FEATURE ARTICLE from Hemmings Sports & Exotic Car

Frankensprite

Hemmings Sports & Exotic Car - APRIL 1, 2010 - BY CRAIG FITZGERALD - BUILD PHOTOGRAPHY COURTESY AARON COUPER

A 3.8-liter Jag engine fits in there?

At first, the very idea of fitting a 1961 Austin-Healey Sprite Mk2 with anything other than the tiny engine it came with seems outlandish, like one of those wrought-iron barroom puzzles, which you'd need to consume six draft beers to even begin to figure out. There's the dimension of the '61 Austin-Healey's bonnet, which is about the size of a small end table. Then there's the bonnet of an E-Type, a veritable parody of the "long-hood, short deck" configuration sports cars and coupes of the 1960s and 1970s were known for. What lies beneath either bonnet would be completely incongruous beneath the sheetmetal of the other, right?

Wrong. Aaron Couper's done it. And he's done it amazingly well.

You'd be forgiven for thinking that a car like this couldn't possibly be well sorted out. That it would be a cacophony of squeaks and rattles. That the front would be impossibly nose-heavy. That the rear axle would be twisting out of its mounts, that tires would be mercilessly rubbing against inner fenders.

And you'd be wrong again.

The car that Aaron Couper has constructed--out of nothing more than knowledge and a whim when he was working on a customer's XK120 and thought "Hey, I wonder if that'll fit?"--is so well put together, you could be convinced it might have come from the factory this way.

The issue that is most obvious is just the physical size of the thing. Aaron knew that some significant sheetmetal work was in store. Behind the Austin-Healey engine are a number of items that Aaron decided would be sacrificial: The heater box was the first obvious thing to go. It's not like he was going to be spending a lot of time scraping ice and snow off the windshield, anyway, even though the car resides in the wintry town of West Pawlet, Vermont. Next, Aaron decided that he'd carve out the space that was normally occupied by a battery tray. That opened up a veritable acre of space beneath the hood, in which two cylinders worth of E-Type engine would tuck nicely. Aaron then "borrowed" an engine from his customer's XK120 as a dry run to see if he'd made his calculations properly. The engine was a perfect fit.

Beyond the physical size, though, there's weight to be considered. The 3.8-liter inline six-cylinder weighs in at about 592 pounds. The original 948cc four-cylinder that resided under the hood of the Sprite was a feathery 253 pounds, just a little less than half the Jaguar engine, which would present some serious handling issues if it were allowed to hang out way in front of--or even evenly on top of--the front wheels. But by hollowing out all that space where the Sprite's ancillary bits once stood, Aaron essentially turned the car into something of a mid/front engine hybrid, with about 5/6ths of the engine's length behind the front wheels. Aaron notes that the car's overall weight is up from 1,575 pounds to about 1,800 with the 3.8-liter engine. But with the fuel tank and passenger compartment empty, that weight is distributed with about 55 percent over the front wheels (the stock Sprite puts about 52.4 percent over the front wheels). With two passengers and a full tank of fuel, the distribution gets even better.

As it turns out, the engine was the easier of two elements to fit. Aaron decided to use the transmission from a 1967 Jaguar E-Type, which is significantly larger than the little cast-iron gearbox from the Sprite. When he made the modifications to allow for the additional length of the engine, Aaron factored in the added girth and length of the transmission, which resulted in a loss of about three inches of foot room on either side of the transmission tunnel. Aaron also took the opportunity to fabricate a completely removable transmission tunnel to provide for easy access for service later on. He notes that he likes the location of the Jaguar's shifter even better than the original Sprite's.

The third member of the driveline team proved to be a weak point that Aaron felt could be overcome by looking elsewhere than Great Britain for parts. Selecting a differential and axle housing from a donor Toyota pickup truck--about as plentiful a part as you're ever likely to find--Aaron got to work narrowing the axle housings to fit the Sprite's svelte dimensions.

As you might expect, there was a fair amount of strengthening to be done behind the scenes to keep the big Jaguar engine's 250hp from tearing the little Sprite's unibody to pieces. A boxed steel cradle acts as the transmission mount, and as a stiffener bracing the giant hole Aaron had to cut in the floor for the transmission to clear.

Suspension modifications up front were relatively straightforward, and what the average Spridget owner might do to improve the handling of his car. The coil springs are the only outlandish bit: 800 pound custom-wound race springs he found on the Internet. Aaron fitted new custom upper A-arms, performed a Girling tube shock conversion and tied the package together with a ¾-inch anti-roll bar, and then swiped front disc brake rotors and calipers from the Spitfire and MGB parts bin.

At the rear, Aaron continued with the modifications. Rather than allow the Spridget's cart-sprung rear suspension to suffice, he instead built a four-link rear suspension with a Panhard rod and coilover shocks. In order for the huge coilovers (with modified E-Type springs) to fit the car's underbody, Aaron cut the wheelwells and boxed in some additional clearance in the trunk.

The car required some additional modifications to allow the engine to work well in its new home. For example, the 3.8-liter engine's oil filter housing made contact with the frame stubs, so a remote oil filter housing moved its location. The seven-gallon fuel tank would empty itself in a matter of minutes, so Aaron had an 11-gallon reservoir fabricated to fit in the same space. And because the battery no longer had a home under the bonnet, it moved to its new home on the right side of the trunk floor, where it's balanced out by a full-size spare tire. When we photographed Aaron's car, he was running Minator wheels with Yokohama Avid tires, but since, he's increased the size to a more aggressive 15x6" Superlite aluminum wheel with polished rims (Aaron's business, Couper's Cars, is a Superlite dealer), shod with 165/50R15s up front, and 175/55R15s at the rear.

Unless you were to hear the Jaguar's growl through its custom stainless exhaust and XK120 mufflers, there are only a handful of tipoffs that the engine is modified. The most notable is the bonnet, which features a very un-Spritelike bulge large enough to clear the front of the 3.8-liter's cam cover. You might think Aaron spent weeks constructing his own custom bonnet with a shot bag, a mallet and an English wheel. Which is exactly what he did, at first. Along with the clearance, he also wanted to provide a bit more hot air extraction. Aaron's a resourceful fellow: He had an old E-Type bonnet lying around the garage. He made a couple of measurements, got out the nibbler and reskinned the Sprite's bonnet frame with that of an E-Type, complete with the requisite bump and air extraction louvers.

Little touches like this appear everywhere you look, and it's what makes this car so special. Our favorite was on the passenger side of the instrument panel: There sat what at first glance looked like some kind of a cool rally clock from the 1960s. Upon closer inspection, we noticed the Cyrillic script: The clock apparently came from a Russian aircraft.

In the driver's seat, you'll first notice that three-inch loss of foot room. It's not annoying at all, but it does make itself known right off the bat. The trek from Aaron's shop down his long driveway to one of Vermont's most scenic byways was long and slow. It's a gravel driveway with a wooden bridge at the halfway mark, and undulations in the surface would play havoc with the low-slung roadster at speed. But once we reached the smooth tarmac, Frankensprite came into its own. It's a beast, full of torque and power and noises you'd never expect from such a small car. The one minor sour note was that the exhaust made contact with the floor, a situation that Aaron has since remedied, and one that we'd happily live with for a hundred years to be able to drive such a well-executed, perfectly proportioned little car.

So why would you take the time to build such a creature? For some, it might be the same reason George Herbert Leigh Mallory set out for the North Face of Mount Everest: because it's there. But Aaron Couper is a professional restorer, engine man and fabricator. This car acts as a rolling business card, shouting to the rooftops, "This is what I can do." We can't think of a better public relations representative.

Contact us Email.  Couper's Classic Cars. 314 Rt 153, West Pawlet, Vermont 05775