Performance heads

A selection of cylinder heads for a variety of performances.

Back (Top) left is a Torroidal chamber for rock crawling torque
Back (Top) right is a Hemispherical chamber similar to DT200, for top speed power
Front (Bottom) left is stock cone shaped chamber
Front (Bottom) right is stock Big Bore Vito's cone shaped chamber


I just happened to have all of these heads off at the same time so I thought I'd share.

Larry's Shee said:

Does the Vito's head have enough "extra" material to allow for rechambering?

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I think it does. It seems to perfectly follow the construction of the stock head, only larger.

I have been working on motorized bicycles for the past couple years as a means to learn more about 2 strokes, and, well, every boy always dreamed about a motorized bicycle, right? The nice thing is the power is so minuscule (starting at about 1.5hp) that gains are easy to measure. Top speed and hill climbing ability were my dynometer, using a GPS speedometer to measure and record results.

I've done a lot of work with oils, oil mix, compression ratios, crankcase stuffing, porting and of course, head and combustion chambers



It even included a few blown headgaskets along the way:


These engines gave me a great chance to experiment quick and easy.
With easy access, a head swap is less than 10 minutes:


Some of the things I've learned is that compression can do more harm than good.
There is more power in head and ports than in compression and stuffing.
Less squish area can give more rpm and power. More can give more torque.
It has been interesting.

Larry's Shee said:

Another question you may be able to answer.
Why does a Blaster have a tighter squish than a Banshee?
Not by much, but is tighter. (From what I've seen)

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RPM.
The Banshee runs 25% more rpm so it is more prone to all the rpm induced geometrical stretch effects on its rod and piston assembly, and has less need of the same level of combustion turbulence at the low rpm the Blaster requires. Turn the rpm up on a Blaster and you should open up the squish as well.

JoeAK47 played with squish in the Blaster, tightening it up to 0.010" or less, as did I and I tried it again with these small Chinese bike engines. Tighter is not better. There is a sweet range where it works best (0.020"-0.050") and beyond that is a waste. It is a well rounded bell curve, so finding the precise peak is difficult and for most of us, pointless.

My son (Triplecrown) has a Banshee that we are working on. He followed all the internet wisdom on making power. It screams but is gutless off the line and under the pipe. We'll be working on it this spring, trying to get more low rpm torque out of it. I've got these single speed Chinese bike motors so I can release the clutch under 1000rpm and have it pull to 10,000rpm with very linear power. I give up some power on top end, but end up with a very broad torque band. Imagine a Blaster that could pull away in 4th gear and chug up to 40mph without shifting!

Colwal91 said:

Can I use a vitos head on a stock jug?? 66.25mm

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Yes but there is no gain. Both the size and the shape make for less performance.
You should also use the larger (more expensive!) gasket. All-in-all a terrible proposition!