Two-stroke performance tuning?

[F5 Dave]

. . .
The porting pics have intrigued me as has the toroidal head.(only just heard about it-Yeah we all have to learn how much we don't know)
I'm guessing some of this could be applied but thats getting many steps ahead of myself.
I suspect some of the bucket tuners have applied some of this as one 50 cc bike seems to have more power than most 100's or 125's.
. . .

My 50 doesn’t need such a head, in fact the sparkplug would be clouted by the piston if so. Bigger the cylinder the more this sort of thing is applicable. Might experiment machining up some domes for my Trinity 496 (essentially 250cc cylinders) in the future . . . –if I ever feel like it is wanting more that 100hp of course.

The more the merrier!

With the Ax100, there is a small problem with tuning, well, that is, they look like "crankcase induction" (like Mb100's, CR125's etc for example), but the reed block location ends up making quite a torturous path through a "piston window", like say an RZ250 (except the RZ intake is mounted directly on the cylinder, and far better in this respect!)

The intake rout is fairly poorly designed (in as much as performance goes), and it could perhaps be considered wise to simply "go bigger" (and try and develop your intake system to simply "flow more", to help compensate for this...........

Personally, with out having one in front of me, it's difficult to say, BUT, I think it may actually be a good idea (in this case), and some good gains could be made!

Does anyone know of an AX100 with a bigger reedblock fitted?

Also do you have the cylinder off the engine?

I found these pictures, so you can see what I mean about the inlet.

Yeah the AX has a weird set up with a reedblock (on bottom of barrel not shown) like an ancient RM (and incidentally my 50) but with no piston ports. Really I have to wonder about developing an AX further due to it’s odd gearbox, however didn’t know there was a 125 version.

[Buckets4Me]

hows that for a start
an rs gp

[Skunk]

Skunk's has a bigger reedblock fitted .

Um, no. Just different.

With the Ax100, there is a small problem with tuning, well, that is, they look like "crankcase induction" (like Mb100's, CR125's etc for example), but the reed block location ends up making quite a torturous path through a "piston window"

Not quite. No piston port - just the reeds. But yeah, crap inlet path.

Yeah the AX has a weird set up with a reedblock (on bottom of barrel not shown) like an ancient RM (and incidentally my 50) but with no piston ports. Really I have to wonder about developing an AX further due to it’s odd gearbox, however didn’t know there was a 125 version.

Never heard of one - and I've looked! 4 speed box is a handicap but the selector set-up is shit. Don't waste time even spending a cent on one of these. Seriously.

[saxet]

[QUOTE=quallman1234;1977942]Hey its an AX100 (yea yea i know).
3 petal reed valve. Standard.

Hate to say it but Skunks got more right to know than most of us.The very basics -If it hasn't been geared down start there. I have found on 5 speeders 1 tooth smaller on the front is a good start if you havn't already.I don't get into top at Slipway or Kaitoke.


[QUOTE=F5 Dave;1979301]My 50 doesn’t need such a head, in fact the sparkplug would be clouted by the piston if so. Bigger the cylinder the more this sort of thing is applicable. Might experiment machining up some domes for my Trinity 496 (essentially 250cc cylinders) in the future . . . –if I ever feel like it is wanting more that 100hp of course.

Don't claim to know whats been done to it but it and you are seriously quick.

hows that for a start
an rs gp

I like the look of that. It's what I'd like to get near with the next motor. As Ive Little experience I'm trying to cheat a bit and avoid some of the trial and error others have had to go thru.. Yeah lazy.

[Buckets4Me]

I'm trying to cheat a bit .. Yeah lazy.

nothing wrong with cheating and being lazy

[SS90]

Skunk's has a bigger reedblock fitted .

Yes i know what you mean about the inlet.
Its going to be difficult getting a v-type reed block in there as well.
Might have to move the reedblock back. What would this effect?

It's a really good question, and it touches on a very complex part of the two stroke engine.

In order to keep it simple, I'll try to be quite general!

Basically, a longer inlet manifold will tend towards developing more "bottom" end power (at the cost of "top end power"), and a shorter on is the opposite (more top, less bottom)

It is quite complicated to calculate correct two stroke inlet manifold lengths (due to the fact that in a two stroke the crankcase volume (which changes with each piston stroke) is included in the calculation of a two stroke manifold length.

As such, the accepted method seems to be "try it and see".

Some rules remain constant though, and the most important is ...

Do not put the reed block too close to the piston (this will upset mixture strength, and make jetting near impossible, as well as reduce the "useable rpm's" of the engine (basically, the engine won't rev out)

Too far, and the symptoms are almost the same, but you will get the jetting set acceptably, but it won't rev much at all (less that too close in my experience).

Some logic applies here, and basically, if it looks too far away, it probably is!

I would suggest at aiming to have the reed block tips 15-20mm away from the liner window.



If you are really keen on this idea, I think it would be wise to go to the effort of completely redesigning the inlet, system....it is clear some improvements could be made there!

I have never tuned an AX100, but had one as a bucket (standard) for my first bucket.

Like F5 Dave said, the 4 speed might start to hinder development though!

[SS90]

hows that for a start
an rs gp

Mate, thanks for that!

Do you know what specs the engine had (i.e, what size is the carb, is it air cooled)

[SS90]

[QUOTE=F5 Dave;1979301]My 50 doesn’t need such a head, in fact the sparkplug would be clouted by the piston if so. Bigger the cylinder the more this sort of thing is applicable. Might experiment machining up some domes for my Trinity 496 (essentially 250cc cylinders) in the future . . . –if I ever feel like it is wanting more that 100hp of course.



I agree with that one. It's debatable if such a head would have any effect on a 125 bucket (with a small carb)...... I have no experience with such a head in such a situation, but I think, from what I see and read, if you are in a situation where the level of tuning is so high, that everything starts to count, this design is of significant benifit.

Like Dave said, he has 100 HP (his trinity engine creation) and some other tuners have 112 or so..... and it seems it takes expensive carbs, pipes, ignitions and heads to make the extra power..... I would be interested to see what the power was with the same extras added, but using the original Trinity heads.....

[F5 Dave]

Numbers are just numbers without the same reference (ie dyno) There is another local dyno that would read it at 115 (and a further one reputed to be more optimistic), my only runs were with totally wrong needles so I could only pull dirty until near peak revs & ran out of jets in the session so I was running 2 sizes too rich in one side, probably right in the other. I choose the path of smaller carbs and low compression for a roadbike on pumpgas. A race engine could pull waay more + add a few revs to boot.

B4me that curve looks real friendly. What type of dyno was that one? Presumably this is since Taupo 'cause it didn't seem anywhere as fast then.

[saxet]

[QUOTE=quallman1234;1977942]Hey its an AX100 (yea yea i know).
3 petal reed valve. Standard.

I can't help thinking that this could be an interesting design experiment but as it's a 4 speed, it's gonna reach it's limits quickly.
In any tuned engine there is a tend ency for power to be concentrated further up the power range.This is where the 4 speed falls down e.g. the gaps between gears can be too big. If, as standard the engine has say a 4thousand useable rev range, after tuning work that may drop to 3 thou useable rev range so when you change up a gear the revs in the next gear drop below this useable rev range.
This is one reason that tuners try to get as much power out of an engine while trying to keep the power spread as wide as possible.
Lowering gearing can help here but a 4 speed is more limited in this respect.

[Buckets4Me]

B4me that curve looks real friendly. What type of dyno was that one? Presumably this is since Taupo 'cause it didn't seem anywhere as fast then.

At Taupo the end of the chamber fell of
the bike is as fast if not faster in a straight line than the one that won the gp but the rider is not.
also I tend to run the main jet a size or 2 too big I know I know but I use to lend the bike out a lot
and I know other people ride it harder than I and I'm not keen on them leaning it out and destroying it
so I play safe

at the 2 hour it was clocked at 30 sec 1 rider and 31 the other in the shoot out
finished 3rd after being droped 3 times and was running faster than 30 sec at one point

but as you say not all dynos are equal and I wouldn't put to much faith into the graph either

[SS90]

[QUOTE=saxet;1980347]

Hey its an AX100 (yea yea i know).
3 petal reed valve. Standard.

I can't help thinking that this could be an interesting design experiment but as it's a 4 speed, it's gonna reach it's limits quickly.
In any tuned engine there is a tend ency for power to be concentrated further up the power range.This is where the 4 speed falls down e.g. the gaps between gears can be too big. If, as standard the engine has say a 4thousand useable rev range, after tuning work that may drop to 3 thou useable rev range so when you change up a gear the revs in the next gear drop below this useable rev range.
This is one reason that tuners try to get as much power out of an engine while trying to keep the power spread as wide as possible.
Lowering gearing can help here but a 4 speed is more limited in this respect.

I agree 100% with the idea that it will be an interesting design experiment, and, with some careful attention to port timing, and some attention to basics you would end up with a very rideable machine (with good low down torque), which, what we always forget, is what a two stroke is very good at!

The engines I work on are only four speed and if you build one with good peak horsepower, the first question an experienced observer will ask is "does it pull 4th", as the ratio from 3rd to 4th is quite far, it can be a problem!

The points about Dyno's and comparisons are valid (I am lucky to operate a very high quality one, that does not vary from shop to shop like some other brands)

As we all know, correction factors are subject to inaccuracies and good software is as important as good components (and experienced operators when it comes to a dyno)

But, apples to apples, oranges to oranges.

But if use the same dyno when developing, no matter what the number, a gain is a gain!

[Skunk]

My exhaust port timing on the AX100 is 189°. The inlet has been tidied, as have the transfers, but I don't know the timings.

[SS90]

My exhaust port timing on the AX100 is 189°. The inlet has been tidied, as have the transfers, but I don't know the timings.

Great start!

There is quite a bit of information you need when you are dealing with two stroke ports (when they start to open, how long they are open for, when they close, etc.....)

It seems quite daunting when you first start to look at it, and this is compounded by some internet based information, that can be not only confusing, but also incorrect!

To measure the timings, the only special tools you really need are a timing wheel, and a dial test indicator.

Some people also use feeler guages (to determine when a port closes, but I tend to use a torch to shine a light through the port....when the light stops shining through the port, the port is closed), but that is an individual preference in my opinion.


These tools are not too hard (or expensive to obtain), and can often be borrowed.

Maybe this could be a good topic for discussion......How to measure your port timings!

[koba]

Just for general interest I measures the a100 exhaust duration at 165 dregrees, but it was done quickly and without the proper gear so it may be a wee bit off.