ChinaRiders Forums - View Single Post - RX3 performance mods? Horsepower upgrade potential?

Jay In Milpitas · 02-05-2018, 03:25 PM

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.

02-05-2018, 03:25 PM	#3
Jay In Milpitas 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.
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