Our first bolt-on came in...
Our first bolt-on came in a big blue bottle. Nothing is as easy or efficient at adding extra power as a simple nitrous kit. This Super Powershot carbureted plate system from the nitrous experts at NOS featured everything we needed to add anywhere from 100 to as much as 150 extra horsepower.
After the sweeping success of the Super Powershot system, we were anxious to get to the cylinder-head swap. Waiting in the wings were AFR 185 heads, which have always impressed us with both their flow numbers and how well those numbers translate directly into power numbers. The AFR 185s topped the list in our "Ultimate Guide to Cylinder Heads," and here was another example of a stroker motor just begging for some additional head flow.
The question now was, how would the power offered by the AFR heads compare to the tremendous gains offered by the NOS system? The head swap required using different pushrods and a fresh set of Fel-Pro 1011-2 head gaskets, but once everything was in place, we were ready to make some noise. As usual, the AFR 185s did not disappoint us, as the power output of the CHP 331 stroker jumped from 347 hp and 398 lb-ft, to 450 hp and 446 lb-ft. Not only did the AFR heads increase the peak horsepower output by more than 100 hp, but the peak torque numbers were up as well (from 398 lb-ft to 446 lb-ft). In fact, the AFR 185 heads improved the power output throughout the rev range, from 2,600 rpm all the way to 6,100 rpm. The AFR heads shifted where the motor made peak power, from 5,600 rpm with the stock heads to 6,100 rpm, a sure indication that the stock heads were a restriction on this application. Compared at 6,000 rpm, the AFR heads improved the power output by an amazing 125 hp.
Next up was a head swap to...
Next up was a head swap to a pair of 185 heads from Airflow Research. While just about any set of aftermarket aluminum cylinder heads would offer gains compared to the stock heads, the AFR 185s have always proven to be impressive performers.
While it may seem beyond belief that a set of cylinder heads can be worth more than 100 hp, know that in our testing for the "Ultimate Guide to Cylinder Heads," a head swap was worth over 200 hp. Replacing the stock E7TE heads on a wild 392 stroker with a set of AFR 205s improved the power output by an amazing 243 hp at 6,500 rpm. Does this mean a set of heads is always worth 243 hp? Heck, no. Of course it would be nice, but as indicated previously, it's all about the combination.
Now the question is, what can be expected of the extra 100 hp? In a heads-up shootout in identical cars, the 450hp nitrous car would certainly win, thanks to the tremendous average power production. Where the AFR heads offered peak gains of 100 hp, the NOS system improved the power output by 100 hp at every rpm range, from roughly 4,000 rpm to 6,000 rpm. The extra 100 hp at 4,000 rpm translates to an extra 128 lb-ft of torque. This compares to the just 40 extra lb-ft offered by the head swap at the same engine speed, thus the NOS car would motor off into the distance. Obviously the ideal combination would be the 331 stroker with the AFR heads and the NOS 100hp shot, but that's a test for another day-albeit one with predictable 100hp results.
The NOS kit featured a plate...
The NOS kit featured a plate with spray bars to evenly deliver the nitrous (and fuel) to each cylinder.
We employed a pressure gauge...
We employed a pressure gauge while testing to ensure the bottle pressure was at an optimum 900 psi.
The extra jetting supplied...
The extra jetting supplied with the kit allowed us to adjust the power gains offered by the kit. We chose jetting to provide an extra 100 hp, and that's exactly what we got. Using the NOS kit, the peak power numbers jumped from 347 hp and 398 lb-ft to 451 hp and (a big-block-like) 526 lb-ft.