You built the engine, wrestled with the headers; picked a converter; sorted out the ignition, cooling, and electrical systems; bought new slicks; and spent the rest of the long winter ironing out the kinks and waiting for the local track to reopen. You were up nights for a week before the big test-and-tune session and passed the time fiddling with last-minute details until the day finally came. You got to the track two hours early, passed tech, waited for an hour in the staging lanes, missed a shift on the first pass, went back to the lanes, waited another hour, launched at the wrong rpm and missed another shift, waited another hour in the lanes, launched great, hit all the shifts, and coasted up to the timing shack ready for the timeslip--that innocuous strip of paper that validates all your hard work. It all comes down to this--a cash register receipt full of digits capable of making you a hero or a chump.
In our experience, that first time-slip rarely lives up to expectations. You've got all the right hardware, but somehow it's just not performing up to par. Or is it? Tweaking a combination for utmost performance takes time and experience. There are so many variables it's tough to know where to start and how they affect each other, which can be frustrating to a beginner. It's easy to chase your tail at the dragstrip, especially if your car--or your driving ability--isn't consistent enough to record small performance gains, and it's tempting to succumb to the temptation to swap parts rather than sort out what you have. On the other hand, maybe you don't live anywhere near a dragstrip or have no interest in driving your car on one (shocking to think that could be true if you're reading this magazine) but still want a way to quantify its current level of performance beyond "it sure feels faster."
Either way, before you start beating your head against the wall; changing carbs, cams, or converters; or just shrugging your shoulders and giving up, it would be good to at least know if you've got the basic kinks like jetting and timing sorted out, or if there are hidden gremlins holding back your horses. That's where a chassis dyno is very useful. In just a short one- or two-hour session, you can run your new engine combo through its paces, isolating all chassis, track, or driver variables.
We had some of these same questions, so we took our SuperNova to a local dyno shop recently to see if it had any kinks we hadn't noticed or worked out the last time we had it at the track (turns out we actually had tuned it pretty close). Follow along as we spend a day on the chassis dyno.
SuperNova on the Rollers!
If you've been following our SuperNova project, you'll remember that we used our '71 Chevy Nova last month as a test mule to evaluate a pair of Bill Mitchell Hardcore Racing crate engines. We tested a 427ci small-block Chevy rated at 520 hp, which ran 11.76 at 113 mph at our high-desert test track (using standard NHRA correction factors for that track, those numbers correct to 11.38 at 117 mph at sea level). Then we swapped in a 540hp-rated 509ci big-block and ran 11.60 at 114.25 (which corrects to 11.22 at 118). With a "3,000-stall" converter, 4.10 gears, 9-inch slicks, and race-ready weights of 3,300 pounds with the small-block and 3,500 pounds with the big-block, all those numbers seemed about right based on our calculations.
After the dragstrip testing, we set up a session at Westech Performance Group's Superflow Auto Dyno SF-840, and spent a couple hours on the rollers verifying that the 509 was indeed a happy camper. We were pleased to find that, as recommended by Bill Mitchell, the big-block made peak power with exactly the same jetting (74s primary and secondary) and timing (36 degrees total), that it was shipped with. Peak power was recorded at 428 hp at 5,400 rpm and 424 lb-ft of torque at 5,200, although we believe the torque production is skewed by the fact that the torque converter was actually stalling at close to 5,000 rpm--far beyond its rated stall speed (see "Drivetrain Losses" sidebar). What this tells us is that the converter we have (a B&M Holeshot 3000) may not be the best choice for this thumping big-block. The Holeshot's stall ratings are based on an "average" small-block making maybe 350-400 lb-ft, not a mega big-block making upwards of 550 at the crank, and the higher the torque the higher the stall, all other things being equal. So we suspect the 509 is actually making much more torque at a lower rpm than we recorded.
By Matthew King
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