Calculating Turbo Size For Engine

Turbo Size Formula:

\[ Turbo\ size = \frac{HP\ target \times BSFC / 60}{Density\ ratio \times VE} \]

HP Target (horsepower):

BSFC (lbs/hp-hr):

lbs/hp-hr

Density Ratio:

decimal

VE (Volumetric Efficiency):

decimal

Turbo Size:

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1. What is Turbo Size Calculation?

The turbo size calculation estimates the required turbocharger capacity for an engine based on horsepower targets, brake specific fuel consumption, density ratio, and volumetric efficiency. Proper turbo sizing is critical for achieving desired performance while maintaining reliability.

2. How Does the Calculator Work?

The calculator uses the turbo size equation:

\[ Turbo\ size = \frac{HP\ target \times BSFC / 60}{Density\ ratio \times VE} \]

Where:

\( HP\ target \) — Desired horsepower output
\( BSFC \) — Brake specific fuel consumption (lbs/hp-hr)
\( Density\ ratio \) — Pressure ratio across the turbo
\( VE \) — Volumetric efficiency (decimal)

Explanation: The equation calculates the required air flow rate (in lbs/min) that the turbo needs to supply to meet the horsepower target.

3. Importance of Turbo Sizing

Details: Proper turbo sizing ensures optimal engine performance, prevents turbo lag (if too large) or overworking the turbo (if too small), and helps achieve the desired power band.

4. Using the Calculator

Tips: Enter realistic values for all parameters. Typical BSFC values range from 0.45-0.55 for naturally aspirated engines and 0.55-0.65 for forced induction. VE is typically 0.85-0.95 for modern engines.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical BSFC value?
A: For turbocharged engines, BSFC typically ranges from 0.55 to 0.65 lbs/hp-hr. More efficient engines will be toward the lower end of this range.

Q2: How do I determine the density ratio?
A: Density ratio is approximately equal to the pressure ratio (boost pressure + atmospheric pressure) divided by atmospheric pressure.

Q3: What if my VE is unknown?
A: For most modern engines, 0.85 is a reasonable estimate. High-performance engines may approach 0.95.

Q4: Does this account for intercooling?
A: Indirectly, as intercooling affects the density ratio. More efficient intercooling allows for higher density ratios.

Q5: What about turbo efficiency?
A: This calculation provides the required flow rate. Actual turbo selection should consider efficiency maps to find a turbo that can deliver this flow at your target pressure ratio.