Best Performance parts

[Steve Best]

I do have my shifter on the left for the exact reason you mention. It is better that way. I'm a motorcyclist so I trend in that direction with my controls. All my bikes have the front brake on the right because that is what I am used to.

I'm a Search and Rescue guy actually Speedy. I love fishing but I'm not good at it. I love eating them too. No catch and release here. Saltwater is my favourite, cod, flounder, mackeral. My sig picture is from an audit of a local river for SAR.

I am still using the standard ignition. KC Vale is doing CDI testing on another forum. Normally it shouldn't be needed until you have a tuned pipe on but I am having high rpm detonation issues even now.

As for plugs, fouling is a factor of plug heat range or jetting too rich. A hotter plug is not the answer to overly rich jetting. I am having good luck with the Chinese plugs Frank. The Chinese quality is better than I'd like to admit.

Did a bunch of pipe testing on the 48cc (stock cylinder, converted back to single speed 56T) and 66cc (44t stock cylinder), both with modded heads.
I have a recently abandoned runway in my backyard.
Level but strong winds, saw speeds of 40-58 kph against the wind and then with it.
Interesting stuff, upwind/downwind, 48cc/66cc.
48cc is in a lightweight 10spd frame (with shifter frame still in place), 66cc in a heavy MTB and big tires.
stock pipe= 44/52, 44/57,
portmatched pipe= 46/52, 46/58
Straight pipe= 40/42, 42/44
Stock portmatched pipe, baffle removed= 42/48, 42/50

Not a lot of difference in power between the two stock engines as tested.

Steve

 

[Deleted member 12676]

The ONLY adjustable CDI for these engines are the ones I make and sell.

Here's the things I recommend for better power:
1. use a good carb (such as the Mikuni VM18mm) and foam air filter
2. plane the stock head down for 135psi compression
3. make your own fiber head gasket
4. widen the intake and exhaust port
5. take some off the piston skirt in order to increase the port duration to 120 degrees
6. use JBWeld to redirect the transfer ports
7. raise the exhaust port for a duration of 157 if you want the engine to rev higher
8. buy an iridium spark plug
9. use my CDI and a Honda CR high voltage coil (or offset the magnetos woodruff key to retard the spark for better “el cheapo” timing)
10. extend an offset intake manifold with 6" rubber tubing for a low-to-mid range bump in power
11. balance the crank wheels for less engine vibration (easy to do by drilling two holes with a 3/8" carbide drill bit)
12. blow thru the stock pipe to make sure there is no flow restriction. If there is then modify the muffler design for more flow.
13. build your own torque pipe and silencer if you want to improve performance over the stock pipe

A stock head shaved down will give more power than a head with a squish band if both are set for the same cranking psi.
Why? Because the stock head has a natural curve to the inner surface that is in harmony with the intake charge flow as it ascends up the back side of the cylinder from the transfers. A head with squish band has the squish area jutting out into the flow path to interrupt it somewhat so that the area around the spark plug at the time of spark is a swirling mixture of exhaust gas and intake charge, not pure intake charge as with the standard head.
Why do all the aftermarket heads cause too high a cranking pressure?
The ledge that creates the squish area in the head takes up space. There is such little space to begin with on a head for a 66cc. And if the designer made the combustion bowl extra recessed to increase the total area (to reduce the compression to 135psi) then that removes the spark plug tip from the flow of intake charge as it swirls up the backside of the cylinder. That leads to inconsistent ignition events.
But why 135 psi? Because higher pressure causes flaking off of the cheap chrome cylinder plating.
How? The cylinder pressure pushes downward and outward on the piston rings. More cylinder pressure = more pressure of rings against cyl wall = chrome plating flaking off.
So with a head with squish band you have too much compression and in most cases an excess of squish area. When the piston is near the top the squish clearance (from piston to head) should be almost nothing so that all the intake charge is in the head dome and ready to burn as one big "ball". A 1mm squish piston-to-head clearance would be the very maximum I would ever allow but most peoples engines have more than that. The result is that portion of the total intake charge is basically harder to ignite because the flame has to flow in that confined space and is so much in contact with two cooling surfaces so that lengthens the total burn time to the detriment of engine power. (Peak combustion pressure from the burn happens between 10 and 15 degrees after top dead center in a well timed engine.) Squish bands are only beneficial to engines with high compression (>150psi) and/or that rev over 9000 RPM.
But owners of aftermarket heads with squish bands all say that they provide more power and take longer to get hot. Yes that is all true but a stock head shaved down will give a fraction more power. As to heat, my modified engine with a shaved down stock head never exceeded the permitable head temperature limit although it reved to 9200 RPM and to test its reliability I screamed it to the max and held it there for prolonged periods. Heat dissipation depends on the exposed surface area. How long it takes to get really hot depends on the surface area and the total mass of aluminum in the head. So the heavier heads do take a few minutes longer to get hot.

How to determine the existing degrees of port open duration
take off the head
move the magneto till the top of the port in question is even with the top edge of the piston
mark both the magneto and the metal frame with a pencil
rotate the magneto so that the piston is descending
when the piston comes up to where it's even with the port then mark the magneto where the metal frame mark is
measure that distance along the outside of the magneto in millimeters
measure the diameter of the magneto with digital caliper
figure the circumference as 3.14 times the diameter
divide distance between marks by circumference and multiply by 360
that gives you the degrees of port opening (if you glue on a printout of 360 degree wheel you can be even more precise)
the hardest part is knowing when the piston edge is horizontally equal with the port edge. that is because there is a clearance space between the piston and the cylinder. and with small engines the smallest of measurement differences can mean a few degrees difference.
If the transfers are not equal then use the dremel to raise the low one to be equal to the high one.

Why I don’t recommend most of the aftermarket expansion chambers
I used to race motocross and can tell by looking that most of these are racing pipes with a strong "hit". How do I know? Look at the baffle (the contracting cone). short and steeply tapered. That creates a strong return wave to the cylinder.
for street you don't want a lag and then a surge in power as revs increase. Racing pipes do that. they get away with it because the bike has a gearbox and the rider stays busy keeping the gearing right so that he always stays within the 2000 rpm powerband. You can't do that on a one gear ride.
How do owners of these pipes like them? Go ahead and ask them how they like the lag in power before it comes on the pipe. They don’t.
or how they like how much harder it is to jet the carb right after putting on the pipe. (the pre-powerband jetting is tweaked by the pipe one way, and then the opposite way for when its on the pipe. but motocrossers don't care because they only keep the engine on the pipe (in the powerband)) Well most motorized bike owners are rookies and hardly even know when their ride is jetted incorrectly so forget that question.

 

[Steve Best]

The more experience I get, the more I tend to agree with Jag, however there are a few things...
I've worked on 2 stroke heads for a lot of years, in several different motors, mostly 125cc to 350cc singles and twins.
I agree that a smooth chambered hemi style head like most of the stock ones "is in harmony with the intake charge flow as it ascends up the back side of the cylinder from the transfers. A head with squish band has the squish area jutting out into the flow path to interrupt it somewhat so that the area around the spark plug at the time of spark is a swirling mixture of exhaust gas and intake charge, not pure intake charge as with the standard head." Absolutely true. This is the best design for efficiency and high rpm power.

What I disagree with is " Squish bands are only beneficial to engines with high compression (>150psi) and/or that rev over 9000 RPM." Au contraire, They are a big help for low rpm and and work well in moderate compression engines to give stump pulling power as low as 500 rpm with reliable ignition and no detonation. High rpm has little need of squish.

The trick to getting both ends of the spectrum is to have a minimal but effective squish area that does not disrupt the harmony of the intake flow. As for actual gap, I see 0.5mm to 1mm as ideal. I experimented with these theories on these motors to find it confirmed my earlier experiences. There are threads and pictures to see some of the work.

This said Jag, this is the ONLY part of your post I differ with, I hold your work in high regard.

Steve

 

[WINDY CITY BOB]

embarrassed idont EVEN KNOW??? Whatt a squish band is ? i have the idea, but messing with it uhh-uh! no-sir-eee-BOB!!!!!! i used to work on cars in high school get pats from the junkyard and ,,,,,,,,well thats as far as i got. they ran good and were cheep

 

[Steve Best]

I think this illustrates it:

The gap is the distance between the head and the piston.
Incidently, this is what the piston on my GT2A 48cc engine is like and this is what I shaped the head to.

Here is an example of 2 different combustion chamber shapes:

The red stripe is the squish band surface.
Left is a torroidal low rpm torquer head, right is a hemi high rpm screamer.
For even more rpm and max power, put even less squish on the hemi, as Jag was talking about.

Steve

 

[Deleted member 12676]

Steve, below is a section from my page http://www.dragonfly75.com/motorbike/Compress.html

I think my tests have proved that they [heads with squish bands] don't offer enough advantage and Gordon Jennings in his Two Stroke Tuners Handbook basically backs me up here:
"But if you want to use a true (measured from top of exhaust port) compression ratio much over 6.5:1, on a high-output engine, combustion control beyond that afforded by a
non-squish cylinder head will be necessary." (he is referring to a head w/squish band being necessary for high rpm engines with more than 150psi)

please read all of my page http://www.dragonfly75.com/moto/SquishVelocity.html
The best of three squish band heads average power increase over a head w/o squish band from 5000 to 7000 is only 1.2%, a very minor amount, so I think this disproves the common concept that squish bands significantly increase engine power. It helps some, but probably mostly due to piston cooling.
And the advantage they have is only when the squish clearance is properly machined to be 15m/s or slightly more. Probably only 1% of people that buy squish band heads for these engines machine them just right in order to have the right squish velocity, so in essence most buyers of them are just shooting themselves in the foot.

 

[WINDY CITY BOB]

Thanks so much Steve that explains it in layman's terms so simply a completely understand it now.
Now I need to GTF OUT OF THIS HOUSE! ITS 90.% & RAINING & I DONT CARE! I can't take this anymore I'm gonna SNAP!

 

[FurryOnTheInside]

My 66cc engine's head came with a FLAT area around the edge and a domed piston. I think I will either have to do like Steve did and use a spare piston to sand out the flat bit into a squish band shape, or just get one of the after market heads (that I want anyway).

 

[WINDY CITY BOB]

pistons are like $6.00 ????

 

[Deleted member 12676]

more like $11-$12 http://www.pistonbikes.com/product-p/epcc25-66.htm