Drag Racing with Jim Hand – Part 8: Common Modifications
As mentioned in an earlier column, I don’t plan to cover the typical “hot rodding” of adding after-market components. Instead, a discussion of techniques to obtain maximum performance at minimum cost, while maintaining excellent driveability, will be furnished. This information is intended primarily for the enthusiasts who would like to improve the performance of their stock or nearly stock vehicles.
The first step in improving performance is to identify the items or techniques that will actually increase power m the RPM range you intend to use! Here are some examples:
- Improved combustion of fuel, and correct fuel mixture.
- Optimum timing at all usable engine speeds.
- Efficient exhaust.
- Increased engine displacement -Not very practical without switching engines.
Note that there is no mention of light weight rods, light weight or other types of trick pistons, super mega ignition systems, huge headers, big cams, race intake manifolds, 1000 CFM carburetors, align boring, porting or even hardened valve seats! These kinds of changes or modifications might help the performance and reliability of high RPM race engines, but are not necessary and will not help performance on stock type engines operated in the factory designed RPM range.
Note the reference to factory RPM range. This is an extremely important concept, and must be clearly understood before starting your improvement project. The factory engines were designed and built to run in a specific RPM range. Their parts were of sufficient quality to run almost indefinitely if the RPM limits were observed. The engines developed maximum power throughout the intended range with the heads, manifolds, cams, and manifolds that were installed. For example, most standard production cars used a large two barrel carb., an #066 cam (also called a #4 in the earlier versions), which is 204 degrees intake duration at .050, and ordinary heads with press-in studs, but having very good low and mid-lift air flow. This combination provides extremely strong low and mid range torque which is exactly what the larger cars with high gears need for good throttle feel and quick response. This type of engine doesn’t develop high horsepower because it will not run much past 4600-4800 RPM and can’t breath enough air at high RPM, but it does develop excellent torque from idle up, and essentially the same total amount of torque as the highest HP engines of the same displacement. The Ram Air IV engine was designed to run to a higher RPM of about 5900. This required more air flow into the engine at higher RPM—thus, the higher flowing heads were incorporated. A longer duration cam was needed to give the cylinders time to fill at the higher RPM. The longer duration cam causes the intake valve to close later in the intake cycle, and this in turn, required more compression. The longer duration cam kills the low RPM power while hopefully extending the upper RPM power. With very poor low end power, a lower rear end gear was needed to provide some semblance of low speed performance. As the engine was so weak at low RPM, power steering and air conditioning were not available, and the engine was available only in the lightest body style vehicles. The result was a higher RPM engine with excellent power from about 3000 to 6000 RPM. This is great for a lighter weight car with a 4-speed, or an automatic with a loose converter for drag racing but it would be a dog in a normal weight street vehicle that needs to be driven from stop light to stop light.
So what is the answer for real performance increase? First, determine what RPM range you actually need and intend to use. If you plan to drive the car for some normal transportation, any idle speed over about 650 RPM will be a constant pain with stock converters. If you want good power and throttle response from idle to 3000 RPM (about 70-75 MPH in high gear), don’t install a cam with more than about 210-215 degrees intake duration as measured at .050 lift. Similarly, don’t install a single plane manifold or a carb larger than 750 CFM (except for an 800 Q-Jet) on this type of vehicle. Be wary of the “Performer RPM” manifold, even though it is a dual plane. It definitely degrades low end power, and only begins to help at around 5400 RPM and up. Remember that low-end power is relative to the size/torque of an engine, and that a 455 will have relatively good low-end with an “RPM” but it will still lose power from idle to about 2000 with it! By staying in the factory intended RPM range, your rods, rod bolts, pistons crank, and oil pump are totally satisfactory for any performance use (assuming they are in normal factory condition). The heads, regardless of type, should have first quality valve guides, a valve seat preparation that optimizes low lift air flow, and matching valves. The exhaust seats do not need to be hardened, because you will never load the engine hard enough for a long enough period of time to damage the seats. Even if you somehow manage to do so, this is not a catastrophic event, and the seats could be changed later if needed.
Unfortunately, the usual approach to increased power consisting of installing a larger cam, race manifold and carb, big tube headers, etc., will always degrade low end power, and if you are really lucky, some increase of power may occur at the upper RPM range. Unfortunately, to utilize it, you would then have to run your engine to top RPM in every gear, because low-end power will always be lost with such changes. The engine will no longer idle properly, will waste fuel, probably overheat, and generally be difficult to drive in city driving.
After you have determined what RPM range you expect to use, plan accordingly If you will run higher RPM than your present engine was designed for, consider what changes will be needed. If you are thinking Ram Air IV range for race only, you may need special rods, forged and/or lightened pistons, vastly improved air flow through your heads, a poorer idling cam, higher performance manifold and headers. If you are thinking Ram Air II level for race and street, all the stock internal parts are totally satisfactory. “Hotter” ignition systems or components will not improve performance over properly operating factory systems. The factory Q-Jet manifold and carb are adequate and actually superior to any aftermarket setups you can buy. The factory ignition points type or HEI, will easily do the job, although the points system must be properly adjusted and maintained. The Pontiac 066, 067 and 068 cams will provide good performance with automatics and 4speeds and the 044 will work well in this moderate RPM range with a 4-speed. The 041, or any cam with more than 230 degrees intake at .050 lift, is not suitable for any automatics you plan to drive on the street unless you use Rhoads variable lifters with it. Stock exhaust or Ram Air type manifolds will work fine, and headers with 1-5/8″ or 1-3/4″ primary tubes can be used if you want to put up with the hassle of leakage, additional noise, poor ground clearance, difficult installation and high maintenance.
What I have called a “RAM AIR II LEVEL” is basically a stock setup, and that is the answer to real “seat of the pants” performance. The Pontiac street engines provided more torque per cubic inch at the low and mid-range RPM than most competing engines. They consistently were quicker to 60 MPH, and the quarter mile, than similar vehicles of other makes. To realize this level of performance, and to improve it, requires good tuning of fuel mixture, proper ignition timing for the engine and fuel combination you will use, properly adjusted plugs of the correct heat range, a good dual exhaust system, a clean and efficient air intake system to the carb, proper operating carb, and good engine condition. If the engine is to be overhauled, do it exactly like the Pontiac shop manuals specify. Relatively minor changes in cam selection, fuel mixture, ignition timing and advance, rear end gear ratio, compression ratios, and carb type can provide some performance increase without substantially degrading driveability. However, large changes to any part of this balanced setup will almost always cause a loss in actual measured performance. The advantages to this approach include reasonable cost, noticeably better performance in normal driving, and measurably quicker times at the drag strip!
The 455 engine in my wagon is a good example of this approach of using a basically stock engine with moderate changes and a lot of fine tuning. It idles smoothly in drive at 650 RPM, has a stock HEI ignition, stock rods, rod bolts, crank and two bolt main caps. The pistons are TRW forged units. 1971 #96 heads are used, and have been milled .060″ and reworked for moderately improved air flow up to .5″ lift. The carb is a Q-Jet and an “RPM” manifold is used. The “RPM” provides about .1 second increase in the 1/4 over a stock manifold on this combination. As you may remember from last month’s column, it consistently runs 12.20’s-12.40’s in normal weather, on 92 octane gasoline exclusively, with a race weight of 4100#, and through a complete quiet exhaust system. So when you see highly modified Pontiacs running 13 or 14 seconds, be aware that well tuned stock type engines using Pontiac components can provide those kind of numbers. Think about that before investing your hard earned money for neat decals, a rough idle, harder to drive setup, a lot of noise, but very little performance increase!