From the image, I can see that your exhaust has been modified into a free-flow design with the following key characteristics:


🔎 Exhaust Characteristics

✅ Pure Cone Design: The internal restrictions have been removed, improving exhaust gas flow and enhancing power at higher RPM.
✅ Extended Barrel (~31mm inner diameter & ~36mm outlet diameter): This longer stinger-style design delays the returning pressure wave slightly, improving top-end power but requiring precise ignition timing control.
✅ Stock Expansion Chamber Profile: While modified for free flow, the chamber retains a shape that leans toward mid-range torque rather than extreme peak RPM power (compared to aggressive expansion chambers).

⚙️ Key Performance Impact of Your Modified Exhaust

  1. Improved High-RPM Power:
    • The unrestricted flow and extended barrel enhance exhaust scavenging at high RPM, which supports aggressive ignition timing in the upper RPM range.
  2. Weaker Low-RPM Performance:
    • Removing internal restrictions reduces backpressure, weakening the low-end pulse strength. We’ll need more ignition advance at low RPM to restore torque.
  3. Mid-Range "Powerband" Stability:
    • Your exhaust still has a moderate cone shape, meaning mid-range power can be enhanced with strategic timing.
  4. Peak RPM Heat Management:
    • The extended barrel will reduce peak RPM backpressure slightly. This means less timing retard is needed than with a fully restrictive exhaust.

🚀 Recommended Ignition Timing & Dwell Map (Based on Your Modified Exhaust Design)

This revision builds on your previous setup but optimizes both ignition timing and dwell to maximize power across the RPM range.

RPM CDI Timing (°) Actual Timing (° BTDC) Dwell Time (ms) Explanation
500 +1° 11° 4.2 ms Extended dwell to restore low RPM torque.
1000 +2° 12° 4.2 ms Slightly richer spark energy for improved idle response.
1500 +3° 13° 4.0 ms Stronger ignition to support low-end power.
2000 +5° 15° 4.0 ms Advanced timing to restore early acceleration.
2500 +7° 17° 3.8 ms Mid-range boost zone to compensate for reduced backpressure.
3000 +10° 20° 3.6 ms More aggressive timing for improved torque.
3500 +12° 22° 3.4 ms Strong advance to improve powerband entry.
4000 +14° 24° 3.4 ms Excellent balance for cylinder filling.
4500 +16° 26° 3.2 ms Building strong acceleration at peak torque zone.
5000 +18° 28° 3.2 ms Aggressive timing to improve acceleration.
5500 +20° 30° 3.0 ms Peak advance for maximum torque.
6000 +20° 30° 3.0 ms Maintains maximum ignition advance for cruising.
6500 +20° 30° 2.8 ms Strong top-end timing for extended power.
7000 +19° 29° 2.8 ms Slight timing retard starts here to manage heat.
7500 +18° 28° 2.6 ms Balanced ignition to control detonation risk.
8000 +17° 27° 2.6 ms Strong timing with safe combustion control.
8500 +16° 26° 2.4 ms Gradual retardation to manage heat.
9000 +15° 25° 2.4 ms Balanced timing to sustain top-end power.
9500 +15° 25° 2.2 ms Less retard needed since your exhaust improves high RPM flow.
10,000 +14° 24° 2.2 ms Revised timing to sustain high-speed runs.
10,500 +13° 23° 2.0 ms Balanced timing for safe red-zone performance.
11,000 +12° 22° 2.0 ms Final reduction to avoid overheating.

🔥 Key Changes to Improve Power with Your Modified Exhaust

✅ Low RPM Power Boost:

  • I increased ignition advance by +1° to +2° below 4000 RPM to compensate for reduced low-end backpressure.
  • Extended dwell time at low RPM strengthens spark energy for better throttle response.

✅ Mid-Range Power Optimization:

  • I maintained aggressive timing in the 4000–6500 RPM zone to maximize cylinder filling and acceleration.

✅ Peak RPM Power Retention:

  • Timing retard starts slightly later (around 7500 RPM) than before to take advantage of your improved exhaust flow.
  • Less aggressive retard in the 9000–11,000 RPM range ensures your power holds longer before dropping off.

🛠️ Step 3: Testing Procedure

  1. Upload the revised ignition timing and dwell map.
  2. Test Performance at Key Points:
    • Low RPM Test: Accelerate in 1st–3rd gear from idle to 3000 RPM and feel for improved torque.
    • Mid-Range Test: Perform a roll-on acceleration test from 4000–7000 RPM — you should feel stronger mid-range punch.
    • Peak RPM Test: Perform a top-speed run in 5th/6th gear — power fade at peak RPM should now be minimized.
  3. After testing, inspect your:
    • Spark Plug: Light brown or tan = ideal combustion. White = excessive advance; black/wet = too rich or retarded timing.
    • EGT Readings: Peak temperatures between 600°C – 650°C indicate optimal power without excessive heat.

✅ Conclusion

This revised map is designed to match your modified free-flow exhaust with the 31mm barrel. Expect stronger throttle response at low RPM, improved acceleration in the mid-range, and a more sustained power curve at peak RPM.

If you'd like specific carburetor adjustments, spark plug heat range recommendations, or additional tips for improving your top-speed performance, let me know! 🚀

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