Super Chevy
Click here to find out more!

Pro Stock Big-Block Performance Tips - 12 Engine Building Tips

Fast Facts

By Wayne Scraba, Photography by Wayne Scraba

Mammoth Ports
Think monster ports make power? Think shiny port surfaces are the hot setup? Wrong. Neither work. When it comes to cylinder heads, the idea is to gain flow by making the port more efficient. A large port is usually lazy. The flow has no energy. Need proof? At one time it was possible to drop tennis balls down the ports of a Pro Stock drag race engine. Today, they're rather small (so small that the exhaust valves typically measure 1.80 inches in diameter, and will no doubt shrink even more over time).

Certainly the port size required for a 500ci Pro Stock engine is larger than for something like a 400ci street engine combination, however the idea is to pack as much velocity into the port as possible. For example, Reher-Morrison has come up with a "smallish" oval port configuration for Big Chief-style 14-degree heads used in any number of Super Category big-blocks. This port is considerably smaller than what is currently in vogue. But there's a catch: While the port looks small, it actually flows well in excess of 500 cfm.

Those are numbers once reserved for the most elite Pro Stock cars, yet today; the configuration is available to anyone. There's more here, too: The port surface found in a Reher-Morrison race cylinder head features a definitive texture. It's difficult to describe, but here's a good analogy: Think of it as a miniature culvert. A series of visually detectable grooves (for lack of a better term) follow the shape of the port. The grooves aren't the result of sloppy workmanship. On the contrary, you can see that a good amount of work goes into to creating the surface finish. Why? The answer is simple: The flow quality improves.

Fresh Firing Orders
A typical Chevy V-8 firing order is 1-8-4-3-6-5-7-2 (aside from late model LS-series engines). For the vast majority of applications, this firing order works very, very well. So well, there's likely no need to change it. But in a high performance (race or otherwise) application, there may be sufficient power available from different firing orders to warrant a change. For example, there are seven other firing order arrangements that can be used without changing the crankshaft layout. These firing orders include the following:
*1-8-4-2-6-5-7-3
*1-8-7-2-6-5-4-3
*1-8-7-3-6-5-4-2
*1-5-4-3-6-8-7-2
*1-5-7-3-6-8-4-2
*1-5-7-2-6-8-4-3
*1-5-4-2-6-8-7-3

Reher-Morrison has tested the various combinations, and has found some interesting results. When the firing order is revised to 1-8-7-3-6-5-4-2, you'll find some power and reliability. Now, if you race a Pro Stock car, this is no secret since the revised order has been in vogue for some time, but for little guys it's also important. You see, with the revised firing order, fuel distribution dilemmas are resolved.

The engine tends to run cooler, and perhaps just as important, the engine is actually smoother. How much extra power is there? Anywhere between 8-10 measurable horsepower. In a well-sorted engine, that's a bunch. There was once a caveat here though: The average racer couldn't easily get a cam with the revised lobe positions. Not so today. Reher-Morrison sells such a package ("Big Stick Cams") for Chevy big-block/Big Chief head combinations.

Blue By You
According to the folks at Fel Pro, the Blue Stripe on Fel-Pro gaskets is a registered trademark and does not indicate the top or bottom of the gasket. Make sure to follow directional stamps and/or the instruction sheet for proper gasket positioning!

Retain This Thought
The fit between the valve spring retainer and the valve spring just might be the most overlooked item in engine assembly. The steps machined on the retainer must match the inside diameter of the spring. Another thing you should look for is this: When installing the retainer on the spring, never force the retainer into the spring. Why not? Forcing the retainer over the spring can lead to premature spring and/or retainer failure.

In Hot Water
The folks from Fel Pro point out that a water temperature gauge only indicates the average temperature of the coolant in the engine. A water temp gauge does not indicate the cylinder head casting temperature. The casting temperature is what the head gasket is subjected to.

Torque Of The TownM
When tightening any assembly held together with a number of fasteners (for example, an engine), Mac Tools states that each fastener should be tightened down a little at a time, going to each fastener in turn, until the specified torque has been reached. Mac Tools suggests you follow this practice when torquing fasteners:
1. Apply 3/4 of the specified torque to each fastener.
2. Reset the wrench and tighten each fastener to the specified torque.

After tightening all the fasteners, repeat the final tightening to make certain all fasteners are at the specified torque.

Plug Heat
In a Chevy engine that is modified (and particularly if the engine has an increased compression ratio) more heat is a byproduct of the added power. That should be no secret. But what's the correct spark plug heat range for something like this? Here's a simple rule of thumb: Use one heat range colder for every 75-100 hp you add, or when you significantly raise compression.

Filter Frustration
How many of you have an oil filter wrench that slips? Plenty we'll bet. Instead of buying another wrench and finding that it too slips after a short period of time, try this: Wrap several layers of electrical tape around the circumference of the wrench. Then try the wrench. Magic! The wrench doesn't slip!

Weak Kneed
Most of the damage associated with an engine valvetrain can be attributed to weak valve springs, particularly in roller camshaft applications. Some enthusiasts (racers included) believe that a very stiff spring stresses the valvetrain and soaks up power as the spring compresses. According to many pro engine builders, that's wrong. Very little drag is actually added by stiff valve springs. Why? There are only so many valves open at one time. In addition, there is always the same number of lifters opening, as there are closing valves. Think about it. It makes sense. Reher-Morrison points out there are limits to the valve opening pressure you can use, based upon the camshaft design you select. Just don't be fooled into using too little spring pressure.

Conditional Requirement
Here's how to jet for conditions: Air density decreases with temperature. Hot air is less dense than cold air. There are fewer air molecules in a given volume of warm air than in the same volume of cool air. Since there are fewer air molecules in warm air, then the air-fuel ratio in the engine has to be changed to compensate. This is accomplished by reducing the jet size or jet number (lean the engine).

How big a change should you make? While there's an old racer rule of thumb that states you should reduce by one jet number for every 20 degrees F or temperature increase, it too isn't cast in stone. The best way to compensate is to decrease jet numbers one at a time until either the performance improvements cease or the spark plugs show that the mixture is too lean. When it comes to jetting, there's also another rule of thumb that states that for every 700-800 foot change in altitude, the jetting should be adjusted. Basically, this is the same thing as an increase in temperature.

As the altitude increases, the available air molecules in a given volume decrease. The solution? Decrease jet size as the altitude increases. Just be positive to use the same "one jet number at a time" methodology, and always double check the spark plugs. Something to consider if you have a good old-fashioned hot rod complete with carburetors.

Bread Basket
You know those little plastic clips that keep bread bags together? You better start saving them. Here's why: Think back to the time you mixed up the ignition wires when you swapped distributor caps. If you had used these tags on the wires, and wrote down the appropriate cylinder number (for example, 1-3-5-7) on the tag, then you would have saved oodles of time.

Filter Folly
Spinning off a used oil filter on your Chevy almost always creates a major mess. One way to stop the mess is to slip a plastic bag over the old filter after breaking it loose with the filter wrench. Then with one hand hold the neck of the bag tight against the engine block use the other to unscrew the filter. The dirty, hot oil will be contained within the plastic bag, and it won't run down your sleeve.

  • «
  • |
  • 1
  • |
  • 2
  • |
  • View Full Article
By Wayne Scraba
Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
Super Chevy