ESE's works engine tuner

[SS90]

I don't think that the MB is crankcase induction either, The reeds go into the back of the barrel.

Ok, thanks, for some reason I thought they where Crankcase induction, I am unsure why I thought that.... I never had one apart!

[SS90]

So the problem is more about increasing the torque than making more Hp.

How can we use the new style of porting to increase the torque? SS90 do you have any suggestions?

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Ok, the first thing you want to spend your time on is more complete scavenging of the crankcase at BDC.

Believe me, this is going to increase your torque dramatically!

Put very simply, the easiest way to make torque in your engine is to pay attention to this part of the cycle.

We looked at your rear "transfer/boost port", and from the piston window placement, it's as high as you can really go.

I will draw an idea I have for improving that on Sunday night and post it.

With the shrouding of your transfer ports via the piston transfer cutaways, you really are losing alot of torque there.

However, as you pointed out, you cannot safely remove too much material from the piston in this area, as it causes failures......

I realise that another piston is not really an option (particularly at this stage), so look at a safe way of unshrouding this area, ( I mentioned small holes around that area as an example, is that possible? as I assure you that this will be a worthwhile effort....

I have seen as much as 15% torque gains from attention to this... (this example was not just a one off engine, it was on a series production cylinder)

Before talking about transfer angles, it would also be VERY prudent to look at the possibility of including a divider between the primary and secondary transfer ports, I realise this is no simple task, but again, the gains you will make are quite astounding.

If you cannot have a divider, then the application of some (though not all) modern porting techniques will be "for nowt", as this (divider) is an important part in the whole cylinder scavenge pattern

Sure, to have one going right up the cylinder is not really feasable, but if you could come up with a way of fitting a divider even just at the top, where they enter the cylinder, you will be well rewarded!

Is that something that can be achieved with this cylinder?

I mentioned a few weeks ago the idea of drilling into the outer liner, and fitting a divider at the port edge, (made from alloy) and then welding it in place....can this be achieved?

Don't get me wrong, if none of these things can be done, I can still help with a scavenge pattern, but if the things I mention can be done, the gains are dramatically better!

If you need some ideas for shaping the piston cutaways, I can post a picture or 2 of ideas that I use.

[TZ350]

Ok, the first thing you want to spend your time on is more complete scavenging of the crankcase at BDC.

Put very simply, the easiest way to make torque in your engine is to pay attention to this part of the cycle.

With the shrouding of your transfer ports via the piston transfer cutaways, you really are losing alot of torque there.

Thank you SS90 for reminding me of these ideas that you have mentioned before.

Crankcase scavenging and transfer port windows that is where I will get busy now.

I am looking forward to seeing your drawing for the rear boost port and would be interested in a pic of the pistons.

I have a bunch of questions but I need to make drawings and pic's to illustrate them.

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[TZ350]

With the shrouding of your transfer ports via the piston transfer cutaways, you really are losing alot of torque there.

so look at a safe way of unshrouding this area, ( I mentioned small holes around that area as an example, is that possible? as I assure you that this will be a worthwhile effort....

Pic 1, is this the port divider you mention? I can do this.

Pic 2, I can cut the GP cylinder away to look like this and drill holes in the piston skirt.

Pic 3, I could open up the secondry transfer window and put a divider here and also extend it down into the crankcase if that would be a good idea.

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[SS90]

Pic 1, is this the port divider you mention? I can do this.

Pic 2, I can cut the GP cylinder away to look like this and drill holes in the piston skirt.

Pic 3, I could open up the secondry transfer window and put a divider here and also extend it down into the crankcase if that would be a good idea.

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Ok, yea, that's all pretty good!

I would just be a little careful of how much I cut the liner away, as you really need to support that piston, don't sacrifice too much safety on that area!

F5 Dave mentioned a while back about putting the cylinder in each case half (as you did of course), this is the best way to decide how to scavenge the cases.



I like the idea of extending the divider down onto the case, it's something I have done before, and seemed to be of benefit.

I remember you had access to an old Honda RS125 cylinder..... is there any way you could spend a few hours with that?

In my opinion, the RS125 cylinder has the best design of all in this area........

The two pictures I have attached relate to the piston transfer cutouts.

The first one ( an old Polini piston with the seizure marks) is what I seem to be able to get away with (as far as increasing the cutout), with out having piston failures, and it certainly works.

It's not semetrical because of the large transfer/boost window on the skirt, and as you know you need to leave more material in this area, particularly because there is very little internal webbing on these pistons......

The second picture is just for demonstration purpose, and is a high quality aluminium/silicone/copper piston, that uses the mould from a TZR250.

I put it in an original 125cc Vespa cylinder (very very low tech)as an example of how different each manufacturer designs their cutaways

depending on if you have Transfer boost ports (like most modern two strokes) is how much attention the Japanese paid to this area.

As such, the use of a modern piston (designed to be used in an engine with systems like transfer boosts etc) face the problem of masked transfers when used in older designed engines, that rely heavily on this area to clear the crankcase at BDC.

Even though you have a little "boost port" in your cylinder, it's quite small, and I am confident too say you will make gains here!

This is why Malossi adapted the extra port system (they call CVF, but really was developed in the 30's by Royal Enfield), and they use extra boost ports on the back wall as well.....basically, it seems you can never have enough ports working on this concept!

Also, "Trinity" RZ350 variant cylinders use this system (as well as transfer boosts)

But, I'm not saying you should do that!

It's just an example of how there are still companies using this "style" of tuning.

If you have transfer boosts, you don't really seem to pay attention (as much) to crankcase scavenging, as it is compensated for by just adding more fuel via the transfer boosts!

It's not good for fuel economy (or pollution), but an easy way to make power!

If you don't (can't) have this type of boost port, then it becomes more important to "work with what you have"

With this piston, you see how big the internal webbing is, which allows you to really "flow" (hate that word actually) this area and unmask it quite well, compared to other pistons, that this webbing is quite often too small to allow any material to be removed.

From the pictures you can get a rough idea of how much you can safely remove with-out compromising strength.

As you know, this webbing on a piston is where all the strength is.

What does this area on the piston you use look like?

Also, can you post a pic (or drawing) of your crankshaft....I'm just unfamilure with a GP125 crank!

[SS90]

O.k,

These are some pictures cylinder of one of my cylinders.

It is "almost" finished in these pictures. (port chamfering to be completed etc), and a couple of other things. And of course the transfer area of the liner is still to be matched to the piston.

At the stage I took these photo's I was still experimenting with piston transfer cutout shapes.

125cc Cast ironed lined. I only used a single ring piston on this one engine, as at that stage it was the only one I could get. I now have a two ring item that I was able to get here.

It was my first experiment with transfer boosts, and divider lengths/angles.

You will see that the divider does not go all the way to the base of the cylinder in this liner, but on this set up it is a hinderance (because of the transfer boost ports), the absence of which (like your cylinder) allows that you can go right to the base.

While it makes good power, I still prefer the non transfer boost cylinders for the spread of power.



You can see my port angles clearly

In regards to the piston cutouts...... Ermmmm.... let's just say this one was "a little too much"

when I changed pistons to the one I use now (that have the extra webbing like my previous post) I was able to keep strength, and unshroud more.

[Yow Ling]

Is the "transfer Boost Port" the same as Boysen Port. A tunnel connecting the transfer port to the inlet ?

[craisin]

Is the "transfer Boost Port" the same as Boysen Port. A tunnel connecting the transfer port to the inlet ?

Its like comparing apples to pears

[TZ350]

Is the "transfer Boost Port" the same as Boysen Port. A tunnel connecting the transfer port to the inlet ?

SS90 I am also unsure what you mean by a "boost port".

Great pictures, very helpfull.

[Yow Ling]

Its like comparing apples to pears

So the new bag of Mexican Tripping weed arived i see.

[TZ350]

Mt Wellington points races. Wound on a bunch of pre-load and increased the rebound setting just like Sully60 sugested and it made a heap of difference. The bike kept a much tighter line and I was able to experiment with getting the power on earlier. Thanks Sully.

The problem now is, that I am arriving at the next corner faster than before and its taking some getting used too. On some accasions I was getting front wheel chatter coming around the sweeper at speed, I will need to look into that. A bit frightening but who cares, things are looking up.

The bike starts like a rocket and in one of the "A" grade points races I was first into the first corner and made a whole lap before being overtaken. Things are starting to look possible. Going to get out for some practice before the next meeting.

And Taupo should be fun.

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[TZ350]

Can you post a pic (or drawing) of your crankshaft....I'm just unfamilure with a GP125 crank!

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GP125 crank with the inlet side champhered and the bigend pin hole bored out from 19mm to 22mm. This was done when I thought that I needed a better rod to withstand the extra reves. As things have worked out the standard rods/bigends have worked well in the other team ESE bikes. The plan is to stuff the ballance holes with devcon F putty.

Pic 1 and Pic 2, modified GP125 crank.

Pic 3 GP125 rod/bigend and on the right hand side RD350 rod/bigend.

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[TZ350]

From the pictures you can get a rough idea of how much you can safely remove with-out compromising strength.

As you know, this webbing on a piston is where all the strength is.

What does this area on the piston you use look like?

Pic-1 the cast reinforcing web that gets cut away to unmask the transfer on my engine.

Pic-2 the Wiesco piston does not have this web and may be a better bet.

Pic-3 a Honda RS125 piston.

Pic-4 Kawasaki cast piston and Wiesco forged piston.

Pic-5 Kawasaki piston with cutouts like SS90 has been discribing.

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[craisin]

So the new bag of Mexican Tripping weed arived i see.

no such luck I think Boysen ports use Boysen Reeds which seems to be 2 sets of reeds arranged in a vee .
And you need a bigger port to accomidate them.
2 strokes are not all the same as you have rotary disk engines that uses a hole in one of the crankcase webs instead of reeds and the air-fuel mixture is inducted into the crancase to the tranfer slots and a cut out in the side of the piston uncover hole thru to the cylinder.

there are heaps of links in this thread that explain the different workings of the different 2 strokes k

[TZ350]

I would just be a little careful of how much I cut the liner away, as you really need to support that piston, don't sacrifice too much safety on that area!

F5 Dave mentioned a while back about putting the cylinder in each case half (as you did of course), this is the best way to decide how to scavenge the cases.

I like the idea of extending the divider down onto the case, it's something I have done before, and seemed to be of benefit.

Pic-1 The cylinder in the case and the liner cutout does not match the transferport exactly.

Pic-2 Shows the size of the transferport window with the piston at BDC.

Pic-3 Shows the size of the transferport window with the long rod and 13mm cylinder packer, the window is much larger and the transfer divider looks like it could be brought down to here.

In pic-3 you can see how much of the pistion needs to be cut away to completly unmask the transfer window. There are limitations of course like leaving enough piston skirt to cover the exhaust port at TDC.

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