ESE's works engine tuner

[Frits Overmars]

Enlarging the entrance to the transfer ports is usually a good thing, but not always. In an Aprilia RSA cylinder you can easily improve the inflow from the crankcase into the B-ports. There's one snag: it will cost power; it will upset the scavenging balance that Jan Thiel established after years of testing.

as always Frits hits the nail on the head,in that although the Aprilia has a very small B port entry area, most of the reduction came from Jan filling in the B duct front wall. By making it perpendicular to the bore,the effect of this along with the large ( wide and high ) port area had a much more beneficial effect on scavenging ( thus power ) than any perceived (real or not) issue with duct volume or flow " ability ".

Yes, Jans modification of the B-ducts front wall caused a reduction of the duct entrance area. But when I said that this area, and the duct volume, could easily be enlarged, I was not thinking of undoing this modification, but of removing material in the direction of the cylinder stud holes.

That seems like a logical thing to do if you look at the backward-leaning B-duct rear wall as it rises from the crankcase to the port, and if you notice the available amount of material between the duct entrances and the studs, both in the crankcase and the cylinder. It would certainly improve the inflow into the duct and enhance the kinetic energy of the flow exiting from the B-window. But that would be too much of a good thing. The B-windows are already higher and wider than the A-windows; increasing their flow even more would push the central scavenging column over to the exhaust side, causing scavenging deterioration and short-circuiting.
This peculiar set of circumstances came into being because Jan was obliged to develop new cylinders that should also do well on older engines.

Below you see an RSA cylinder with its small B-duct entry area and the extra area that seems so inviting to be added, but that would do the scavenging no good.

[adegnes]

First time on the roller for my spx/m50 creation.
There's power!
Alot of stuff needs sorting;
More belt tension for obvious reasons and the carb is hopelessly out of tune. A clutch, variator tuning, higher octane fuel etc.
It's fierce on the pipe, and dead below it.
I'm excited!

[nasone32]

Adegnes, great to see your work, can you provide more details?

[adegnes]

Adegnes, great to see your work, can you provide more details?

Thanks!
Shure! I've posted some info here in this thread, just search for posts by me containing "spx"

I've also documented it pretty well on mopedarmy.com
Here's the thread where it all started:

http://www.mopedarmy.com/forums/read.php?7,3494948

This is the continuation and where I went custom cases and rotary valve:

http://www.mopedarmy.com/forums/read.php?7,3747121

These threads are basically documentation of my journey through the two stroke world. Lots of stupid ideas and failures, but I've kept at it, and still do!

[breezy]

Thanks!
Shure! I've posted some info here in this thread, just search for posts by me containing "spx"

I've also documented it pretty well on mopedarmy.com
Here's the thread where it all started:

http://www.mopedarmy.com/forums/read.php?7,3494948

This is the continuation and where I went custom cases and rotary valve:

http://www.mopedarmy.com/forums/read.php?7,3747121

These threads are basically documentation of my journey through the two stroke world. Lots of stupid ideas and failures, but I've kept at it, and still do!

looking good ... good work

[wobbly]

I would like to believe that moving the rear Aprlia studs and then pulling back the rear wall would have a positive effect if that
operation reduced the backward lean of the B duct ie getting rid of the two dimensional bending of the flow around the corner into the port..
But as you say Frits this would upset the scavenging pattern by increasing the B port flow regime, but if the extra space gained was used then to increase the A port
flow area, this may then restore the balance - and gain an overall increase in transfer Cd.
That would then maybe allow slightly lower timings, to increase the all important ( and ultimately power limiting ) blowdown STA.
We started this discussion when it was suggested we look at ways of "improving " what Jan had achieved, but unless the same effort was put into restoring the leaning tower
geometry, then failure would be more than likely.
As we know well, several geniuses in R&D had a go at improving what Jan had done,as of course its obvious the crank needed cheek plates to reduce the case volume - only
to find the bikes thus delivered to the teams were somehow slower.
As it stands the only really optimistic direction of improvement would be to try my Ex duct length/area recommendations that work so well in the sim, and
maybe to improve the Ex duct cooling by having water all the way up to,and around the back of the spigot that I know works well in KZ2 engines.

[AndreasL]

Well done adegenes!

The moped army forums format is criminal at best though. Grrr

[adegnes]

Well done adegenes!

The moped army forums format is at least criminal at best though. Grrr

Thanks!
I think you will have a much better experience with it if you switch to "Flat view". You'll find it near the top of the page when you're inside a thread. "Threaded view" is just hopeless! Can't believe it's the default setting!

[marsheng]

Just stripped my Macio after a day's of testing and I have this strange carbon build up on the piston. It has had around 30 min running time.

It looks like the frying pan after cooking honey bacon. (Now I feel hungry)

It has these miniature hills and valleys. Any suggestions ?

Thanks Wallace.

[Frits Overmars]

Just stripped my Macio after a day's of testing and I have this strange carbon build up on the piston. It has had around 30 min running time. It looks like the frying pan after cooking honey bacon.

It looks like a lot of bad oil in the mixture and a piston that didn't get hot enough to keep its nose clean. Maybe the engine has been slurping gearbox oil through a faulty oil seal.

[Grumph]

It looks like a lot of bad oil in the mixture and a piston that didn't get hot enough to keep its nose clean. Maybe the engine has been slurping gearbox oil through a faulty oil seal.

I looked in at the track briefly. LACK of heat wouldn't have been an option - 30 deg plus air temps with a dry wind blowing and an air cooled 250....
Oil would be my guess - either gearbox or the mix has gone off.

[F5 Dave]

Never seen such goop. But I do feel like some bacon. Its a superfood don't you know?

Hey 10 more posts and we'll be at #22222.

[wobbly]

It looks like burnt oil residue on top of more burnt oil residue.
My guess, you have had oil separation at some stage, and a period where the thing has been burning a mixture of mostly oil, with little fuel.
Many oils will separate under certain conditions - many semi synthetics do it all the time in AvGas without something like acetone in the mix.

[Grumph]

It looks like burnt oil residue on top of more burnt oil residue.
My guess, you have had oil separation at some stage, and a period where the thing has been burning a mixture of mostly oil, with little fuel.
Many oils will separate under certain conditions - many semi synthetics do it all the time in AvGas without something like acetone in the mix.

Bet he's using the avgas available at Ruapuna....

[adegnes]

My comuter-scooter had similar stuff on it's piston after running 5% r40 for a short period of time. Also ran a very tight squish. The goo/tight squish combination quickly destroyed my piston, small end bearing and wrist pin. The wrist pin was missing 1mm from the bearing surface. Never heard it detonate.
Yep, I use my daily driver as a test bench.

Must add; it was not running particularly hot