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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.
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| 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 |
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| MAX HP: |
305 @ 5000 |
| MAX Torque: |
381 @ 3500 |
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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.
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| 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 |
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| MAX HP: |
311 @ 5000 |
| MAX Torque: |
391 @ 3500 |
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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.
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| 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 |
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| MAX HP: |
322 @ 5500 |
| MAX Torque: |
376 @ 3500 |
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Combo 58.
Combo 58 changes the rocker arm ratio of the exhaust valves in Combo 57. This exhaust rocker ratio increase creates 4 more HP and 2 more ft-lbs of torque. The increase here is not as pronounced as the difference between rocker ratios when the milder cam was used. Apparently the other cam was not letting the engine breathe as much as it wanted, and the extra exhaust lift really helped. Once the more aggressive cam was installed, the engine was breathing at a better level, and the rocker ratio change did not help as much.
Compared to the engine with the milder cam and 1.6:1 exhaust rockers, this combination made 15 more HP and 13 less ft-lbs of torque.
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| 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. (Corrected valve lift with 1.6:1 exhaust rockers is 0.454/0.512 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 |
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| MAX HP: |
326 @ 5500 |
| MAX Torque: |
378 @ 3500 |
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Combo 59.
Combo 59 uses both 1.5:1 ratios and the milder cam, but the heads are bowl-blended. They are not ported, but the bowls are cleaned up a bit. Compared to the baseline engine in Combo 55, this combo produced 14 more HP and 9 more ft-lbs of torque.
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| Displacement: |
355 cu. in. |
| Carburetor: |
Holley 650 double pumper |
| Heads: |
Dart SR, with 1.94/1.50 in. valves, 4-angle valve job, bowl-blending, intake gaskets are matched to the intake |
| 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 |
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| MAX HP: |
319 @ 5000 |
| MAX Torque: |
390 @ 3500 |
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Combo 60.
Combo 60 uses 1.6:1 rockers on the exhaust valves, and this is the only difference from Combo 59. The increased lift produced 4 more HP and 2 more ft-lbs of torque.
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| Displacement: |
355 cu. in. |
| Carburetor: |
Holley 650 double pumper |
| Heads: |
Dart SR, with 1.94/1.50 in. valves, 4-angle valve job, bowl-blending, intake gaskets are matched to the intake |
| 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 |
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| MAX HP: |
323 @ 5000 |
| MAX Torque: |
392 @ 3500 |
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Combo 61.
Combo 61 goes back to 1.5:1 rockers on the exhausts and uses the more aggressive camshaft. Compared to Combo 59, with the same rockers and the lower-performance cam, Combo 61 makes 24 more HP and the same amount of torque. As expected from the longer duration cam, both the torque and power peaks are 500 rpm higher than with the 260° cam.
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| Displacement: |
355 cu. in. |
| Carburetor: |
Holley 650 double pumper |
| Heads: |
Dart SR, with 1.94/1.50 in. valves, 4-angle valve job, bowl-blending, intake gaskets are matched to the intake |
| 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 |
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| MAX HP: |
343 @ 5500 |
| MAX Torque: |
390 @ 4000 |
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Combo 62.
Combo 62 is the last of the combinations with this engine. 1.6:1 exhaust rockers, the 272° cam, and bowl-blended heads are used. This combination produces 349 HP and 390 ft-lbs of torque.
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| Displacement: |
355 cu. in. |
| Carburetor: |
Holley 650 double pumper |
| Heads: |
Dart SR, with 1.94/1.50 in. valves, 4-angle valve job, bowl-blending, intake gaskets are matched to the intake |
| 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. (Corrected valve lift with 1.6:1 exhaust rockers is 0.454/0.512 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 |
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| MAX HP: |
349 @ 5500 |
| MAX Torque: |
390 @ 3500 |
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