Pontiac Supercharger Kit Installation - Double Down

The Test
We met in New Era, Michigan, at New Era Racecraft for the dyno test. Owners Steve Morris and Kyle Kirker have made quite a reputation for themselves building large-displacement, centrifugally-supercharged big-block Chevys. Steve's '95 Impala wagon with a 2,200-horse 540 Chevy goes 7.51 at 193 mph with a stock chassis, 315/60-15 drag radials and no wheelie bars. Chevy or not, the track videos of the wagon on their website are a blast for any car nut.

Rather than see all of these Pontiac people as GM Divisional rivals, or simply dismissing the project as a waste of time, Steve and Kyle were very interested in working on the blown Pontiac, sort of like meeting up with long-lost cousins. They obviously are very well versed on centrifugally supercharged engines and Steve's dyno experience was very valuable for the testing.

The test was broken down into two sections, the first was getting a baseline on the normally aspirated combination and the second was installing the supercharger system and getting the numbers with that combination. All testing would use 94-octane pump gas and the timing was locked in at 34 degrees total advance to keep the variables to a minimum.

Generally speaking, if one can get an additional atmosphere of air into an engine (14.7 psi at sea level), it will double its horsepower. As we will see, that very generalized projection isn't too far off, though other factors came into play.

Once the engine was bolted up to the dyno and it was brought up to temperature, the first pull was made. It became obvious that the engine was running rich and was actually misfiring at higher rpm. The A/F ratios were deep in the 10s when they should have been well into the 12s. Still, the engine made 458.9 hp at 5,300 with 492.1 lb-ft of torque at 4,200. The numbers, while actually short of what was hoped for (475-480) were actually impressive, considering that the engine was drowning in fuel.

Admittedly, the carb was set up for a blow-through application and was not close to optimal for the normally aspirated pulls. Nevertheless, it did give an idea of what the engine was capable of and was within 20 hp of theestimate.

Without the luxury of time to mess around with different jetting or other tuning factors, the engine was shut down and the supercharger kit was installed.

The process took less than an hour, and once done, the engine was fired up. It immediately took on a new persona; the supercharger let out a distinctive whine and the exhaust note became a little sharper, even at idle. Once again the engine warmed up and pulls were made.

Under boost, the 455 let out a wild-sounding shriek that no doubt could be heard for miles. After a few mishaps with water hoses flying off and a misaligned starter, we received the pull and a backup that told the story.

With the supercharger installed, the previously overly-rich A/F ratio actually came up slightly lean at 12.5:1, for a forced-induction application. The idea is to run the engine rich to make use of the cooling effect of the gasoline vaporizing. It does sap a little bit of power, but it gives a good deal of added insurance.

In this particular case, the safety factor came in the form of the air-to-liquid intercooler. With a garbage-can reservoir full of ice water circulating through the cooling element, the inlet temperatures were kept well under 100 degrees Fahrenheit. This kept the exhaust temps within reason and eliminated detonation.

Why was the engine running a bit lean? One reason was that the power valve wasn't reading the boost referencing correctly. The other problem is that the carb simply wasn't large enough, an 850 or even a 950 Holley would have been a better choice, as their internal fuel passages would have allowed more fuel through, regardless of boost pressure.