Hot, Hot, Hot, Part II

422 HP From A Budget Vortec Head/HOT Cam 355ci Mouse

Jeff Smith Nov 1, 2001 0 Comment(s)

Step By Step

The GM Performance Parts dual-plane intake manifold combined with the Demon carburetor worked extremely well on the dyno, making 422 lb-ft of torque and 412 hp at 5,600. These are excellent numbers for a pump-gas street engine.

As tested, we configured the Vortec-headed small-block with a set of 1-5/8-inch headers, the single-plane intake, a set of Moroso polished valve covers, plug wires, and a trick distributor cap.

The dual-plane manifold (bottom) offered increased torque, while the Edelbrock single plane (top) made more horsepower. Yet even as the power curves varied, the average torque remained within 1 lb-ft over the entire power curve.

The Demon 750-cfm mechanical-secondary carburetor performed flawlessly in this test. It only required minor jetting changes to optimize the power in both intake manifolds.

This test required a full street exhaust system, so we bolted on a set of Hooker 1-5/8-inch headers along with a pair of 2-1/2-inch exhaust pipes clamped to a pair of Flowmaster mufflers.

Swapping intake manifolds was easy since the Vortec intake is only held in place with eight bolts. The hardest part is replacing the distributor, and that’s not difficult at all.

Note the spark plug–wire boot we melted in the first test.

Most Chevy heads place the spark plug squarely between the head bolts.

The Vortec head moves the spark plug closer to the exhaust valve, which can cause clearance problems for some headers.

SuperFlow recently redesigned its computer screen using a WinDyn software that we think is kinda cool. The dyno operator can custom-design his screen to look at any number of parameters.

Some things are difficult to improve. It’s tough to come up with an improvement on the wheel, and when it comes to small-block Chevy engines, it used to require considerable skill to make 400 hp with stock iron heads and a streetable cam—and all this on a budget. Now we’ll show you how anybody can do it.

In the previous story we introduced you to budget-buildup artist Tim Moore’s 355ci small-block featuring its stock Vortec iron heads, GM Performance Parts HOT cam, and 9.75:1 compression ratio. By rebuilding a one-piece rear-main seal, hydraulic roller cam small-block using cast pistons and a stack of high-perf GM Performance Parts goodies, we estimated over 400 hp. The best part is that we did all this for under $2,500.

But going in, we only guessed how much power this engine was going to crank out. So we trucked this iron-headed small-block out to Westech Performance and let John Baechtel and Steve Brulé abuse this Mouse on their SuperFlow dyno. Moore elected to use an old Stinger electronic ignition distributor to trigger the MSD 6 box used on Westech’s dyno. This also required a special melonized GM distributor gear to ensure the gear would live when used with the GM Performance Parts HOT hydraulic roller camshaft. This gear is not cheap, but it does work. As for exhaust, we bolted on a set of Hooker 15/8-inch headers along with a 2½-inch exhaust system plumbed to a pair of Flowmaster mufflers. For the final piece of the puzzle, we added a Barry Grant Speed Demon 750 mechanical-secondary carburetor to ensure that the carburetor would not restrict power.

Test Time

Since this was a newly rebuilt engine, we pre-oiled the assembly and set the static timing to allow it to fire up immediately. Moore set the total timing at 34 degrees and then allowed the engine a short 20-minute break-in session. Finally, with a nice leak-free engine, we loaded up the fuel cell with 92-octane 76 gasoline and pulled the handle.

For this initial test, we used the GM Performance Parts dual-plane Vortec intake manifold. The first thing we wanted to see was how well the engine idled. The motor responded with an amazing 14 inches of manifold vacuum at 850 rpm, which means this could easily support vacuum-operated accessories like power brakes. The first few pulls looked slightly rich, so Brulé pulled two jet sizes out of the carb, but first we had to do a minor tune-up on the driver-side header.

One reason the Vortec heads work so well is because of the superior chamber design and the fact that the engineers moved the spark plug closer to the exhaust side of the chamber. Vortec heads are a straight-plug design that sometimes can cause header clearance problems. In the case of the Hooker headers, the No. 5 spark-plug boot was pushed too close to the header tube and melted. This required us to heat and dent the header to create enough air gap to protect the spark plug–wire boot.

Once we had all eight cylinders firing with slightly leaner jets in the Demon carburetor, the 355 pulled up some impressive numbers. Even at 2,500 rpm, the 350 managed 359 lb-ft of torque with a max torque of 423 lb-ft at 4,400. Peak horsepower came in at 412 at 5,600 rpm, creating a somewhat narrow powerband of only 1,200 rpm, but looking more closely at the numbers reveals the engine is punching out 400 lb-ft from 3,500 all the way through 5,300 rpm.

While these numbers are respectable, we also wanted to try the Edelbrock Super Victor single-plane intake for Vortec heads. We expected the single plane would trade power below peak torque for more power above peak torque. Generally, this is not a good trade for street engines, but Moore also plans to use nitrous on this engine and felt that the single-plane intake would work better with a plate nitrous system.

Changing intakes was a snap, and once again we were working this small-block. After a few minor tweaks, the numbers looked very good, but we also decided to try adding a 1-inch spacer as well as an additional ½-inch spacer to simulate the nitrous plate. We also experimented with reducing the timing to 32 degrees total instead of the previous test’s 34 degrees.

Not surprisingly, the 355 did sacrifice some power down low, but actually very little. What was more surprising was the 422 hp (a 10hp gain) at 5,700 rpm we saw over the dual plane. The trade-off was torque, where the single-plane intake managed to still muster 418 lb-ft of torque at 5,000. The peak horsepower rpm points were almost identical, yet the single plane managed 10 more horsepower and created a virtually identical average torque figure.

Conclusion

What this all comes down to is a great small-block. The dual plane made at least 360 lb-ft of torque from 2,500 to 6,000 rpm, and the single plane was only slightly behind. But the single-plane version cranks up the horsepower with well over 420 ponies.

We didn’t try this, but with only 32 degrees of total timing, it’s entirely possible that despite its 9.75:1 compression ratio, this engine might run just as hard on 87-octane gas as it did on 92-octane gas. This is a direct result of a tight quench area, an excellent combustion-chamber design, and careful attention to assembly. Add the 150-175hp nitrous system that Moore wants to run and we’re talking about a thumper 11-second street car. Even with a Demon carb, headers, an ignition, and a nitrous kit, you still could build this complete engine setup for under $4,000, and that’s if you bought everything new. That’s a winning combination any way you look at it.

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