55-57 combo

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Combo 55.

Combos 55-62 come from pages 30-34 of the April 1991 issue of Hot Rod Magazine. All 8 combinations use the same 355 cu. in. block. Both stock and ported versions of the Dart SR (now the World Products S/R Torquer) are used on this engine. Also, different cams and rocker arm ratios are used to vary power and torque.

Combo 55 has Stock Dart SR heads, a 650 cfm carb, a 260° camshaft, and 1.5:1 rockers. This combo makes 305 HP and 381 ft-lbs of torque.

 

Displacement:

355 cu. in.

Carburetor:

Holley 650 double pumper

Heads:

Dart SR, with 1.94/1.50 in. valves, 4-angle valve job

Intake:

Holley Contender

Camshaft:

Crane 260, with 260/272° of duration, 204/216° of duration @ 0.050 in. lift, and 0.427/0.454 in. of lift

Rockers:

1.5:1 intake and exhaust

Headers:

Hedman 1 5/8 in. headers with Flowmaster dual-crossflow mufflers

Pistons:

Summit cast

Rods:

Summit

Crank:

Summit cast

Distributor:

MSD

Comp. Ratio:

9.0:1

MAX HP:

305 @ 5000

MAX Torque:

381 @ 3500

Combo 56.

Combo 56 only changes the rocker arm ratio of the exhaust valves in Combo 55. This increase from 1.5:1 to 1.6:1 creates 6 more HP and 10 more ft-lbs of torque.

 

Displacement:

355 cu. in.

Carburetor:

Holley 650 double pumper

Heads:

Dart SR, with 1.94/1.50 in. valves, 4-angle valve job

Intake:

Holley Contender

Camshaft:

Crane 260, with 260/272° of duration, 204/216° of duration @ 0.050 in. lift, and 0.427/0.454 in. of lift. (Corrected valve lift with 1.6:1 exhaust rockers is 0.427/0.484 in.)

Rockers:

1.5:1 intake; 1.6:1 exhaust

Headers:

Hedman 1 5/8 in. headers with Flowmaster dual-crossflow mufflers

Pistons:

Summit cast

Rods:

Summit

Crank:

Summit cast

Distributor:

MSD

Comp. Ratio:

9.0:1

MAX HP:

311 @ 5000

MAX Torque:

391 @ 3500

Combo 57.

Combo 57 goes back to 1.5:1 rocker ratios for both intake and exhaust. However, a more aggressive cam is used. Compared to Combo 55, with the same rockers, this combination produced 17 more HP and 5 less ft-lbs of torque. As cam duration grows, cylinder pressure drops. This decrease in pressure causes a decrease in force pushing the piston downward, and thus the torque is reduced.

 

Displacement:

355 cu. in.

Carburetor:

Holley 650 double pumper

Heads:

Dart SR, with 1.94/1.50 in. valves, 4-angle valve job

Intake:

Holley Contender

Camshaft:

Crane 272, with 272/284° of duration, 216/228° of duration @ 0.050 in. lift, and 0.454/0.480 in. of lift.

Rockers:

1.5:1 intake and exhaust

Headers:

Hedman 1 5/8 in. headers with Flowmaster dual-crossflow mufflers

Pistons:

Summit cast

Rods:

Summit

Crank:

Summit cast

Distributor:

MSD

Comp. Ratio:

9.0:1

MAX HP:

322 @ 5500

MAX Torque:

376 @ 3500

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