calling all knowledgeable 2smokers, brace your self .. 3d ignition questions!

[Reino]

In the next 3 years i would probably have gathered enough money to start my project (don't ask its a secret till its done).In the meantime i am doing research especially on 3d ignition maps, but so far i have not yet found a collection of 3d maps or good explanations on what happens under load in 3d maps.I am replacing the cdi on my 250sx with a system that can do anything so it would be a shame not to use a 3d map.

my questions:

1-is a 3d map worth it

2-what happens under load

3-how would a 3d map look like (i am well informed about 2d maps)

I live in Namibia (just above South Africa) so because of my time zone i would probably take a while to respond.

[Reino]

so no replies, well thanks anyway .

Can someone just answer one of my 3 questions?

[Low Budget]

Best to ask these questions over on a Honda RS board or a Yamaha TZ website.

Its a very complex tech question. Far beyond a simple ignition advancer. Way beyond my grey market 2 stroker knowledge, sorry.

[Reino]

thanks for the reply, around 2 o'clock this morning i found a guy by sheer luck on the interwed that may be able to answer my question.

[Shocktower]

Dam n00bs , good luck with that, I had no idea WTF he was talking about, if it does not have points whats the points

[Reino]

good points .

[hrcs90]

I think load is going to be pretty hard to determine on a 2 stroke. I would maybe look at tying into a knock sensor.

[Reino]

The load i am referring to is throttle opening which is measured by a tps in % or vacuum by the map sensor in pascal.

ignition curves for cr500 below

http://i870.photobucket.com/albums/a...396/graph9.jpg

A 2stroke ignition sees most advance in the early parts of the rpm range (30 degrees) to get the exhaust temp high to maximize scavenging and drops after max torque to something like 9 degrees btdc to maximize over-rev, this is for a 2d map of coarse but you get the point.

I thought about this topic for a while and realized an expansion chamber's scavenging effect is optimized for a certain temp, so with less load you can effectively increase advance to increase exhaust temp for throttle response. under load you would retard to decrease temp to decrease chance of melting the piston.

this is why i love 2strokes, deceptively complex bastards.

[Low Budget]

Not sure how this will tie into your design theorys, but, sometimes builders use thermal retention pipe wrap on expansion chambers to increase the working temperature of the pipe itself.

You see this on two stroke snowmobile race engines sometimes. No idea the adverse effects if run in a application where it would make the pipe run too hot.

Most also run EGT sensors a specific distance from the piston skirts in the headpipe of the expansion chamber to keep a close eye on how hot things are running, and to help judge if their air / fuel mixture ratio is right at different throttle positions.

[Reino]

Thanks for your input low budget, i am probably going to use a EGT to measure my temp so that i am just under melting a piston at every rpm and load situation under max torque.

I Know the yz250, rs250, tz250 and tzr250 used 3d maps.

But i am still not certain if it is worth while to use a 3d map, at the moment that's my biggest problem.

[Low Budget]

Yes, a good quality EGT gauge thats located in the right spot will let you know when things are getting to hot early enough to shut it down before damage.

It reacts very fast, and is a better indicator than a typical engine temp gauge as to whats going on at that moment in the combustion chamber.

Once you have a engine setup all dialed in, and note the EGT running temp at a given situation, you can then use that number as your benchmark for doing further tuning. Like rejetting for altitude differences or temperatures and humidity changes.

You may very well be OK with a 2d ignition and other things than be overly complicated trying to combine the extra variables of the 3d .

Its all rocket science at that point !

[Reino]

i think i should drop 3d map and stick with a 2d one. I have a big test on the 7th next month on centriods and moment of inertia. My time is better spent studding. Afterwords i am going to have a lot of these and do a lot of this and this .

[Reino]

I know this thread is old but, I have my answer.

My assumption was correct. The less load the more advance there is below peak torque the difference becomes less the more you rev the engine.

Finally some closure!

[Twin-shocker]

The dynamics of a 2T motor are entirely different to those of a 4T, and unless you have access to a dyno, and have an ignition system which can be programmed, you are going to be wasting time and money with this.

[Reino]

I am well aware of the differences regarding 2t and 4t. As i have explained in my first post, I am scrapping my cdi with a programmable unit.

I am not going to stop at the ignition side. Also having access to a dyno is not a problem for me.

This is going to be a long term project (3 or 4 years).