Part 3: Attack of the Weight Weenie
by Dave Coleman
Project Miatabusa's theoretical claim to Awesomeness doesn't come from power alone, but from the unique combination of power, lightness, and soul ripping sound. Power, by itself, will be entertaining but far from impressive. At 173 hp stock, the Hayabusa engine is only making the kind of power you would expect from a mild turbo kit on a stock Miata engine. Add in the roughly 170-pound weight savings from the engine itself, though, and multiply by the wail of 11,000 rpm, and its a spine quivering equation. (And of course, just wait until we turbocharge it…)
To make this swap really pay off, though, we need to add as much lightness as possible. Lightness is the fuel that feeds nimbleness, responsiveness, and raw performance in all four directions, not just the direction you travel a quarter mile at a time. There is nothing more effective at improving the overall performance of a car than a good diet.
A Miata seems like a tough candidate for a diet, though. Inspired by the Lotus Elan, lightness was designed in from the start, with extravagances like a featherweight aluminum hood already built in. And the design team's much touted “gram strategy” focused on shedding weight–even tiny amounts of it–from even the most mundane parts of the car, on the theory that if you add together enough inconsequential little details they'll add up to something meaningful. This suggests that they probably didn't leave that many weight savings opportunities on the table.
I have access, with my day job, to some of the earliest Miatas in existence. Cars #13 and #15 reside in Mazda R&D's basement, and I recently put #15 on a scale. It was 2163 pounds with a full tank of gas.
As with most cars, though, the purity of purpose that defined the original was watered down as the years went on. Bigger engines, more airbags, bigger brakes. The refinements that differentiate this 1996 Miata from the 1989 original each seem a perfectly reasonable compromise in isolation, but added together they reveal a 156-pound bloating. The day after I bought it, project Miatabusa tipped the scales at 2,319 pounds.
We still don't know exactly how much weight the Hayabusa engine swap will save. We do know the stock 1.8, with alternator and power steering pump, but without the flywheel, weighed 296 pounds. We also know the Hayabusa engine, without gearbox or header, weighed 135 pounds. So on the surface, it looks like we should have 161 pounds shaved right off the bat. We still haven't accounted for the added weight of the new flywheel shaft and bearings we're adding to the Hayabusa engine, the weight of the new engine mounts, or the weight savings from our unfinished tubular subframe, though, so its premature to put an exact number there.
That 161 pound savings will only bring us back to approximately where the original 1.6 Miatas were. Some of the difference between that original Miata and our 1996 are parts we plan to keep, like the bigger, stronger diff, bigger brakes and more serious door bars, but there are still plenty of pounds on the table.
As a start, we've managed to save another 73 pounds just by discarding the parts of the car that are really only required by the kinds of people who wouldn't put a Hayabusa engine in their Miata in the first place. The following is the result of a simple afternoon's work. Consider this a warmup, both for us and for you. Check out our progress and then put your brain to work. Where else can we shave pounds? Drop your suggestions in the comments, below.
License Plates – 2 lbs
The first pound saved was simple. The previous owner was a USC alum, and somehow felt the need to inform the world of this fact with a depleted uranium license plate frame. Seriously, this cast pot-metal license plate frame weighed a full pound. Unacceptable. It nearly tore a hole in the garbage bag on the way to the curb.
Another pound was found on the front plate, but it wasn't as easy.
The factory front license plate mount is a crappy piece cobbled together from some weak steel bar stock. Ours was bent and barely attached via some loose, rusty nuts.
As with almost every Miata front plate, the mounting bolts were installed with the long, pointy bolt shaft pointed at the nose of the car. At least they had the decency to use lightweight plastic hardware…
The inevitable result of this sloppy mounting is the park-by-braille crowd denting your front bumper. It's virtually impossible to find an NA Miata that's free of these license plate dents. If you remove the front bumper to access the back of these dents, you can do a decent 80% fix with nothing but a heat gun, your fingers, and some gloves.
Ok, there really isn't much weight in the license plate itself, but there is wasted space. The Miata's radiator intake is relatively small, and filling it with license plate is not a good way to keep it cool. Normally I'd just leave the damn thing off, but with the rampant proliferation of red light cameras comes the militant enforcement of front plate laws. Not running one is just begging for trouble.
It could be argued that doing this to your front plate is also begging for trouble, but to any clear-thinking person, this is a reasonable compromise. The plate is now small enough to fit the Miata's bumper, and still clearly shows the tax collectors what they need to know. Sadly, clear-thinking people seldom sign up for jobs that require bullet-proof vests. Only time will tell how well we can get away with this one.
The plate is mounted with lightweight plastic fasteners like the ones holding the fender liners in place. This required drilling holes directly into the bumper, a practice I'm normally violently opposed to, but this bumper is far from pristine and seemed ready for a little experimentation.
I'm not entirely thrilled with the way the size and location of the plate makes it look like a little numerical Hitler stache, but the whole drilling-into-the-bumper thing makes this a pretty hard one to change your mind on. If you've got any better suggestions, bring 'em on.
All together, the mounting hardware and discarded plate parts took another pound off the extreme end of the car.