ESE's works engine tuner

[wobbly]

The accepted norm for a race engine with everything well set up is 15* at peak power.
If you cant run this due to getting into deto, then its usually due to low com and or excessive squish velocity.
If it runs fine below this , then its screaming out to be advanced.
You have plenty of com for the fuel at 16:1, and the scavenging is not too bad,so if it likes more than 15* at peak then go looking for something that itsnt optimum.
My first guess is the carbs are too small, and or the reed area isnt sufficient for the big cylinder.
All mods are aimed at increasing the dynamic com, so getting more air in there will do this and end up limiting what can be achieved with advance.

[Yow Ling]

Hi Wob, could you explain what "excessive squish velocity "means

[richban]

The accepted norm for a race engine with everything well set up is 15* at peak power.
If you cant run this due to getting into deto, then its usually due to low com and or excessive squish velocity.
If it runs fine below this , then its screaming out to be advanced.
You have plenty of com for the fuel at 16:1, and the scavenging is not too bad,so if it likes more than 15* at peak then go looking for something that itsnt optimum.
My first guess is the carbs are too small, and or the reed area isnt sufficient for the big cylinder.
All mods are aimed at increasing the dynamic com, so getting more air in there will do this and end up limiting what can be achieved with advance.

Ok cool. The first heads the numbers all added up to 38 mvs at 11800. So good. With the new heads the squish was to big 0.12 so the numbers come in at 34 mvs at 11800. We tried pulling some advance out and it lost power straight away. So the lesson I take from this is find the mechanical squish limit the design the head around the limit. With brand spanking crank the other engine has run a .65/.7 squish and no sign of touching.

I do have a det sensor but have not installed it as yet. Will buy a long head stud this week and sort it.

It has some very short 38's YZ250. I was thinking about chucking some Vforce reeds in as new reeds are a good idea anyway.

I will pull the heads tonight and see what is what.

[richban]

Do you have an ignitech?

Yep yep.....

[wobbly]

In a NSR250 using VF3 is worth 4 Hp, and remember that the Aprilias ran 41/42mm carbs.
If the squish is very close and the width is too wide the MSV goes over 40M/Sec, this can and does limit peak and overev power considerably.
I would imagine the effect is caused by very high turbulence in the end gases, and this actually adds up to increased flame speed.
This is actually the same as having too much advance.
I have tried very high MSV with retarded spark to help make it rev and not deto, but this route looses alot of power.

[richban]

In a NSR250 using VF3 is worth 4 Hp, and remember that the Aprilias ran 41/42mm carbs.
If the squish is very close and the width is too wide the MSV goes over 40M/Sec, this can and does limit peak and overev power considerably.

Hummm. Also these barrels are quite close to stock. The engine has out preformed my expectations for sure. I am now itching to build another one but more carefully.

[Neal]

The husqvarna cr125 VF3 fits the nsr cases and the inlet stuffer is slightly less obtrusive than the honda cr125 one , but they both need to be shaped to mach the inlet rubbers .

[RomeuPT]

As above a Viton O Ring on the spigot face.I have had the oval to round transition made in alloy 7075 as well as some in simple mild steel.
Biggest issue is trying to get enough weld far enough into the duct,its a real bitch to get even a tiny Tig into the right places.
Im about to try some alloy stick welding rods, to build up the intake floor on a poxy Triumph 750 head,so this technique may save a hell of alot of drama.
The rods are only 3mm thick, so it should be easy to add material where needed, and even if it turns out a bit porous,its the shape that matters.

Wob, I am sorry for get back to this. I am thinking in build a spignot flange, instead of making pipes to fit direcly.

Is there any difference in performace or something else in making a mild steel instead of alloy? Or is just a question of wheight?

[richban]

My first guess is the carbs are too small, and or the reed area isnt sufficient for the big cylinder.

Sounds like a job for the flow bench. V force3 on the way as I need new reed's anyway.

[wobbly]

Alloy spigots wear out and leak in no time - even with a Viton O ring or two,in the female cup on the pipe.
Big thing to remember is getting water around the Ex port duct in the cylinder to keep it cool, even going to the lengths of drilling into the case
and getting water into the cylinder from under the Ex duct.
The very latest TM125 kart engine has only just had this homologated - 5 years behind as usual.

[F5 Dave]

jus' like my 1982 RG50.


which doesn't excuse a plethora of other design features.,.

[Bert]

The accepted norm for a race engine with everything well set up is 15* at peak power.
If you cant run this due to getting into deto, then its usually due to low com and or excessive squish velocity.
If it runs fine below this , then its screaming out to be advanced.
You have plenty of com for the fuel at 16:1, and the scavenging is not too bad,so if it likes more than 15* at peak then go looking for something that itsnt optimum.
My first guess is the carbs are too small, and or the reed area isnt sufficient for the big cylinder.
All mods are aimed at increasing the dynamic com, so getting more air in there will do this and end up limiting what can be achieved with advance.

Ok cool. The first heads the numbers all added up to 38 mvs at 11800. So good. With the new heads the squish was to big 0.12 so the numbers come in at 34 mvs at 11800. We tried pulling some advance out and it lost power straight away. So the lesson I take from this is find the mechanical squish limit the design the head around the limit. With brand spanking crank the other engine has run a .65/.7 squish and no sign of touching.

I do have a det sensor but have not installed it as yet. Will buy a long head stud this week and sort it.

It has some very short 38's YZ250. I was thinking about chucking some Vforce reeds in as new reeds are a good idea anyway.

I will pull the heads tonight and see what is what.

Igntech..

Yep yep.....

We should look at the base advance again to ensure that we are firing where we think we are.. Currently 14 degrees at peak power.

[wobbly]

Pick an advance number ( I usually use 28* that is the initial straight line on the ignition graph from 2000 up to say 7000 rpm ).
Convert this to mm down the bore, and use a DTI to set the piston exactly at this number.
Then arrange a scribe or white pen line on the rotor and stator that is easy to see with your strobe.
Fire it up and strobe the lines mechanically set at 28* holding the rpm steady between 2000 and 7000.
Adding more base timing will retard the firing line and visa versa.
This will ensure you are mechanically and electrically on the money in the Ignitech.
I have found that the only strobe that is dead accurate is the old, super el cheapo ones, that are in line with the plug leads.
Used to be $12.00 at Repco.

[Grumph]

In a NSR250 using VF3 is worth 4 Hp, and remember that the Aprilias ran 41/42mm carbs.
If the squish is very close and the width is too wide the MSV goes over 40M/Sec, this can and does limit peak and overev power considerably.
I would imagine the effect is caused by very high turbulence in the end gases, and this actually adds up to increased flame speed.
This is actually the same as having too much advance.
I have tried very high MSV with retarded spark to help make it rev and not deto, but this route looses alot of power.

Interesting....getting more diesel like all the time. Might be worth pursuing if you were limited either by regs or circumstance to crap fuel.
i'd have thought the hotter ex gas temps may have helped the pipe effects ?

[husaberg]

Sorry to interrupt this Honda love feast.
Swiss Auto Pulse ROC MUZ.
They had the flying web crank so were narrow.
Seeing as Wob and likely few others have seen the insides of one.
Was here charge robbing with the shared crankcase for the pars did not have the conrod shroud of the earlier pics I first seen.
Anyone got anymore pics of the internals.
It looks to me as if the engine was designed around the reed valve, Looks to be the best compromise with width vs cylinder spacing.