Holley Carburetor Tuning - 10 Power Moves

As competitive as circle track racing is these days, a racer cannot afford to give away even a very small speed advantage. But as I wander around the infield on my near weekly visits to Hickory (North Carolina) Motor Speedway, I see very few crews touching their carbs to tune for weather changes. Maybe most racers consider the carb calibrations for afternoon qualifying and evening racing too small to worry about.

Let me ask a question here: Is 10 hp worth worrying about? That can easily be the amount lost due to inappropriate weather-related jetting. I'm sure most teams would push hard for an extra 10 hp at the track and would pay big bucks just to have it. Well, here's a potential 10 hp right at the time it really counts-race night.

You should consider these 10 tips when tuning your carb. If you follow them, you'll gain power.

1. Chassis Dyno is Crucial
I have often been asked by other competitors why my engines seem to have an edge. "What's your secret?" they'll say. I get them to promise total silence on the deal and then give away (as always) my number-one secret: "Get on a chassis dyno at a shop with top-grade carb calibration capability."

This answer often disappoints the questioner because it doesn't seem like a secret at all. But the bottom line is that most racers don't do it, and-9 times out of 10-this move really pays off. You may think that if your motor has been dyno'd and calibrated on an engine dyno, there is not much left to do in this department. If this is the case, think again-the underhood conditions in a race car are far from the same as those in the dyno cell. The calibration needed in the car is typically two jet sizes smaller all around than the settings that made the most horsepower in the dyno cell.

However, if we are to get the best performance at the track, there is more to it than just passing the job of calibration to the dyno operator. If part of your job description as a race team member is finding power, then you really need to know at least the basic calibration and tuning procedures for your engine's carburetion. Let's lay the groundwork for finding that often elusive last 10 hp.

First, I prefer to use a Dynojet chassis dyno. The first of this breed originated in my shop in California, where I contributed a few design details. As long as no one tampers with the computer software, this type of dyno cannot give an incorrect result unless the laws of physics are temporarily changed. This means, assuming the roller bearings are OK, the results from one test to another are always very close, which is good if you need to dyno test away from your home base.

Although not totally essential, a dyno with mixture-analyzing gear is of great value. It speeds up the process, and the results are almost always better. Here, my choice is a wideband O2 sensor. In fact, this should be your preferred analyzer, even if the motor was previously set up on an engine dyno. If the engine dyno is relying on exhaust temperatures to indicate mixture ratio-spread the bad news-almost everything you might have learned is suspect. For the record, Dynojet units have a pro quality wideband O2 sensor, as do Innovate Technology units.

Here are a few rules of engagement to keep in mind prior to starting any calibration moves. First, only dyno with the hood on, and have a large fan blowing into the radiator area. If underhood temps are not simulated, then part of the reason for being on the chassis dyno in the first place is invalidated. It is also a good idea to check inlet air temperature at the track and then make sure this is what is seen during the chassis dyno test. It is entirely possible to see 200-plus degrees F if zero precautions have been taken to keep intake temps down. It is also entirely practical to get that temperature down to the 120 mark, and that's worth almost the 10 hp we are trying to gain.

When you dyno test, record the air temperature, pressure, and humidity measurements so that you have a baseline from which subsequent trackside re-calibrations can be made for prevailing race time conditions.

There are some things that need to be done before going to the chassis dyno if you want to save on dyno time costs, and some things that will be done on the dyno at test time.