421 cheetah help

[alex2218]

Totally amazing work cbrian, i have seen you post long time before, result is very clean and nice
I had exactly the same problem as you with my radiator so i had to make my own part like you

Can i ask you the final ignition map you are using and your volumetric ratio

[cbrian]

Alex,

I'd like to tell you my volumetric ratio but am having trouble finding the documents at this time (my office is a wreck). What I did find is my ignition advance information which is a little changed from when I posted it on my build thread. It is;

0-2000 rpm = 17°
3000 = 24°
3500 = 27°
5500 = 24°
7500 = 20°
9000 = 17°
9500 = 10°
11000 = 9°
12000 = 8°
12500 = 7.5°
13000 = 7°

It won't ever rev that high, but I had the extra set points installed in the case that I wished to modify the curve. This way all I would have to do is move the data instead of adding new points.
If you have any more pictures of how you routed your coolant lines, please post them, I'm curious. C'est bon!

[alex2218]

I can't believe your engine is running good with that map

This is similar from what i had when i started and the engine was running like shit, taking LOTS of rev but no power
Also, if you go higher than 10.500 rpm you will simply destroy your crank

[cbrian]

Look at the stock curve that Martin posted on the previous page, mine is almost an exact copy of that. It should be as I referenced Martin's work when I was creating my own ignition advance curve, he was very helpful answering questions of partial throttle advance points too. I'm making around 90 hp so it's proof that this curve works for me, the weak point in my system now is the rider. I'm no tuning guru but I would assume that the nature of the cheetah cylinders port timing is quite different from my serval and that would make my curve unusable for you. I would also revisit the setup on the base timing, make sure you're starting from a good foundation.
"Lache pas la patate"

[alex2218]

If i knew you were using a SERVAL before i should have understand !
Of course its totally different, but your advance still very low, 90 hp with so low advance is really interesting

Yes i "lache pas la patate"

Have a look on how was my engine at the very first testing day with a poor mapping :

https://www.youtube.com/watch?v=MNRHwjhHSyU&t=565s" onclick="window.open(this.href);return false;

[MK]

The focus of your work should be the falling slope from about 6-7k.
What I usually do is a base curve following the Bill Givens estimate.
Then try to rotate that downslope up until you notice no more power gain. Flat spots can also be cured by introducing some up/down bumps in that slope (nobody said it must be a straight line).
If you're finished with that, introduce a second, steeper slope starting at the rpm of max performance. Try to turn that one down until you have a better overrev.

The absolute values of ignition advance will be somewhat different as it depends on compression, head shape, chamber design, carb setup, ...
So usually it doesn't make sense to think you can use someone else's curve and it'll work just fine for you without any work (that's the dream of every lazy student...).

Best aid here is certainly a dyno, but in a mild form you can do it with s good butt feeling.

PS: I'm not only helpful but also open to donations: https://www.paypal.me/MartinKieltsch" onclick="window.open(this.href);return false;

[alex2218]

I never feel any flat spot and please remember it's a race stroked engine without any exhaust valve. Expecting an "easy" to ride engine is just non sense on that setup.
THIS is an hard to ride violent engine with a flat spot : https://www.youtube.com/watch?v=gzgttgaG_x8&t=81s" onclick="window.open(this.href);return false; ( But this engine has 100hp so it still huge )
Problem is lot of people think a violent engine is more powerfull but sometimes its just a feeling and also it is much harder to ride.

Every engine needs is own setup, i made mine but i wanted to compare, since cbrian has a WAMPUS it's useless but i would see an onboard video !

[MK]

My comment wasn't meant as an offense to anyone special. Just my general observation.
Don't worry, if I answer technically, everything is ok.

If people ask VERY stupid things, I usually answer that they should outsource the work to someone skilled. The usual outcome is that I get added to the ignore list of one pissed off guy ....

[two-stroke-brit]

THIS is an hard to ride violent engine with a flat spot : https://www.youtube.com/watch?v=gzgttgaG_x8&t=81s" onclick="window.open(this.href);return false;

Every engine needs is own setup, i made mine but i wanted to compare, since cbrian has a WAMPUS it's useless but i would see an onboard video !

i liked the vid from "BRANDS HATCH" it brought back memories from a race school weekend i attended.

[alex2218]

Then try to rotate that downslope up until you notice no more power gain. Flat spots can also be cured by introducing some up/down bumps in that slope (nobody said it must be a straight line).
If you're finished with that, introduce a second, steeper slope starting at the rpm of max performance. Try to turn that one down until you have a better overrev.

Yes the best is a dyno.
I fear it is very hard to feel the difference for 1 or 2 degrees of advance, did you done this way ? Also, you said to "turn it down", what do you mean ?

I'm planning to buy this http://www.knockgauge.eu/products-listing.html" onclick="window.open(this.href);return false;
It seems to be adjustable but i don't know how to get the detonation frequency for this engine

[(F5)]

If you have the gauge mounted securely on a water cooled engine (Iused a random sensor from a Subaru car) its pretty obvious when things are going wrong. A bit of green flicker is normal but when it goes red crazy trouble is going on.

You can even run an output from the gauge into the ignition, which an ignitech for example can be set up to back ign off say 3 degrees. Not sure about modern zeels. I have a zeel on RZ but its ancient.

[alex2218]

Guys,

Anybody know the maximum clearance between piston and cylinders in a cheetah cub ?

Received the pistons but the rings are missing so i have some time left to do more checks....

[alex2218]

Hi guys

Engine is running now with new Wiseco forged pistons and a better ports preparation.
I'm having some heating issue with the engine :

Engine is running very strong and the power/driveband is totally insane but the engine temp is reach easily 72° when i push it to the max on 6.
When i was lapping the engine on the first ride, the temp was only 46° under 6000 rpm, i had to tape the radia.
Cooler is from a Ducati ST2 and i can't use a bigger one.

I noticed with the stock ignition map it's not heating at all but since i'm using a map designed for maximum power it is heating much more.
Also stinger are 23mm, domes are 21cc, 1mm squish with 98 pump fuel

2 stroke engine should be between 50/55°C as far as i know but 250 KTM exc run at 70°C so i would have some advices

[justind97]

You're overheating issues are most likely due to so much advance. The more you have ignition advance, the hotter the engine will run.

Finding the balance point is key. 72 degrees is getting borderline. At that heat, over a long period of running, say 20-30 mins of hard running and the engine will heatsoak. Meaning it will slow down.

[MK]

If you lower the advance, the exhaust gas temperature is rising as you virtually blow the performance through the pipe. That should be sorted on a dyno where you vary the advance until the performance drops while you're monitoring a healthy EGT.

If you can't fit a bigger rad, try a thicker one and/or increase the water flow rate (wider impeller, electrical or mechanical water pump). Also very helpful: changed flow direction in the head (i.e. input, where the current thermostat is)

Maybe you can fit additional radiators with fans like the
Benelli Tornado http://www.motorcycledaily.com/wp-conte ... 1side1.jpg" onclick="window.open(this.href);return false;
or the VTR 1000 http://www.superhawkforum.com/forums/at ... -st2-d.jpg" onclick="window.open(this.href);return false;