Frankenmiata: Dyno Secrets Revealed For The First Time!
by Dave Coleman
One of the best things about LeMons (and there are a lot of great things…) is the complete engineering freedom to do whatever you want (if you can pull it off for $500). This freedom, and full access to MD Automotive's dyno, welders and machine tools, has given us the opportunity to learn a lot about the untested world of crudely-tuned low-boost turbo Miata endurance race engines. It's finally time to share what we've learned. Here's the whole story of the Frankenmiata's, long slow climb from 101 hp to 192 hp as told through 11 dyno charts.
Dyno chart #1: Our base engine was cobbled together from old parts salvaged from 4 different free, blown-up engines. Remarkably, this flailing box of crud put down a respectable-for-a-1.6-Miata 101 hp in naturally-aspirated form.
It seems comically conservative now, but at the time we were so unsure the turbo system would work that we built a non-turbo downpipe, and carried around a stock intake so we could un-turbocharge the car mid-race, if necessary. We also designed the exhaust manifold so we could easily swap manifolds mid-race, assuming the crack-prone stock manifold would shatter when faced with the heat of turbocharging, and made an intercooler bypass pipe to install in the event that some stray auto part pierced our intercooler. None of these precautions ever turned out to be useful.
If you don't remember how we turbocharged this engine for $95, go read about it here.
Dyno Chart #2: The first pull with our newly turbocharged engine was equal parts successful and terrifying. 163 hp wildly exceeded our expectations for our first guess, but it also wildly exceeded what we thought the car could support. Boost first stabilized around 5 psi, down at 3000 rpm, but started creeping as the revs increased. By 7000 rpm, boost was up to a terrifying 7 psi.
Why were we scared by a paltry 7 pounds of boost? First of all because this is endurance racing, and not only do we have to survive 14 hours of constant abuse to finish a race, but we planned to run several races with this engine. Durability was our most important consideration. Most terrifying, though, was our fuel pressure. Our only fuel management was a used Vortech rising-rate fuel pressure regulator that added something in the neighborhood of 10 psi for every pound of boost. Since fuel pressure starts out at 43 psi with no boost, our 100-psi fuel pressure gauge was pegged before we even crossed 6 psi! Not only did we imagine our fuel pump crapping out after a few hours of this kind of abuse, we also had visions of a fiery death when every fuel line in the car ruptured under the strain. (Because of that second bit, we did replace every fuel hose in the car, including the often-forgotten ones back at the tank, with brand new 250-psi GoodYear hose.)