Ht Performance Porting Success

[Quenton Guenther]

Hi 210061741,

Several factory race bikes were given to me to race with lighter flywheels, & several with lightened & balanced crankshafts. It made a very interesting motor, but be sure the bottom end power will suffer greatly.

On a Ducati Desmo single the flywheel was replaced with a spacer and the throttle simply became an "Off & On" switch. It reved very quickly, but also shut completely down when the throttle was closed. On a Kaw 100 [baby green streak] with a lightened & balanced crankshaft the power came on so quickly it was impossible to ride on a dirt track because the rear end broke loose too quickly in the corners [fell down a lot].

I guess the best part of stuffing the piston is it doesn't disturb the fuel flow inside the crankcase.

Why not try "finger ports" on a HT motor. I moved a Kaw 100 from 18.7 HP to 21.8 HP by stuffing the piston, adding "finger ports", and cutting the rotary valve.

Another neat trick to get a small 2 stroke to perform is by using a "reed" or "pumper" carburetor. Simply drill a hole in one of the transfer ports, install a hose fitting to supply vacumm to the carburetor, and watch it rev higher than you would think possible [if it doesn't blow up].


Have fun,

 

[craisin]

well reeds sounds like the go.
and as our experienced friend has indicated cutting the bottom 1mm off intake side of the piston, I am wondering if you filed a pattern like a row of saw teeth on that side of the piston
May help inducing swirl and may help to cool the piston.

So sounds like where you put the reeds would determine crankcase size to try to reduce recipricating weight.

 

[craisin]

save stuffing the piston.

 

[AussieJester]

reed valves would make a HUGE improvement, problem is though making these motors rev aint the best thing, they are **** quality and will destroy themselves, you need to upgrade bearings and conrod crank and piston if possible. I would be looking at pocket bike 47cc motors you can get performance parts for these you can buy them off the shelf with 10hp plus and watercooled. You will definitely make the HT motors **** but they wont hold together long can guarantee you that. Like these noddies popping turbos on their stock four packs getting all impressed with their improved performance until their car is on the side of the road with blown motor... If you work the 'top end' you have to beef up the bottom end too

Best of luck...

KiM

 

[210061741]

Yes i do agree on the bottom end.

That might explain why some people have better luck with the 48cc.

I believe the 48 and the 60 have the same bottom end.
Somehow that don't seem right.
Either one is stronger than need be or the other is too weak.

We know the answer to that.

So far i have expected my 48 to blow a gasket !!!!
LOL

But it hasn't and still puts it all out there.

I think and soon will find out that there is a series of things within these motors that must balance each other out.
Not the crank either LOL

If one peformance upgrade is done without the other you start getting things out of balance.

If you work the engine as a whole and Balance the modification out i believe things will go smoothly.

Obviously if you run your motor hard it won't last as long.......

But if you have 2 motors.
1 in operation and one in standby.
If you notice a funny noise spend the 30 min swap motors and tear that baby down.

Parts are cheap if you don't destroy the motor completly.
Fix it before it breaks.

Then like changing the oil in a car change motors after certin # of miles when you know things are getting rough and repair before there is a major problem.

Thus far i've only had the 48cc but i have run 6000 / 8000 rpm for a long time and it's holding up good.

I have a 66cc Jet coming next week.
I plan to tear it apart and build it up before it ever sees the bike.

Maybe some $20.00 a piece 6202-2RS hybred ceramic stainless mainbearings.
Easily available.

The needle bearings are a little more difficult and i got to get the motor apart before i can work on thoose.

It seems though that the lack of thrust washers and the incredable amount of space for them to float around are the worst problem.

So hopefully i can get a wider set of needle bearings with the same dimensions and better quality to take the extra abuse.

The limiting factor of the motor should be the Max Velocity of the piston.

With the 66 im gonna try a differant approach.
I'm gonna mod it for the best low end torque at a useful rpm and run a much smaller gear.

The 48 take advantage of the rpm.
The 66 take advantage of the power.

If i can get the speed i need without the rpm that is wonderful.
If not i'll push the envelope.

Worst case i'm out $100 bucks.

I have been known to spend that on dinner and a few drinks.

So i guess to make a long story short if it cost me $$ as long as the fun i had was worth it i'm happy.

Hopefully this 66 dosen't change my tune.....
Iv'e realized there a different animal.

 

[AussieJester]

At the end of the day its all good fun aint it, sounds like your going about it the right way too. I would definately get onto the reed valve setup for the carby though honestly the difference it will make is light and day...Could eeeeasily adapt a carby manifold and reed valve from a pocket bike motor to the HT motors too.

Best of luck

KiM

 

[210061741]

Well i guess it's time to learn about Reeds now.

I haven't done so yet cause i read somewhere they wouldn't work right with our HT motors. I guess it is time to find out.

 

[Quenton Guenther]

Hi 210061741,

Reed valves will increase low end torque, but will decrease the top end speed. Reed valves restrict the flow at high RPMs because it is an obstruction in the intake manifold/port.

Motorcross riders use reeds whereas high speed dirt track bikes don't. As a rule reed valves remove approx 10% off the top end, however the gearing can be adjusted to make use of the additional torque at lower RPMs.

Have fun,

 

[210061741]

If iv'e learned anything here at all Ive got to say when you really get into it you find out the smallest changes really do make a big diff.

Now the bottom end porting wasn't small.
Very effective too.
Ran it for a week screaming down the road.

When i first put it back together i used no Bottom Jug Gasket.
The motor has been running smoothe at high rpm but tougher at idle.
I prolly still had some air leak somewhere too.
It either didn't idle or wouldn't stop ideling at high Rpm.
But ran like a champ going down the road.

So in my infinite wisdom i decided to double the base gasket pushing the ports up higher than normal.

Normally the base gasket is about .045 inch thick.
I put .090 under the jug.
Raised ports .090 from where they were and .045 from stock.

With that extra height from the base gasket this thing won't run right.
Just can't seem to get the carb adjusted correctly.
Usually it hits a spot where it just kicks in and smoothes out.
But now i have 4 stroking symptoms across the board.

I guess i'll take it apart again ant try with just the .045 thick gasket.

Just goes to show ya..... .045 inch isnt very much at all.
So whichever port dosen't like this.
If you ground .045 off the top of it.
You wouldn't be very happy.

The only problem i have right now is my muffeler broke loose from my SBP expansion chamber.

So thats the question is my missing muffeler causing my poor running or is it the extra base gasket.

BTW
The bike sounds sweet with no muffeler. But Loud as Heck.
I got a Lawn Mower Muffeler hoocked to it Now.

Still loud as all ..... and running like poop.

Gotta give it to the guys at SBP.

There muffeler Rocks....

Anyway i'll let you guys know about the base gasket deal when i figure it out.

 

[210061741]

I have now tried a couple of different mufflers.
Running a little better but it was running soo much better before.

I'm gonna pull 1 of the base gaskets out tonight.

This configuration dosen't seem to be working for me.

My low end did improve alot.

But my top end is all but gone.

Glad i'm playing with gaskets before cutting ports.

If i had cut them it would be over now.