3xv rear cylinder leg modification. SP 3xv-10 cylinders??

[EEKNOWS]

So the next crazy idea is - How much would it cost me to have 2 cylinders cast by an enthusiast with all these Aprillia improvments ?

I think there is significant scope to incorporate many improvements within the 3xv cylinder already, no worth it trying to re-engineer the engine completely. Just get a 3MA frame and stick a Rotax 256 with FPE/RCS/PVP cylinders on it and go directly to 85HP with 38/39mm Delorto's or 90 odd HP with the 42mm carbs. There is no way you see those sorts of numbers from TZ's even.

PS carbs on their way over neal

[maccas]

Hi guys,

Thank you for all the replys 

Paul,

Thanks again for the pictures of your cylinders, on closer inspection Graham has kept the length of the legs the same and just rounded off the backs of them by quite alot. This is probably to try and keep the engine more reliable than anything else by giving the rear of the piston more support at BDC.

Neal,

Thank you very much for the pictures of the 3xv-50 cylinder. Are you happy for me to post the pics up here?

Lozza,

When you say the cylinder looks blowdown limited are you refering to the black staining in the crankcase on my engine? I would also agree that this would pin point to there not being enough blow down. However in this case it is not the cylinders fault. The engine came from Japan a couple of years ago and by the look of how standard it was when I had it in bits it looks like it had only ever been ran with the standard 3xv-10 cdi. This is known to be a very restricted cdi and I doubt that the powervalves even get anywhere close to being fully open, hence the limited blowdown signs.

The stock SP port map looks like this:



Pauls cylinders transfer heights are approx 2mm lower than those in the port map at approx 40.5mm from the top of the cylinder so he probably has more blowdown than my cylinders but then I don't know the exhaust port height on Paul's cylinders so it is difficult to comment.

On the 3xv-50 cylinders the sub ports are closed by separate powervalves. The sub ports on those cylinders look to be larger than the ones on my SP cylinders. Obviously the sub ports can be made wider without sacrificing bottom end power as the sub ports are kept closed for longer and then opening at the top end giving greater exhaust port area and blowdown TA.

Regarding my original question:

Should I add material to remove the step on the inside wall of the transfer tunnel? I think yes I should especially as Lozza has pointed out that the mixture hugs the inside wall of the transfer tunnel. A smooth continuous radius from lower cylinder wall to port window should help here I believe.

I think a little bit of work on the rear cylinder legs won't do any harm either. I won't go quite as far as TZ extremes but somewhere inbetween that and what I have now can't do any harm I don't think.

Dan

[Paul]

I don't know the exhaust port height on Paul's cylinders so it is difficult to comment.

now you do, 25.4mm

[EEKNOWS]

Black in the cases  That port map has 30 deg of blowdown angle and precious little area, Pauls' does better with 37deg of BD angle. Look at the size of the legs on the RSA cyl  round or big square mofo's makes not one bit of difference. The shorter that inner wall the better (an old TZ/LC trick) long columns take forever to start flowing then don't want to stop, short columns flow early and are easy to stop. How much thought have you extended to what happens between BDC and the squish band starting to work (say approx 30deg BTDC)? If you were at all like me until 2010 I didn't think much at all. At this point you will see the brilliant simplicity of why the Aprilia GP bikes won all those races and championships.
At BDC intake charge begins to form a 'rising column' , the intake streams gently collide and rise in the cylinder , hit the head and come down to meet the rising piston. Intake streams out of the transfers must have as little turbulence as possible. Turbulence while the exhaust port is open means mixing of intake and spent gasses. That costs HP and piston cooling.
Now you start to see why blowdown is so important, if you have say 120psi cold cranking then you will have 1200psi after the mixture goes bang, all of that heat and pressure must go out the exhaust before anything comes out of the transfers

[Neal]

Go for it Dan , I can try and send better quality pics to you if needed . I will try and do a port map again . Would you like TZ pics too ?

[maccas]

Paul,

Again thank you for that information, that is very very interesting. Slightly higher exhaust port timing than a stock SP cylinder but with 'R' model transfers.

Neal,

Sweet, I'll photobucket them and put them up. If you have the time to take better pics that would be really appreciated. TZ pics would also be greatly appreciated  thank you very much. I would guess that the exhaust port on the -50 cylinder will be a couple of mm lower than that of the TZ.

Lozza,

Again thank you for that information. I've been scouring the net to try and find a picture looking through the intake port in the RSA crankcases with a cylinder fitted to see how much the legs "hang down" into the intake flow. Sadly I haven't been able to find such a picture  But what I did find is that the intake legs on the RSA cylinder are 21mm in height from the gasket face. Looking at a picture of an RSA crankcase half it looks as though the thickness of the metal where the cylinder fastens too is roughly 15mm (a rough guess). Added on top of that is the base gasket thickness (probably very thin) so the legs look to hang down around 5-6mm into the intake flow. The backs of the legs are nice and round which will help in directing the flow into the transfer tunnels. So what I am trying to say is, on an RSA the legs are big and chunky yes, but they have been designed with the crankcase in mind to not hang down into the intake flow much.

The 3xv as you can see in standard fettle has huge rear legs that really hang down in the flow. They must hang down ~ 25mm into the reed valve housing/upper crankcase roof. I think that shortening the legs to open up the space a bit could help. The result would be a more synergistic crankcase/cylinder base combo geared up to help direct the intake flow to the transfer tunnels.

The TZ cylinders look to be a good improvement on my stock 3xv-10 cylinders in this area and the yamaha engineers gave the TZ a layout like this for a reason. Obviously I'm not looking to make a 80 hp TZR but if this small change can unleash 0.5hp anywhere in the rev range with no losses then it is worth doing and I have learnt more about workings of the TZR's engine in the process. Sadly I don't have a spare pair of SP cylinders in order to do a back to back comparison on the dyno  I will certainly try and employ some of the tricks from an RSA where I can.

Dan

[Warwick]

Yada, yada... Have a scope through the old, old forum Dan. Think I posted pics of my own base mods up in there somewhere a few years ago? No real idea how effective or inneffective they were on their own, but overall I'd think you are probably better off taking your cues from TZ cyls on the whole really as they are a proven design on this kind of engine; the 3XV is not a 'priller GP motor afterall... I wonder to what extent the diff' bore & stroke of the 'priller motor is a factor in ideal port design criteria?

Later SP cyls (20, 40 and 50) were basically the same broad design as TZ cyls with slightly tamer porting (not by that much though) Interesting to see how similar the RSA port layout is to the early 3XV layout  though...? 

[EEKNOWS]

C port flow goes through a 20mm wide gap between the rear legs, the back of the legs fit in the crank case. Aprilia had a full time staff of 100, working 5 days a week, 2 dynos running continuously testing 3-4 different cylinders per day from 1995-2007 all under the watchful eye of probabaly the best 2T tuner ever.End results was the most powerful and reliable 2T engine ever. Safe to say if it works it's on a RSW/RSA cylinder if not you don't need to worry about it.The transfer flow is helped by duct geometry and the pipe sucking hard at BDC.
As I said before short, long,square or rounded legs  will make SFA difference on the track or dyno in fact I would be inclinded to make them larger.
Lately the Aprilia ducts have be copied from 50cc to 300cc bores with the same result more power better and piston cooling.

[Warwick]

C port flow goes through a 20mm wide gap between the rear legs, the back of the legs fit in the crank case...
As I said before short, long, square or rounded legs will make SFA difference on the track or dyno in fact I would be inclinded to make them larger.

Well, there you go then. Weld those suckers up and file 'em nice and square. Who am I to argue with that... 

[maccas]

Warwick,

Thanks for that, I will more than likely copy the TZ layout to a certain extent.

Lozza,

The lugs can't be made bigger because the reed valve is in the way. The reed valve is in close proximity to the rear legs of the cylinder. Much like it is on a 3ma. Making the lugs bigger would mean spacing the reed valve out with a spacer plate. This would be OK on an open carb set up but would make fitting the airboxes back on tricky.

Cheers,

Dan

[EEKNOWS]

Weld?? Who said anything about welding ??. This will survive replating and can be made any shape you want.
Posted on prev page
http://www.sylmasta.com/acatalog/Creative_Kneadatite_Putties.html

Even the best have little idea what happens to the intake charge under the influence of  the spinning crank and rod.

[Warwick]

Fill with weld or putty... I'd trust weld more there myself...

Though I'm not sure you'd be suggesting bunging that area up at all if you'd actually had a good look at a 3XV motor I have to say?  . 

As mentioned, I've not had the opportunity to dyno test my own cyl base mods in isolation, but personally I wouldn't think it at all useful to create additional intake restriction in this area.

Build a plugged-up 3XV motor. Prove me wrong?  . It's all just good development as far as I'm concerned  .

[EEKNOWS]

If 3xv's were not so scarce here I would be churning them out. There is no proof the legs are a "restriction" and the spinning rod and crank have by far the biggest influence on what happens in a crankcase.There would be no way of separating if there was a "restriction" or simply the engine wanted more case volume once you added better pipes/cylinders. JB welded pistons no problems.
Something like this will further your cause.

[casal-fan]

Interesting.
Eeknows, I´m not 100% sure, but don´t both RSA and RSW have a rotary intake system?
The RSW being a "rear loader", and the RSA a side loader?
They also have longer rods (115-120mm?), and the cylinder is quite short/engine block high, all this making for more place for an uninterrupted flow of incomming charge?
If so, these are different designs in comparisson with the reed valve TZR engine, as incomming charge from the reeds meets these cylinder protrusions instantly after the reed petals, and maybe that is not the case?

I recall reading a page or 2 about the negative effect that the rod had on the charge flowing into the crankcase on the sideloader engine.
Maybe that had something to do with the rod being an obstacle, very close to the point where the charge comes into the crankcase?

[mbsteve]

Casal-fan, Yes both Aprilias are rotary valves and they do make more power than a reed valve engine. It is like comparing apples to oranges in terms of power. Reed valves make better power down low compare to the rotary engines. Also inside the engine you want everything with large round edges and also very smooth where you do not want oil to stick to.

Chuck Sorensen's RSV made 82+ Hp at high altitude and the same bike was 75-76 at sea level - Something about rotary valves vs. reed valves at altitude? Rich Oliver's TZ250 made 74 to 76 Hp on the same dyno in 2003. Eventho the Aprilia made more power than Rich Oliver's bike but Rich won every AMA 250 race that year.


Here is a couple of pics of a port job that I just finished for a customer




Polished TZ250 crank