The Horsepower Chain Book



The Horsepower Chain -
Racing Engines Explained Through Hardcore Math

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The 4 stroke internal combustion engine first ran in 1876. This engine design, known as the Otto cycle, has been thought of as having the following strokes - intake, compression, expansion and exhaust. This design is used in the vast majority of racing engines today. Engine builders, and racers alike, think about improving the performance of their engines using this 4 stroke approach, or what I prefer to call the “old 4 process.”

Sometimes people focus on the 4 critical camshaft timing events – intake valve opening (IVO), exhaust valve closing (EVC), intake valve closing (IVC), and exhaust valve opening (EVO) to characterize engine performance. This was a good step forward, but a finer breakdown is needed to really understand racing engines.

Instead of the traditional 4 strokes, the modern high performance engine should be thought of as having 7 distinct individual processes. This “7 process” approach focuses on air flow through the engine and is a result of two decades of research while developing the worlds most popular racing engine software -- Quarter Jr's "Engine Pro"

The new 7 process engine modelThe New 7 Process Model:

  1. Intake pumping
  2. Intake ramming
  3. Compression
  4. Fuel burning and expansion
  5. Exhaust blowdown
  6. Exhaust pumping
  7. Valve overlap

These 7 processes are linked together and affect each other in turn. In other words, the output from one process defines the input for the next. It follows logically that each of these 7 processes must be fully optimized in order to achieve the highest engine performance possible.

However, the overall engine is only as good as the weakest link in this chain of processes. Some changes may well improve one process, but hurt another. Identifying which of these 7 processes is holding the engine back is key to improving your engine’s performance.

The physics behind each of these 7 processes is very different. All we can adjust/change is the shape of the components that make up the engine. What is the absolute best combination of components? How do we find that best combination without just throwing parts at the engine?

Announcing: "The Horsepower Chain - Racing engines explained through hardcore math"

About the Book:

  • Includes the math behind the world's most popular engine simulation software -- "Engine Pro"
  • These equations were developed and tweaked during two decades of real-world testing from hundreds, if not thousands, of racers.
  • Includes practical advice for each of the seven processes -- specific advice you can apply today.
  • This is an updated edition of "Engine Pro - The Book." It has been expanded and professionally printed in the US.
  • Authored by Don Terrill - Former pole winning Nascar engine builder and owner of - Racing's best tech forum.
  • Includes a Bonus CD for a limited time - see details below


  • Which process needs to be optimized to reach VEs over 100%, and specifically, which 3 items need to be improved.
  • There is one trend leading engine development -- miss it and you'll be left behind.
  • Everyone knows IVC is the most important valve event, but the second most important is not far behind and will surprise many
  • What is the source of many horsepower anomalies? Ever have an engine that just doesn't run right?
  • Which process is a strongest predictor of the location of Peak TQ and HP
  • The only guaranteed, and simple, trick to improve the overlap process -- Less than 1% of racers are doing it
  • Simple power mods many are missing -- they are staring you right in the face
  • The small things that can net big gains
  • The revolutionary way to test exhaust flow (exhaust blowdown process). I don't know of anyone doing it.
  • What one airflow measurement will predict 95% of your engine's peak power
  • What lifts and pressure drops to measure your heads. Everyone I know is doing this wrong.
  • Which process is by far the most important and how to improve it
  • How to optimize intake pumping pulses, pressure waves
  • What 3 items control intake pressure waves
  • What small mistake can kill critical exhaust pressure waves
  • What is the optimal timing for finite amplitude pressure waves
  • What positive changes to intake pumping will negatively affect intake ramming
  • How to get the most energy out of your fuel
  • Which 3 engine design features control rpm range
  • Which 3 engine design features control peak torque
  • Which 4 engine design features control peak horsepower
  • What is the ideal intake pumping process
  • What is the ideal intake ramming process
  • What is the ideal compression process
  • What is the ideal fuel burning, expansion process
  • What is the ideal exhaust blowdown process
  • What is the ideal exhaust pumping process
  • What is the ideal overlap process
  • Which engine features control the intake pumping process
  • Which engine features control the intake ramming process
  • Which engine features control the compression process
  • Which engine features control the fuel burning, expansion process
  • Which engine features control the exhaust blowdown process
  • Which engine features control the exhaust pumping process
  • Which engine features control the overlap process
  • How to improve the intake pumping process
  • How to improve the intake ramming process
  • How to improve the compression process
  • How to improve the fuel burning, expansion process
  • How to improve the exhaust blowdown process
  • How to improve the exhaust pumping process
  • How to improve the overlap process
  • The 10 places to look for frictional losses
  • The optimal cooling system strategy
  • How to calculate the best cam lift for your application
  • How to calculate minimum recommended intake port area
  • How to calculate maximum recommended intake port area
  • How to balance negative work prior to TDC with positive work after TDC
  • When do we want pressure waves to arrive at the intake valve
  • Which valve event has the least affect on power
  • Which items need to be hot, and which items need to be cold
  • There's a lot going on during overlap. What one modification helps both intake and exhaust
  • The ideal state before opening the intake valve
  • How intake pumping pulses affect plenum conditions
  • How the number of cylinders connected to the plenum affect conditions
  • Minimum volume for intake plenum
  • Max volume for intake plenum
  • Is there a reason to flow the throttle body and intake manifold together
  • Bore diameter affect on flow
  • What is the second most important process and how to optimize
  • Optimal intake cam duration @ .050"
  • How critical is it to have the right cam
  • How stroke affects required cam duration
  • What's the number one thing to consider before deciding cam duration
  • How are valve lift and piston speed tied together
  • What is the critical effective compression ratio limit for each fuel type

May well become the most significant book ever written on racing engines

Included Equations

  • Engine design equations
    • Recommended intake lobe centerline (InLobeCL)
    • Best Exhaust duration (ExCamDur)
    • Best Lobe separation (LSA)
    • Recommended intake valve lift (InVL)
    • Intake valve diameter (InVD)
    • Total intake tract volume (InVol)
    • Total intake tract length (InTL)
    • Intake suction wave (InTL.1)
    • Intake closing wave (InTL.2)
    • Max intake cross-sectional area (MaxInArea)
    • Min intake cross-sectional area (MinInCSA)
    • Recommended intake plenum volume (PlnVol)
    • Recommended exhaust flow (ExCFM)
    • Recommended exhaust valve diameter (ExVD)
    • Max exhaust valve lift (ExVL)
    • Min exhaust cross-sectional area (MinExCSA)
    • Max exhaust cross-sectional area (MaxExArea)
    • Primary header tube diameter (ExTD)
    • Primary header tube length (ExTL)
    • Collector diameter (ExCD)
  • Engine performance equations
    • Shift RPM
    • Redline RPM
    • RPM @ Peak TQ
    • Gross Peak TQ
    • Net Peak TQ (Peak TQ)
    • RPM @ Peak HP
    • Gross Peak HP
    • Net Peak HP (Peak HP)
  • Other equations
    • Max piston speed
    • Equivalent piston speed
    • Normalized equivalent piston speed
    • Crank Pin speed
    • Mechanical efficiency
    • Pumping Losses
    • Friction Losses
    • Port velocity
    • Intake flow flux
    • Ideal intake flow flux
    • Intake flow coefficient
    • Exhaust flow flux
    • Theoretical HP per CFM for different fuel types
    • Critical effective compression ratio limit for each fuel type
    • Thermodynamic cycle efficiency
    • Compression Ratio Volume Factor
    • Effective compression ratio
    • Trapped cylinder pressure
    • Actual engine compression ratio (accounting for the IVC angle)
    • Piston Position
    • Intake Ramming VE%
    • Intake Ramming Function (this equation was “stumbled” upon)
    • Intake Pumping VE%
    • Throttle Body Pressure Loss
    • Throttle Body VE%
    • IR Throttle Body VE%
    • Power loss to curved runners
    • Plenum effect for different type manifolds
    • Intake manifold flow factor
    • Recommended bore to throat ratio
    • Potential power from multi valves
    • Loss of rpm range from too small a cam
    • Loss of torque from too small a cam
    • Loss of rpm range from too large a cam
    • Loss of torque from too large a cam
    • How VE% affects effective compression
    • Energy content per fuel type
  • Constants and Correction Factors
    • Camshafts constants (CamK)
    • Multi-valve constants
    • Conversion factor used in the calculation of horsepower
    • Conversion factor used in the calculation of RPM from piston speed
    • 18 more...

Companion CD

CD Contents:

  1. Companion Audio (mp3) - 20 minutes of straight to the point audio on the important points from the book and how to apply them.
  2. Audio Interview with the "Engine Pro" Developer (mp3) - This is the 70 minute interview I did for SpeedTalk. We talk about the book and how to apply the information. A must listen.
  3. Transcription of Founder interview (pdf) - I had the above 70 minute interview transcribed into a written document for those that prefer to read.
  4. Sample Excel Spreadsheet (xls) - If you want to create your own spreadsheet using some of the math in the book, this spreadsheet will get you off to a good start.
  5. Engine Pro walk-through Video (flash) - Don't own Quarter Jr's "Engine Pro" software? This video goes through the software's function to give the book greater context. Want to own the software? Today is the day -- I've included a special offer below.

Want Proof


(1) "Fantastic. Will make a lot of other texts obsolete. I have recommended it to others. Well done. Let me know when there will be another ." -- Craig Shepley

(2) "Quite impressed. Knowledge like this is an absolute bargain. If you can use the information to reduce your testing by only one cam or if it helps you build a better engine through greater understanding, then it's probably the cheapest horsepower you'll ever buy." -- John Murray

(3) "Excellent book - The depth of information was outstanding." -- Tim Steen

(4) "Enjoyed the book as much as I enjoy the forum!! Bought the book the day it was announced." -- Bruce Brisson

(5) "Your new book is superb! -- Ed Harris

(6) "I'm really enjoying The Horsepower Chain and I thank you for putting so much effort into developing all of this info. I've found the calculations to optimize what's happening on the intake stroke to be extremely useful. Again, great book" -- Shawn Watson

About the Authors:

1st edition Author:

  • Master's degree in Mechanical Engineering
  • 3 NHRA National Records in Competition Eliminator
  • Awarded the "Best Engineered" vehicle for his record holding racecar
  • Member of the Society of Automotive Engineers (SAE)
  • Author of numerous technical articles for several automotive magazines
  • Developer of industry leading racing software -

2nd edition Author:

  • Over a dozen NHRA national records, including 3 cars during the same day at Indy
  • 3 Poles during the only year he worked in Nascar - Atlanta, California & Pocono
  • 2 Number two qualifiers during same year - Indianapolis & Martinsville.
  • Quotes about Don’s Nascar performance: (1) "Don was a valued employee in our engine dept. his engines combined for three Winston Cup poles." -- Sabco RaceOperations VP (2) "Don is one of my favorite resources. Sabco's qualifying performance speaks volumes." -- Head of Comp Cams R&D


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You will not find a single book that even comes close to the depth and usability of the information included in The Horsepower Chain. Just one idea from this Book and CD will pay for your purchase many times over.


This product is based on the physics behind Quarter jr's "Engine Pro" software. If you don't already own "Engine Pro", I would like to make you an offer, for today only, to include the software. "Engine Pro" is normally $199 and is currently on sale for $149. But, if you buy everything today, I will include the software for $99 - making the total price $196 - Click here to purchase this package now! If you want just the Book and CD, click the "Add To Cart" button above.

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