Recover Acceleration After Retarding Timing to 6° BTDC

 

Is 19T Too Small to Fully Recover Acceleration After Retarding Timing to 6° BTDC with High Compression Ratio?

Since you retarded timing to 6° BTDC for better top-end power, but now need to ensure that acceleration remains strong, we must analyze if 19T primary gearing is enough to recover the lost acceleration—especially since you have a high compression ratio (CR).

1. How High Compression Ratio (CR) Affects Ignition Timing & Acceleration

Your high CR increases combustion pressure, meaning:
✔️ More explosive power per combustion cycle, improving torque and acceleration.
✔️ Faster burn rate, meaning less ignition advance is needed to reach peak cylinder pressure at the right time.
✔️ More resistance to power loss after retarding timing, since compression compensates for reduced ignition lead.

📌 Key Takeaway:

  • Since high CR helps maintain torque even with retarded timing, 19T gearing has a better chance of restoring acceleration.
  • However, if gearing is too short (19T), acceleration may improve, but you might shift through gears too quickly, limiting top speed.

2. How 19T Affects Acceleration Recovery with 6° BTDC Timing

✅ Advantages of 19T After Retarding Timing

✔️ Shorter gearing compensates for the slight loss of low-end torque from retarded ignition.
✔️ Improves throttle response, making the engine feel quicker in gears 1-4.
✔️ Works well with high CR, as the engine already makes strong torque.

❌ Potential Downsides of 19T with 6° BTDC Retarded Timing

❌ Shifts too quickly through the powerband, meaning you might run out of RPM in each gear too fast.
❌ At high speed (180 km/h+), engine RPM may be too high, making it harder to hold speed efficiently in 6th gear.
❌ Less effective if the engine already has high torque from high CR, meaning a taller gear (like 21T) might be better.

📌 Verdict:

  • If your goal is acceleration, 19T will work well.
  • If you want BOTH acceleration & top speed, 21T may be a better choice to balance out gearing and timing.

3. Comparing 19T vs. 21T with 6° BTDC & High CR

Since you have high CR, your engine naturally makes strong low-end torque, meaning you may not need 19T to compensate for lost acceleration.

Primary Gear (T) Effect on Acceleration Effect on Top Speed Best Use Case
19T Strongest Lower top speed Best for city, quick acceleration
21T Balanced Moderate top speed Best for street & highway performance
23T Weakest Highest top speed Best for sustained high-speed riding

📌 What This Means for You:
✔️ 19T will make acceleration strong, but it may shift too quickly, limiting high-speed performance.
✔️ 21T allows better balance, giving acceleration while also extending top speed.
✔️ If your high CR already makes strong torque, 21T is likely a better choice than 19T.

🔥 Final Answer: If your goal is the best balance of acceleration and high speed, 21T is better than 19T. If you only want acceleration, then 19T works.

💬 Do you want help deciding between 19T vs. 21T based on your riding style? 🚀🔥

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