Do slant heads really make a difference in power?

[xlite]

Yes, IC now . Thank you. That is the best description of "corrected" vs "uncorrected" to come along in a while. I am more familair with 4 stroke technology. This forum is an incredible source of information like that.

 

[Riding Rich]

Youre welcome.
This place has helped me out alot too.
6 mo ago i didnt even know what a HT was. LOL

Look at me now.

READ READ READ READ READ and the READ some more.
Then try to sleep wile dreaming about everything you read.
In the morning you might be tired.....
But your mind shall be enlightened.

 

[K.i.p]

Darn good thread, I have a generic slant from Zoom, 80cc, and same builder as the PK-80. It sounds like it would not hurt to shim the head up a little the first time I try to fire it. I'm a light guy and don't want launch over the bars after dropping the clutch at full pedal!

 

[Riding Rich]

Not sure.
I only go about 160 lbs. myself.
Plan on installing this PK over the weekend.
So i guess i'll find out saturday.

Even though supposed to get 12 inches of snow tommorow.
Will be even more interesting on ice.

yipieeee

 

[Riding Rich]

anyway i'm pretty sure that slant zoom is the same as the PK80-J.
I wouldn't shim the head up.
Try it first.
Just don't stop peddeling.
I milled the crap outta my Grubee head.
And i do feel the difference.
But im a try it before any changes.

 

[K.i.p]

Took a close look at my generic "Pizhou Yongxing Gasoline Engine Factory" 80cc today. Although it has the slant head the piston does not rise above the jug at TDC. Also the piston has a flat top with the number "two" stamped but no arrow. It would seem there are destinctions between the PK-80 (also "Pizhou Yongxing Gasoline Engine Factory" ) and my less expensive generic. I just thought I would add to the data base.

Below: the bottom of my head after dremel and polish work. Also a couple pics of the motor straight from the box.

 

[xlite]

Took a close look at my generic "Pizhou Yongxing Gasoline Engine Factory" 80cc today. Although it has the slant head the piston does not rise above the jug at TDC. Also the piston has a flat top with the number "two" stamped but no arrow. It would seem there are destinctions between the PK-80 (also "Pizhou Yongxing Gasoline Engine Factory" ) and my less expensive generic. I just thought I would add to the data base.

Below: the bottom of my head after dremel and polish work. Also a couple pics of the motor straight from the box.

Does it have the wide front mount?

 

[Upshifter]

I haven't had a chance to mount and run my Pk49. slant, yet. But I like it. It looks like it will fit in frames that will not take an upright spark plug.

 

[K.i.p]

Yes, wide front mount.

 

[xlite]

Yes, wide front mount.

Thank you. Now I am curious if my Zoom slants have the dome piston and what determines which one you get. I wonder if you can tell by looking in the plug hole.

 

[Riding Rich]

Well that is interesting.

I got 66/80cc Jet Silver Limited Edition Bicycle Engine.
From Pirate Cycles.

Maybe it's something to do with the limited Edition.

The piston has #5 and arrow on it.
I also notice the fins on the head are rounded more.



K.I.P

What is the Displacement listed on the Emmisions sticker ?
The PK80-J is 68.5cc.

If you have a flat top piston i would get rid of the head gaskets.
Use the thinnest aluminum you can find to make a new one.

 

[Riding Rich]

To see what piston you have turn the motor so the piston is at Bottom of stroke and look through the exhaust port.

Or just take the head off.

 

[flybytaco]

Took a close look at my generic "Pizhou Yongxing Gasoline Engine Factory" 80cc today. Although it has the slant head the piston does not rise above the jug at TDC. Also the piston has a flat top with the number "two" stamped but no arrow. It would seem there are destinctions between the PK-80 (also "Pizhou Yongxing Gasoline Engine Factory" ) and my less expensive generic. I just thought I would add to the data base.

Below: the bottom of my head after dremel and polish work. Also a couple pics of the motor straight from the box.

nothing generic about that phizou yongzing its a power king awesome motor. yes the slant head adds power all around i did a run with the straight head and followed by the slant and it was way more powerful..

 

[Riding Rich]

PowerKing - Jet Silver/Black 80cc Gas Bicycle Engine Kit | Hobbies and Interest | Online Catalog

Main importer i believe.
This is what i got from pirate cycles.

 

[skipu]

No the PK80-J is allmost 69CC total. like 68.8 something. "stroke X bore dia."

But to find compression. "Corrected Compression"
We use the swept volume of the piston above the exhaust port.
Compression dosent start until the exhaust port is closed so we use the volume of the cylinder above the top of the exhaust port.

So thoose numbers at like 15 :1 or 16:1 compression are UNcorrected.
They take the complete volume of the cylinder and use for calculation but with the ports open there isn't much compression yet.
Other than the PSI in the CrankCase and PSI caused by Expansion Chamber slammin fuel back in the chamber.

Which will add some PSI to the actual calculated compression.

But lets see.
69cc / 5cc = 13.8 :1 Uncorrected Compression Ratio.

So be careful when you talk compression and make sure you know if were talking Corrected or UNcorrected compression.

It makes a big difference in the numbers.

Going much higher than 9:1 Corrected Compression probably won't help much.

at a certin point you actually have a detrimental effect.

Make sure you cange that caged needle bearing if you go high comp.
It puts much more strain on things.

GREAT INFO IM GOING TO BUY 1 OF THOSE PK 80 NEXT THANK YOU FOR POSTING THIS KIND OF MATERIAL !!!!!

 

[Riding Rich]

Your welcome

 

[Riding Rich]

My PK80-J says on emmisions tag.

Family 9PZHS

 

[K.i.p]

Interesting to compare details. My tag states
68.5cc
family: 9pzhs.0695pp

Here are some photos where the piston can be observed. The head and jug where much more angular and square. I have contoured them to make them more rounded so as to better suit my build. Also I have sand blasted and polished the side covers and head. The original color of all assemblies was silver/grey.

 

[K.i.p]

And yes about the gaskets!

 

[K.i.p]

Complete tag from "80cc" non-descript slant head motor purchased from Zoom