cylinders (P4 having the highest "stock" output) were not imported to the US.

P3 Ports 2.jpg

These are P3 ports. P3 is better than our "normal" P2 cylinders.

P4 Ports 2.jpg

These are P4 ports. The largest/most powerful ports to come from Honda. The dimensions aren't too good, though.

Bobotech Ports 2.jpg

Not sure what Bobotech is, but since the cylinder was stock diameter, I thought that it may be of use to somebody.

Stocko-shocko port map

This is the port map of a 60cc "stocko-shocko" cylinder. It is broadly similar to P3 and P4 cylinders above, but not exactly the same.

This is an example of a P1 cylinder exhaust port that's been raised and widened within safe limits. Notice the heavy chamfer on the flat section of the port window where the rings will experience the most stress.


This is an example of cleaned up transfers.

Pa1 Transfers.jpg

Cylinder Summary

This is a summary of Honda PA cylinders.

I know it's not much (Not nearly as complete as the Puch summary) but it's a start.

You can make this better by adding your own experiences, adding timings, port shapes etc. Look at the Puch wiki and be inspired.

50cc Stock Honda


By far the most reliable cylinder. But it's also by far the slowest.


50cc Italkit

No picture

Fast 50cc with bigger ports than stock cylinder. Pretty rare.

K-star 50cc


Good cast-iron cylinder. Out-performs the stock Honda cylinder, but just slightly.

60cc K-star


Cast-iron cylinder with slightly larger bore.

65cc DR


Cast-iron 65cc kit. Pretty good price/quality ratio. Torque cylinder.

65cc Polini Air cooled


Cast-iron 65cc cylinder kit. Little torque but high top speed.

Neither case nor cylinder skirt modifications are required for installation to PA50I.

65cc Malossi


Cast-iron 65cc cylinder kit. Best AC cast-iron cylinder available. Good torque and good top speed.

65cc Metrakit


65cc kit. Little known.

65cc Zeta / Parmakit


Formerly Zeta with hard chrome wall.

Now Parmakit with nicasyl wall.

65cc BiTurbo


Aluminium cylinder with good performance for it's price. Pulls well and has decent top-speed.

65cc Proma

No picture

Very rare cylinder.

65cc Fast Arrow

No Picture

No information.

65cc Polini Liquid Cooled


Cast-iron watercooled cylinder.

68cc Malossi Liquid Cooled


Aluminium watercooled cylinder.

70cc Athena


By far the best cylinder available for the Honda PA. Aluminium with nicasyl wall.

Translated by SchijnHeilig

Original from

Performance Reeds


The following text is from Boyesen:

We have a few reed options available for this reed cage. The reeds we have found are a very close match, however, not a perfect match. Depending upon the width of the reed cage, you may need to slightly sand the sides of the reeds so they will fit properly.

We have a light material dual-stage fiberglass reed set, part # 6108. The price for this reed set is $25.95 USD + shipping.

We offer a heavier material dual-stage fiberglass reed set, for a modified engine, part # 712. The price for this reed set is $25.95 USD + shipping.

We also have a single stage Carbon Tech carbon fiber reed available, part # CT110LT (low tension material) for better low to mid range, or part # CT110HT (high tension material) for top end power use. The price for either Carbon Tech reed set is $32.95 USD + shipping.

All reed sets include 2 reeds, enough for one reed cage.

With best regards,

Cheryl Boyesen Engineering 8 Rhoades Road Lenhartsville, PA 19534 USA tel # 610-756-6818 / 800-441-1177 fax # 610-756-4102 E-mail:

"Boyesen Installation Instructions"

1197817878 boyesen instructions.jpg

"Various Pictures"





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