ESE's works engine tuner

[oldjohnno]

I'll take a stab at this. The quantum change was the shift in reliance on using the bottom end as a pump, to the pipe creating increasingly stronger forces. Everything else then needed to evolve to keep in step with that and transfer control became critical as did more and more blow down area.

As usual you have to change everything to gain proper advantage with less detrimental effects that warned off early experiments (Jennings working with limited resources).

And possibly the new exhaust ports, having more area at the top (in order to improve blowdown) had a side effect of providing a stronger initial wave in the pipe, which in turn provided a stronger negative wave to pull from the transfers?

[Grumph]

I wonder, was that because they didnt have a decient ignition to compliment it?

Around the time of the Starmaker there were some pretty good aftermarket ignitions about. The two Starmakers that i've had through the workshop weren't stock in that area. One had points and a battery powered coil. I converted that to a Pertronix trigger with a good modern coil. Goes well with extra transfers and the squish set correctly.
The other one has a Femsa self generating ignition. I believe a period available aftermarket fitting. Probably originally for a Bultaco. Still pretty stock elsewhere. Goes well.

These engines are much underrated. Compared to traditional Villiers they're night and day.

I suspect the toroid was expensive to produce and didn't produce any more power than a conventional squish head. Production engineering wins out.

[peewee]

hey guys im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.
the other thing im trying to figure out is if you lengthen the exh passage how will the pipe react . original the passage length is 85% of bore. now its 171%. do you think the pipe might need to be significantly shorter or it wont matter much ? engmod could probly tell me but im not that good with using it

[wobbly]

The toroidal shape of the Starmaker has a fatal flaw , the turbulent eddies off the squish corner don't impinge at all on the main body of the chambers trapped A/F volume.
Those eddies are pointed at the plug , but the vast majority of the compressed volume is shrouded - thus wont see the effect of turbulence increasing the flame speed at all.

As far as the gradual change in design approach after the 70's period , is that prior to this point it wasn't appreciated how important Blowdown STA was to achieving power gains.
Thus we had amazing new high tech graphs , showing Transfer and Total Exhaust angle area only.
Case pumping only works in lawnmower 2T's , and as pipe design efficiency slowly increased so did the cylinder depression created around BDC needed to draw mixture thru the transfer ducts.

Then it soon became obvious that the old first tuning choice of case stuffing , didn't work anymore.
At that juncture making the Transfer STA bigger didn't work for two reasons , flow reversal into the transfer ports due to way too high remnant blowdown pressure , and secondly the bigger exit area compromised the flow streams
coherency due to lack of velocity.

Moving ahead to todays SOTA approach , we now end up with all the available radial area filled with transfer width , and the axial heights are set such that both the Blowdown and Transfer STA match synergistically.
Move the transfer axial height up , and blowdown is compromised , move it down and you loose transfer STA , but just as important is that an excess of Blowdown STA reduces the available remnant pressure.
The correct amount of this is needed to maximize the efficiency of the transfer stagger concept , on the scavenging and trapping regimes.

[andreas]

hey guys im trying to make a paper template of the exh roof then cut it out to mark the bore for grinding but its looking more arched than i thought. i used what frits posted. 75% bore is center radius. maybe i bungled it somehow. but see the photo to be sure.
the other thing im trying to figure out is if you lengthen the exh passage how will the pipe react . original the passage length is 85% of bore. now its 171%. do you think the pipe might need to be significantly shorter or it wont matter much ? engmod could probly tell me but im not that good with using it

There is something called a flat-width in the drawing, What is it? Seems like it should be the chord width, but here it is 51 mm. I belive Frits suggests smaller radius at the corners also. How is the ex-duct lengthen? Generally the tuned length should be same, unless you wish to alter it.

[peewee]

There is something called a flat-width in the drawing, What is it? Seems like it should be the chord width, but here it is 51 mm. I belive Frits suggests smaller radius at the corners also. How is the ex-duct lengthen? Generally the tuned length should be same, unless you wish to alter it.

yes there will be corner radius but i didnt draw it yet because the roof looked more arched than what i thought it would be. i might not understand what 75% bore=center radius.
45.5mm chord is 51mm flat on paper to draw the shape if that make sense.
the passage is lengthen by cutting off the outer shell and welding on a extra passage and welding back on new outer shell

[andreas]

I see now, it's for the templet. Would suppose the formula is for the port as it appears in the cylinder, and not the templet. If the tuned length is increased by 55mm, that isn't peanuts.

[husaberg]

The toroidal shape of the Starmaker has a fatal flaw , the turbulent eddies off the squish corner don't impinge at all on the main body of the chambers trapped A/F volume.
Those eddies are pointed at the plug , but the vast majority of the compressed volume is shrouded - thus wont see the effect of turbulence increasing the flame speed at all.

the sales blurb had the toridal head i assume in grossly exaggerated form
i did a bit of digging and the original engine drawings never had it .
The starmaker was by pommy standards of the time a pretty nice try.
The designer had spent a fairy bit of time with Herman Meier.
They used all the knowledge they had.
later variants were to be unit construction the diaphragm clutch is pretty cool and predates the other British ones.
i believe the biggest flaw was the 4 speed gearbox.
According to the person that designed it they made 100 6 speed I only have seen mention of maybe 10.


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[Grumph]

The six speed box is a nice piece of work. Needle bearings everywhere. One of the 2 through here had the six speed fitted to the engine but the frame had not been altered to fit it. I finished the job. Amusingly, when contacted, Fluff Brown's son in the UK who now runs the Starmaker business, had never seen a six speed box. He had to ask an old guy on staff how much and which oil it took. Nothing's written down apparently. FWIW, there's a level plug. Oil is your choice.
Some things never changed even though the design was a huge step forward.

Again FWIW the CR 4 speed box suits the standard porting and pipe quite well. No problems keeping it on the pipe on track at all. If they'd got their act together in good time, they could have sold a lot of entry level 250 racebikes. Next step up - and better engineered - than the Greeves. Probably cheaper to run - in the UK - than a TR250 or TD2.

[andreas]

Something I never quite understod: tire grip depending on contact area, obviously area is irrelevant for friction with solid materials. I've thought this applies to tires also, but general consensus seem to disagree. What say you?

[F5 Dave]

Look up Shear

[andreas]

Dave, which Shear is that?

[F5 Dave]

Well don't Google Sheer. That will probably get you pictures of Tights. So the other Shear..

10 second Google search which i haven'treally read bit should get you started. :

https://pediaa.com/difference-betwee...ion-and-shear/

[andreas]

Thanks for clarifying that.

[husaberg]

Something I never quite understod: tire grip depending on contact area, obviously area is irrelevant for friction with solid materials. I've thought this applies to tires also, but general consensus seem to disagree. What say you?

In NZ Tyres are anything but solid objects contact patches move and are dependant of shape and pressure and the tire is part of the suspension system whether we like it or not. With friction. why have a slipper pistons single rings skinny tyres on racing pushbikes small frontal areas large disc brakes fat rear tires on drag lso bikes. When the area or cross section is smaller with these things they tend to be also lighter skinnier more area and slippery so whilst it was seem not to change due to the other factors it does overall.
i know what you are saying in regards to Physics with the solid objects, but there are more factors than friction and area

The force due to friction is generally independent of the contact area between the two surfaces. This means that even if you have two heavy objects of the same mass, where one is half as long and twice as high as the other one, they still experience the same frictional force when you drag them over the ground. This makes sense, because if the area of contact doubles, you may think that you should get twice as much friction. But when you double the length of an object, you halve the force on each square centimeter, because less weight is above it to push down. Note that this relationship breaks down when the surface area gets too small, since then the coefficient of friction increases because the object may begin to dig into the surface.

Frits can fix what i have wrong

This doesn't explain why its easier to push things with wheels .............