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Combo 81.
Combos 81-84 come from pages 40-46 of the July 1997 issue of Hot Rod Magazine. These combos compare rebuilt GM #882 heads and L31 Vortec heads. The baseline engine makes 275 HP and the best Vortec engine makes 375 HP.
Combo 81 is the baseline engine for the test. The #882 heads have 2.02/1.60 in. valves and 1.5:1 rockers. A low-performance, stock camshaft is used with only 0.390/0.410 in. of lift at the valves. |
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Displacement: |
350 cu. in. |
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Carburetor: |
Quadrajet |
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Heads: |
GM #882 heads, rebuilt, with 2.02/1.60 in. valves. |
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Intake: |
Edelbrock Performer |
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Camshaft: |
GM stock hydraulic, with 194/203° of duration @ 0.050 in. of lift and 0.390/0.410 in. of lift. |
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Rockers: |
roller, 1.5:1 |
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Headers: |
Hooker 1 5/8 in. |
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Pistons: |
Speed Pro forged |
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Rods: |
Federal Mogul |
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Crank: |
Federal Mogul |
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Distributor: |
HEI |
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Timing: |
34° |
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Comp. Ratio: |
9.0:1 |
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MAX HP: |
275 @ 4400 |
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MAX Torque: |
351 @ 3500 |
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Combo 82.
Combo 82 changes the stock cam from Combo 81 to a Federal Mogul grind, with 0.472/0.496 in. of lift at the valves. The cam swap results in 21 extra HP. |
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Displacement: |
350 cu. in. |
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Carburetor: |
Quadrajet |
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Heads: |
GM #882 heads, rebuilt, with 2.02/1.60 in. valves. |
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Intake: |
Edelbrock Performer |
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Camshaft: |
Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift. |
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Rockers: |
roller, 1.5:1 |
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Headers: |
Hooker 1 5/8 in. |
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Pistons: |
Speed Pro forged |
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Rods: |
Federal Mogul |
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Crank: |
Federal Mogul |
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Distributor: |
HEI |
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Comp. Ratio: |
9.0:1 |
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MAX HP: |
296 @ 5000 |
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MAX Torque: |
349 @ 4200 |
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Combo 83.
Combo 83 is much different than the previous two combinations. The heads are swapped for GM L31 Vortecs, and 1.6:1 roller rockers are used. A Holley 750 cfm carburetor is used, and the power jumps to 375 HP with 413 ft-lbs of torque.
Note that this combo is very similar to another combo from a separate test, Combo 78. Combo 78 has 2 less compression points and a slightly less aggressive cam, but it still makes 15 more HP and 13 more ft-lbs of torque. This is interesting, and it shows the variations between engines and dynos. |
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Displacement: |
350 cu. in. |
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Carburetor: |
Holley 750 |
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Heads: |
GM L31 Vortecs |
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Intake: |
Edelbrock Performer RPM Vortec |
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Camshaft: |
Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.503/0.529 in.) |
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Rockers: |
roller, 1.6:1 |
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Headers: |
Hooker 1 5/8 in. |
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Pistons: |
Speed Pro forged |
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Rods: |
Federal Mogul |
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Crank: |
Federal Mogul |
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Distributor: |
HEI |
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Comp. Ratio: |
10.6:1 |
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MAX HP: |
375 @ 5400 |
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MAX Torque: |
413 @ 4300 |
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Combo 84.
Combo 84 takes the previous combo and swaps the cam to one with more intake duration. The result is a loss of 11 HP and 29 ft-lbs of torque. This loss is very large for only a 10° change in the intake duration at 0.050 in. of lift. The small increase in valve overlap usually does cause the cylinder pressure, and thus the peak torque, to drop. However, because of easier breathing, the peak power usually increases with such a change. The power increase did not occur with this combination though. |
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Displacement: |
350 cu. in. |
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Carburetor: |
Holley 750 |
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Heads: |
GM L31 Vortecs |
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Intake: |
Edelbrock Performer RPM Vortec |
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Camshaft: |
Federal Mogul, with 224/224° of duration @ 0.050 in. of lift and 0.480/0.491 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.512/0.524 in.) |
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Rockers: |
roller, 1.6:1 |
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Headers: |
Hooker 1 5/8 in. |
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Pistons: |
Speed Pro forged |
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Rods: |
Federal Mogul |
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Crank: |
Federal Mogul |
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Distributor: |
HEI |
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Comp. Ratio: |
10.6:1 |
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MAX HP: |
364 @ 5900 |
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MAX Torque: |
384 @ 4400 |
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