I'm gonna have to head down to the garage & measure some angles soon so I have something "on-topic" to add to this thread.
I'm gonna have to head down to the garage & measure some angles soon so I have something "on-topic" to add to this thread.
If you are referring to RS125's, they have never come out stock with a powervalve. Yamaha's TZ had a powervalve around that era (but still couldn't keep up with the hondas) but around 2000 (give or take) they reverted to no powervalve. Only the kits have powervalves, I believe they don't make any more power but give a bit more torque in the mid range.
Shirt K you are totally right, last night in my mind I was questioning the later RS models I have seen & couldn't picture pvs. Hmm something is wrong with memory, The CRs did, the NSRs did, so it was a bit queer. Sorry for the brain fart.
Don't you look at my accountant.
He's the only one I've got.
http://www.sp125racing.com/FRS%20Kit%20RS125%202007.htm
Who's got the money![]()
"Instructions are just the manufacturers opinion on how to install it" Tim Taylor of "Tool Time"
“Saying what we think gives us a wider conversational range than saying what we know.” - Cullen Hightower
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FYI.....Gordon Blairs book on basic 2-stroke design refers to the returning pressure wave in the expansion chamber as a "Plugging Pulse".
I have seen plenty of references to "Supercharging" in books but this is the first time I have seen it referred to in any literature as a plugging pulse.
SS90 tried to introduce this idea to us but got distracted by the need to win some spurious argument.
.
of course the real reason for the performance increase is the chemical transformation caused by this plugging action, with the rapid cooling of the gas in the pipe and 2ndry compression by the pluging (which occurs after the primary supercharging, but not 2ndry), the gas is separated & transformed breaking down the oxygen, sometimes up to 5 times so we get a reasonable nitrous oxide effect but with less nitrogen. So all this messing about with ports is a bit of an irrelevancy.
[stands back 6 paces]
Don't you look at my accountant.
He's the only one I've got.
It's a little untidy but this is the current port map. The grid is 5x5mmThe piston actually extends 2mm above the top line. Now I should write a spreadsheet formula to calculate crank angles versus piston position with the 105mm rod. Actually it'll be interesting to do a side-by-side comparison with a stock 100mm rod.
We just got home and I am a little "Pissed", so no heroics just now, but I am just thinking about your posted transfer times, compared to the fact that I know realise that you have a 105 mm rod........
That is going to change everything.
The port timings (transfer duration) that your have posted will be significantly different to what was origonaly designed......which will explain the discrepency with the numbers.
Obviously exhaust duration will be the same, but transfer duration will be longer (hence the long blow down period, compared to the measured transfer duartion)
Apparently I need to "Ins Bett jetzt!".....![]()
Here is how I make it Speedpro.
100mm rod
Transfer 123.7
Exhaust 187.9
105mm rod
Transfer 123.1
Exhaust 187.2
The transfer duration just seems a little "tame" to me.
I may be speaking out of turn, but the blowdown times (32 degrees) just don't match the durations correctly, it could well be though that we are all about to learn a big lesson!
My experience suggests that this is not well suited to the style of exhaust you have, but like I say, I may well be about to be given "the learn!"
The port map of the rear transfers looks a little unsymmetrical between the sides, but I suspect this is more, how it has been traced.
Don't you look at my accountant.
He's the only one I've got.
The map is not particularly well drawn. I will be making further attempts at a better job.
As for the transfers, the desired time/area value is supposedly achieved with the port timing as measured, more or less. Remember it is the time/area value that is important, not the duration. I need to measure more accurately and then do the calculations.
I'm not totally happy about the port roof angles either and have been investigating having them machined. It isn't as easy as I first thought. With the primary ports roof angle being 20deg you can cut the required 5-6mm back into the port without taking too much of a dent out of the barrel below the port. It's the setting it all up on the mill and making the cut at the right angle whilst keeping the top edge of the port horizontal in the bore. Things have to move in 2 axis for it to happen as the cut is made because of the angle the port enters the bore.
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