[Bill Harris]

You need a PhD in insanity to read the Classification guides... My wife says I'm certifiable so here goes:

The asteriks in the columns denote Stock and S/S. I notice in the 1978 Chevy guide they are screwed up and the footnote says that a single asterik is both Stock and S/S, probably a typo. Normally the single asterik is the Stock column and the double asterick is the S/S column.

The number in the Body/Engine matrix is the HP/weight factor and converts directly to the "natural" Stock or S/S class for that car. Look at the 1978 Monte Carlo with the 305/145 engine for example. The factor is 16.09 for stock and 15.24 for S/S. That would put it in P for stock (16.00 - 16.99) and in N for S/S (15.00 - 15.99).

The line labelled S/SS Factors is the NHRA factored HP. So the 305/145 engine in the Monte Carlo is NHRA rated at 180 HP while the same engine is rated at 190 HP for S/S.

If you pan over to the greyed area to the right in the chart, the data is presented as shipping weights instead of HP/weight classes. So for the Monte Carlo, the shipping weight is 2896 lbs. You can get that same number in the left (white background) chart by taking the HP/weight factor and multiplying it by the NHRA factored HP. So for stock, 16.09 * 180 = 2896, and for S/S 15.24 * 190 = 2896. The shipping weight is always constant. When NHRA gives or takes HP for a combo, they change the number in the S/SS factors row and recalculate all the HP/weight numbers using the constant shipping weight. Nowadays they add an entry under the NHRA HP factor that says when the number was last changed. So for the Monte Carlo in Stock (single asterik) the 180 HP factor was set on June 2, 2003.

Remember that you can run the car at the bottom of the class, so to figure out your minimum race weight you take the NHRA factored HP and multiply it by the lowest HP/weight for the class. For Stock in P, that is 16.00 so the minimum race weight for the 305/145/180 in P is (16.00*180) + 170 = 3050 lbs. The 170 lbs is always added for the driver weight. You can also run one class lower than the "natural" class or one class higher. So the Monte Carlo can run O, P and Q stock. Minimum race weights in the three classes would be:
O/S : (15.00 * 180) + 170 = 2870
P/S : (16.00 * 180) + 170 = 3050
Q/S : (17.00 * 180) + 170 = 3230

Totally confused now???

Good luck!