ESE's works engine tuner

[Buckets4Me]

In the picture showing installing the piston clips I notice the cutouts behind the transfer cutouts appear not at all symetrical, in fact not even similar. Is it the photo angle, an optical illusion, or some sort of 'trick' grind?

I belive they have been playing around with flow benches and trying to get even flow across the piston
also nothing is square in the gp engine the transfers are on an angle

[TZ350]

There are basically two commonly utilised methods of stating a given engine's compression ratio:

The "Uncorrected Method" (sometimes referred to as the Geometric or European method)

The "Corrected Method" (sometimes referred to as the Trapped or Japanese method)

At elevated engine speeds (rpm), the piston is moving so quickly that it will actually "outrun" the fuel/air mixture to the "leak" and "trap" a much larger volume of fuel/air in the upper cylinder than just the static volume above the exhaust port. This "trapping efficiency" improves with more rpm's.

And of course, when the bike is up on the pipe, the leak is being plugged (the 2-stroke supercharging effect) with a high pressure pulse from the expansion chamber.

So the final compression pressure is much higher than the "Corrected" compression ratio would suggest.

[bucketracer]

Starting to really come together now




Increased size of the boost port, we could have covered the old gash port but decided we would try enlarging it and drawing from the crankcase and under the piston together.



Plenum extension so the cover is not too close to the inlets bell-mouth.



Oil sucker. hopefully this will cure the oiling problem by sucking up the oil that collects at the bottom of the plenum.



Wrong ring gap, brand new piston kit, if we hadn't checked the ring gap (0.004" per inch of bore dia) we wouldn't have found that a std ring had been shipped with a 0.5 os Wiesco piston.



A view of the primary inlet tract from the plenum to the crankcase. This needs to be the correct length, or at least long enough, we found that if it was too short, we got a mid-range Blarrr problem.

There is a relationship between inside diameter, length and the inlet closing point that's important.

After retarding the inlet closing point without success to cure the mid-range Blarr problem, it was found that having the inlet too short for its ID was the real cause of the Blarrrs. Probably took TeeZee a couple of nights to figure it out, or at least the time it took to try several rotary valves with shorter timings.

[bucketracer]

Copper Cooling Fins..........

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Copper block placed so as to pick up the heat entering the cooling system from the exhaust port and dissipate it through the extra copper fining.

TeeZee has the idea that there is a lot of heat here that comes from the exhaust gases spraying directly down onto the port floor from the port window as the piston just cracks the port open.



The copper block and how it presses onto the copper cooling fin for heat transfer can be seen here.



And here......



The start of the cylinder cooling fin.



Drilling a center for the combustion chamber, the stud and screw holes for holding the fin onto the head for ease of handling.

[bucketracer]

Cutting out the combustion chamber..........



We used a hole saw for cutting out the combustion chamber.



To get a good finish to the hole its important to use a guide pin (clutch push rod from a GP125 fits) and not a drill bit as the flutes of the drill will chew out the guide hole and the finish of the hole being cut will be sloppy.



Start the cut but don't cut right through.



So there is not a lot of burring, I finished the cut from the other side.



Then I Cleaned the finished cut up with some emery and a battery drill.

[Spearfish]

Just a thought, would some CPU heatsink grease between the block on the port and fins help increase the contact patch?

[Spearfish]

doubled up

[TZ350]

Just a thought, would some CPU heatsink grease between the block on the port and fins help increase the contact patch?

Bucket used copper coat, (plenty of that around work) but I think your right CPU grease would probably have been better.

[bucketracer]

Setting the compression ratio.

From what I can see the corrected compression ratio ranges from 7-9:1, 7-8:1 for air-cooled 125 engines and 8-9:1 for high performance water-cooled ones.

Its tempting to go for the highest possible, but aside from problems with the bike going flat on top and not revving out Graham Bell in his book, Two Stroke Performance Tuning, Table 2.2 lists his ideas of permissible uncorrected compression ratios. For a 125 running 100 Octane he lists 14.3:1 and for 100/130 Avgas 15:1 as the upper limits.

Its easier to get a corrected compression ratio of 8:1 from a motor whose exhaust opens 96 degrees after TDC than one that opens 81 degrees ATDC and stay within the limits suggested by Bell. Because 96 has more volume above the exhaust port and requires a bigger head volume than 81 does.

Thomas and I chose a cylinder head volume of 9.5cc for a corrected ratio of 7.3:1 and uncorrected ratio of 14.2:1.




A quick calculation of the volume in the squish area and copper head fin leaves 6cc for the head. Pouring 6cc into the head gave us an idea of how much needed skimming from the head as a first cut.



Then it was all assembled up and measured with syringes filled with anti freeze solution. Anti freeze wont rust the engine and is easy to see, the syringes we used were a plastic 5cc and two 3cc units purchased from the local Chemist, they were only $2-3 each.



Several cuts later we got the 9.5 cc we wanted, in checking the head volume we filled the chamber until the first thread of the spark plug hole was almost covered. The top of the piston and head joint were sealed with a smear of grease.

As an added benefit, because the copper fin takes heat from the squish area and distributes it twice as quickly as the alloy head can by itself, with copper the outer fins can pull more of their weight dissipating heat.

As the heat path is longer to the outer fins, the outer fins wouldn't normally do as much work as the inner fins but with the extra copper fin, the copper carry's heat out to them as well as being a heat radiating surface itself.



Having sorted the head we made a cushion for the plenums blow off valve by gluing silicon on the cover and lightly screwing the plate to it, when the glue has set we should have a soft, flat sealing surface.

Of course non of this is the last word in 2-stroke tuning but for what its worth, its what we are up to at Team ESE.

Dad, NedKelly and Chambers have had me make plenty of parts for them before, but with Thomas's help I have been really enjoying working on my first complete motor.

Now to get this sucker fitted into TeeZee's FZR frame and see how it goes.

[SS90]

[QUOTE=bucketracer;1129874434]


Increased size of the boost port, we could have covered the old gash port but decided we would try enlarging it and drawing from the crankcase and under the piston together.

The picture of the boost port looks much better, feeding from the crankcase as well should see some real gains.

Have you tried this boost port set up with a standard induction set up? It would be interesting to find out what the results are from no other mods other than that.

On the GP Hundy of chambers if that has not been done, I believe there would be good gains there too.

Also, try 65 degrees on the boost port top edge.

[F5 Dave]

Attachment 220224

The best tool known to man for pulling lock tabs up tight and removing frost plugs from car engine blocks.

Where do you keep your tools? outside in a fish bin? Or was that one salvaged from Auckland Harbour?

[TZ350]

Where do you keep your tools? outside in a fish bin? Or was that one salvaged from Auckland Harbour?

Yes it looks pretty ugly, I shuddered when I saw Buckets picture, the boys often have to work on site with some nasty corossive materials, tools will rust like that overnight after being out on a job the day before. They have found it pays to let the tools dry out completly before CRCing them again.

[Chambers]

.

Whats this TZ?

[F5 Dave]

um, an RG50 with Simon's old tail-peice & my old swingarm?

& probably rear sprocket, which I don't think I ever got paid for. Bloody Si.

[Buckets4Me]

um, an RG50 with Simon's old tail-peice & my old swingarm?

& probably rear sprocket, which I don't think I ever got paid for. Bloody Si.

na it was TZ making sure he stayed in second place in the points ahead of CHAMBERS

even if it did mean that he was passed on the OUTSIDE by a GIRL trying to lap him

TZ350 76 points and second
CHAMBERS 62 points and thirds