Drag Racing with Jim Hand – Part 7: About Those Easy Speed Secrets
(Ed: As we publish various writers’ and readers’ insight and experience in Pontiac performance and racing, we are bound to find differing opinions and actual findings. This article illustrates this situation. Jim invites all to share their views here. And, as he points out, the actual proof has to be in your own testing on your own Pontiac. Read and enjoy!)
During the past 10 years, I have conducted many tests on my ’71 LeMans wagon at the strip in an attempt to gain performance. Concurrent with the testing, I have performed technical research with the most knowledgeable and unbiased written and people sources I could find. The research tended to confirm what I actually found during testing. Following are comments about some of the tips or techniques tried, and short explanations as to why they did or did not help performance.
- Changing to a cold heat range spark plug does not help performance on a normal street/strip car, and very likely will degrade the idle. The heat range of a spark plug is designed to keep the firing tips clean under all anticipated service in a specific application. If the range is too hot, the tips may melt/erode under extreme service, and if too cold, the tips will not be able to burn away the deposits, thus causing misfire. Heat range has absolutely nothing to do with the ability to conduct the spark across the tip. For race engines that develop very high heat in the combustion chambers, a colder plug is needed to prevent possible pre-ignition caused by the plug electrodes over heating. Again, the colder plug by itself does not increase performance. Use the plug that is recommended by your favorite plug manufacturer for your vehicle.
- Changing to a “hotter” ignition system, or components, from a properly adjusted and operating factory HEI system will not normally help performance in any street/strip engine running less than 6000 RPM. A factory points system relies on the points to furnish adequate current (power) to the coil to develop suitable high voltage. Worn or mis-adjusted points, a defective condenser, a faulty ballast circuit, or a defective coil will lower the available high voltage. Most aftermarket ignition amplifiers are not dependent on the points to furnish the power for the coil, and may allow a marginal points system to develop more spark, which in turn, will allow the plug gap to be widened to .045-.050. A race engine with a wide overlap cam and high RPM manifold may start and run better at low RPM with an ignition system featuring increased spark duration and/or multiple sparks at lower RPM. However, on all normal engines, only about 15,000-20,000 volts is required to fire the spark plug gap, and while it is firing, the voltage will never increase above that value. Correctly operating HEI and points system will easily develop in excess of 25,000 volts to 5500 RPM, and the HEI will maintain that level of voltage past 6000 RPM. When the plug initially fires, a small flame kernel is developed at the spark. If a normal fuel mixture is available in the chamber, the flame expands away from the spark, and the spark has no further effect on that cylinder firing, regardless of the spark power or duration. The most critical aspect of any ignition system is to make it fire at the optimum time throughout the RPM range in use. See next paragraph for timing information.
- An aftermarket ignition advance kit will not automatically help performance. Most of the lower cost kits actually degrade the advance curve. The desired curve must be determined with a distributor machine, or on the engine using accurate timing lights and properly located timing marks. The optimum total mechanical timing (initial timing plus the mechanical advance provided by the springs and weights) is the most critical aspect, and must be found by trial and error on each vehicle. Vacuum advance has absolutely no effect on full throttle performance, because the vacuum unit retards to zero when the vacuum drops below about 5 to 7 inches, and most engines at full throttle have about 2 inches or less. However, vacuum advance is desirable for improved drivability and gas mileage.
- Disconnecting the alternator will not usually make a measurable difference in acceleration. The normal electrical load without lights and fans is about 4 amps (for ignition system) and that represents less than 1/4 HP load on the engine. However, disconnecting the alternator drops the available voltage from the nominal 14 to the ambient battery voltage of 12.4. That represents a loss of 11% of available voltage for the ignition, and the high voltage to the plugs will drop by about the same percentage. The disconnect exercise may appear to pay off if the vehicle is run first with the alternator disconnected, and then with it reconnected. Running without the alternator discharges the battery, and when it is reconnected, the alternator will charge as much as 35 amps to recharge the battery, as well as affect the engine. However, testing in the correct sequence will reveal no gain and possibly a loss in acceleration due to the reduction of the high voltage to the plugs.
- Removing the front sway bar may not improve traction, and may even degrade it by allowing the car to twist to one side on acceleration. The sway bar is not fastened tightly to the chassis, and thus does not impede front end lift. It merely ties the left and right suspension together so when one wheel either lifts or drops quickly the bar transfers some of the developed energy to the opposite side thus minimizing rolling or wallowing of the vehicle.
- The rear sway bar also helps keep the vehicle level from side-to-side which generally helps traction. Concerning the approximately 15# weight, it is located at the optimum spot and that 15# weight may actually help reduce wheel spin.
- There are various methods of increasing engine RPM capability. However, increased RPM does not automatically improve acceleration. Each vehicle has unique gearing, weight, and engine power range. For optimum acceleration, the engine should be operated such that it stays in its fattest power band through each gear. For example, if the engine makes good power from 3200 to 5000, it makes no sense to shift at 5500 because you not only lose acceleration from the 5000 to 5500 range, but when you shift to the next gear, the engine will only drop to about 3500, thus losing the power from 3000 to 3500. Regardless of your engine characteristics, you must try shifting at various RPM points to find the best overall point for your combination.
- A vacuum modulator on GM automatic transmissions does not control full throttle shift points. Again, as there is essentially no vacuum at full throttle, the modulator has no effect at full throttle. The transmission governor, detent system, and oil pressure determine the full throttle shift points. The vacuum modulator does control part throttle shifting, and is critical for good drivability.
- A shift kit will not improve acceleration providing the transmission is operating correctly. As the GM transmissions pick up the next higher gear off the lower gear when shifting, they never actually come out of gear. Thus, as long as there is no slippage between shifts, or hesitation, acceleration will not be improved with a quicker/harder shift. A severe shifting unit is much harder on the entire drive train, and may actually yank the engine down to a lower RPM when shifting, and that could hurt acceleration.
On the positive side, here are some tips that do usually help.
- Cooler air into the carburetor helps performance, because cooler air contains more oxygen per cubic foot than heated air.
- Anything that reduces rolling resistance (increased front tire pressure, radial tires on front, properly adjusted wheel bearings, correct front end alignment, less total weight, etc.) will help.
- Good exhaust systems always help. Smoothly bent pipes, relatively free flowing mufflers, and a balance pipe will help. A 2-1/2″ system is adequate for most street cars, and 3″ exhaust pipes might help slightly when you begin to run in the mid 12’s. The 3″ tail pipes and mufflers are not needed until you get well into the 11’s. Most “high performance” mufflers provide similar acceleration performance, so select the ones that provide the desired sound control and reliability at the price you want to pay. Remember that mufflers with larger diameter inlet tubes are always louder than those with smaller tubes. Four tube headers will slightly out perform three tube and Ram Air manifolds, and the three tube headers and RA units are a little better than stock manifolds. However, most Pontiac standard exhaust manifolds are relatively efficient, and do not hurt performance as much as the aftermarket would have you believe. The headers should have 1-5/8″ primaries for most vehicles, while higher performance street/strip cars may run slightly stronger with 1-3/4″ primaries.
- Carb spacers and carb re-jetting usually help, but it requires trial and error to find the best combination.
- Lower restriction filter housings help slightly, and clean elements are essential. We have never found any performance gain with the expensive air filter elements, although they may show higher dyno numbers. The slightly increased air flow capability they may have is usually not needed until relatively high RPM.
- Removing the power steering belt will usually help by several hundredths. Theoretically, this should not help because there is little if any load on the steering pump while running straight ahead. Apparently, the combination of belt tension and the larger and heavier pump pulley do present a noticeable acceleration load on the engine. The only downside to removing the belt is the harder steering.
Pontiac Engineering incorporated all of the easy things that helped performance. We should assure that our vehicles run at least as well as the factory designed them, and then look for minor enhancements that were not options for the engineers. We can modify the timing, run a little richer fuel metering, install a bit noisier exhaust, use slightly different converter and gears, use a different air intake system, and each of these changes may help. You can be sure that the Pontiac engineers knew these tricks, but they were obviously bound by emissions requirements, warranty issues and corporate policy in their overall designs.
None of this is intended to contradict any of the writers/enthusiasts that have worked so hard to help us all, but it does reflect what I have found in the past 10 years of research and testing. What have I gained from; this 10 year effort? In my opinion, will have obtained excellent performance from a remarkably close to stock vehicle combination, and most importantly, a lot of fun. My 455 powered wagon ran a best of 12.21/110+ at our last 1995 bracket race (NHRA track) and never slower than 12.27 in 5 time trials on 92 octane pump gas. It weights 4100# with driver in race trim, and that includes a full over the axle quiet exhaust system. It idles in drive at 650 RPM with 15″ of vacuum. It is equipped with 3.55 gears, 28″ McCreary DOT tires, 041 ~ factory grind cam, 1.65 rockers, and Rhoads variable lifters, ’71 #96 heads with moderately improved air flow and 9.95 CR, 800 CFM Q-Jet, Edelbrock “RPM” dual plane manifold, and is shifted at 5500 RPM.
If any readers have contradictory information from that listed, or have any similar data/information on performance, please furnish it and I will publish it. However, it must relate to street/strip vehicles, must be documented at a drag strip, be compared to a correctly operating stock system, be the only item changed for the test, and be first hand reliable data. Larger dyno numbers do not necessarily translate into improved drag strip performance, and second or third party bench racing stories are not considered reliable in the context of actual acceleration performance improvements. The ultimate test of any technique is to try it at the strip and determine if it works on your vehicle!