GM Pistons, Vintage Air System & 1979 Chevy Malibu - Performance Q&A

Kevin McClelland Dec 1, 2008 0 Comment(s)

B.C. Truck
Q I am caretaking a mint '86 Chevy C10 Shorty 2x2. It is equipped with an H-code 305 and a TH350-C transmission with a five-pin HEI, 3.73:1 posi rearend with 30-inch rubber. It has 11/2-inch ceramic headers, long. I have lightened the front end with an Edelbrock water pump, electric fans, and an aluminum rad. I've even rebuilt the Q-jet and installed an aluminum GM Q-jet manifold with EGR. I back-cut the intakes on a set of iron 1.84/1.50-inch valve heads with 1.5 roller-tip rockers with koolnuts and used the Mr. Gasket 0.028-inch-thick head gaskets.

I'm cheap and I have a new cam that I'll probably never use in anything else. It specs out at 0.390/0.410 inch max lift, 256/262 advertised duration, 194/203 degrees duration at 0.050-inch tappet lift, and is ground on 116 separation angle. This is pretty much a stock 350 cam. Do I keep the five-pin HEI with the knock sensor or go with a more common four-pin? Also, should I use a Y-pipe with a single Flowmaster 70 series or go with duals with/without an H-pipe?

I should mention I have an OTC five-gas analyzer (portable) and an Innovate wideband O2 meter that I know how to use. A steep, long hill provides the dyno. The annual sniff check for a 22-year-old truck is doable. I'm green when it doesn't cost too much, so I'll probably use a high-flow cat(s). Thanks for the help.
Ian McFarlane
Vancouver, B.C., Canada

A You're stepping over dollars to pick up pennies. However, you've put together a very tidy package of lightweight components and small efficiency increases. Just because you have that camshaft may not be enough of a reason to install it.

The stock LG4 305 camshaft specs out at 178/194 degrees duration at 0.050 inch tappet lift. I did a great deal of work with these engines back in the mid-'80s when I was at Edelbrock. We developed a camshaft that ran well with all the factory emissions controls and the electronic controls on the engine. It spec'd out at 194/214 at 0.050 inch tappet lift, 0.398/0.442 inch max lift, and was ground on 112 centers, installed at 107. We probably worked our way through 30 camshafts on both the engine dyno and in the car, an '84 Z28 Camaro. Finally, with this camshaft we saw what were sellable gains.

As for your current camshaft, I don't like the wide centers that are on 116 degrees. With the small duration you need a slight amount of overlap, and the 112 separation angle makes a big difference. If you're going to the trouble of replacing the camshaft, a better choice might be Edelbrock PN 3702.

We'd recommend sticking with the original five-pin HEI. This system will not accept the more common four-pin due to connector and wiring pin-out differences. Also, the knock sensor is a very nice feature with the quality of fuel we have today, and with the price of fuel you'll want to run on 87 octane. To round out your exhaust, we'd recommend going with a Flowmaster Y collector, PN Y250300, into a single high-flow 3-inch cat. With this collector you'll be able to build a very nice headpipe system from your headers. Then complete the system with the 70 series you mentioned. Flowmaster offers that muffler in either a single 3-inch outlet or dual 21/2-inch outlets so you could create your own dual-outlet exhaust. The single 70 has more than enough flow capacity to support your modified 305 and has great sound control. Watching your dollars in any buildup is very important. Making your money last the length of the buildup is the key. Enjoy your truck!

Cast Repeat
Q I actually have a question that was asked in the July '08 issue. It was titled "Cast in Stone" and inquired if the cast crank could withstand the author's new combination. You said the cast crank can hold up very well and that the forged cranks are better, but where do you draw the line between using a cast crank and needing the forged crank? If you intend to spray the engine, how big a shot can you use on a cast crank? I'm just looking for something to work off of before I start putting together the next engine for my vehicle.
Eddie Henselder
Via email

A The standard answer for nitrous shots on stock bottom ends is 125 hp max. Basically, this refers to a stock engine producing around 250-300 hp. When you add the nitrous, you're in the 375-425 hp range. If the engine you're planning on building is stock, go for it. However, when you say you're "looking for something to work off of," this leads me to believe you're going to wring out as much horsepower from the components you assemble. Then you're looking to add nitrous into the mix? For instance, you build a nice little 350 small-block with a hydraulic roller, a good set of aluminum heads, decent compression, and good intake, carb, and headers, you'll be knocking down 400-425 hp on motor alone. Throw the 125hp shot on top of this engine and you could be running on thin ice. As we stated in the July answer, the main problem with cast cranks is when the engine runs into detonation. Pushing the stock package up into the 400-plus horsepower range naturally aspirated is getting you there on pump gas. The massive increase in cylinder pressure when the nitrous is first applied could cause the engine to rattle and it won't take that for long. For a safe horsepower max, we recommend staying below 450 hp on the stock cast cranks.

With all the affordable aftermarket crankshafts out there from Eagle, Ohio Crank, Scat, and others, you should look to a forged crank if you're going for decent power. I've driven over a crankshaft before and it wasn't pretty. Luckily, I didn't find any guardrail, but it did kill a really nice set of Lee Shepard ported D-port aluminum heads. This happened all because I couldn't afford a four-bolt block for my big-block. It pulled the front main caps right off the block, but that's another story.

Technical questions for Kevin McClelland can be sent to him at


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