ESE's works engine tuner

[TZ350]

Port Angles.

Definition of terms: Axial is how much the port points up and tangential is how the port points towards the back wall.

Port angles as best as I can measure them, Tangential frontwallangle/rearwallangle.

GP125
Main Transfer Port Axial 10 Tangential 60/65 Inner Radius 10 Outer Radius 24 Area 3.9
Secondary Trans Port Axial 40 Tangential 140/130 Area 1.2
Boost Port Axial 55 Area 0.7
Total Transfer Port Area 10.8cm#
Exhaust port width 64%

RM125
Main Transfer Port Axial 10 Tangential 70/70 Inner Radius 12 Outer Radius 28 Area 2.9
Secondary Trans Port Axial 30 Tangential ?? Area 1.7
Boost Port Axial 30 Area 1.8
Total Transfer Port Area 11cm#
Exhaust port width ??

RGV250
Main Transfer Port Axial 20 Tangential 45/65 Inner Radius 9 Outer Radius 24 Area ? Secondary Trans Port Axial 10 Tangential 70/80 Area ?
Boost Port Axial 50 Area ?
Total Transfer Port Area ?
Exhaust port width ?

A previous post has a port drawing:- http://www.kiwibiker.co.nz/forums/at...0&d=1238281402

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[SS90]

I am going to have to formulate an action plan. One of the problems I have is working out how to get a main port that is angled up at 10 degrees to 65 degrees. I can't just file away at the port, it still has to retain its timing.

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Yea, I understand 100% on this one, it can be frustrating!

Just as an idea, could you CAREFULLY dremel out the cylinder area of the port (much more than you need to), and simply rebuild it (with Devcon) to the angle (and timing height) that you need.

It is something that I do, and have had success with, but only with rear auxillery window fed transfers, and some rear boost ports..... I have never tried it with main transfers....... I looked at using Devcon to build a "kicker" in a transfer port once, but was advised against it, as it was suggested that the heat would be too much for the devcon..... I couldn't really see why, as it (Devcon) survives the temperatures in the boost port quite nicely!

But, if you where confident that it would "stay put" there is no reason why you couldn't build all your "scavenge patterns" out of Devcon.......

I have never done all ports like that, but I have done boost ports and rear auxillery transfers!

Of course, as has been pointed out by Speedpro...... Devcon seems to work in everything EXCEPT the exhaust port!

[SS90]

Barrel Pic's.

Pic's 3 & 4 show an early 70's TM barrel with the traditional "Two" transfers.

Pic's 1 & 2 show a brand new late 70's GP125 barrel with rear gully port and two secondry ports.

The GP's secondrys look like after thoughts when you look at the ugly way they have been siamesed into the main transfer port ducts, pic-2.

I was thinking of opening these up and adding dividers between the mains and secondrys.

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OK, I rotated the picture of your boost port set up which makes it easier for me too see.

I read back at what both you and Saxet have said in regards to "the secondary transfers being an after thought", and now that I see them (and with a little time looking at the set up) I would think that it's actually a very well thought out concept..... BUT only for low R.P.M!

I believe that because of the close arrangement of the boost/transfer secondaries, Particularly at high RPM, you will get a degree of "short circuiting", of the transfer/boost port streams, whereas, in the low RPM the gains made from more complete cylinder scavenging ( via the high placed boost port hole in the piston) compensates for this loss.

I see from your posts that the boost port is originally at 55 deg.....

Now.... this is only theory, but , if I am right, (and at high RPM, the close arrangement is causing short circuiting),what about the idea of simply increasing the width of the boost port (top and bottom), so that it feeds into the secondary transfers the whole time?, and also, increase the size of the "BOOST PORT" hole in the piston, and effectively turning it from a "boost port", into a 5th transfer...... Kind of like a "scavenging transfer"........

As a suggestion, perhaps it would be a good idea to go to the effort of building a perspex "case" you could feed either water or coloured smoke, and if you put the piston in the cylinder at BDC, and used such a device you could better asscertain if you are indeed getting "short circuiting".

As another thought, if that is the case, could you just use the boost port as a "sacrifice", direct it straight across the bore, (at the exhaust port), and use it (this sacrificial stream) to "curtain" the primary and secondary transfer streams.........

That is quite an easy thing to try, and, with devcon is reversable if it brings poor results......

I would certainly be putting a divider between the primary and secondaries...with out hesitation...... of course you cannot (easily) put a divider from the bottom of the liner, and all the way up, as nice as it would be, and really are limited to just at the port edge (perhaps made from devcon), but what about cutting a hole from the out side of the outer wall the side of the cylinder (in line with the transfer port edge), and simply making an aluminium "plug" to fit in, that has a divider included, and simply welding it place... that way it would be easier to ensure you had the angle of the dividers the same, as if you make them from devcon, in place, they never will be the same angle, no matter how hard you try!

And, as such, you would not get any gains (because the streams are mismatched), and it would all be for nowt!

And you remove the risk of them failing (if they where made from devcon)

The important thing to remember about this level of porting is that there is not so much chance of "making a lemon" (as is the case of exhaust port height etc),

BUT..... if you get the transfer flows (scavenge patterns) uneven, or pointing a few degrees the wrong way, it's not so much that you loose power ( peak power is more or less the same compared to before you did the mods), it's more common to loose low RPM torque, and make a more narrow power band...

This is why many people find out about this tuning, then try it, unwittingly make a mistake/miscalculation, and, when they test it, it feels "almost the same", or "a little bit less" then, claim that "it's all rubbish", just because they didn't know what they where doing.

But, if you get it right, as you are now aware, the gains are quite amazing........

I personally believe there is tremendous gains in this "boost port/secondary transfer" set up....

My opinion is that to make measurable power gains in a two stroke (at least initially) you need to increase the strength of the power stroke, (other things like lighter flywheels, better ignitions, expensive carbs etc are, in my opinion secondary....) this can be done (as you are aware) with high cylinder compressions (among other methods), but also can be done by ensuring "more complete cylinder filling", which, if you achieve this via modern scavenge patterns, you not only fill the cylinder more, but also stop more fuel heading out the exhaust (using transfer/boost port streams to achieve this is one way).

This is why modern two stroke chamber design is so different that years gone by..... there is less need for the chamber to "suck" fuel back into the cylinder, as less fuel is wasted than in times before......

This (more effective cylinder scavenging) has enabled pipe designers to build and develop pipes with a bigger spread of power.

Modern cylinders are very sensitive to pipe changes..... older stuff (with older porting), less so.

On the point of cylinder filling, while it is not really an option to have a complete transfer divider.... I can recommend also having some aluminium added to the crankcase section of your transfers, and adding a " stream divider" at that end..... while you won't have a divider all the way up, you will get an advantage by having a divider for the streams when they leave the case to head up the cylinder liner, as well as having a divider before they enter the combustion chamber..... Don't make it symetrical though..... your scavenge pattern starts HERE, and should have the same angles at the bottom, as they do in the top.....

[SS90]

I just had a thought......

You use a "flat top" piston (with a small "dish" if I remember correctly)...... With such a piston, an angle of 55 deg on the boost port is VERY wrong, well, it is wrong in so much as with a flat piston...... with out the convexity of a "standard" piston 55 deg is simply too low.........

Looking at your figures of port angles (axial) 55 deg boost, 40 deg Secondary is where I would have started....... but with a flat top piston....yea........ummm..... I think "substantually higher" would be the order of the day (for both the boost and the secondary transfers, but the boost more so than the secondary transfers)...

Lacking the convex piston crown is a "good news/bad news" situation, and unfortunatly, in my opinion, you would not be able to take any modern engines as an example.......

However, the advantages of a flat top piston allow you to use a "kicker" in the boost port..........

You really need to point that "boost stream" straight up into the head (because of the flat piston crown).... what about raising the height of the boost port....say 2mm, and increase it's depth into the liner, and THEN putting a "kicker" (made from devcon) into the top of the boost port...... Hopefully, if the kicker is aimed correctly, you may see benifit from the "dish" in the piston......

It (the dish) may well cause a situation where the boost flow will "shield" the primary and secondary transfer streams from the exhaust, as the "boost stream" deflects from the combustion chamber, (and if all is aimed correctly) into the dish............. , and in doing so, the boost stream crates it's own "loop"

A little bit like combing a "cross flow" cylinder scavenge system, and a "closed loop" scavenge system......

Of course, for this to work, the angles of your secondary transfers will have to be very well thought out......certainly a few degrees lower than the boost... if not, short circuiting for certain!

Instead of using a kicker on the piston (like a cross flow cylinder scavenge system) to stop the transfer flows going out the exhaust port.....use the boost stream to achieve the same job.......

That would also stop any "short circuiting" of the secondary transfer/ boost streams as well (if that is happening).....

You may also have to run your cylinder compression a little lower though.....(and a slightly narrower squish area) but I don't think it will cause a power loss if you do.....

[F5 Dave]

Gee TZ you get a 25% power increase & you are still quibbling? I think the next thing to do is ride the thing & see if the power characteristics suit the bike esp considering the 5 speed gearbox. Many people forget the whole package approach if there is a compromise like a gearbox. But with such a wide spread it likely will be a non issue. The thing should feel like a complete monster in comparison. Or you might find it feels mellow but just much faster. Often you have to retard things if revving considerably higher than std.

Amusing to think that the main gain after 50 pages of thread is that a few runs on the dyno with an experienced operator has netted such a gain & pointed to your 'heat' issues. Over advanced is obviously bad, but well over rich will fade power as it gets hot.

[SS90]

Gee TZ you get a 25% power increase & you are still quibbling? I think the next thing to do is ride the thing & see if the power characteristics suit the bike esp considering the 5 speed gearbox. Many people forget the whole package approach if there is a compromise like a gearbox. But with such a wide spread it likely will be a non issue. The thing should feel like a complete monster in comparison. Or you might find it feels mellow but just much faster. Often you have to retard things if revving considerably higher than std.

Amusing to think that the main gain after 50 pages of thread is that a few runs on the dyno with an experienced operator has netted such a gain & pointed to your 'heat' issues. Over advanced is obviously bad, but well over rich will fade power as it gets hot.

f5, you are not wrong in your observations..... and all the things you have just pointed out have been said (like you point out..... pages and pages ago!)

But, I can't help but think what sort of curve he would end up with, when he applies even SOME of the things we have written about...... With such low primary compression,standard (old school) scavenge patterns... Shrouded transfer areas.... changing these things will not overly increase peak power, but will certainly give it a much longer power curve (make it less peaky), and more low end torque.... and some observers will also undoubtedly be keen to try some of these concepts on their own engines........ worth 50 pages I think!

From his curves, I would say it would indeed feel "mellow, but much faster", I think compared to the last time he rode it it will be much easier to ride, and therefore his lap times would drop considerably!

It's a common mistake to make.....you make a set up change (that makes the bike more peaky, but less power), and because the power "comes in such a rush", it feels like a monster, when infact it's slower!

[F5 Dave]

Yeah I have a special sneer for the 'now it wheelies changing into 3rd' crowd. Which can range from I've put a big pilot jet in which bogs till it clears out to I've changed the handlebars.

My H used to do the most ridiculous wheelies (high bars, supercross design pipe where I went a bit far on the diffuser). One round I spent the day on a carpark track perfecting my stand up wheelies. With a leakdown tester I found some issues & fixed them. It was far more effective.

But I have never been able to wheelie like that since. A part of me considered introducing that reedblock leak again

[Buckets4Me]

Yeah I have a special sneer for the 'now it wheelies changing into 3rd' crowd. Which can range from I've put a big pilot jet in which bogs till it clears out to I've changed the handlebars.

:

it wheelies in 4

nothing big and nasty unless you dump the clutch but just lifts the wheel up and carries it for a bit

[TZ350]

Yeah I have a special sneer for the 'now it wheelies changing into 3rd' crowd.

I am pleased to have found a few extra ponies, let me count them 1, 2, 3.....19.5 and Ohhhh F5 by the way, did I mention that it now wheelies in 4th. see you at Taupo.

[F5 Dave]

Well maybe I'll bring my F4 bike this time to make it a fair fight. Actually I'll have my hands full this year so we'll see what happens.

Or I'll move the seat right over the rear wheel & it'll wheelie in 6th. No amount of power will make your bike do that.

[TZ350]

Well maybe I'll bring my F4 bike this time to make it a fair fight. Actually I'll have my hands full this year so we'll see what happens.

Or I'll move the seat right over the rear wheel & it'll wheelie in 6th. No amount of power will make your bike do that.

"A Fair Fight" I never said you were allowed to make it a fair fight! I need all the advantage I can get.

Wheelie in 6th now your being cruel!!!!

I am not 100% sure how this inertia dyno business works but I suspect that 19.5 RW-HP with short Mt Wellington gearing is not going to be 19.5 hp at the rear wheel on long Taupo gearing.

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[speedpro]

I've only just put it all together with this talk of Taupo. It just shows you the sad state of bucket racing currently that a 14hp bike came third in the GP on a big track. You should have been getting lapped every 8 laps or so by a dozen 20+hp buckets fighting for 1st. No offence intended, just an observation.

[speedpro]

As I've found with the switch from old #6 to new #6, a lot of the wheelie potential of a machine is down to piss poor suspension. Old #6 would wheelie in 3rd if you changed direction fast enough and new #6 is reluctant to wheelie even doing all out drag starts.

[TZ350]

As I've found with the switch from old #6 to new #6, a lot of the wheelie potential of a machine is down to piss poor suspension. Old #6 would wheelie in 3rd if you changed direction fast enough and new #6 is reluctant to wheelie even doing all out drag starts.

Yes there are a few piss poor suspension problems with the bike. I am looking forward to getting on to them.

I have also heard of bikes tuned on the dyno expiring on the track, so I am a little worried about that.

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[TZ350]

I've only just put it all together with this talk of Taupo. It just shows you the sad state of bucket racing currently that a 14hp bike came third in the GP on a big track. You should have been getting lapped every 8 laps or so by a dozen 20+hp buckets fighting for 1st. No offence intended, just an observation.

Yes I know, 14hp comining in the GP, how sads that. But I did lean forward going down the hills and I am sure that helped a bit.

Also F5 Dave kindly waited for me on the straight bits so I wouldn’t feel left behind and lonely, thanks F5.

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