Weekend project engine upgrade

[gary55]

Swaped out a engine on one of my builds. Owner wanted more power. Wish I could talk him into a good pipe. This thing runs strong with the stock pipe. Would love to see what it would do with a big bertha pipe on it.

Runwell PK80 with G4 cyl. and 6cc head.

Exhaust at 30.3mm Transfers at 34.8mm 1mm ramps at exhaust and transfers making E 29.3 T 33.8 with same 4.5mm blow down.

Made a rookie mistake and ramped according to arrow then realized it was marked wrong so had to do another ramp. Luckily the ramp on the intake side wasn't low enough to peek into the intake port. If this was a B type engine I could have had a problem there.

Matched the case, Widened the intake and dropped it 1mm. Widened the exhaust removed the partition and using a .6mm copper H gasket squish gap was .83mm with BMW head.

The advertised smoothness is true. Way less vibration then the Zeda. These will be my go to engines for future builds. Just have to use up my remaining Zeda engines first.

Before and after.
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Project dammit project.

 

[Spare_Parts]

Like how you do the ramps and case matching. Very minimal. Black engine and forks look much better imo.

 

[gary55]

Thanks Eric.I see a lot of people making the ramps blend into the top of the piston very gradually. I don't know if I'm right or wrong in my thinking but it seems to me if they are at about a 45% angle the first portion of the charge will be sent dirtectly to the top of the cylinder maybe causing a little more swirl and less lost to the intake. With the G4 ports being so low it seems like the ramps are worth it for longer transfer duration.

 

[GreasyChris]

Dang that's another sweet looking bike Gary, kick ass work as always.

 

[gary55]

Dang that's another sweet looking bike Gary, kick ass work as always.

Thanks Chris. He picked it up a little while ago. I had taken it for a test drive then let it cool to re torque everything. Tryed to fire it up for him when he got here and it wouldn't start. Pulled the plug, no spark. Pulled the mag cover to ohm out the mag, reads dead short. then it hits me the kill button is a little sticky. Give it a little tap, button pops out, mag reads good, were all happy campers. Pretty sure I got him talked into a pipe like the one on the top for next week.
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[Tyler6357]

Awesome work Gary! I like the riser on the handlebars, you don't have to always be leaning forward, you can kick back and ride.

 

[GreasyChris]

That's a cool looking pipe. Where did you get that from? Have you used that one before? How do they work?

 

[Spare_Parts]

Thanks Eric.I see a lot of people making the ramps blend into the top of the piston very gradually. I don't know if I'm right or wrong in my thinking but it seems to me if they are at about a 45% angle the first portion of the charge will be sent dirtectly to the top of the cylinder maybe causing a little more swirl and less lost to the intake. With the G4 ports being so low it seems like the ramps are worth it for longer transfer duration.

When I first started with engine mods I tapered the ramps about halfway to the center of the piston. Then one day it hit me, that is just killing the squish area. And the case matching is the same deal. Too much and you are just adding case volume. All minor stuff but it adds up. Hope you talk him into the pipe. Think it will make him much happier.

 

[gary55]

That's a cool looking pipe. Where did you get that from? Have you used that one before? How do they work?

MZMiami use to sell them on ebay, but haven't seen them for a while. I think the MZ65 became so popular they took over the niche. I think they still have them in their store. While the 65 is better for top speed the bertha is better for a long power band starting at lower rpm.

 

[Spare_Parts]

And they are loud as f*** lol.