ESE's works engine tuner

[F5 Dave]

Of course you used to be able to get leaded high performance petrol, probably still can. People have used it in RS125s in the past, but adds another layer of expense. The change over to unleaded as you say esp on RSs means a heap of different parts, ign curves to take advantage. A proper 125GP bike will rev a lot higher than a GP125 (sheesh that gets confusing) though.

[k14]

Of course you used to be able to get leaded high performance petrol, probably still can. People have used it in RS125s in the past, but adds another layer of expense. The change over to unleaded as you say esp on RSs means a heap of different parts, ign curves to take advantage. A proper 125GP bike will rev a lot higher than a GP125 (sheesh that gets confusing) though.

Yeah I think when I looked into the VP good stuff (maybe 120 octane or so?) it was roughly $8 a litre. Then I have heard the elf is around twice that. Gets pretty expensive when you are going through 30L a weekend. I will stick to the tried and true $1.67 a litre avgas from the airport!!!

[TZ350]

As I said though, all my experience is from 125GP bikes and you are dealing with a completly different kettle of fish. Sorry for the slight hijack.

Its all good. Interesting that the lead helps engine life.

A possibility for team ESE would be to make up two premixes 91 and Av Gas, then mix a small batch 50/50 like F5 Dave, do a dyno run. Dilute the 50/50 mix with some more 91 premix to say 60/40. Do another dyno run, dilute again Etc and see what happens.

From what Iv'e read recently. It takes about 50-60 degrees for the fuel charge to burn. Higher octane slower burn. Given the correct compression ratio and octane rating, ignition timing is adjusted so peak pressure occurs about 15 degrees ATDC.

A faster burn, needs less advance to peak at 15 degrees ATDC and creates less negative pressure (orange bit in pic) on the piston before TDC resulting in better BMEP or torque.

From what I understand, the calorific value or heat released per quantity of fuel burnt or power of the fuel does not matter, low calorific value, like methonal you just burn more of it.

What maters is how much oxygen (air) you can get into and keep in the motor.

More oxygen burns more fuel and that makes more power.

If the fuel burns faster and the fire can be lit later this means less negative pressure on the piston BTDC giving even more power at the back wheel.

The trade offs are compression ratio, octane rating, burn rate.

Whether we can get more power using faster burning 91 in the mix, who knows, when we can we will look into it.

F5 thanks for the tip about poor throtle response with Av Gas, I am having trouble with throtle response too.

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[SS90]

From what Iv'e read recently. It takes about 50-60 degrees for the fuel charge to burn. Higher octane slower burn. Given the correct compression ratio and octane rating, ignition timing is adjusted so peak pressure occurs about 15 degrees ATDC.

A faster burn, needs less advance to peak at 15 degrees ATDC and creates less negative pressure (orange bit in pic) on the piston before TDC resulting in better BMEP or torque.

From what I understand, the calorific value or heat released per quantity of fuel burnt or power of the fuel does not matter, low calorific value, like methonal you just burn more of it.

What maters is how much oxygen (air) you can get into and keep in the motor.

More oxygen burns more fuel and that makes more power.

If the fuel burns faster and the fire can be lit later this means less negative pressure on the piston BTDC giving even more power at the back wheel.

The trade offs are compression ratio, octane rating, burn rate.

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This all touches on a very interesting part of two stroke tuning... I used to think that attention to such details was not so important for low BMP stuff (for the likes of 125 GP bikes and upwards), but I have since learned otherwise.

In simple terms-

advancing produces a stronger mid range, and increases the "grunt" ( more Torque actually!) at the beginning of the power band, by allowing more time for peak-pressure to do work on the piston before the exhaust port opens. But this is over taken by the turbulance (correctly called "maximum-squish-velocity") at high RPM ( lets say above 7500 RPM ), and too much advance, as we all know causes detonation (or worse), but what so many people don't realise is that the reason too advanced timing causes such heat (and therefore heat related damage) is simply because you a firing too much before "peak pressure" and simply overheating the combustion chamber (and piston crown), as it is "fighting" itself, as it (the burning fuel) is trying to "push" the piston down, while inertia is trying to push the piston up!

retarding the timing at high RPM, causes heat to transfer from the cylinder to the pipe, keeping the cylinder cooler, and making sure peak-pressure occurs long enough AFTER TDC to prevent detonation. The extra heat in the pipe causes the tuned frequency to move upward - WIDENING (HINT HINT!) the power-band at the top end, and allowing the engine to over-rev more easily.

However, if you have your timing too retarded at this point, (too many degrees AFTER TDC) let's say the exhaust port is "half open" when it "burns", and this causes a huge flame front to "rush" out the now open port (that would usually/ideally be closed at this particular moment) this in turn causes more localised heating of the crown on the exhaust side, and so many people believe that this type of damage is only caused by compression ratios, or jetting, or TOO ADVANCED timing.... when quite often it is because of too much dynamic retard (firing too much after "peak pressure"

As you are aware, you are also fighting the resonance of the pipe, and as ignition timing effects your exhaust temperature, which if too retarded (hotter exhaust temp), will cause power loss below the resonance.

Unless you are lucky enough to have a full "programmable ignition" (that you can adjust every aspect of the curve) really (in my experience) the only gains you will realistically make with having a basic retarding ignition (such as what you use) on such low BMP engines is more "over-rev" at the end of your power curve, (and lower cylinder temp in the higher RPM as well, that is unless you retard it TOO much, which will cause increased localised heating of the exhaust side of the piston crown) however, if you do have the fully programmable item, AND an exhaust temp sensor AND a dyno then you can set the ignition (by changing curves) to really make serious gains, even on low BMP stuff.

I have personally seen 10% gains on more that one machine, just with the manipulation of the ignition curves, and I can tell you that is a big gain, just from ignition settings alone!

[F5 Dave]

. . .
From what I understand, the calorific value or heat released per quantity of fuel burnt or power of the fuel does not matter, low calorific value, like methonal you just burn more of it.
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Yeah but like methanol or CNG whilst the Octane is super high the calorific value is low, (You pour in as much to match the air in, as you state for good combustion. That there is less energy is the problem.) but you can crank the compression up high enough to take advantage of the other side of the compromise.

When I changed from leaded super to Av gas I lost 1/2 hp (would hardly run on the 95 that we first got during the unleaded change over) on my 50. Despite any number of jetting ignition changes & about 6 different cuts of head with MSV, shape & comm alterations I never got it back. Old leaded pump gas was better fuel. Simple as that.

[TZ350]

Yes...... sometimes things just work better.

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[Brian d marge]

What maters is how much oxygen (air) you can get into and keep in the motor.

More oxygen burns more fuel and that makes more power.

If the fuel burns faster and the fire can be lit later this means less negative pressure on the piston BTDC giving even more power at the back wheel.


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Fuel doesn't burn faster , the reason you want a LOT of oxygen in there is to sniff out that naughty fuel molecule hiding round the back of the cylinder ,,, and get a complete(er) burn

Thats why Ducati back in the day started winning WSBK , they swapped over to fuel injection and started running HUGE big inlets ...what are they now 60mm?

With my Enfield I have retarded the valve timing to give better cylinder entrapment at low RPM , as I also run on a tight track and most of my throotle work is off the bottom ( no point tuning for top end when its all off the bottom !")

Also Ignition , you will be surprised how often the spark DOESN'T fire , off the top of my head around 17% that s a lot of wasted power right there !

Stephen

[Buckets4Me]

[TZ350]

I also run on a tight track and most of my throtle work is off the bottom ( no point tuning for top end when its all off the bottom !")

Also Ignition , you will be surprised how often the spark DOESN'T fire , off the top of my head around 17% that s a lot of wasted power right there !

Stephen

no point tuning for top end when its all off the bottom!

you will be surprised how often the spark DOESN'T fire.

Two very good points to think about, thanks.

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[TZ350]

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After retarding the ignition and leaning it out and racing Kaitoke and Mt Wellington I lifted the head tonight for a look.

Pic-1 the dark ring on the head is where the inner edge of the barrel is and the copper inside that is the squish band. It all looks good.

Pic-2 is the piston, looks much better than it did after Taupo. In fact it looks pretty good.

Pic-3 checking the ignition timing with a degree wheel. Ignition was 17 degrees BTDC. I will file the stator plate slots to give myself more adjustment.

F5 we made a brass thingy for holding the degree wheel like you suggested.

Specs are:- Ex opens 81 ATDC 71% bore width, Trans open 114 ATDC, Inlet opens 142 BTDC closes 87 ATDC, Ignition 17 BTDC and compresion ratio 7:1 corrected and 13:1 uncorrected. Av-Gas 20:1 premix. RM125-spec pipe from G Bell's book.

The bikes making more power and is less thermaly stressed after its tuning session on Johns dyno.

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[SS90]

Hi Teezee,
In picture number 2, I am making the assumption that the exhaust side is on the right..... if that is the case, the oddball transfer/boost port arrangement of the GP125 works quite well!

Interesting about 17 deg for the ignition timing..... I was quietly estimating something between 17 and 20 deg static for your engine!

[TZ350]

Hi Teezee,
In picture number 2, I am making the assumption that the exhaust side is on the right..... if that is the case, the oddball transfer/boost port arrangement of the GP125 works quite well!

Interesting about 17 deg for the ignition timing..... I was quietly estimating something between 17 and 20 deg static for your engine!

No. Exhaust is on the left, I should have said that when I posted the pic.

I will modify the backing plate so I can get more adjustment.

I would also like to try an ignition modual that has some built in retard, say about 10 degrees coming in near peak power. I have a RM125 black box to try.

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[TZ350]

If anyone wanted to know:………..

Engine power was greatest with the compromise bore/stroke ratio of 1.0 or 1.2
Combustion efficiency tended to decrease with increasing bore/stroke ratio.
Mechanical efficiency tended to increase with increasing bore/stroke ratio.
The specific fuel consumption tended to rise with increasing bore/stroke ratio.
The experimental investigation concluded that a square or slightly over square bore/stroke ratio produces an engine with the best brake performance.

From SAE Paper:- http://www.sae.org/technical/papers/1999-01-3342

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[SS90]

No. Exhaust is on the left, I should have said that when I posted the pic.

I will modify the backing plate so I can get more adjustment.

I would also like to try an ignition modual that has some built in retard, say about 10 degrees coming in near peak power. I have a RM125 black box to try.

.

Oh, I was a little hopeful on that!

In that case, you are not seeing a "scavenge pattern" on the piston for one of two reasons....either the rear boost/transfer set up is "short circuiting", (small pattern on the rear at the area of the boost/transfer ports) or the exhaust port is too wide, and heating that area of the crown too much (white colouring).

72% ( what you have from memory) is not enough to do this in my experience!

The pattern is "forming" though, and you can see the primary and secondaries showing a pattern (see pic)

As I wrote yesterday, having an ignition with too much retard will make you r piston crown exhaust side look like this (as well as too big exhaust port)

For some reason I thought you had a retarding ignition!

The correct setting (retard point (RPM) and amount of advance (degrees back) should help in this problem, but it may take a few different coils (that is where the "curve" is stored) as the wrong curve will make it worse!

I have found that almost all japanese twist and go scooter ignitions have between 7 and 11 degrees set in them.....is it easy/cheap to get a second hand one in NZ?

[TZ350]

72% your probably right, I was working from memory for the width, I should have checked.

When I looked at it in the flesh, the piston was a uniform colour all over with a grey colouring on top that looks like it was just misted over lightly with a spray gun after the piston was painted brown.

The ports are not square across the engine but are turned like a T500 Suzuki's. The rear boost/transfer port would be at the 2oclock position and the exhaust port at 7 oclock in the pic.

The dark area in the dish at 2 oclock, is that the boost/transfer port blowing straight across the piston towards the exhaust? And the lighter areas either side the mains and secondrys blowing towards the back.

I have been working on a retarding ignition, it appears in earlier posts. I intend getting back to it.

My CDI unit consists of three main pieces, stator coil, black box and high tension coil. When you say the "Curve" is stored in the coil, which coil do you mean?

I will look into the possibility of a scooter ignition, thanks for the tip. I have several RM black boxes and plan to make a wiring adaptor and try them. I will get something sorted very soon as we plan another trip to the dyno at Henderson Yamaha and I might get to run my bike this time.

My bike is still "as is" from the first dyno session at Johns and it would be good to get a graph to compair to the others done at Henderson Yamaha the other day. If I can I will have a retarding ignition to try too if I can make something that simply plugs in/out.

Dynos are becoming addictive.

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