ESE's works engine tuner

[Grumph]

That example has already been compromised - probably by packaging constraints. The inlets are not on the cylinder centerlines.

The bigger the single disc the harder it becomes to package it.

The simplest drive for this layout is a twisted toothed belt. But if the drive can also be a balance shaft there is logic to the layout.

[husaberg]

That example has already been compromised - probably by packaging constraints. The inlets are not on the cylinder centerlines.

The bigger the single disc the harder it becomes to package it.

The simplest drive for this layout is a twisted toothed belt. But if the drive can also be a balance shaft there is logic to the layout.

that one is slightly offset but wobs need not be. Whilst every design is a compromise, the winner has less compromises where it really matters, or has advantages that outweigh they ones the decided to make.
That said i have never seen the drive you had on the supercharged kawa.

[diesel pig]

As you are going to have to space out the cylinders for clearance with the transfers anyway if it was a supersized sharred single disc with twin ports wouldn't it have a better time area period. Than twin small discs? simplier drive to.
i am thinking like a jetski or snowmobile rotax.

I have not worked out the numbers but I do not think a single disc would work with parallel twin with big ends spaced 90* apart. I am sure the inlet timing would not work.

[Grumph]

that one is slightly offset but wobs need not be. Whilst every design is a compromise, the winner has less compromises where it really matters, or has advantages that outweigh they ones the decided to make.
That said i have never seen the drive you had on the supercharged kawa.

Just a 30mm wide polyvee belt. Never gave a problem.

[husaberg]

I have not worked out the numbers but I not think a single disc would work with parallel twin with big ends spaced 90* apart. I am sure the inlet timing would not work.

Hadnt considered that
I actually missed that I thought wob had had issues with the tss500 with the 90 set up.? rocking couple I assume?
I think at least one version if not all the KTM twins were 90.s. so maybe smaller bore and less spread still works?

[Frits Overmars]

I have not worked out the numbers but I do not think a single disc would work with parallel twin with big ends spaced 90* apart. I am sure the inlet timing would not work.

In theory it could work, but you'd need a huge disc, causing so many other problems that it wouldn't be feasible.

[flyonly]

Just a 30mm wide polyvee belt. Never gave a problem.

Do you not need a toothed belt to keep the timing of the valve?


Sent from my iPhone using Tapatalk

[Peter1962]

I think Jans passing comment that the RSA could have been better if the valve was on the front with a rear Exhaust seems quite prophetic.
Yes a rear ( straight ) pipe would make more power , as would the shorter stinger , but I have read several comments that the RSW chassis handled
better due to the RSA front pipe header dictating negatively the engine position in relation to the front wheel.

Dr Henise and I are doing a project at the moment with a parallel twin, like the KTM 250GP engine - firing at 90*, but with twin Rotary Valves across the front
and a balance shaft to drive them as well.

Sounds fantastic. Will you also incorporate Fletners 'sliding gibs' on the intake ?

[wobbly]

It does not matter how you drive it , a single RV has two issues.
Firstly getting the ports on bore center needs a huge valve, creating large unwanted increases in rotating friction and inertia that has to be accelerated.

Not getting the inlets symmetric on the bores proved to be a big power issue in the CPI Cheetah cylinders designed to fit on the Banshee bottom end.
The large CR250 reeds were offset 10mm each side of the centerlines to make them fit, and no matter what we did that asymmetric flow entering the cylinder ruined the scavenging
so badly it was very obvious on the piston wash , and power was severely reduced.
I fitted slightly smaller reeds , back on center , with a stuffer plate down one side and that fixed everything immediately.

But no matter how I visualize it I cannot see how the single valve can achieve asymmetric timing events that are spaced out 90* apart.
It works perfectly in a 180* twin as per the Rotax snow and watercraft , as the opening and closing events occur evenly across the valves horizontal axis - but
those ports are nowhere near on center.

Having the balance shaft across the front makes it easy to implement that as the RV driver as well ,and the bevel system is well proven in the Rotax engines.
That balance shaft is mandatory as I discovered , much to my annoyance with the TSS500 , and of course KTM knew this and used one to correctly balance their 90* odd fire 250GP parallel twin.
And finally yes , stealing Niels Gibb System makes perfect sense ,as long as we dont copy KTM and try to patent the damn thing.

[Grumph]

Do you not need a toothed belt to keep the timing of the valve?


Sent from my iPhone using Tapatalk

Husa sidetracked into 4T territory. It drove a Roots supercharger.

[F5 Dave]

It does not matter how you drive it , a single RV has two issues.
Firstly getting the ports on bore center needs a huge valve, creating large unwanted increases in rotating friction and inertia that has to be accelerated.

Not getting the inlets symmetric on the bores proved to be a big power issue in the CPI Cheetah cylinders designed to fit on the Banshee bottom end.
The large CR250 reeds were offset 10mm each side of the centerlines to make them fit, and no matter what we did that asymmetric flow entering the cylinder ruined the scavenging
so badly it was very obvious on the piston wash , and power was severely reduced.
I fitted slightly smaller reeds , back on center , with a stuffer plate down one side and that fixed everything immediately.

But no matter how I visualize it I cannot see how the single valve can achieve asymmetric timing events that are spaced out 90* apart.
It works perfectly in a 180* twin as per the Rotax snow and watercraft , as the opening and closing events occur evenly across the valves horizontal axis - but
those ports are nowhere near on center.

Having the balance shaft across the front makes it easy to implement that as the RV driver as well ,and the bevel system is well proven in the Rotax engines.
That balance shaft is mandatory as I discovered , much to my annoyance with the TSS500 , and of course KTM knew this and used one to correctly balance their 90* odd fire 250GP parallel twin.
And finally yes , stealing Niels Gibb System makes perfect sense ,as long as we dont copy KTM and try to patent the damn thing.

Interesting. The Cheetah kit comes with rubber manifolds that are also offset to move the carbs closer together.
On top of that they crack, as I found when I couldn't understand the tuning got worse and worse until I looked down with tank off. . Can I see . . ? Pokes finger in hole. Oh shit. Billet ones fixed issue but central shot. Custom made Airbox didn't fit anymore. Grr.

[diesel pig]

In theory it could work, but you'd need a huge disc, causing so many other problems that it wouldn't be feasible.

I will have to admit I was only thinking about a Disc the size in Husaberg's picture But thank you and Wobbly pointing out it could be done with a bigger Disc but in it's self would lead to bigger problems.

[Storbeck]

I dont understand any of your post Storbeck.
It is a parallel twin - like a Banshee , but fires at 0 - 90*.
The balance shaft is needed to correct the wildly varying primary resultant of one piston being at TDC , as the other is at peak velocity half way up the bore.
Thus it is across the front of the engine with bob weights on each end , one being the drive down to the clutch gear on the end of the crank.
It also happens to have two bevel gears to drive the pair of RV blades - as due to the asymmetric firing you cant have a single large valve operating two ports
like a Rotax snow or water craft that fires at 180*.

Somehow my mind turned 90 Deg into 45 degree then pictured something that makes no sense in retrospect.

Sounds like a very cool project.

[crbbt]

this parallel twin wouldn't happen to be about 600cc would it?

[wobbly]

Have a think about how long a 300cc pipe would be , off the back of a reverse cylinder parallel twin engine.
Not going to happen.