02-05-2018, 02:22 PM
|
#1 |
Join Date: Feb 2018
Location: RDU, NC
Posts: 677
|
RX3 performance mods? Horsepower upgrade potential?
I'm looking at buying an RX3 later this year, and I've read about a guy who bought a cylinder head for the CSC cafe racer, and noticed severe blockage in the exhaust port. He ported and polished it, but hadn't installed it or ran the bike with it yet. I'm wondering if the RX3 has similar blockages in the cylinder head, and might benefit from a porting and polishing job.
I'm also wondering if the airbox and exhaust are restrictive, and could potentially be modified for more power. Is there a restrictive cat? Is the muffler restrictive? Also a problem I see is that the RX3 has EFI, not carburetors. Porting the SG250 would be easy, as it has a carburetor and fueling can easily be changed. But what about the RX3? Is the ECU re-mappable? If so are there maps out there? If not, is there a fuel controller that will work with the RX3? Most EFI components are relatively standardized, so a universal kit might work, but I don't know much about EFI honestly, and Zongshen might be using their own in-house parts for their EFI. I'm basically curious about basic performance mods for some more low-end grunt and potentially achieving slightly higher top speed. I know port/polish isn't basic, but that only costs me time and a few dremel bits. Intake/exhaust is a pretty standard thing to modify... Charles. |
|
|
02-05-2018, 03:05 PM
|
#2 |
|
Join Date: Feb 2016
Location: Portsmouth, Virginia, USA
Posts: 632
|
Charles, you ask about getting more power out of a RX#. I'd recommend calling CSC and talk to Gerry. He's the service manager and the guy that set up Roland Wheeler's bike for the track. Roland won first in his class last year and just took first last weekend in another WERA race. Gerry ported the head on that bike. They also messed with the exhaust, not sure about the intake. I bet they put the bike on a dyno so you might even get some hp figures to see if all this work is worth it for a street bike.
As for the ECU, it's a Delphi unit that is used on lots of other small engines. We (this forum) have wondered about options for tuning or even just diagnostics but so far I'm not aware of anything similar to what is available for Ducati or Guzzi. Most RX3s seem to run so well right out of the box that it's hard to justify tinkering with the map. Odds are that any user changes will just screw things up unless you really know a lot about FI maps. I can tell you that it's far more complicated than just tweaking the fuel delivery at a given point in the RPM range. There are sub maps for things like altitude, air temp, throttle position, water temp, and lord only knows what else. They all interact. A few riders here have changed the exhaust without making any other changes. The air cleaner is so basic I doubt you can get anything less restrictive. When you get your bike please let us know what changes have worked for you. Peter Y. |
|
|
|
02-05-2018, 03:25 PM
|
#3 |
Join Date: Jul 2015
Location: Milpitas, CA. USA
Posts: 775
|
Start with considering that it's only a 250 cc single. It can be optimized for high power at high rpm, low rpm pulling power, or broad range overall utility the way it is. To increase one usually diminishes others.
Exhaust: It has a Cat, but it is hardly restrictive. On occasion I (unintentionally) bounce my engine off the rev limiter (about 10.5k) while on the freeway in 6th. That indicates the exhaust isn't corked. Some folks have changed to different mufflers which are lighter, but I have never seen a before & after dyno comparison for evidence of improvement. Intake: Again, no valid measurements of modification. There have been reports of owners noting reduced power after cleaning the air filter and not leaving enough oil in the foam. Porting: Meh. Allegedly every RX-3 engine gets a dyno pull to ensure it meets design parameters. It would take serious casting core shift or other issue to cause flow to prevent meeting specs. It might warrant a look, but not sure porting on it's own is necessary. On a track environment for a 250, if you are at a competitive racing weight of about 150 lbs. and need to gain another 0.04-0.06 seconds per lap, then port away. EFI: The RX-3 uses the Delphi MT-05 engine management system. It's not exotic, and I don't think it can be Mapped. There are things that can be done to optimize the operation. One thing that seems to give the best impact is changing the coolant thermostat for one with a higher opening rating. You might be able to diddle the Oxygen sensor portion to change mixture. You may also be able to alter ignition timing and advance curve somehow. The throttle body and injector are plenty capable of doing about anything you would want of a 250. Zongshen is not using "in house" components, rather off-the-shelf as provided by Delphi. Yes, you can convert to a carb, but I am really enjoying easy push button starting with no throttle fiddling and automatic mixture correction with altitude change. In my opinion the one single thing that would most impact performance change in this engine would be a change in cam grind, if you can find a company willing to do a one-off for you. My personal preference would be for slight reduction of 1st & 2nd gears (to equate to a 13/45 sprocket set) and reduced intake noise. Okay, nap time.
__________________
Horse holder at Madame Orr's House. |
|
|
|
02-05-2018, 11:19 PM
|
#4 |
Join Date: Feb 2016
Location: George West, Texas
Posts: 4,097
|
Jay, pyoung...
 And the big bore kit , sounds like it's mainly a torque booster , always a good thing to help maintain speed
__________________
***************************************** 2015 Bashan"Blaze" BS250GY-31 (DB-07K-250) GONE 2017 Suzuki V Strom 650 XT "We are all born ignorant, but one must work hard to remain stupid." ~Benjamin Franklin~
|
|
|
|
02-06-2018, 01:53 AM
|
#5 |
|
Join Date: Feb 2018
Location: RDU, NC
Posts: 677
|
There is a big bore kit? Tell me more? Or is there a link?
Charles. |
|
|
|
02-06-2018, 06:20 AM
|
#6 |
Join Date: Dec 2016
Location: Western PA
Posts: 363
|
The pushrod engine your mate polished up is known for having a pretty restrictive head - it's the same engine as the TT250 and Hawk.
The 4-valve OHC motor in the RX3 is a step up in sophistication, and I think it's about as good as it's going to get without compromising reliability. When you get into small bikes, you start to realise that looking for performance can be a bit of a fool's errand; the gains are so small they're hardly worth it. There are exceptions; the pushrod 229cc in the Hawk and TT250 respond well, but they're quite restricted in factory form. For example, I own a Ninja 300 and that engine is just about 'there' from the factory. The only tuning changes I wanted was a smoother power curve, and an EFI map did just that. I don't think anyone has had more than 3-4hp extra on a full system, which is nice on track but you'd barely notice on the street. I would see how you get on with it first, then look at gearing. That's where your going to be able to have the most influence on the bike's performance. |
|
|
|
02-06-2018, 12:40 PM
|
#7 |
|
Join Date: Aug 2016
Posts: 24
|
I believe that there is a big bore kit out there.
Look on the dual sport section of this forum for Chonda's posts in the pitster pro LXR. I think it's a 82mm big bore cylinder and piston. Around 283cc's, but it's called the NC300 kit. The cylinder head and ports on this engine are actually quite good as they are, I don't think you would get any noticeable gain with port work, in fact, I'm fairly certain port work would hurt low speed and mid-range torque. The intake and exhaust systems are not exactly restrictive either. It's a 250cc engine pumping out 24.8hp, that's really quite pretty good! Compare that to the: CRF250L @19.6hp KLX250 @19.5 Xt250 @17hp Wr250@ 24.8hp. The numbers don't tell the whole story of course, the important part is the useful power available during normal riding conditions, (the area under the curve)but it does show that the NC250 is right in the ball bark with any of the "major players". Like any engine, I think that you can extract more power from the NC250 engine. However, at some point I think reliability and durability may decline. If it is strictly a play bike, like the Pitster pro LXR, then I think you can get away with it. If you need the bike to get you out to the trails and then back home again, then I'd leave it alone. That being said, a big bore kit shouldn't effect reliabilty if it is a good quality kit. YRMV! If you like the bike, buy it for what it is, not what it could be. (I might catch hell for that line!) Last edited by Thunder; 02-06-2018 at 03:19 PM. |
|
|
|
02-06-2018, 02:32 PM
|
#8 |
|
Join Date: Feb 2018
Location: RDU, NC
Posts: 677
|
I never buy a motorcycle and leave it stock. Where's the fun in that?! :P
Just knowing there is upgrade potential will make me happy. I'm always looking for new fun projects over the winters. Charles. |
|
|
|
02-08-2018, 12:43 PM
|
#9 | |
|
Join Date: Jun 2017
Posts: 382
|
Quote:
TW bored and stroked to 276cc, XT225 6-speed, clutch, and kick start, ported and polished TT230-R head with bigger valves and more radical cam, custom stainless exhaust with reverse cone megaphone dumping into tubular glass pack followed by spark, arrestor, MicroSquirt/Delphi EFI (home built, almost the same as RX3), ..., adventure accessories, pretty much rides like a RX3. Tdub2. Similar engine with TT-R trans (closer low gear ratios) and clutch, head shaved for a bit more compression but otherwise similar, bit more radical cam, similar exhaust with shorter pipes (favors high rpm power), but a fatter Mikuni instead of EFI, in highly modified TW frame with aluminum swing arm and graphite/ceramic 17-inch wheels, sticky barely legal sport tires, and triple discs. It takes a highly modified Ninja to keep up. Tdub3. Similar engine to Tdub2 with stock valves, less porting, RX3 Delphi EFI, milder cam, XT trans and clutch, 26/8.00-14 Carlisle Terrathon rear, stock rear front, triple discs. Tdub4. There are a couple fun projects for you, any will cost triple what a RX3 does if you are a good scavenger, and really not a whole lot better. 21.0, 24.6, and 31.3hp, not in that order. Well, the café racer is a lot better at going fast on tight, paved roads, but only until the ergos cause back pain. The mud hawg passes stuck 4x4 wheelers on a regular basis, but pretty much sucks on the highway. Retiring with no responsibilities, no debts, and severe boredom results in such things. What's next? Now I'm tinkering with a 2003 Nighthawk 750, minimum maintenance with 0-ring chain and hydraulic followers, and no jetting with the MicroSquirt/Delphi EFI now going together. This bike will be a cross country touring standard. I really enjoyed my last Nighthawk 750, except the handlebars and footpegs were both to high, and the seat was a bit too hard. Adding a layer of foam under a custom cover will make all the rest of the stock parts fit. A couple teeth on the wheel sprocket will make the aeros of luggage less a factor. I don't cherish the thought of 300 pounds more weight slinging around a Gold Wing or Ultra Classic would require. |
|
|
|
|
02-10-2018, 12:57 PM
|
#10 |
|
Join Date: Aug 2016
Posts: 24
|
|
|
|
|
02-10-2018, 05:46 PM
|
#11 | |
|
Join Date: Jul 2015
Location: Milpitas, CA. USA
Posts: 775
|
Quote:
__________________
Horse holder at Madame Orr's House. |
|
|
|
|
02-10-2018, 06:50 PM
|
#12 | |
|
Join Date: Aug 2016
Posts: 365
|
That's Not An NC250
Quote:
|
|
|
|
|
02-10-2018, 07:47 PM
|
#13 | |
|
Join Date: Aug 2016
Posts: 365
|
Quote:
|
|
|
|
|
02-11-2018, 08:39 PM
|
#14 |
|
Join Date: Jul 2015
Location: Milpitas, CA. USA
Posts: 775
|
I fuched up.
I screwed up, Thunder. First I saw your link to the big bore kit, then your post about "This gives me about an extra 20 hp", so I connected the two statements in my medicated mind.
Good luck on your build.
__________________
Horse holder at Madame Orr's House. |
|
|
|
02-12-2018, 02:28 AM
|
#15 | |
|
Join Date: Feb 2016
Location: George West, Texas
Posts: 4,097
|
Quote:
__________________
***************************************** 2015 Bashan"Blaze" BS250GY-31 (DB-07K-250) GONE 2017 Suzuki V Strom 650 XT "We are all born ignorant, but one must work hard to remain stupid." ~Benjamin Franklin~
|
|
|
|
|
|
|
 |
|
|
Linear Mode
