ESE's works engine tuner

[Peter1962]

The position of an egt probe is relatively simple - 3X bore from the piston face is a good rule of thumb.
The raw numbers are a bit harder to nail down.
On track, the rule is to watch the egt and cht rising in unison,if the egt rises then drops whilst the cht continues to rise you are into deto.
But even easyer is to start rich and drop one jet at a time, and you will quickly discover that the temp will drop a set amount per jet size.
As soon as the egt delta temp drops from say 50*F to 20* with one jet leaner you are seeing the beginning of deto - go back one size.

One small element will change the egt's response in overev, if you have been clever and flat line the advance when approaching the mechanical rpm limit, the egt will
also flatline ( NOT DROP ).
This helps to keep using fuel to make power, not using fuel to control the continually rising egt due to ignition retard putting more and more heat into the pipe.
I use the max egt as seen with max power on the dyno ( at a specific RAD ) to construct a jetting chart,where for every weather data point I hit a specific best power egt number.
This egt ,over a fairly narrow sample range of jetting, will translate into a straight line relating RAD to jet size.

The last real trick to nailing best power jetting is to " read " the bottom face of the ring.
At peak power you will get tiny localized points of detonation of the gas trapped under the ring.
This "power deto " isnt enough to eat a piston crown, but indicates you are right on the limit - just safe enough for a 25 lap final.

Wobbly, I seem to recal that for EGT you once gave an optimum value of 660*F ? Is that correct ? And is that a constant value (when using regular pump gas) or is this different for say a 50cc engine or a 250 MX engine ?

[seattle smitty]

Oh good grief. I'd never think of looking at the bottom of a ring for jetting spec. Guess I'm well too lazy on top of tu stoopid.

Same here, Dave!!; I've seen it and guessed it meant that I'd turned the groove in the piston wrong in some dimension (we used to be able to buy semi-finished "blank" pistons).

Wob, you're The Duke!!! I've got to make a print copy of that post and carry it around to memorize! A question: Does the use of straight (with castor or other lube) methanol alter any of that, given that Methanol is a bit more forgiving of being somewhat over-rich (though not at all forgiving of being lean!)??


To anyone, what if any wheeled 2-stroke racing is done with methanol nowdays, other than maybe some open-class dragbikes or streamliners? Long ago, some of the kart racers could run fuel, IIRC.

[guyhockley]

To anyone, what if any wheeled 2-stroke racing is done with methanol nowdays, other than maybe some open-class dragbikes or streamliners? Long ago, some of the kart racers could run fuel, IIRC.

In Britain, on tarmac, hill climbers and pre 1973 racers with the British Historic Racing club can use methanol but you have to stick a big day glow disc on your bike! I think grass track and classic MX may allow it, too, but I haven't been recently perusing their rulebooks...
Speedway?

[wobbly]

The optimum egt number depends on the setup and the fuel.
Working in *F if you must then AvGas ( and similar leaded racegas ) seems to like around 1280 max.
But when using 110 leaded as is allowed in USA kart racing, we see as much as 1360,due to no deto and the high temp makes rpm.
This fuel likes com, and can be run retarded with high com to get big egt numbers that force the pipe to rev on.
But unleaded,be it racegas ( like ELF as was used in 125/250/500 GP ) or high octane pump makes best power closer to 1180.
What is apparent is that the lower octane burns faster in general, thus cannot stand as much timing/com combination.
It likes ignition more than com as a general rule.

[diesel62]

How do you get away with over 700 C and not have a melt down is the piston/bore clearance increased?

Sent from my SM-G900F using Tapatalk

[wobbly]

[QUOTE=diesel62;1131052022]How do you get away with over 700 C and not have a melt down is the piston/bore clearance increased?

The CR125 engines as used in SKUSA are stock com and are run retarded on VP C12.
This is way too good fuel needed for the tune,and the retarded timing allows the high octane to run real hot to get extra overev.
The drivers gearchange at 12400,and they will run to 12600 in top gear.
On the 98 unleaded used previously any more than 1260* was a meltdown and they only just went to 12,000 - so many pistons were being destroyed the Yanks idea of a fix was to run
way way better fuel, so you can be real dumb on the jetting at still get away with it.
Now the bottom ends blow up due to the revs unless regularly maintained.

[chrisc]

Well, the SX50 ex duct might be on the large size at 27x29mm but at least it's not SX65 big! Exhaust mani is from the SX65 on SX50 cylinder.


Untitled by Chris Cain, on Flickr

Extending the aux port duct to the end of the duct and into the new spigot to form ears will be on the cards as has been advised on this thread. I'm wondering though, will the downsides from increasing duct volume in an already too large duct overcome the positive effects of increase the aux ducts to the spigot?

Another for ref:

Untitled by Chris Cain, on Flickr

[breezy]

ok Frits thanks for reply. im sure you may have read this at some point which is an extract from a document,

" the pressure ( in the crankcase) may be either controlled manually or automatically. A higher pressure results in higher rotational speed and increased oil thickness or viscosity"

rightly or probably wrongly, i have thought that the "higher rotational speed", refers to the crank rpm. which is what im trying to understand.

so its high a pressure oil lubricating system to reduce friction and improve piston ring sealing.....increasing ability to rev.... maybe

[Frits Overmars]

Well, the SX50 ex duct might be on the large size at 27x29mm but at least it's not SX65 big! Exhaust mani is from the SX65 on SX50 cylinder.

The standard KTM 50SX exhaust duct diameter is way too big, and so is the 65SX header diameter. Below left a standard 50SX duct, right and a sleeved-down duct.
This is still a dry sleeve; a much cooler-running wet sleeve with extended aux ducts is on the drawing board.

[Frits Overmars]

im sure you may have read this at some point which is an extract from a document,
" the pressure ( in the crankcase) may be either controlled manually or automatically. A higher pressure results in higher rotational speed and increased oil thickness or viscosity"

I'd sure like to know what you're talking about, Breezy. Which document? Which engine? And which pressure? Scavenging pressure? Lubrication pressure?

[jasonu]

The standard KTM 50SX exhaust duct diameter is way too big, and so is the 65SX header diameter. Below left a standard 50SX duct, right and a sleeved-down duct.
This is still a dry sleeve; a much cooler-running wet sleeve with extended aux ducts is on the drawing board.

How does a company like KTM with presumably huge resources and cash get something like this wrong?

[G Jones]

Re the GRM crank with add on web plates.
This is exactly what some new R&D idiots did to the Aprilia after Jan retired - sadly for them it suddenly lost a heap of power.
In a reed engine there is a bottom limit to the case volume that sits at around 1.3 in my experience.
The RV engine loves additional volume than that,so removing the plates on the GRM reed,and using Mallory may not work if the case becomes too big.

Just what is TOO big though ?

[dutchpower]

How does a company like KTM with presumably huge resources and cash get something like this wrong?

If you have 99,9 % of the market why bother

Exh . duct is already to big to start with

[jfn2]

dutchpower:
I'm sorry but I don't quite understand your attached pic. Are the red lines measurements?

[dutchpower]

Tool to measure