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318 Street Recipes - From High Performance Chrysler Engines (Best of Hot Rod Series)

Below, excerpted from an article that originally appeared in Hot Rod Magazine, are the dynamometer (dyno) results from a baseline test of a stock 318 engine, and the horsepower gains recorded after various modifications.  These results will give you an idea what to expect if you decide to upgrade the 318 engine in your M-body.

• 186 HP at 4000 RPM (Base Platform):
  • 318 non-roller 8:1 compression cop car short block
  • Production 318 cam with 240* adv. dur. .390"/.400" lift
  • Heads were the 4323302 casting (302s) high swirl mileage/emissions heads with the heart shaped chamber (9.0:1 compression installed)
  • 4BBL cast iron cop car intake manifold
  • Thermoquad carburetor
  • Stock exhaust manifolds
  • Factory stock (non lean burn) electronic ignition system
• 217 HP at 4200 RPM:
  • Added a 360 2BBL cam (252* adv. dur. .410" lift)
  • Mopar Performance Electronic Ignition conversion kit
  • Cam and MP Electronic Ignition swap was good for a 31 HP increase.
• 225 HP at 4500 RPM:
  • Added stock 1.88" intake/1.60" exhaust 360 heads with stock springs, retainers and keepers
  • Gave the heads a performance valve job
  • Head swap was only good for an 8 HP increase.
  • Power was weaker than the swirl head combo below 3500 RPM.
• 251 HP at 5000 RPM:
  • Added Mopar Performance P4120249 valve springs to the 360 heads
  • Added Mopar Performance P4286669 cam (260* adv. dur. .430" lift)
  • Holley 0-3310 750CFM vacuum secondary carburetor
  • Edelbrock 2176 Performer aluminum intake manifold
  • Mopar Performance P4286437 headers (1 5/8" primary tubes with 3" collectors)
  • The above items added 26 HP.
• 290 HP at 5250 RPM:
  • Ported and polished the heads
  • Upgraded heads to 2.02" intake and 1.60" exhaust valves
  • Added Mopar Performance P4452033 chrome-moly valve spring retainers with 8* keeper grooves
  • Mopar Performance P4120620 8* hardened valve stem locks
  • Added Mopar Performance P4286671cam (272* adv. dur. .455" lift)
  • Mopar P4120600 Gold Box competition ignition control unit
  • This combo added 39 HP
• 331 HP at 5750 RPM:
  • Swapped the 360 heads for ported and polished 302 heads modified with 1.88" intake/1.60" exhaust valves
  • Mopar Performance P4120249 valve springs
  • This combo produced a 41 HP increase over the previous combination, netting 1.12 HP per cubic inch!
  • This combo also produced more power than all of the other combinations from the lowest RPM on up

Notes:

• All tests were conducted on an engine dyno stand with an unrestricted exhaust system.
• 4323302 casting heads (302s), 4343646 castings and similar castings are 1.78" intake/1.50" exhaust high swirl mileage/emissions heads that were used on all civilian duty M-bodies from late-1985 to 1989.
• Actual cop car engine compression per the 1987 Factory Service Manual was 8.4:1 due to the open-chambered 360 heads. Compression for civilian model 318s with closed-chambered factory 302 heads was 9.0:1.
• The base HP for civilian model 2BBL 318s was about 140, so expect HP numbers a bit less than the above baseline test if you add a 4BBL intake/carburetor and convert to electronic ignition.
• Modifications usually work together to produce results. The 41 HP increase recorded in the last dyno test was achieved because the camshaft was much stouter than a production cam, and it was designed to take advantage of superior breathing heads. A similar increase should not be expected with the same heads and a stock cam.

Related Topic:

• 400 Horsepower 318 Builds

Sources:

• High Performance Chrysler Engines (Best of Hot Rod Series - CarTech Books) - 318 Street Recipies by Marlan Davis
• Chrysler Rear Wheel Drive Factory Service Manual
• Standard Catalog of Chrysler - 1914-2000 - Edited by James T. Lenzke

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