ESE's works engine tuner

[kel]

So this picture of the Aprilia 250 inlet and disc has intrigued me for some time



it was suggested the acute angled edge (if thats the correct way to describe it?) was the closing edge, thus giving a soft closing effect. I couldn’t make sense of this, yet it didn’t seem logical for it to be the leading/opening edge either as this would surely just give away time area.
So it came up recently on pit-lane.biz “All that you wanted to know on Aprilia RSA 125 ...“ thread. The following summarises a very interesting discussion


Manuel Rainer = i am driving a 125 ccm TM KV 95 rotary valve kart engine with 86°-160° timing made like this:



and i also testet one like this:



but it doesnt works reali well.

MIC = This is because there's a big difference between your KV95 engine and the RSA. On the KV engine the inletport is above the rotary valve's centerline while on the RSA it's on the right side. The best flow with partial open carburator is by opening the inlet port from the bottom up. This is easily done on the RSA by having a disc as seen on picture. On the KV you need something like the "grinding" picture to get a similar result.

Howard Gifford = Our engine has a design drawback in that one inlet port opens from the bottom and one opens from the top. The one that opens from the top has less airflow and I suspect less power than the one that opens from the bottom.

Jan Thiel = I thought about this when we designed the RSA. And made the inlet open from the bottom!

So there you have it from Mr Thiel himself, the inlet port should open from the bottom up. The angling of the disc as per the first picture is implemented in this way to best simulate the effect of opening from the bottom up!
edit; the third photo is of the FPE's RSA inlet.

[kel]

Frits, I have a question on the above post re disc valves if I may. The angled opening edge of the valve will sacrifce time area, in my engine this is a problem as the time area is borderline for the power Im wanting out. To recover the time area should I start experimenting with opening the inlet earlier? (keeping in mind the tight nature of the kart tracks our machines are used on). Current timing is 140/80 which while not radical is nearing the limits for kart track use, or is it?

[husaberg]

As I mentioned above the disk is a limiting factor, the diameter is 106 mm.

Measuring inside a spare GP125 cover the disk looks to be 115mm diameter.

Somebody asked about the Aprilia's inlet disk diameter. From memory I would say it was 126 mm.

Its definitely a 125 Gav.
end goal is a kart track useable rwp 24hp (50% more power than my FXR).

Frits, I have a question on the above post re disc valves if I may. The angled opening edge of the valve will sacrifce time area, in my engine this is a problem as the time area is borderline for the power Im wanting out. To recover the time area should I start experimenting with opening the inlet earlier? (keeping in mind the tight nature of the kart tracks our machines are used on). Current timing is 140/80 which while not radical is nearing the limits for kart track use, or is it?

[wobbly]

One of the fastest open class kart engines in the country is a Pavesi 144 I built a while ago.
Its RV timing is 140/88 with a 39mm carb on pump gas.
Open any earlier and the jetting becomes impossibly finicky to get right, close any later and it loses all the mid power, due to no PV.
But close any earlier and it wont rev to 13800.
As always a compromise has to be struck.
The RV is 126 dia thus port time area isnt the issue, its the shape of the powerband needed to be fast that has to be right.

[Frits Overmars]

Frits, I have a question on the above post re disc valves if I may. The angled opening edge of the valve will sacrifce time area, in my engine this is a problem as the time area is borderline for the power Im wanting out. To recover the time area should I start experimenting with opening the inlet earlier? (keeping in mind the tight nature of the kart tracks our machines are used on). Current timing is 140/80 which while not radical is nearing the limits for kart track use, or is it?

Wobbly said it all. Closing the disc later than 88° aTDC costs top end power; closing it earlier would give more bottom and mid power, but with a 39 mm carb the engine would run out of breath too soon. Aprilia used 42 or 43 mm carbs (most riders preferred the 42) and a closure timing of about 85° aTDC.
What you can do with any carb, large or small, is to shorten the inlet tract as much as possible. This may allow you to close the disc earlier, giving a more civilized engine behaviour, and still maintain decent crankcase filling at high revs.
Or you could go the opposite route: increase crankcase volume, increase inlet tract length, and leave the inlet disc out altogether: 24/7-inlet. But then you will need some sort of hinged reed to enable starting. And I don't think anybody will manage to get decent carburation in both the reed-phase and the 24/7-phase; It will take fuel injection to get both phases right.

Opening the disc earlier in order to increase inlet angle.area will function mathematically but angle.area is only one of the factors affecting intake flow. It would not be very wise to open the disc when crankcase pressure is still higher than the pressure upstream of the disc.
The lower the revs, the more time there is available for the crankcase pressure to drop; at 9000 rpm you could open the disc before BDC to good effect; crankcase pressure would not drop so far and scavenging flow would not be slowed down so much, resulting in more mixture reaching the cylinder. But such an early opening timing would seek revenge at higher revs.
Another effect, also mentioned by Wobbly: the earlier you open the disc, the smaller the pressure difference between crankcase and inlet tract and the weaker the suction pulse at the needle jet, which makes setting the carburation increasingly difficult.

[kel]

Thanks guys. I will cut the disc to the same base timing as per the regular disc, test and compare, then add a couple of degrees to the closing point and test again. Probably should move the entire inlet to the rotor side of the crankshaft as this would give the shortest possible inlet plus I wouldn't have to remove the clutch etc to change disc.
Maybe an emot conversion kit is called for http://www.emot.nl/webwinkel/index.p...&productId=148

[F5 Dave]

So your new Avitar; Are you practising levitation, or just giving the beast a good kicking while its down?

[husaberg]

Thanks guys. I will cut the disc to the same base timing as per the regular disc, test and compare, then add a couple of degrees to the closing point and test again. Probably should move the entire inlet to the rotor side of the crankshaft as this would give the shortest possible inlet plus I wouldn't have to remove the clutch etc to change disc.
Maybe an emot conversion kit is called for http://www.emot.nl/webwinkel/index.p...&productId=148

This fellow also does one as well.
http://www.vrm.se/
Click on the UK (flag unless of course you can read Swedish)then click on the picture of the reed valve .

[kel]

or just giving the beast a good kicking while its down?

Hey the Beast is my friend. Sure its a little wild and needs breaking ... seems the feeling was mutual

[cotswold]

Hey the Beast is my friend. Sure its a little wild and needs breaking ... seems the feeling was mutual

It does that to everybody, beasts aren't friendly.

[Kickaha]

Anyone for a new Konny engine?

[TZ350]

We ended up wining the 24 hour open class scooter race on the weekend. Scooter sat at 13500 rpm or close to it for 24 hours. I will pull it down in a few weeks and see what it looks like inside

Sorry, I have been away for work for a while, just got back.

Congratulations on your win, any pictures? and I would love to see some pics of the engine when you get to tear it down for inspection.

[wax]

Sorry, I have been away for work for a while, just got back.

Congratulations on your win, any pictures? and I would love to see some pics of the engine when you get to tear it down for inspection.

Thanks alot. if you pm me your email I will show you some pics when I tear it down.

[TerraRoot]

start a new thread, i'd like to see too.

[cotswold]

I think we will stick to eventful as a description of this weekend.
Saturday was practise and we went richer on the main and leaned out the needle ( ask Rob he knows ) and the beast spent a few laps doing what it does best until it developed a phantom problem that needed a bit of attention. I took the beasts little sister out to qualify for sundays race and managed 11th even though I only got 3 laps in due to carb sticking issues (float needle valve). That was it for saturday. Sunday saw Rob spilling the beasts innards all over the grass to find out what was causing saturdays problem, I fixed the other bikes carb and took it out for morning pratice, when I got back in it was straight out on the beast to see how it was after a bit of surgery. It was like a different bike from Mount wellington and pulled out of the corners very nicely and Rob is working on fattening up the mid range so look out.

Race one
11th on the grid and the beast hurtled away and we worked our way up to 5th within a couple or 3 laps, the fast 4 were still in sight and it looked like I may have a fast but lonely race in that position until at the end of the straight just as I was tipping in for the right hander the beast nipped and threw us both down the road for a skid, no damage to bike or rider.

Race two
Out on the little sister and 11th on the grid equated to 11th in the race util I lost concentration and binned it at the hairpin, got on and finished where you would expect.

Race 3
In a solid mid pack and back concentrating (still on the little sister) I had a recurrence of the float sticking and retired.

What this weekend showed me was that the Beast with a pretty average over 50 rider on board can mix it with the fastish boys but the same rider on a bike with 20hp can't

The seizure was a bit of a story in it's own right and I'll let Rob walk you through that one