ESE's works engine tuner

[Niels Abildgaard]

Peewee,
At 7000 ft, the density would be around 1.0 compared to 1.225 kg/met^3 at sea level.
If you come down from that stratosphere, you might get 20% more power.

Attachment 329048

But You will need more power for same speed due to more air-resistance

[ken seeber]

But You will need more power for same speed due to more air-resistance

Correct if you were going for a LSR where aerodynamic drag is the dominant load.
However, if you were in a kart or on a motocross bike where the aero load is small in relation to the % of time accelerating, then doing this at sea level would be better.

[breezy]

You're on the right track with 'no atmospheric pressure i assume would be no air flow' but you could say it even shorter: ''no atmospheric pressure would be no air'.
And no air = no combustion = no power at all.
I'm not sure where you're going with your second question. Motoring a sealed engine requires some energy, even if the seals are free of friction, because the air inside is pumped from one corner to another and back. And this energy raises the air temperature, which in turn raises the air pressure inside the engine. But if you stop motoring the engine and allow it to cool down, the internal air temperature and pressure will return to their initial values.

To answer your initial question: increased atmospheric pressure augments engine power, as Lohring described.

i had been trying to seal the crankcase from beneath the barrel with a nitrile rubber boot set up.. trying to determine why katinas engine had a burst of high rpm ..could it be the piston crank set up or the sealed crankcase. .. the experiment was a disaster due to to both boots i made being torn to pieces very quickly. on my first attempt to start the enginei almost broke my wrist using my old clutch-less high torque drill it seemed i had maybe some kick back or massive build up of compression when cranking the engine over.... the bike did fire up.. but to keep it running i had to have the throttle more than half way open. it sounded dull and tight, but on blipping the throttle a couple of times it did rev out... then the seal broke and drew oil out the crankcase filling the garage with dense smoke... this happend twice... no real conclusions... the crankcase wasnt vented, i wonder if the pressure inside the sealed crankcase had risen high enough to turn the nitrile boot into a balloon destroying it by the descending piston. could such pressure be vented elswhere for some benificial use.At this point having not destroyed my cagiva barrelled bantam engine i called it a day.. another way of sealing the crankcase in mind for another day and another less precious engine.....thanks to all for answering my, vague at times, questions

[F5 Dave]

Darren Gosper's Pete Sales tuned RG50 was making 14hp a long time ago, and was a tractor to boot, unlike his flatmate's 50

Yeah, he was a turkey that guy, esp when blowing on the internet after a few drinks, like a few pages back

[F5 Dave]

But we were getting 11 and 12hp (Dynojet 100) out of crappy old Suzuki RG50's 20 years ago.

And to be fair they were originally supplied to customer with a natty little packrack for tieing your sandwich box to, on your way to school or work.

[jasonu]

esp when blowing on the internet after a few drinks, like a few pages back

and prolly later this afternoon too...

[monkeyfumi]

Yes, very interested. Thanks Nathan, for the great idea of using a MAP sensor to measure the pressure changes in the exhaust system so as to see the changes in bulk air flow through the engine, I wish I had thought of that ages ago.

https://www.hpacademy.com/technical-...ssure-sensors/

A car and fourstroke based article, but I found this a good comparison of Mass Airflow vs Manifold Air Pressure sensors and their various benefits/drawbacks.

[SwePatrick]

About barometric pressure.

If the pressure is 'low' and oxygenlevel is 'high'
The engine gives the 'same' power as if the pressure is 'high' but oxygenlevel is 'low'.
The thing to measure is the density of air.
To do that with simple tools you calculate with moisture and temprature.
The moisture is complicated enough relativly to temp and pressure.
Thereby there´s an formula to calculate with relativitly moisture.
You can all find this info in dynocorrection standards, they calculate from different 'origos' but they do about the same job all of them.

To set things in perspective:
If a raise in atmosphere pressure is double, but density is half.(from originally situation)
The engine will not produce any more power.
Probably it will loose power as that situation only accurs in bad boostsetups.
(heatproblems)

Rgds.

[husaberg]

about barometric pressure.

If the pressure is 'low' and oxygenlevel is 'high'
the engine gives the 'same' power as if the pressure is 'high' but oxygenlevel is 'low'.
The thing to measure is the density of air.
To do that with simple tools you calculate with moisture and temprature.
The moisture is complicated enough relativly to temp and pressure.
Thereby there´s an formula to calculate with relativitly moisture.
You can all find this info in dynocorrection standards, they calculate from different 'origos' but they do about the same job all of them.

To set things in perspective:
If a raise in atmosphere pressure is double, but density is half.(from originally situation)
the engine will not produce any more power.
Probably it will loose power as that situation only accurs in bad boostsetups.
(heatproblems)

rgds.

rad.......
using your swede
http://www.swedetechracing.com/techt...et-Chart/63165

i haven't actually read it but i am sure its rad.
http://www.intercompracing.com/docum...ir_density.pdf

http://www.dtec.net.au/Air%20Density%20&%20Tuning.htm

Re LSR attempts on the salt.
I built the pipes for Kiwi - Cory Bertelson's records on a Honda RS250 at Bonneville and as far as tuning is concerned with a
two stroke there are two important factors.
You must run a flat line advance thru the area used from peak Hp into the overev region.
This is to prevent the natural cycle of more retard = more heat = more power = more rpm = richer jetting needed when sitting at your peak speed due to aero and friction.
Once the motor/pipe temp stabilizes, the pipe heat remains constant, as does the fueling then needed for that power level.

Second thing, is to get on the pace as fast as possible,as the weather changes during the day, you should already have a RAD jetting chart done with a load control dyno
so you can do constant rpm at peak power - long enough for the power and egt to stabilize.
If you jet for peak power on a specific day,this will translate into a specific egt number, at a specific RAD.
Do this twice with very different weather combinations, and you can then draw up a chart with a straight line relationship between RAD and jet size.

Here is one for a KZ10 kart engine ( that also has by the way, a straight line ignition ) that was generated using 3 different days, but hitting the same egt on
each day of 640*C ,that was also the peak power egt, before deto, on a constant accelerating inertia dyno - exactly the conditions the kart engine runs under.
This has been used for probably a dozen completely differing RAD days, and I usually change jets every heat race to stay exactly on 640*C, no guessing at all involved.
It has won every race meeting except one second place last year, when we fucked the good motor by leaving all its water on the track.

https://srgclub.org/Jet_BL.html
http://www.tz250.com/forums/archive/...hp/t-4295.html
http://www.everything2stroke.com/for...0&d=1140811026.
https://wahiduddin.net/calc/calc_hp.htm

[chrisc]

The only simple position guide I can give is to say about 3 X Bore down the header from the port face.
You are trying to get out of the unburnt air/fuel zone that sits in the header - but not so far down as to see the gradual temp drop from wall heat radiation.
As far as depth into the header, do what ever you can to get it as close to the middle as possible.
The short,capped end 5mm probes some suppliers sell are useless for reliable use as a tuning tool.
This makes a HUGE difference , believe it or not.

In a 125 kart engine at the Nationals, I got completely lost for 2 days practice trying to get it tuned.
The egt said it was on the limit at 660*C, but the piston and plug were nowhere near,and we were 3/10 sec off the pace.
Luckily on the morning of the final I noticed from the outside that the probe seemed to be pushed in along way.
It was a long exposed tip Stinger type from EGT Industries ( the best and only guaranteed probe you can buy ) with a 90* bend just above the ferule and locknut.
And sure enough, it was 10mm too far in ,past center-line.
I pulled it back up to on center and in the warmup, what was 660*, now read as 610*.
At least an easy 2 jet sizes too rich.
We won, having been second all thru qualifying and the heat races.

As you are running a 10.4 cc head, you will be on Avgas, so in F you are looking for a minimum of 1220 and a max close to 1280.
Start rich, and go down a jet at at a time,you should see around 30 to 40* F increase in temp each change.
If you go down a jet and only see a 20*F increase ,or even worse it stays the same ,or real BAD it drops - then Mr Deto is in the house - go back one, or two in size.
Just remember that ignition timing affects the reading as well,+2* will drop the temp around 2 jet sizes in a RS125 - so then the delta temp change rule becomes even more important.

Thank you Wob!

[oldjohnno]

Anyone have any rules-of-thumb for carb sizing with reed valve engines? Working back from some existing engines I get something like throat dia = √(hpx32), though there's a lot a variation. Does this sound like a reasonable place to start?

[husaberg]

Anyone have any rules-of-thumb for carb sizing with reed valve engines? Working back from some existing engines I get something like throat dia = √(hpx32), though there's a lot a variation. Does this sound like a reasonable place to start?

There is a rule of thumb per the reed valve vs Carb area i think it was .8.
Pretty sure Frits and wob have both mentioned it.
Ages ago i posted an old graph for carb size per HP.

I do know that a 24mm carb will flow 30HP (TZ350's bucket)
Plus a 28mm carb will flow 35HP (Numerous RD yamahas)
But i doubt that means they are the optimal size.
why not scale the carb size by area from a known well developed engine.

[richban]

Anyone have any rules-of-thumb for carb sizing with reed valve engines? Working back from some existing engines I get something like throat dia = √(hpx32), though there's a lot a variation. Does this sound like a reasonable place to start?

I reckon this is a good way to get very close. http://www.underdogsracing.com/fospipe/ And you get a pipe as a bonus.

Input all the relevant bits and it will recommend the exhaust port diameter for the engine. The 2 engines I have at the moment use the crab size that this calculator recommends as exhaust port dia. Good place to start I reckon.

[shnaggs]

Was thinking this afternoon (I know I shouldn't do such a thing), about CFM vs HP and how this may correlate to the 2 stroke. Now I am NO engineer, scientist, etc. so most of my research is the search button on Google

according to a website, you need 33.31 cfm to make 48hp...now I know there are multiple variables that you need to take into account before assuming such a number, but doesn't 33 cfm seem rather low? I mean a 38mm carb can flow a shit tone more air then that (obviously the test pressure would need to figured). So what am I missing??? Why don't we run smaller carbs and smaller intake ports and ramp up velocity? It would appear from my untrained eye that everything seems to be on the big size.

Please educate me!

[wobbly]

Re carb and reed size for a race engine.

Here is a note I had Neels add to the help file of EngMod


" For high performance, high BMEP, applications a quick check through the areas generated by the software will give a good indication of the engines overall efficiency, and thus a in pointer as to where to devote time with changes to an input.

In these cases the carburettor inlet area, the reed effective area, and the total exhaust and transfer areas will converge to equality, as each of these elements is optimized. Using this technique a "too small a reed" for example will quickly become evident – and a change to improve this, will immediately give a power increase when the simulation is re run. "

The reed block port dimensions are more important than the petal curtain area, as small petals will self compensate somewhat by staying open longer.