1997 Mazda MX-5 Miata: Kraftwerks Supercharger Kit Meets Three Dynos
January 25, 2011
You've seen Project Miata's baseline output numbers. To recap, there were two sets of baseline dyno data since the car's cam timing was off when we bought it. Blame the primates. Once the cams were set to stock and the car's health confirmed, we forged ahead with the installation of the Kraftwerks supercharger kit in confidence.
This situation precluded measuring the car's real, actual, proper baseline output on our usual dyno -- MD Automotive's Dynojet. We've built a large library of dyno runs for dozens of cars on this dyno, and I try to be scrupulous about capturing each change here so that we can compare to other cars we've run. I had the foresight to run a baseline dyno test on the Dynojet, but that was when the cam timing was unknowingly jacked up.
In this quandary I saw opportunity. We can turn this frown upside down and quantify the differences between three dynos. Yes, three -- along with Kraftwerks' Superflow dyno and MD Automotive's Dynojet, I ran the now-supercharged car on Church Automotive Testing's Dynapack dyno.
If all you want to know is how much sauce the Kraftwerks supercharger kit added over stock, look no further than above. Peak power rises by 60 horsepower, while peak torque ratchets up by 37 lb-ft over the baseline post-cam adjustment run.
Hey, the math is easy on this one -- that's a 60% increase in peak power. As you can see from the torque curve, the kit's effect at high revs is more pronounced than in the lower reaches of the rev range, but there's no denying the across-the-board increase.
With the supercharger, our Miata's 1.8-liter four drives in a nicely linear fashion -- the power rises in lockstep with your right foot's position, and this effect makes it feel simply like a larger, more rev-happy version of itself. It's worth revving now. I dig that. It's not hopelessly slow anymore, either, and I dig that, too.
So what'd it do on our standard dyno, MD Automotive's Dynojet? See here. Just a day after running the supercharger's numbers at Kraftwerks, with the same fuel in the tank and pressure in the tires, we have about as apples-to-apples a comparison as we can get.
What stands out here is that the Dynojet says peak power is now 173 horsepower and peak torque is 141 lb-ft.
Green lines are supercharged. The purple traces are the pre-cam adjustment baseline numbers, of course.
Moving right along to Church's Dynapack (orange traces to your right), the measured output of the supercharged setup is higher still -- 187 horsepower and 157 lb-ft. Again, same fuel in the tank, and run within hours of hitting MD's Dynojet.
What's going on here is painfully obvious but lost on many performance enthusiasts -- different dynos are different. The Dynapack, for example, attaches directly to a car's hubs, thereby eliminating any tire slip losses. It's a loading-type dyno like the Superflow, the ramp rates of which can be set differently.
The Dynojet is simply a large drum of known mass with no provision for holding load points or modifying ramp rates. Great for consistency, but tuning part-throttle and steady state stuff is difficult unless you spring for one of Dynojet's newfangled dynos. MD's Dynojet 248 is the OG inertial-only one.
Here's an overlay of the our supercharged Miata's torque (easier to visualize than power) as measured by the three dynos. In the case of the Dynapack, perhaps there's more going on than just the tire slip losses, as those would increase with engine speed. Here the difference is not rpm-dependent. Hmm.
Weather is another factor to consider, particularly in regions that aren't southern CA where the girls are hot and the weather consistent. We applied SAE weather correction to all runs here as per SAE's procedure and saw less than a couple percent correction applied among all three dynos. It is worth noting that the air density in the supercharged car's intake manifold isn't necessarily fully represented using ambient conditions as the basis of correction. But weather correction is at least a step in the right direction, particularly for normally aspirated and supercharged (but not turbocharged) cars.
With that said, we tested on all three dynos within 18 hours, and the weather conditions in southern CA are as stable year-round as one could ask for. Still, we observed some variation in ambient pressure at each shop. There might be some variation from sensor to sensor, and the way to address this is to bring a weather station to each shop, something I might undertake if there is interest in more of this dyno-a-thon-ing (plus I'd add a Mustang dyno to the mix, use an n/a car, and quantify 2WD vs 4WD).
But your average enthusiast doesn't have this luxury. The numbers he gets are what he gets. What's important are the gains observed on a given dyno rather than the absolute numbers.
And in our case, observing 60 additional horsepower in Project Miata is a step in the right direction.
Jason Kavanagh, Engineering Editor