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Hot Rod Home School (Lesson #5): Firing Orders, Essential Formulas & Other Engine Basics

Next up on our quarantine classroom lesson plan: engine basics.

“Engine basics” is a very broad term, and fans on Summit Racing’s Facebook page suggested covering things like firing orders and vac gauge readings. We’ve opted to equip novice mechanics enrolled in our Hot Rod Home School with a few tools (in this case, figurative tools) to help with a variety of current and future jobs.

To start…common V8 firing orders:

Firing Orders

  • AMC (most V8 engines): Clockwise 1-8-4-3-6-5-7-2
  • Buick (most V8 except HEI): Clockwise 1-8-4-3-6-5-7-2
  • Chevrolet: Clockwise 1-8-4-3-6-5-7-2
  • GM LS: 1-8-7-2-6-5-4-3
  • Small Chrysler: Clockwise 1-8-4-3-6-5-7-2
  • Big Chrysler and Hemi: Counter-clockwise 1-8-4-3-6-5-7-2
  • Most Ford V8: Counter-clockwise 1-5-4-2-6-3-7-8
  • Ford (5.0L HO, 351W, 351M, 351C, 400): Counter-clockwise 1-3-7-2-6-5-4-8
  • Most Ford modular (4.6/5.4L): 1-3-7-2-6-5-4-8
  • Ford 5.0L Coyote: 1-5-4-8-6-3-7-2
  • Oldsmobile (1967 and up): Counter-clockwise 1-8-4-3-6-5-7-2
  • Pontiac (most 1955-81 V8 engines): Counter-clockwise 1-8-4-3-6-5-7-2

Formulas

Racing Carburetor CFM
Racing Carburetor CFM = RPM x Displacement ÷ 3456 x 1.1
Note: Summit Racing also offers this CFM Calculatoto make the job easier.

Displacement
Displacement = .7854 x Borex Stroke x Number of Cylinders

Correct Compression Ratio (CCR)
CCR = FCR (Altitude/1,000) x .2
Note: You can also take this Compression Ratio Calculatotool for a spin.

Rocker Arm Ratio and Valve Lift
Gross Valve Lift = Camshaft Lobe Lift x Rocker Arm Ratio

Horsepower
Horsepower = (RPM x Torque) ÷ 5,252

Torque
Torque = (5,252 x HP) ÷ RPM

Rod Ratio
Rod Ratio = Rod Length ÷ Crank Stroke Length

Average Piston Speed
Average Piston Speed = Crank Stroke x RPM ÷ 6

Rear Gear Ratio
Rear Gear Ratio = (RPM at Finish Line x Tire Diameter) ÷ (MPH x 336)
Note: You can also save this link to a handy Gear Ratio calculator.

Volume (CCs) of Deck Clearance
CCs of Deck Clearance = Bore x Bore x 12.87 x Depth of Deck Clearance

Volume (CCs) of Head Gasket
CCs of Head Gasket = Bore x Bore x 12.87 x Thickness of Head Gasket

Compression Ratio
Combined Chamber CCs + Gasket CCs + Deck CI CCs + (Displacement x (N)) ÷ Combine Chamber CCs + Gasket CCs + Deck CI CCs

(N) = 2.0483 for  8-cylinder. (N) = 2.7311 for 6-cylinder. (N)=4.0967 for 4-cylinder.

Calculators

8 Comments

  1. Pingback: Hot Rod Home School (Lesson #5): Firing Orders, Essential Formulas & Other Engine Basics

  2. Earl Bowyer says:

    Really enjoy your On All Cylinders column!!

  3. Thanks for this great formulas! Keep it up | hammtreeservice.com/

  4. Amazing formulae –

  5. WOW….thanks

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