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Hellgate
06-19-2015, 04:30 PM
Can anyone suggested a good thread on the site to read up on RS125 performance mods? I recall one from several or more years ago but I can't seem to find it. Thanks!

maddad
06-20-2015, 12:46 AM
You may have to scour the 125 sportsbike forum UK one ,there has been a lot done over there between the bitch slappin.:lol:

L.T.R 250
06-20-2015, 01:38 AM
34mm carb
racing reed block
arrow pipe
good race tune

All i would do and be well quick enough

morad
07-04-2015, 10:22 PM
Too right Maddad. The carry on that goes on at that forum is ridiculous, handbags flying all around the place!

I don't know of any concise threads put together that give a straight forward approach to tuning the 125.
I did/do specific searches on all the different areas of potential gains and then sieve through the bullshit to find the stuff worth paying attention to.
Compression ratio
Squish
Pipe
Ignition
carb
chain and sprockets
porting
cooling system.

there is gains everywhere to be had on these bikes. Depends of course on budget, skill level, intended use etc.

Stuvvie
07-05-2015, 04:44 PM
Could you be more specific in terms of the ignition and cooling system? I have no idea about the mods on those area's

morad
07-05-2015, 10:01 PM
The stock ignition curve, on the later bikes atleast is very retarded and can only be rectified with a Zeeltronic or similar CDI controller.

Like the mile wide squish stock clearance, copper plated big-end cage and 520 chain, all are spec'ed according to the target market of clueless spotty faced teenagers.

I intend to redesign my cooling system to incorporate a bypass thermostat and build a larger radiator aswell. Like aircooled 2t there is power to be had if the engine temp is lowered.

I believe the kart version of the 122 runs a thermostat that opens at a lower temp.

2T Institute
07-06-2015, 08:02 AM
Can anyone suggested a good thread on the site to read up on RS125 performance mods? I recall one from several or more years ago but I can't seem to find it. Thanks!
To get a decent performance increase is quite easy a well worn path of a V F/Boyensen/Adaige/Italkit reed cage, decrese squish gap, a decent pipe, 34mm VHSB carby and a programmable ignition. That will take you to around the 30hp mark, but it will no longer have the on/off power delivery will actually have some mid range.
Next after that I would not bother chasing hp, fix the suspension and look for some lighter wheels, battery and what ever else.
More HP will require higher RPM and shorter maintenance schedules

djr100
07-06-2015, 03:28 PM
Any info on getting more performance than 30 BHP. As this bike is a racer , mileage and essential engine maintenance isnt a problem .
Have all the suspension and weight saving done , still need more power to beat the 250s 4T twins in the class

L.T.R 250
07-06-2015, 04:40 PM
Get a good tuner to tune the engine and have all the right tuning parts.

djr100
07-07-2015, 03:06 PM
Cylinder is tuned . All the right tuning parts ? Lots of info on here for simple tune ups, but no one seems to bother, or is successful with getting 35 + bhp . Which ignition is best, Ignitech , zeeltronic , HPI , Italkit, ? Arrow pipe kills the top end rpm . Hung an RS125 Honda pipe on it on the dyno and it has loads more midrange and revs, but not a lot on top end. Getting a pipe made in the next few weeks.
From what I have learned is , 1 std ignition is retarded to far @ high rpm to prevent the kids from overrevving the street bike, 2 Cyl head design needs a full revamp to get volume and squish somewhere near the ballpark , 3 Most available pipes are designed for the street bike and are not ideal for racing.

L.T.R 250
07-07-2015, 03:12 PM
Belive the susperteen bikes run from 30bhp to 33bhp with just a arrow pipe and a tuned cylinder.

I never had to mod the head to get the right compression ratio or squish. Ran stock ign. Ran arrow pipe the tune was done to work with this. Did try a honda pipe didnt work as well as my arrow due to the tune been sent to work with arrow pipe

morad
07-08-2015, 07:30 AM
I have a Zeel that I have yet to fit but their customer support is praised widely across the net which is important because once you let the smoke out of them little black boxs it's extremely hard to put it all back inside. They also have good spark energy, multi functions and are made for a wide product range which should be an indication of their R&D and general standing in the market place.

With higher spec fuels and a CR to suit I reckon there is power to be had out of the humble Rotax.

I have read comments that the Tyga and Arrow pipes are not much removed from the stock pipe dimensionally speaking. Putting a Honda NF4 RS125 pipe besides my stock Aprillia pipe illustrated just how much different they are tune wise if their overall dimensions are anything to go by.

Seeing a NF4 RS Honda engine apart recently astonished me because there was nothing inherently different about the basic architecture of both engines. The Honda has no PV, a tiny flywheel and case reed induction, but no water jacket extending down into the cases like the Aprillia, or balance shaft.

Is there RS Honda power levels in the Aprillia, given race bike component service life or there something inherently wrong with the design of the Aprillia holding it back from customer GP spec power levels?

morad
07-08-2015, 07:47 AM
As far as the chassis goes what do you do with a 125 with the dimensions of a 250?

Wheels are a problem to find a replacement for, although I have seen BST's fitted to one by Mathias and a set of marchesini's to another which aren't available anymore and hideously expensive.

Changing out the seat sub-frame to aluminium , ditching the starter and auto oil system and a strict diet of Ti bolts will get the overall weight down but won't do the sprung to unsprung weight ratio any good. On a track it's probably not much of an issue but could negate some power to weight gains if the heavy wheels can't be controlled by the suspension adequately. I'm keen to push the envelope with the little prila but time is in short supply ATM.

Hellgate
07-08-2015, 07:59 AM
Nice input everyone, thank you.

djr100
07-08-2015, 02:11 PM
Morad has posed a good question guys , any further input.

"Is there RS Honda power levels in the Aprillia, given race bike component service life or there something inherently wrong with the design of the Aprillia holding it back from customer GP spec power levels? "

L.T.R 250
07-08-2015, 03:12 PM
Well my race bike about 8 years ago did more power then a stock honda gp125 both tested on the same dyno

bigpt
08-14-2015, 04:00 PM
R6 radiator fits on and is bigger also buy the 55degreas thermostat from the kart section on ebay 15pds posted

mattology
08-16-2015, 01:11 AM
Seeing a NF4 RS Honda engine apart recently astonished me because there was nothing inherently different about the basic architecture of both engines. The Honda has no PV, a tiny flywheel and case reed induction, but no water jacket extending down into the cases like the Aprillia, or balance shaft.

Is there RS Honda power levels in the Aprillia, given race bike component service life or there something inherently wrong with the design of the Aprillia holding it back from customer GP spec power levels?

Morad,

I can possibly provide a little bit of input on this subject.

It was June 2009, and I was a new Aprilia RS50 owner. I bought the bike with low miles from a buddy of mine, and the transmission soon failed afterwards. I had thought about rebuilding the motor with a big bore cylinder kit and upgraded transmission, but instead opted to go for a 125cc swap.

Fast forward over six years, and my CR125 swapped RS50 is a well running reality, and my quest for both peak power and broadness of torque has been a very rewarding learning program for me.

I have not directly messed with the RS125 Rotax motor, but I have spent some time trying to make my 1991 CR125 motor behave more like it's roadracing RS125 NF4 counterpart. Here are some things that I have learned.

1) they are both non counter balanced motors, although the later generation RS125 motors, NX4 and beyond, do have balance shafts

2) the port area on both the exhaust and the transfer ports on the NF4 and NX4 RS125 are much more aggressive than the CR125 cylinders.

3) the squish height is very important to the RS125 NF4/NX4, you have different part numbers for base gasket thicknesses etc, and on the CR125 you don't have multiple gasket thickness part numbers, you just put it together and go. the RS125 runs a very tight squish, which means you will have to replace crankshafts sooner as the bearings wear out and the close squish on a worn crank is a recipe for a piston hitting the cylinder head.

4) the piston ring is thinner and the piston itself is a slightly different design on the RS125, both of these I believe are for higher rpm operation than the CR125, with shorter maintenance intervals in between.

5) the connecting rod is longer on the RS125 compared to the CR125. The CR has 104mm connecting rod while the RS has a 110mm connecting rod. This in theory produces fewer side loads on the piston and better power from more time spent from tdc to exhaust port open for a given crank angle, but may require larger port timing in order to do so.

6) the intake on the RS125 is straighter than that of the CR125 motor. Little changes in flow may make significant differences down the road.

7) operating temperatures are ignored on the CR125, there isn't even a water temp gauge on the dirt bike. on the RS125's , correct operating temperature is everything. You tape the radiator and add/remove tape to get the operating temperature to 55-58C. anywhere outsdie of that operating range and you will be down on power 10% easily. If you operate grossly outside of that temperature range and you will seize the engine. the same can be said about exhaust gas temperature gauge. The RS125 tuners are all using EGT gauges to set their jetting correctly on the track. if they aren't hitting 1100 F / 593C at max speed at the end of the fastest straight, they are tuning down the jet. likewise, many of them use the HRC detonation counter and they are checking their detonation for timing and jetting as well.. the engines are tuned much more on the edge.


I have done my best to try and bring the CR125 motor closer to that of the RS125 motor..
1) I have replaced the curved intake manifold with a straight one, and upgraded to VForce reeds. Some more blending of the intake will be required with epoxy, I believe.
2) the cylinder has had the power valve eliminated with blended plugs in its place for high end power, similar to the RS125 cylinder.
3) the dirt bike ignition has been replaced with a Zeeltronic PCDI-11
4) the 34mm keihin carburetor has been replaced with a 38mm Mikuni TMX and I added a power jet as well for high rpm fueling.
5) the bike is utilizing an NX4 RS125 exhaust pipe now, modified to fit the Aprilia RS50 with CR125 engine
6) the bike has an Aprilia RS125 radiator with no thermostat, I manage the temperature with radiator tape like on the RS125. it is usually around 58-60C in operation.
7) the cylinder head has been uprated to a billet head with changeable inserts, and the squish is closed down to ~0.75mm / 0.030"

I also have a 1995 NX4 cylinder that will fit right on to my CR125 cases without much modification other than setting the cylinder height to line up with the squish, and I have different piston options that I can try. Apparently the 2005 CR125 piston is the best piston to use for CR125's in road racing applications. we will see. I believe it has the thinner lighter piston ring for higher RPM operation but I have not verified it.

So that's where I am with my bike. I believe that many of these differences are going to be the same when comparing the rotax engine to the Honda NF4 engine. Perhaps if we try to make many of these changes, we can get the little aprilia to make more power.

I would love to get my hands on a real Aprilia RS125 someday. Until then, here's what I have, along side my RS250's.

http://i.imgur.com/DdSX61u.png

Here is how my CR125 originally dynoed.
http://i.imgur.com/N9FOmXk.jpg?1

After making some of the changes above, here is where i am now. This is still with the stock ignition.

http://i.imgur.com/Vup3Zrv.jpg

I have yet to dyno it with the Zeeltronic ignition. That is next.

http://www.apriliaforum.com/forums/showthread.php?244445-Hey-guys-long-time-no-post-New-project - here is the thread that started it all, and I continue to update it to this day.

I don't know if this helps, but hopefully it maybe gave you some more ideas on where to look for more power.

morad
08-24-2015, 09:20 AM
This is a very cleverly put together bike. In concept and execution.
Been very busy doing house renovations so can't add much now.
Keep the updates coming.