ESE's works engine tuner

[F5 Dave]

The street bike sold only in Japan was sold everywhere in the world except US. Along with several variants of models from different manufacturers.

at a min
4 from Honda
3 from Suzuki
1 from Yamaha but also basis of the TZ (in road guise but cases sameish)

[husaberg]

v formation was all mainly about packaging, it allows slimmer designs and less rocking couples with space for decent swooping transfers. In the case of the twin crank designs it allows better weight distribution whilst maintain a suitable short wheel base plus space for reeds in the v4s.
It allows significant packaging advantages with regards to pipes on a solo compared to a inline 4 such as the TZ500

[Drew]

I shouldn't think there's a great deal can be done in the way of mechanical traction advances with a two stroke. V-twin and crossplane inline four cylinder four strokes are better for tyre grip at peak torque, since the tyre gets a good rest between pulses, but there's no way to fake that on a two stroke.

[Drew]

Though, having said that there's a noticeably smoother power from a V-twin two stroke over a parallel twin. More again with a V-3 Honda, which is odd since the two front slugs fire together yet all three slugs are of equal displacement.

To it's natural conclusion, the one slug firing by itself would be half the output of the two firing together on said Honda. In effect, giving the tyre a rest.

Always just figured it was about getting the right square of bore/stroke for the desired capacity, those cheeky wee Honda fellas!

[wobbly]

Opposed 180* twins have perfect primary balance but are a nightmare to fit on a bike, easy on a boat.
The V twin is easy to package on a bike and has no issues with transfer width over the outside of the cylinders.
They have perfect balance when set at 90* with 90* firing, but need a balance shaft when using odd angles as Honda did in late model 250GP bikes.
The cylinders can be set very close together longitudinally so reducing the rocking couple across the crank.

A parallel twin is always a compromise, between wide bore centres causing an increasing rocking couple Vs room for the transfers.
They have perfect primary balance when at 180*, and if the static balance factor is done correctly for the inclined cylinders they can be very smooth
if mounted correctly - despite the rocking couple frequency causing some buzzing at the bars.
The same engineer ( Furusawa ) at Yamaha who did the detail design of the RZ 250/350 balance and mounting did the odd fire M1/R1 race engine design.

Then finally we have a wide cylinder spaced parallel twin, firing at 90* with a balance shaft to correct the primary imbalance.
This is the scenario chosen by Bartol for the KTM250 GP engine as it gave perfectly symmetrical intakes and pipes.
If the balance shaft is used as a drive to the clutch it involves an extra pair of gears in the drivetrain, with inherent ( 3 to 5% ) power loss but KTM decided
this was a small price to pay for a reverse crank rotation,big bang ,good package size and symmetric cylinder operation - the last never achieved in a V twin on a bike.

There have been years of discussion over what effect the big bang engine has and its implementation on a bike to increase corner exit traction.
Furusawa simply said that the odd fire M1 crank reduced the regular shaped,varying inertia torque, as seen in the symmetrical fire engine, and as this crank inertia "noise "
increases as the square of rpm, at 14000+ the crank inertia effect becomes greater than the individual full power cylinder combustion pulses.
Thus the rider cannot "feel" as well,the power pulses effect on rear grip thru the contact patch.
The irregular firing in an inline 4 helps to simulate what the V5 Honda had naturally, and what the Ducati finally had when they also found that the even fire screamer V4 was impossible to ride fast.
This effect should really be described as " long smooth bang " as this reduces the vibration effect of regular power pulses at the contact patch.
Big V twins have always had big bang with only 2 power pulses hitting the tyre per 4 stroke cycle,and helps to explain Ducatis dominance of Superbike for many years.

[Frits Overmars]

The problem with making all your power with an opposed-twin with two cylinders that go bang at the same time is that it really puts the fear in your lower unit gears. To reduce drag, a racing lower unit needs to be as sleek and streamlined and SMALL as possible, with a pair of tiny bevel-gears transmitting those big bangs to the propshaft.

I love opposed twins. And for a boat, where you don't need a gearbox, I wouldn't choose anything else.
Smitty, what does the connecting shaft between crankshaft and bevel drive look like? If it has any length to speak of, it could serve as a torque shaft. The smaller its diameter, the more the firing pulses will be smoothed by the time they arrive at the bevel gears. But the boat people will have thought of this, won't they?

[Frits Overmars]

V-twin and crossplane inline four cylinder four strokes are better for tyre grip at peak torque, since the tyre gets a good rest between pulses.

The tyre is there to work, not to rest. Smoothing the pulses will lower their amplitude, which will permit the use of a softer, grippier tire compound. The 'rest between pulses' originates from an erroneous big-bang explanation. You may want to take a look here: http://www.pit-lane.biz/t1461p32-tec...moteurs-motogp

[wobbly]

Re the pipe temp issue Rob, the original pipe wall temp at 50* is correct - you need to get the latest version and always input
the values of 325*C at the bottom of the usable powerband and 425*C at peak Hp, say 9500 and 13500 in the RG project.
The red line graph with 50*C has another issue that is stopping the VERY short 660 pipe from working with the engine specs - what is the advance curve.
Every time you change the pipe length you have to optimise the advance to work with that length, not the other way around.
But I suspect the very wierd arse pipe design with the steepest diffuser ever known to man isnt helping.
In reality a 660 pipe is way,way too short - in the RG50 sim I am doing there is still good power past 14000 with a 735 pipe length.
And this setup is to try to get as wide a powerband as possible for kart track use with no PV or electronic PJ available ( yet ).
Baselines to remember here are that an Aprilia with 200* and 800 pipe revs to 14500, but needed an electronic powerjet to do this.
A 125 ICC kart engine with 84* and a 760 pipe will rev to 14500 + even with a flat line ignition, 30mm carb and no electronic powerjet.
But both of those scenarios are very well worked optimisations of the parts available.

[FastFred]

If you want to win races it pays to think outside the square .......

[husaberg]

Then finally we have a wide cylinder spaced parallel twin, firing at 90* with a balance shaft to correct the primary imbalance.
This is the scenario chosen by Bartol for the KTM250 GP engine as it gave perfectly symmetrical intakes and pipes.
If the balance shaft is used as a drive to the clutch it involves an extra pair of gears in the drivetrain, with inherent ( 3 to 5% ) power loss but KTM decided
this was a small price to pay for a reverse crank rotation,big bang ,good package size and symmetric cylinder operation - the last never achieved in a V twin on a bike.

.

Anyone got any pics of the inlets of the twin crank NSR250? i wondered if that was what Honda were trying to achieve
Could never figure out another ,unless it was to make it more slippery by being thinner but i can't see how that would work esp when they then made it wider by sticking on side mounted radiators....

[Frits Overmars]

Anyone got any pics of the inlets of the twin crank NSR250? i wondered if that was what Honda were trying to achieve. Could never figure out another ,unless it was to make it more slippery by being thinner but i can't see how that would work esp when they then made it wider by sticking on side mounted radiators....

This is the only picture I got from the twin-crank NSR inlet side. HRC didn't exactly invite photographers to their (then very troublesome) worksbikes.

[peewee]

Neels recently updated the pipe temperature model. You'll need to add ~300C compared older simulations if you installed the V5.2.1 update.

when was this update ? i dont recall getting the email about it

[TZ350]

Gigglebutton let me play in his workshop tonight so I could use his benders etc to form the copper head fins. The motor is a little offset to one side in the frame so the room for the fins is a little longer one side and a bit cramped on the other. So I bent the fins differently, same Fin area both sides though.



Square fins for the purists.



Sun Burst for the adventurous.



This is going to be my interpretation of Seattle Smittys suggestion for header pipe finning.

[TZ350]

Re the pipe temp issue Rob, the original pipe wall temp at 50* is correct - you need to get the latest version and always input the values of 325*C at the bottom of the usable powerband and 425*C at peak Hp, say 9500 and 13500 in the RG project.

Thanks Wob....



Making progress.



But I am still not sure about the 50deg, as I upgraded and the field I am looking at says "Exhaust wall temperature at Max Power". Anyway I will get to have a better look at it over the weekend.

[teriks]

when was this update ? i dont recall getting the email about it

Subject line:
"EngMod2T Updates 26 September 2014"