Got a 2010 Honda Fit Sport Manual USA Spec. Have HPS Short Ram Intake and IK22 Spark Plugs installed. Getting a Ktuner. Can you please detail how I can get to 150 WHP NA? Here are the parts you might consider: Full Cat Back exhaust with headers 87 oct, 91 oct, 93 oct fuel (please use the lowest possible) Throttlebody (what size - want to maintain current torque?) Intake manifold (see attached) and/or Cam maintain current 7k RPM fuel cutoff.

Let’s break down your goal of reaching 150 wheel horsepower (WHP) naturally aspirated (NA) on your 2010 Honda Fit Sport with a manual transmission, while maintaining the 7,000 RPM fuel cutoff and using the lowest octane fuel possible (87 octane). The stock 1.5L L15A7 engine produces around 117 crank horsepower, which typically translates to about 100-105 WHP due to drivetrain losses (roughly 10-15%). Achieving 150 WHP NA is ambitious for this engine, as it requires a ~45-50% increase in power without forced induction. Here’s a detailed plan based on your current mods and the parts you’re considering.

Current Setup

• Engine: 1.5L L15A7, naturally aspirated, 117 crank HP (~100-105 WHP stock).
• Mods: HPS Short Ram Intake (SRI), IK22 spark plugs (Denso Iridium Power, likely one heat range colder than stock).
• Incoming: KTuner for ECU tuning.
• Goal: 150 WHP, maintain 7,000 RPM fuel cutoff, use 87 octane if possible.

Step-by-Step Upgrade Plan

To reach 150 WHP NA, you’ll need to maximize airflow, optimize combustion, and tune the engine efficiently. Here’s how your proposed parts fit in:

1. Full Cat-Back Exhaust with Headers

• Why: The stock exhaust system is restrictive, limiting power at higher RPMs. A full cat-back exhaust (from the catalytic converter back) paired with aftermarket headers will reduce backpressure and improve exhaust scavenging, boosting power across the RPM range.
• Recommendations:
  • Headers: Look for 4-2-1 headers (e.g., DC Sports, Skunk2, or Weapon-R) over 4-1 designs to preserve low-end torque, which aligns with your goal of maintaining current torque levels. These typically add 5-10 WHP when paired with tuning.
  • Cat-Back: Options like Skunk2 Mega Power (60mm), HKS Hi-Power, or GReddy EVO2 offer good flow and sound. Expect 5-8 WHP gains with a high-flow cat or test pipe (legal in some areas, check local laws). A full system might net 10-15 WHP total.
• Impact: With your SRI already installed, this could bring you to ~115-120 WHP after tuning.

2. Fuel Choice (87 Octane)

• Why: Higher octane (91 or 93) resists knock better, allowing more aggressive timing and compression tweaks for power. However, you want 87 octane, which limits how much you can push the engine without detonation.
• Feasibility: The stock compression ratio (10.4:1) and KTuner’s ability to adjust ignition timing and air-fuel ratios (AFR) should allow safe operation on 87 octane with moderate mods. Avoid aggressive cam profiles or significant timing advances that demand higher octane. With proper tuning, 87 octane is viable but may cap your gains closer to 140-145 WHP rather than 150 WHP.
• Approach: Use KTuner to optimize AFR (target ~12.8-13.0:1 at WOT) and pull timing slightly if knock is detected on 87 octane.

3. Throttle Body Upgrade

• Why: A larger throttle body increases airflow into the intake manifold, supporting higher RPM power without sacrificing low-end torque if sized appropriately.
• Size: The stock throttle body is ~50mm. Upgrading to a 54-56mm unit (e.g., Skunk2 or Blox) is a safe bet for maintaining torque while adding 3-5 WHP with tuning. Avoid oversized units (60mm+) as they can reduce throttle response and low-end power on a small NA engine like the L15A7.
• Impact: Paired with the SRI and exhaust, expect ~120-125 WHP after this step.

4. Intake Manifold and/or Camshaft

• Intake Manifold:
  • Why: The stock manifold is designed for efficiency, not peak power. An aftermarket manifold (e.g., Skunk2 Alpha or a custom ported OEM unit) can improve airflow and volumetric efficiency, especially at higher RPMs.
  • Considerations: Without seeing your attached file, I’ll assume you’re eyeing a performance manifold. Gains are typically 5-10 WHP with tuning, but low-end torque might drop slightly unless paired with a cam that complements it.
• Camshaft:
  • Why: A performance cam increases valve lift and duration, allowing more air and fuel into the combustion chamber. This is critical for hitting 150 WHP NA.
  • Recommendations: Look at mild stage 1 cams (e.g., Skunk2 Stage 1 or Brian Crower Stage 1) to maintain drivability and compatibility with the 7,000 RPM cutoff. These can add 10-15 WHP with proper tuning, though aggressive cams might push you toward 91 octane.
  • Valve Train: Upgrade to stiffer valve springs and retainers (e.g., Skunk2 or Supertech) to handle the cam and maintain reliability at 7,000 RPM.
• Impact: With both, you could reach 135-145 WHP, depending on cam choice and tuning.

5. KTuner Tuning

• Why: KTuner is your key to tying everything together. It adjusts fuel maps, ignition timing, VTEC engagement, and throttle response to maximize power from your mods.
• Settings:
  • Lower VTEC engagement (e.g., 4,800-5,000 RPM) to broaden the powerband.
  • Optimize AFR for 87 octane (richer mix if needed to avoid knock).
  • Adjust cam angles if installing a performance cam.
  • Maintain the 7,000 RPM fuel cutoff as requested.
• Gains: Proper tuning could add 5-10 WHP beyond hardware gains, pushing you toward 145-150 WHP.

Estimated Power Breakdown

• Stock: ~100-105 WHP
• HPS SRI + IK22 Plugs: ~105-110 WHP
•  
  • Full Exhaust/Headers: ~115-120 WHP
•  
  • Throttle Body (54-56mm): ~120-125 WHP
•  
  • Intake Manifold: ~130-135 WHP
•  
  • Mild Cam + Tuning: ~140-150 WHP

Challenges and Realism

• 150 WHP Feasibility: Most NA L15A7 builds with bolt-ons (intake, exhaust, headers, tune) top out at 130-140 WHP. Hitting 150 WHP typically requires extensive head work (porting, larger valves) or higher compression pistons, which might not play well with 87 octane and the 7,000 RPM limit. (*I think going to 91 oct or 93 oct fuel is FAR BETTER than getting into the Fit Engine internals)
• Torque Tradeoff: Your current torque (around 100-105 lb-ft at the wheels) should hold steady with a 4-2-1 header and moderate throttle body. A cam might shift torque higher in the RPM range, but a mild profile minimizes losses.
• 87 Octane Limit: This is the biggest constraint. Without knock, 145 WHP is plausible; 150 WHP might require 91 octane for safety with aggressive tuning.

Final Recommendations

• Parts List:
  • 4-2-1 Headers (DC Sports/Skunk2) *(found an integrated Magnaflow header & upper CAT for ~$1k)
  • Full Cat-Back Exhaust (Skunk2 Mega Power 60mm or HKS) *(2.5" with 2.5" Resonator)
  • 54-56mm Throttle Body (Skunk2/Blox) *(I would probably try 56MM)
  • Skunk2 Alpha Intake Manifold *(does not exist - see attached though)
  • Mild Stage 1 Cam (Skunk2 or Brian Crower) + valve springs *(custom grind)
• Tuning: Use KTuner with a dyno to fine-tune on 87 octane, targeting 145-150 WHP.
• Next Steps: If you fall short (e.g., 140 WHP), consider a high-flow cat *(already included in above?) , lightweight crank pulley (e.g., Unorthodox Racing), or a ported head for the last 5-10 WHP *(go up to 91 or 93 oct fuel instead).

With this setup, 145 WHP is highly achievable on 87 octane, and 150 WHP is within reach with perfect tuning and execution. Dyno-test each mod to confirm gains and adjust as needed. Let me know if you’d like further clarification or help with specific part sourcing!

Notes: Supercharger might be cheaper and likely more powerful, K-swap same (& potentially cheaper?).

Your thoughts?
Yo
PS: please note 150 WHP is 100 per liter which is roughly what a bone stock S2000 puts down. Your Fit will probably be Louder and will be slower. Is Grok 3 AI realistic or not?

 

Seems like a bunch of broucher power estimates fluffed with a vague definition of how internal combustion engines work. Typical A.I. slop. And unfortunately, I can't shake the feeling that by simply pointing this out I am helping it.

 

Thanks for the reply. Good point.

 

You forgot the NOS....