Below, excerpted from an article that originally appeared in Hot Rod Magazine, are the dyno results from a baseline test of a stock 318 engine, and the horsepower gains recorded after various modifications.
- 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.