ESE's works engine tuner

[bucketracer]

Bike holders shouldn't be allowed to leave the grass. That's the rule in welly. No pushing.

A little bird has told me that things are going to change and Bike holders won't be allowed to leave the grass next year.

[wax]

http://www.youtube.com/watch?v=BbUll...ature=youtu.be

This is the 50cc scooter on a shake down for the 24hour

[chalkie]

question for anybody who has an opinion,
if you cylinder only has a single exhaust port,how soon would you make the transition from the oblong
shape to the round header diameter?
the port from piston face to start of stub is 20mm,also ,would the aprillia flange missmatch work on a single port?
finally,is there an optimum angle for the exhaust port as it exits the cylinder ?
have been reading this forum for a while now,guess that Frits & Wob would be the guys in the know!
thanks in antiscipation,
chalkie,group 4 Lambretta engine,UK

[Frits Overmars]

question for anybody who has an opinion

That's a dangerous way of asking, Chalkie; you'll risk getting all kind of stupid answers, including mine.

if your cylinder only has a single exhaust port,how soon would you make the transition from the oblong shape to the round header diameter?

I would take my time. And if the header is curved, as normally found on a bike with a forward-facing exhaust, it will even flow better if you keep the flattened profile all the way through the bend.

would the aprillia flange missmatch work

Funny question, that. I never considered Aprilia a dating agency

finally,is there an optimum angle for the exhaust port as it exits the cylinder ?

The optimum roof angle is about 25°; the duct floor should be shaped so that the duct volume is minimal.

[husaberg]

no particular order and so forth click on the arrow after the posters name and it will lead you to the original post for the additional information.

That depends on the port width. A single port will not be as wide as the total width of a bridged port, so the effect will be less pronounced, but the principle remains the same: each particle of exhaust gas wants to leave the building ASAP and the shortest path is radially outward. Therefore the radial lines from the center of the cylinder bore to the edges of the exhaust port describe the initial shape of the exhaust duct's side flanks.
But the duct volume should be no larger than absolutely necessary, so continuing those radial lines would be counter-productive. As the exhaust duct floor drops, these side flanks can be curved towards each other, keeping the flow cross-area of the duct constant. The picture shows the underside of the duct.

The exhaust port isn't canted downward 30°. The flange mounting face is canted downward 30° but the roof of the exhaust duct exits the cylinder at 25°.
The reason is that this angle gives the best flow.

The power valve starts opening at 10,000 rpm and it is fully open at 12,000 rpm. It can keep up with acceleration in any gear. And when you blip the throttle in neutral, the power valve servomotor moves almost as quickly as the revcounter needle.

As a side point to what Frits was saying re 25* down angle giving the best flow.This also reduces the duct area by the cosine of the exit angle,thus reducing the duct
volume.
And this then also allows steps and transitions in the flange to promote the flow exiting the Aux Ex ports,helping blowdown efficiency.
The main handbrake at the limits of power production.
The flow exiting into the duct, just as the piston cracks open the port,is dropping over a cliff - the piston face.
This is why the down angle helps flow,it is " pointing " the exiting gases toward the duct centre,not keeping it attached, normal to the piston dome.

So the reduction in cross sectional area at the bottom of the RSA exhaust port works like an integrated oval to round transition?

Do you remember the percentage of the reduction in cross sectional area, Frits?

Attachment 270001

The trend has been for a long time to reduce the volume of all the ducts in modern engines.
Aprilias Ex duct had the bottom filled in such that it was higher than BDC and the corners filled to reduce short circuiting from the A ports.
And the cylinder duct vol was CNC machined to be smaller and smaller in total vol,but in the process heavily promoting flow from the Aux ports to increase effective blowdown flow.
One of the transfer duct entrys was smaller than the port area ( the B and biggest port ) and for sure the ratio between the A and B port duct entry areas was tested
to death within the limitation of the case available area between the studs, by several of the 100 R&D festerers.
The idea here is to reduce the inertia of the initial volume available to the cylinder,that has to be accelerated out of the duct by the negative pressure ratio across the port.
That Cagiva cylinder is very "old" technology.

Yea but Lozza was it a R3,5 and was the port at 70 + % and did it pull 14500,or even closer to the moon.

The curved convex shape of the Aprilia duct corresponds directly with the area increasing due to the Aux ducts entering the main.
Again the idea is to keep the duct volume down.

The 75% area at the cylinder exit is just something I discovered after running hundreds of sims, most of them worked best with an oval to round transition in the flange that started with this area
and the pipe header diameter equalled the total effective area of the ports.
Its been tested and proven so many times now, by so many other people, that it should be the first mod to make to any T or tripple port engine.
Here is a pic of one I have just done, that happened to have a tapered spigot - enabling the Aux ducts to be run all the way down into the pipe.
Check the big rad on the transfer duct/bore edge.

Simple answer re the odd shape and reduced area of the Ex duct exit is that with a 3 port cylinder, the area of the main port is plenty big enough to support the gas flow
created by the power being made.
The big Aux additional area allows better Blowdown STA, but this area is only needed above TRO.
Thus having a huge duct simply drops the velocity, reducing the wave amplitude into the header.
The Aprilia shape promotes the flow from the Aux ports by keeping the extra horizontal area all the way into the pipe - thus helping blowdown flow and overev power..
Reducing the duct vol by having area reducing steps, keeps the velocity high and again promotes the flow regime in the side ports.
There may be a case to say that the steps reduce backflow from the pipe at low rpm when it is too short,but for sure there is no outflow disruption,and in any case tests showed that power went up as the duct became smaller.
I have exhaustively ( pun ) tested the vol/shape effects on a T port ( as has Mr H ) and an oval to round transition with no steps works better.
A factory A Kit has a very small 41 by 32 oval, with a CNC transition into a 41 header.

Here is an oval to round spigot for Robs GP100 with RGV cylinder.
36mm pipe ID, oval shape at the duct exit is 36 wide by 27 high = effective area of a 31mm round..
This nozzle effect doesnt work on single port engines - I have tried.

Re stinger nozzles - if running a 18mm nozzle on a 100cc then you could connect a 20mm stinger tube to it in basically any length and this would not affect the power at all - in fact using the nozzle with a tapered section out to the bigger tube makes more power.
Aprilia/Derby twins do this as the top pipe has a stinger 60mm long, the bottom one is closer to 220, but the effect works on any 2T.

Some more RSA125 development info from Jan Thiel

"No pressure transducers were ever used in our engine development.
And time/aerea was never calculated.
The port timings remained practically the same during 15 years!
What we did was trying different angles and radiuses, mainly on
the transfer ducts. I think we tried 40 different types of transfer ducts
that did not chanche the time/aerea. It was all about in which direction
the charge entered the cilinder and how the tranfer streams influenced upon
each other! Also about 200 different exhaust pipes were tried. After 2004
nothing much was changed but we improved with different power jet and
ignition mapping. It seemed nearly impossible to improve the transfer ducts
any more. The exhaust ducts were CNC machined, using different programs,
mainly to reduce exhaust duct volume. Also about 100 head designs were tried"

Didnt calculate time area? Im guessing that means the time area requirement hasnt changed any in the last 15+ years.
So there you go its all about the transfer ducts, now where have I heard that before?
Check out the attached photos, I guess the idea of thinning the transfer duct bridge has gone out the window, and the exhaust duct hows that for a crazy shape


Attachment 231454
Attachment 231455
Attachment 231456

As an addition to what Wobbly said about the exhaust duct-flange diameter, there is this quote from pitlane.biz:



and the photos of RSA's duct/flange

Attachment 251236
Attachment 251237

These changes in section at the exhaust, I have been trying to understand why they work. I lost 1 bhp on one of my old engines, after I had modified a port and a step in the exhaust, yes typical idiot, but no time no money so go for it! Unfortunately the engine granaded itself in the next meeting so could not go back to check out the changes. The port mod I have since repeated on another engine, and I'm reasoably certain it was not that. The exhaust port was round with just a step at the manifold. In checking out potential reasons I have noticed in a HRC tuning manual for the RS125 that you can remove the top mismatch on the port to manifold joint but not the lower one. So it suggests that oval is not mandatory but a step is.

Not certain if I have been sniffing too much Avgas/Castrol R, but I was wondering if the step sets up a sonic shock wave across the port, so engine side is sub sonic, and waves still go up and down pipe at supersonic speed. Therefore the width of the step and its proximity to the open port is critical, just like a jet engine intake. The advantage being possibly that it stops the shock wave going into the cylinder, from my understanding if a shock wave goes into a cavity it cause chaos to any flows (jan's comment keeping exhaust and inlet seperate). Has anyone any thoughts about this or am I off my head?

Nothing to do with ducts

[TZ350]

I was sent these pictures of another sweet little F5 bike that is coming together, its made for F5, Mini Motard and Flat Tracking and looks like a very good value for money little racer that's been well engineered, I like it.

[TZ350]

After the first North Island round I thought I had better take a look at the Beasts piston top and cylinder as Cotswold had reported a knocking from the engine.



Piston crown and bore look Ok.



Transfer side, the clean outer edge corresponds to the squish band in the head. I have no idea what the other flow patterns on top of the piston mean but they look nice and even.



Head looks Ok, no over heating or signs of the piston touching the head even though the squish clearance is 0.6mm



You have to look deep down in the plug to where the ceramic meets the steel shell to be able to tell anything about the mixture, it looks OK.



This was the cause of the knocking a broken front engine mount. The small side mounts have broken off and the screw driver points to where the main spar is nearly broken right through.

[cotswold]

274141[/ATTACH]

This was the cause of the knocking a broken front engine mount. The small side mounts have broken off and the screw driver points to where the main spar is nearly broken right through.

If you need a spare down tube I cut one off one of my donor bikes

[chalkie]

thanks Frits & Husaberg for your prompt replies,was able to cut the exhaust duct this afternoon!
just need to make a new improved stub now,will let you know if it makes more power.
cheers chalkie

[jasonu]

I was sent these pictures of another sweet little F5 bike that is coming together, its made for F5, Mini Motard and Flat Tracking and looks like a very good value for money little racer that's been well engineered, I like it.

Not that it bothers me but are XR's bucket legal?

[TZ350]

Not that it bothers me but are XR's bucket legal?

This was done to death on some other thread but I can't remember what the outcome was.

And it is not one of our bikes so I don't know what all the technical details are, but it could be a perfectly legal XL, SL, CB100 engine/parts in an XR frame, hopefully the owner will fill us in.

[jasonu]

This was done to death on some other thread but I can't remember what the outcome was.

And it is not one of our bikes so I don't know what all the technical details are, but it could be a perfectly legal XL, SL, CB100 engine/parts in an XR frame, hopefully the owner will fill us in.

Fair enough mate. I hope it all goes well, F5 needs all the help it can get.
BTW any idea how No Mates' bucket went at HD last weekend?

[TZ350]

any idea how No Mates' bucket went at HD last weekend?

I don't think he ran, not enough entrys, so the mixed class got canned.

[richban]

Fair enough mate. I hope it all goes well, F5 needs all the help it can get.
BTW any idea how No Mates' bucket went at HD last weekend?

Mylaps tells some of the story. Qualified 18th and a DNF. So not so good. I would have expected that bike to smoke the 250 clunkers.

[husaberg]

Not that it bothers me but are XR's bucket legal?

This was done to death on some other thread but I can't remember what the outcome was.

And it is not one of our bikes so I don't know what all the technical details are, but it could be a perfectly legal XL, SL, CB100 engine/parts in an XR frame, hopefully the owner will fill us in.

Well the MNZ classifies the XR80 and XR100 as a trail bike. So its pretty cut and dry
So anyone who wants to argue that,they can take it up directly with them.............

Ps Rob tell the guy who's building it that i am pretty sure the MB50 transmission will go in without too much fuss.....