Hot, Hot, Hot, Part I

An Inexpensive Roller Cam 400hp Small-Block

Jeff Smith Oct 1, 2001 0 Comment(s)

Step By Step

The heart of this budget Mouse is the combination of the GM Performance Parts HOT hydraulic roller cam and a set of Vortec heads.

Combine these pieces with 9.6:1 compression, a 750-cfm carb, and a decent set of headers and you have 400hp potential.

The heads use 1.94/1.50-inch valves, a 64cc combustion chamber, and 170cc intake ports.

Using the HOT cam also requires modifying the valve seats for larger valvesprings. You must also trim the inside diameter of the valve guides to clear the inside diameter of the springs.

GM Performance Parts sells both a dual plane (top) and a single-plane intake manifold for the Vortec cylinder heads. The dual plane is the better choice for a street engine since that will pump up the torque curve, making the engine more streetable.

Scoggin-Dickey supplied an entire valvespring kit, which is also in the GM Performance Parts catalog. The spring kit includes LT4-style springs, lightweight retainers, and the proper keepers to install the springs on the Vortec heads.

The production GM roller-cam block uses taller lifter bores to support the hydraulic roller tappets. Roller tappets must not rotate in their bores, so small cast retainers tie pairs of the rollers together. This large stamped-steel “spider” keeps the retainers in place.

Factory ’88-and-later roller-cam engines use a different mounting face. Use the GM cam drive kit, which sells for $40.

The HOT cam also uses a normalized iron distributor gear that does not require a bronze gear.

All ’87-and-later Chevy blocks come with a one-piece rear-main seal. This requires the use of a late-model one-piece rear-main seal crank. Starting with the ’88s, most passenger-car engines converted to hydraulic roller cams that required a spider. This is a truck block where the spider mounting bosses are not drilled and tapped, because the truck engine used a flat-tappet cam. These can be easily drilled and tapped to mount the spider for a hydraulic roller cam.

Tim also used a set of rail-style 1.6:1 roller rockers. The small rails locate the rocker arm over the valve.

Face it: Everybody’s looking for The Deal—you know, the 400hp motor for $100. We’re not there yet, but we’re always searching for better ways to build a small-block and we think we’ve stumbled onto one that is plenty hot. The key to a strong engine is the combination of great heads and an excellent camshaft. Improved airflow is usually accompanied by a hefty price tag, but check out this combo: Start with a late-model roller cam 350ci block. Bolt on a set of Vortec iron heads and a GM Performance Parts HOT hydraulic roller cam. Sprinkle on an aluminum GM Vortec dual-plane intake and you have an outstanding combination of all-new parts, with the heads, cam, and intake costing less than $800!

Our pal Tim Moore is building this exact package. But before you dive right into this deal, there are a few important details that you need to know that could save you money. The hinge pin to this plan is an ’88-or-later 350ci roller-cam cylinder block. Chevy put these engines in Camaros, Firebirds, police cars, some Caprices, and ¾-ton truck chassis also used in motor homes. These roller cam blocks differ from earlier blocks in several significant ways.

Block Tech

Starting in ’87, Chevy converted all small-blocks to a one-piece rear-main seal combined with an excellent one-piece oil pan seal. Chevy followed that in ’88 with hydraulic roller cams in most V-8 engines. To accommodate the taller hydraulic roller lifter, Chevy increased the height of the lifter boss. This also required two small cast-in bosses in the middle of the lifter valley to mount the sheetmetal retainer, called the “spider,” which retains each pair of lifters.

All this block information is given for several reasons. The GM Performance Parts HOT hydraulic roller is a great, affordable cam ($175 from Scoggin-Dickey Performance) and begs to be matched with a set of Vortec heads. This OEM-style roller cam is intended to work in ’88-and-later roller cam small-blocks, because it requires a production thrust plate. However, according to our erudite engine enthusiast Kevin McClelland, you can use this cam in an early two-piece rear-main seal block. Trim the ears off the production roller-cam thrust plate and use it as a spacer between the cam gear and the block. Then employ a thrust button to control cam endplay. This will require using aftermarket hydraulic roller tappets, which are more expensive than the factory hydraulic roller tappets. This way, you could use your existing, older two-piece rear-main seal block.

Since Tim was building a whole new motor, he latched onto a used roller cam 350ci short-block that came out of an ’89 Caprice police car. He disassembled it, had the crank machined and the rods rebuilt, and added a set of Federal-Mogul hypereutectic pistons. He also measured the deck height and had the block milled to establish a 0.005-inch piston-to-deck clearance. He also used the inexpensive GM Performance Parts cam drive assembly for the roller cam that is a screamin’ deal at $40. Tim re-used the stock hydraulic lifters, oil pan, and timing chain cover to keep the price down. To top it off, he bought a new oil pump from PAW and bolted the short-block together.

Vortec Head Mods

Before Tim could bolt the Vortec heads on the engine, the castings required a slight tweaking to accommodate the larger HOT cam. The stock Vortec valvesprings cannot handle the HOT cam’s 0.525-inch lift using the 1.6 roller rockers, so the tops of the valve guides must be machined shorter to clear the retainer. The spring pockets must also be opened up for the slightly larger-diameter springs. Tim also had the heads machined for ARP screw-in studs, but he did not use guideplates because he was using rail-style rocker arms.

The machine work for the springs configures the heads for the LT4 valvesprings that can handle the 0.525-inch lift and are also durability tested by Chevrolet to withstand performance abuse for hours on end. In fact, these heads and springs have individually been tested with Chevy’s 300-hour wide-open throttle durability test and passed without failure. That’s how good these components are.

Because the Vortec heads use a 64cc chamber, Tim used a Federal-Mogul hypereutectic 10cc dished piston to keep the compression ratio in line. Even with the 0.005-inch deck height and the Fel-Pro composition head gasket, the compression is still streetable at 9.6:1. That’s at the high end of a streetable compression ratio with iron cylinder heads, but combined with this camshaft should make excellent torque and not suffer from detonation.

Conclusion

Because of time constraints, we were not able to dyno-test this combination, but we will follow up with a test as soon as we can bolt the motor on the test stand. According to informed sources and our previous experience with the Vortec heads, this combination should make between 400 and 415 hp at 6,000 rpm, and around 420 lb-ft of torque at 4,000 rpm. These are excellent power numbers, especially when you consider that the long-block could be constructed for under $2,500. Taken as a whole, this is a great engine combination at an incredibly inexpensive price.

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