34 tooth swap, down hill, new personal best!

[StevenMain]

90 degree oat, 49% humidity, Density Altitude 3,000 feet
Going down a moderately sloped hill but unsure of the grade.
GPS logged on "speedometer gps" android app.

51.45 mph! I fixed the high rpm surge, the carb needed to be mounted more level and I adjusted float height. The 34 tooth sprocket is way too much though since the bike still could have gone faster I just ran out of hill. On level ground it will sustain 44 mph.

Next I need to do some quality mag wheels and a fairing of some sort.

 

[StevenMain]

Post script. .
I was wondering if there have been many people to hit 50mph on level ground? Or if it's even possible?

Stuffed case
Balanced bottom end
Fully ported Jug with 3rd Transfer port
Ported lower block halves
Windowed piston
Arrow style reed block
Keihin 20mm slide carb
Custom x pipe.
HD cdi ignition.
Milled stock head
NGK pkug

I would be happy with the performance the 44 tooth offered but I can't get the engine to continue pulling over 9700 rpms maybe try a different x pipe I've run out of ideas.

 

[Venice Motor Bikes]

This bike clocked 56.4 MPH on flat...

Keep in mind that this was on a real good day! (It will do 53-54 every day).

It has a 30T sprocket & tons of internal engine work.

 

[0megaMan]

That's fast on a bicycle!

 

[StevenMain]

I'm wondering what a better chamber and head will do for me. I'm skeptical on the head but I feel I've taken the jug to the absolute max .

 

[Venice Motor Bikes]

Post a pic of you bike so we can see what you've got

 

[StevenMain]

Hope these links work. My stuff is worn out and I can probably go a bit faster on a fresh piston and jug and now I know what it likes for porting ill spend more time on the next jug.

This one is just to show the windowed piston, I have since ported the intake as pictured above.

 

[Venice Motor Bikes]

What's going on with that boost port cut in the cylinder???

 

[StevenMain]

Just been experimenting, thinking a small jet or air and fuel could help induce swirl and gain a bit on the low end. It performs very well but obviously not 54mph on level ground like you. I don't know what you have done to get that kind of performance! I've tried about 5 different cylinder variations on porting so far and this one has the best top end and better than stock low to mid range.

I have yet to try a cr machine head but I don't know how it could possibly boost any performance. I have piston interference with one head gasket so I run two. I have a very very tight squish band.

 

[sbest]

<SNIP> I have piston interference with one head gasket so I run two. I have a very very tight squish band.

Try running 2 base gaskets and removing one of the head gaskets.
If that works well, run 3 base gaskets and use a twisted rope of teflon plumbers tape for a head gasket.

Steve

 

[StevenMain]

Good idea sbest I'll be sure to try it..... Edit... I was thinking about it though, but technically I raised ALL the ports already with porting so IDK it that would gain me anything.

 

[StevenMain]

I need this in my life

 

[sbest]

Good idea sbest I'll be sure to try it..... Edit... I was thinking about it though, but technically I raised ALL the ports already with porting so IDK it that would gain me anything.

It would tell you if raising MORE would help.
Awesome picture!
I love it. Are you Canadian?

Steve too (or is that Steve II ?)

 

[Venice Motor Bikes]

Don't touch the stock port heights!
That changes the port timing, lowers compression (& lowers performance).

 

[StevenMain]

No, the above photo is a vintage downhill bike. Just saying I need a fairing like that. That is not me!

 

[StevenMain]

Venice MB I only changed the exit angle to have the transfer charges converge just below the deck. I'm actually removing the cylinder right as we speak, going to completely full the transfers with JB weld and form an altogether new transfer port shape with correct aim, correct radius throughout, and smooth contours, not like the stock garbage ports which make a hard right 90 degree turn and aren't aimed correctly.

 

[Tyler6357]

I have yet to try a cr machine head but I don't know how it could possibly boost any performance.

If your squish gap is about .03" you will get more compression with a FredHead, also, the Fred will run the engine cooler too.

 

[StevenMain]

When I finish my CFI training and start flight instructing I'll finally have time and money, something I haven't had in a while as a college student.

I plan to prototype a heavily modified 6 port version of this engine, it will be made from stock parts, I'll tig and re machine them. If it performs amazing I'll try to set up a go fund me or something to see if I can get a foundry to produce new case halves and cylinders the end user can just slap together.

 

[sbest]

Don't touch the stock port heights!
That changes the port timing, lowers compression (& lowers performance).

For a novice, that is very good advice Venice. Typically things only get worse if you touch the height. The goal when raising port height is to trade off torque for higher rpm HP. Touching the exhaust port height with a cutter has always been a last resort for me, and only after testing with extra base gaskets or a chamfered piston.

The exhaust port on these motors are a bit taller than needed for the 38mm stroke crank, so there is lots of room for extra basegaskets. I did find a gain in my motor with extra basegaskets, so I would recommend experimenting with it, at least with gaskets.

Wow! Ambitious work with the JB Weld Steven!
At least it cuts easier than aluminum. I think I would have cut the aluminum first and filled in where needed with the JB Weld. I think the JB Weld will be less likely to come loose doing it the way you are. Keep us informed, great photo!

Steve

 

[StevenMain]

I finished the porting and got the bike back together. The ports are just as big as I had them before (BIG) and with the same timing as before, but much much better angles, AND the ports are L shaped from the factory. The added JB weld has made them more of a smooth "j" shape now. They are also angled better to point more towards the intake. I will wait until night to test top speed but one thing I've noticed immediately was that my bike actually idles AGAIN. before this the ports were too big and the L shape made low rpm total garbage and I would have to roll on the throttle slowly to 15 mpg or it would go flat. Now I can slam open the throttle and it just goes. This tells me I'm getting much higher quality flow since the ports are just as big.