Dyno Tuning Basics - Jets, Timing, Camera, Action

As you gaze out your window and wonder when winter will finally break-at least enough so that you can safely open up the garage and fire up your Pontiac without fear of engulfing it in a swirling maelstrom of snow and ice-take solace in knowing that there is a way to test the effectiveness of your "winter" performance upgrades without hitting the dragstrip.

For those lucky few who live in climates that support year-round dragstrip operation, hold off a few minutes before heading out the door to test again. While dragstrips are certainly fun, and in many towns a great place to meet and participate in the Pontiac hobby, they do have their limitations for A-B-type testing of performance products.

Floyd Hand's '66 Tempest runs a 0.030 over 10:1 compression 455 and ported (248 cfm) 7K3 iron heads to the tune of 11.50s at 117 mph on a 1.57 60-ft. The engine features a 950 cfm carb, Performer RPM intake, 234/244-deg Bullet cam, Hooker 1.75-in primary headers, 3-in x-type crossover and tailpipes from Pypes, and 2.5-in Straightline Performance mufflers. It's also equipped with a Turbo 400 automatic transmission, a Continental/Jim Hand 10-in 3,200-rpm stall converter, and an 8.5-in Corporate 10-bolt with 3.42 gears.

Since new or modified engine combinations often require extensive tuning, it may take 10 quality passes or more to get your combination dialed in. Invariably, things don't always go as planned. In many cases, you end up waiting and getting in only three runs, of which one was invalidated due to poor traction or some other variable. By the time you arrive back home, tired and frustrated, the mental financial calculator has already clicked off $100-$150 of wasted funds, paid for tow vehicle fuel, race car fuel, food and gate fees.

Sure, you can head back out at the next available time or try another track, but what happens if at the next date the weather is 20 degrees warmer and the barometric pressure has swung wildly? Will the changes that you made following the first testing session show improvements or will you simply be compensating for other variables, and continue chasing your tail until the perfect set of circumstances allow you to get your Pontiac dialed in?

For years, the only methods available for hobbyists to test their high-performance modifications included a street-based "seat-of-the-pants" approach or the dragstrip. With the introduction of the inertia-based chassis dyno, the Dynojet and the iconic Dynojet 248 model, dynamometers offer enthusiasts and tuners alike a tool to measure horsepower and torque in a controlled environment.

Now a mainstay of both the aftermarket shops and the OEMs, chances are there is a performance-oriented business in your area that will provide you with dyno-tuning time so you can objectively quantify a baseline, then make changes to optimize your tune.

Regardless of the brand or technology employed by the "chassis dynamometer," the object of dyno tuning is to allow you to get your Pontiac dialed in so that when it's driven on the street or the track, it's very close to being optimized. Whether it's equipped with a classic Pontiac running a traditional carburetor and distributor, or the latest LS-offering from GM, the same principles apply. Optimize the fuel delivery system and ignition timing for maximum safe power.

Strap yourselves in as we roll on over to Real Performance Motorsports (RPM) in Lewisville, Texas, and dyno-tune Floyd Hand's '66 Tempest. Is there power to be gained by tuning this well-sorted out combination or will we simply be spinning our wheels?

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Here are a few tips for your dyno excursion: Before leaving for the shop, pull a spark plug and examine it for detonation and/or abnormal wear. Replace your plugs (and properly gap them) if there is any wear, and don't forget to make sure that you have fresh fuel, a fuel filter and a PCV valve (if so equipped).	If there is any doubt as to the internal condition of the engine, perform either a compression and/or leak-down test before dyno testing. An engine with low compression in any cylinder won't impress you on the dyno.	Rather than relying upon the shop to supply tuning equipment, come prepared and bring your timing light. A modern-dial back-to-zero timing light like this unit from Craftsman works well and is affordable at Sears.
In addition to bringing a distributor wrench, remember to carry along spare belts, as well as screwdrivers, wrenches and any other basic hand-tool you may need.	For carburetor adjustments, organize your carburetor tuning kit. Holley-style carburetors need jets, shooters and a spare power valve (if applicable). Shown here is the author's own Quadrajet kit. (Even though Floyd didn't use the Q-jet in this story, you get the idea.) In addition to main jets, there is an assortment of secondary rod hangers and metering rods. Spare hose clamps and vacuum accessories (T's and vacuum caps) fit nicely into a clear plastic organizer.	After strapping the Tempest to the dyno and warming up the engine, it set a baseline of 354.9 horsepower and 427.9 lb-ft of torque. Timing was set at 28 degrees total with 10 degrees initial. This carburetor began life as a mechanical secondary 850 and has been professionally modified by BG to flow 950 cfm. It was equipped with No. 82 jets in front and No. 92 jets in the rear. According to Keith Lohse of RPM, "The overall air/fuel ratio was rather rich at 10.0:1, considering that carbureted applications generally perform best between 12.4-12.8:1."