[swift8847]

A KnN is not really need for a babe like RX. But if you are really interested in getting it then as the others have said, you'll have to upsize the jet. And about the fitting, you can go to DAM motors. He is really good with 2 strokes plus he can also tell you as to what jet size you ll need for the bike. I got my air filter fitted and the jetting done there. Havent faced any problems with the fitting at all.

Another reson as to why i go there is that i get to see the RD's which are ready for drags. I Keep drooling looking at them.

[ScarySkulls]

Originally Posted by ananthkamath

When I said small I was referring to drilling holes in the airbox. I've been there, done that, and therefore don't recommend it to anybody specially if they're looking for performance.

Oh! Sorry for the misunderstanding on my part then

Originally Posted by ananthkamath

Also, what did you mean by static and dynamic? The stock RX's timing advance changes as per RPM. The bike wouldn't run otherwise.

Static = Fixed. Dynamic = moving or changing.

An analogue CDI will give static timing. At least all the common units here like RX135 etc. So it works like the points ignition on the RD. Example -> if you set the timing at 2mm BTDC. It remains at 2MM BTDC.
Where as with digital CDIs, tHe timing is not static. It changes based on RPM, normally referred to as the timing curve, where for a given RPM the timing is known.

What they do with Digital CDI is that, when RPM's are low and Scavenging is at its worst, timing is ramped up to extract every ounce of power. Thus boosting the power the most under peak Torque RPM.
Then, at around peak when power is on par with stock except for the increase from better burn, timing is backed off which pushes heat into the pipe, allows the engine to run cooler AND a slight increase in the power by allowing increased revs. (Ah well, maybe not MORE power, but more USABLE power. he he ).

For anyone wanting to upgrade ignitions, check following three points:-

1. Spark / Energy strength:- Research the market out there and see which is the best one for this. The info is all out there on the internet.

2. Spark timing / The Ignition map you land up using:- Carefully check this point as this is the loophole exploited by all the Con-artists out there. Carefully check it's NOT some Four Stroke Bike CDI that is being sold to you as a Digital CDI upgrade. Sure, the timing maybe Digitally/Dynamically controlled, BUT you are using a 4 stroke timing curve on a two stroke. Example:- Bangalore/Bombay guys will know how they used to cheat RD guys by offering something like a Scooty Pep "Digital" CDI.

3. The accuracy maintained between each time the spark fires:- Very critical and has the largest bearing on the smoothness of the engine. With the company CDIs, most running slow processors, (Example:- at 4 Mhz) The timing is never going to be accurate. Between each RPM, timing is going to be jumping around by a few degrees. Simple cause - Anything from the company has only one criteria. L1 or cheapest quote.
Find an upgrade that has a good, high speed processor which will hold timing accurately between each RPM.


I think I have gone way too much offtopic. Sorry guys.

As regards the topic of this thread, UNI is what gets my vote. With proper upjetting, ofcourse.

[shazikon]

thats very good education Mr.scaryskulls.. while you are at ignition and timing.. could you explain this bit to me

when RPM's are low and Scavenging is at its worst, timing is ramped up to extract every ounce of power. Thus boosting the power the most under peak Torque RPM.

How does power increase when ignition timing is ramped ( is it advanced or retarded?) what are the fuelling requirements at different RPMs and corresponding timing..

Then, at around peak when power is on par with stock except for the increase from better burn, timing is backed off which pushes heat into the pipe, allows the engine to run cooler AND a slight increase in the power by allowing

and how does this happen, if you back off timing, heat is pushed to the pipe??

[ScarySkulls]

Originally Posted by shazikon

How does power increase when ignition timing is ramped ( is it advanced or retarded?) what are the fuelling requirements at different RPMs and corresponding timing..

Yes, it is advanced to give a boost to the midrange. Fuelling requirements are unique to each bike. Timing map is kinda same for pretty much all. Normally only a change of the base timing is needed (by moving around the stator plate)

Originally Posted by shazikon

and how does this happen, if you back off timing, heat is pushed to the pipe??

Two Stroke timing curves normally start to back off at higher revs. Thus, the retarding the time means that mixture gets burnt closer to TDC and will leave the cylinder earlier than a mixture that ignited away from TDC (advanced timing) and fought a battle against the rising piston.
Trying pushing a bike with static timing. Example all RX's and a popular bike CBZ or classic pulsar. They tend to be harsh at top end. The newer bikes in market are very smooth in climbing to their redlines. All because of dynamic timing. :-)

I really really recommend reading of Bell and Blair to anyone even moderately interested in 2 strokes.

[ananthkamath]

Originally Posted by ScarySkulls

Static = Fixed. Dynamic = moving or changing.

An analogue CDI will give static timing. At least all the common units here like RX135 etc. So it works like the points ignition on the RD. Example -> if you set the timing at 2mm BTDC. It remains at 2MM BTDC.
Where as with digital CDIs, tHe timing is not static. It changes based on RPM, normally referred to as the timing curve, where for a given RPM the timing is known.

Offtopic again, but this is how all ignition units work, even the stock factory CDI ignitions that came on two-stroke bikes. If timing remained the same amount at 1200 rpm and 4000 rpm, the bike wouldn't even run. In other words, all CD ignition units are dynamic by your definition. In still other words, all CD ignition units are programmed with a timing curve. Its basic engine design. No engine on god's green earth will run properly with the same amount of advance at all RPMs.

If you open up an RX or KB service manual, you will see that the standard test procedure is to use a timing light at idle and at a higher rpm, say 4000. If the advance at idle is X deg. BTDC, then the advance at 4000 rpm will be (X+Y) deg. BTDC. Meaning, it is not the same as at idle.

Maybe what you're saying is that digital CDI's provide more precise angular control of the spark advance, as well as an advance curve that is tailored more towards power (sometimes for a specific expansion chamber) than emissions or fuel economy.

Originally Posted by shazikon

and how does this happen, if you back off timing, heat is pushed to the pipe??

At higher RPMs, normally the spark will start earlier before TDC (i.e. more spark advance), because there is less time to burn the mixture. A two-stroke equipped with a chamber is a slightly different animal. Typically the expansion chamber is tuned to a specific range of RPM. Its length depends on, among other things, the exhaust velocity, which depends on the exhaust gas temperature (EGT). EGT in turn depends on the spark advance, more the advance, less the EGT in general. The higher EGT caused by a "backed off timing" will re-tune the chamber to that specific RPM, therefore making use of its scavenging effect much better. That is why spark advance curves are closely matched to the specific expansion chamber being used.

[ScarySkulls]

Originally Posted by ananthkamath

In other words, all CD ignition units are dynamic by your definition. In still other words, all CD ignition units are programmed with a timing curve. Its basic engine design. No engine on god's green earth will run properly with the same amount of advance at all RPMs.

Nope. Not all. And you hit the Bulls eye in the last line.

Originally Posted by ananthkamath

Maybe what you're saying is that digital CDI's provide more precise angular control of the spark advance, as well as an advance curve that is tailored more towards power (sometimes for a specific expansion chamber) than emissions or fuel economy.

ummm....Not exactly power. But overall efficiency. This is exactly why that, while you don't see much change in peak power, the midrange is more healthy, bike feels peppier to ride around, emissions are down, fuel economy is up, engine runs cooler.

Originally Posted by ananthkamath

At higher RPMs, normally the spark will start earlier before TDC (i.e. more spark advance)

Naughty naughty. Stop playing around with the boys now. he he.

Originally Posted by ananthkamath

A two-stroke equipped with a chamber is a slightly different animal. Typically the expansion chamber is tuned to a specific range of RPM. Its length depends on, among other things, the exhaust velocity, which depends on the exhaust gas temperature (EGT). EGT in turn depends on the spark advance, more the advance, less the EGT in general. The higher EGT caused by a "backed off timing" will re-tune the chamber to that specific RPM, therefore making use of its scavenging effect much better. That is why spark advance curves are closely matched to the specific expansion chamber being used.

Hello Shazikon. The above explanation is pretty good and easy to understand.
Just to add a very little to it,

At high levels of tuning, chambers have been shown to boost power by upto 80%. But the deal with such high boost chambers is that the problem is the more effective a pipe is in outright terms, the narrower is the power band.
Normally, we would all want the pipe to work well and be able to do that over a wider band. The most ideal solution for this will be having a pipe which is variable in its length. i.e. the tuned length of the pipe should change based on the RPM. This is so that the suction and the plunging pulse are timed right.
(This is like the Variable OHC system found in cars. One set of Cams for low RPM and one for High.)
All things being standard and fixed, this plunging pulse will arrive at perfect time in only a particular band where the pipe was tuned to work. At other RPM's, low or high, it arrives back too either too early OR too late. This is why there is a sudden drop in power in the higher RPMs in some bikes.

Now, this above said time taken for a plunging pulse to return to the exhaust port is directly proportional to the length of the pipe and inversally proportional to the square of the Mean gas temperatures.

Now since the chambers we see normally fitted on our small two strokes here are not of variable length, we turn towards playing with the Gas temperatures by controlling the various parameters of the ignition system basic idea being that we *Try* to fool the engine into thinking the pipe length is dynamic and has now changed. This can be done to a certain degree and accuracy because the Gas temps play a critical role in the timing of the pulses. So it is possible to change the way the engine responds by controlling/manipulating the EGT.

Hope this was useful.