Smogger Dyno - 420+ HP (Cont.)

Next, we put on the PCIII intake (Pg 21), which is a ported Edlebrock, with the necessary mods to enhance low-RPM transition, high RPM flow, cylinder balance, and fit on the engine right out of the box, which will be used throughout the rest of this buildup. Not worth any HP at this point, but improved EGT consistency and got back a few of those missing Ft-Lbs at the bottom end. The next addition will be our CTA 205TD cam (Pg 12), installed ‘straight up’ and not degreed, though it is ground advanced (we recommend following the cam installation and degreeing instructions provided with out cam kits, as they work even better that way - all cams in this group of runs were installed straight up to save time and tool $, as most guys doing their first cam swap don't have the time or tools to fool with it anyway). This change brought a 25 HP gain, with the peak at 3800 RPM and a 30 Lb-Ft gain with a 3000 RPM peak. There is the rest of our missing torque.

Our next change was exhaust. We replaced the OE cast manifolds with Sanderson’s 1- 7/8" primary/ 3" collector block hugger (shorty) headers. While this gave us a gain of 10 HP and 15 Ft-Lbs, smaller primaries (such as the headers we now carry (Pg 28) provide) would have been more effective.

It's common knowledge among Cad enthusiasts that the stock valve train wasn't designed for high lift, high spring pressure (remember the OE springs floating at 4200?), or high RPM (when this engine family first went into production, the common diff. gear ratio was under 3:1. As new replacement parts are being obsoleted as the inventory from the last run of parts is depleted, not to mention expensive, and are still no stronger than the originals, excepting the lack of wear. At this point, we chose our Stage II Shaft Rocker Assembly (Pg 15). The 10 HP gain was mostly the result of the increased ratio (1.72:1 compared to the OE 1.65:1), though on higher lift cams the increasing friction and geometry losses would make a noticeable portion of the gain. We now have 368 HP and 522 Ft-Lbs, and the graphs show us that his baby still wants more cam. At this point, it is still a cream puff, with a nice cruiser idle, great vacuum, and very drivable part throttle response.

To take it to the next level, we bolted on a set of our Pro Street heads (see specs on the head page, Pg 13). If you're building your own heads, basic porting guidelines come with the valves (Pg 14), for those of you with the skills and time. The valves are supplied at the correct length to avoid valve train hassle.

Pro Tip: All valve stems must be fairly close in height (±.010" or so) the whole length of the head, to get consistent lifter preload, when using non-adjustable shaft rocker setups, such as the Stage II setup we chose for this example. Oh BABY! We gained 34 HP (402) and 6 Ft-Lbs (528)! Note that we only moved the torque peak up by 200 RPM while making our 34 HP gains - these are not race heads, so don't listen to your Chevy pals telling you that bigger valves will always kill off the bottom end.

Now we'll switch to mid length headers (Pg 28), which are the style that is a bolt in for the cars most of you are swapping your 500’s in to. While 1 7/8" primaries sound small to guys familiar with Chevies, remember that we don't have to wind up the big cad like a tabby cat strung out on caffeine to make power. Our new line of headers with 1 3/4" primary tubes gave us a gain of 12 HP and 15 Ft-Lbs over and above the power we were making with the 1 7/8" primary headers, indicating that we not only improved the torque peak, but widened the curve with the smaller primaries. The smaller primaries also allow our headers to tuck in closer to the block and offer a better fit and easier installation as compared to similar headers with the larger primary tubes.

Our next step was ignition. While the MSD Pro Billet distributor (Pg 25) gained only 2 HP and no torque, keep in mind that we are still working with very low RPM combos at this point. Besides, at $315, the gorgeous MSD unit is a steal for a completely new unit, while the old HEI is a tad bulky looking and has 30 years of wear and tear on it. While playing with the ignition, we found that at this point going one step colder on plugs (from Autolite 646 to #65), and running a .040" gap instead of .060", gave us another 4 HP and 5 Ft-Lbs, for a total of 420 HP and 547 FtLbs.

When going over the charts the dyno was spitting out, we noticed that we could carry over 4 PSI of fuel pressure through the entire run. By the time we broke 400 HP, fuel pressure was dropping down, nearly to 2 PSI, well before the end of an 8 second pull. That begs the question of how the engine will fare while pulling a long hill, which can surely take more than 8 seconds, and it leans out because the carb’s fuel bowls are dry and starts detonating… We cured it by swapping in our chrome high volume pump (now available with a billet steel arm, Pg 24), but some of you will chose to use an electric pump. There is an even bigger mechanical pump in the works, which should be available by summer of ‘04, for those of you needing more. Experience tells us that most folks who use a high volume pump without a pressure regulator regret it eventually. Get it, set it, and keep the headaches away.