If you’ve taken a peek under the hood of any car built in the past decade, odds are you

were greeted by a great big expanse of plastic bearing the manufacturer’s logo smack-dab

in its middle. These covers serve a variety of purposes—hiding the potentially dirty bits

of the drivetrain from the blissfully ignorant masses, for example—but one of their primary

functions is packaging. If nothing else, a big plastic cover gives the

impression that it’s shielding an equally large complex of performance equipment, privately

chugging away. If you can’t see the pavement when the hood is up, then certainly it’s because

every square inch of space in the engine bay is being used to generate power, right?

A few quick turns of a wrench, however, can remove these plastic covers and peel

back the facade, and doing so often invites disappointment. If the plastic veil is stripped

away and air is found underneath, our natural response is to want to do something about it.

Ideally, we’d prefer to pop the hood and see a massive lump that threatens to dent the engine

compartment from the inside thanks to its sheer imposing volume.

Aaron Couper isn’t the first person to put a bigger engine in his car, but his story is a twist

on the standard monster V8 shoehorn story. After all, big is relative when your starting

point is a diminutive 1961 Austin-Healey Sprite. For Aaron, there was no better choice

for his Sprite than the robust 3.8-liter Jaguar straight-six.

Aaron, who’s originally from New Zealand and now makes his home in West Pawlet, Vermont,

 first encountered the starting point for this project some 15 years ago. “I found the Sprite in an

 alley in San Diego,” he reports. “The price was right at $200.”

As the all-in-one owner, chief restorer and self-described floor  sweeper of Couper’s Classic Cars,

 Aaron spends most of his time working on customers’ cars. As a result, his Sprite sat idle for the

better part of those 15 years. The eureka moment came one day, as such moments do,  unexpectedly.

“I had sort of started on the Sprite and built up a 1275  turbocharged engine to put into it,” Aaron

 continued. “I was finishing a customer’s Jaguar XK120, and as I went past the Jag engine

on the stand, I said, ‘I wonder.’”

Just like that, the turbocharged 1275cc engine was pushed to the  side. Aaron started measuring up

 a big Jaguar six he had at the shop and compared the numbers to the available space in the Sprite’s

engine bay. “I love Jags,” he confesses. “I just said, hey, why not?—mostly

because there’s no way a Jaguar engine would fit into an Austin- Healey Sprite,” he laughs, echoing

 the sentiment of those who caught wind of his plan in the early stages.

Once he started work on the car, Aaron learned that there was a semi famous

1959 Sprite Mk I that had received a bored-out 4.2-liter Jaguar  six. The car was built in England in

in Australia. If nothing else, word of The Fright was proof of the concept’s viability, and

by all accounts the car was a missile. Aaron continued with his plan.

After taking  measurements, Couper was a bit surprised to discover that the big Jaguar

six would fit in the Sprite’s engine bay without any dramatic surgery. The transmission,

however, would not be so accommodating. “The Jag transmission is kind of wide—once I got it in there wasn’t much

room for the seats,” Aaron recalls. “Everything else was pretty straightforward. The engine

mounts bolted right up to the original Austin-Healey mount position.” There was one casualty, however

 “I had to cut the heater out,” he explains, but it didn’t seem to concern him too much. “No need for a

heater when you’ve got a British piece of iron!”  To make it all fit, Aaron also had to fabricate a removable transmission

tunnel. In the end he sacrificed about three inches of leg room on each side of the foot well in the firewall area.

It’s cozy but not uncomfortable for the average driver.

Dual SU 2" carburetors feed the hungry block. The exhaust is a mix of Jaguar cast-iron headers, some custom

front pipes and the stainless steel dual-pipe exhaust from an XK120. The torquey 3.8-liter Jag block was far too lusty for

 the little Sprite differential, so Aaron needed to find a suitable upgrade for the stock pumpkin.

A trip to the junkyard bore fruit in the form of a Toyota pickup truck rear end. “The price was right, something like $75 for the

rear end,” he recalls. “I ended up making a four-link rear end with a Panhard rod and coil-over shocks.”

The shocks came from eBay, and the generic springs were soon found to be too soft. Aaron cut some XKE springs

and was happy with the end result. Up front, Aaron mated the Sprite’s stock lower A-arms to custom

upper A-arms and once again turned to the Internet for the finishing touches.

The front springs came from eBay. They’re 800-pound inch springs—the biggest you can buy for

a Sprite off the shelf is a 500-pound spring. This guy paid big money to have them made in some race

shop and no one bid on them. He basically gave them away.”

Jaguar-powered 1961 Austin-Healey Sprite

the hood was in need of some alteration. Aaron initially broke out the hammer and English

wheel to modify the stock piece, adding a 2 1/2-inch bump to clear the cam covers. It was

an attractive solution that did the trick, but he wasn’t in love with the end result.

“I was also thinking about the heat issues,” he explains, “It’s one thing getting air into

the engine bay, but it’s another to get it out. I happened to have an old E-type hood that was

all ugly around the edges. I cut about 13 inches or so out of the middle of it, wheeled it and

got it all nice and smooth. I cut the old skin off the Austin-Healey frame and it just kind

of fit on the frame.” The E-type hood provides functionality thanks to the large stock vents

near the windshield, and it also hints at the nature of the beast lurking beneath.

Thanks to years of experience and more natural talent than Aaron would ever admit

to having, little guesswork was involved in the build. As a result, the Sprite came together as

precisely as if it had begun life with the big Jag block in the nose.

“The first time I drove the car, it was about three o’clock in the morning. Everything

worked well together, I was very surprised. Iran it with no doors. It would spin the wheels

in first and second—way too much torque for the car,” he recalls.

Traction is tricky when you’re dealing with big power in a small chassis, so an upgrade to

the wheel and tire combo was necessary. He chose 15x6-inch Superlite wheels fitted with

165mm wide tires up front and 175s in the rear.

The larger wheels also allow for bigger brakes, so he opted for Spitfire rotors and

MGB calipers up front, a common big-brake setup among Spridget owners. A vacuum

booster from a Mini keeps the pedal effort reasonable. “If I stand on it, it pulls up pretty

quick,” he reports. Most people expect that the addition of such

a massive engine into such a tiny car would send the handling to the dumps, but that’s not

the case. Aaron says that the despite its length, the engine is still mounted behind the front

wheels. As a result, only 55 percent of the car’s 1820 pounds rests on the front end. He assures

us that with two people and a full tank of gas onboard, the balance is just about neutral.

Aaron admits that the great looks of the Jaguar engine were as big a factor in his

decision as the power. In contrast to the ambiguous response that a plastic cover would

generate, for example, the shapely and massive straight-six in his Sprite has an almost physical

impact, even when it’s not running. “The other day, one of my daughters said,

‘Dad, your car makes people swear!’ when I open the hood,” Aaron laughed. Good thing

his daughter can’t hear what they must say when he hits the gas.

Aaron Couper recently gave Classic Motorsports Publisher Tim Suddard the opportunity to drive the Jaguar-powered Sprite. Tim was not expecting such a well turned-out driver’s car. “Suspecting the worst, I was pleasantly surprised with the way this Jaguar-powered monstrosity drove,” he reports. “I was expecting very heavy steering, excessive cockpit heat and poor handling. What I found was a car that felt more like an 1800-pound XKE than a Spridget with too heavy an engine in it. “The Sprite started and ran like a brand new car. Other than the wide transmission tunnel, the conversion was totally unobtrusive—until I planted my right foot against the accelerator pedal, that is. “The power came on evenly and didn’t seem to overwhelm the well-sorted chassis. While some 250 horsepower is a lot for a Spridget, the combination seemed to work really well, and this was one of the most satisfying conversions I’ve ever experienced. The steering was light and pleasant, the brakes seemed to work well and the handling was not bothered by the extra weight of the XKE engine at all. There was no axle tramp, either. Overall, it’s a very well-engineered and -sorted project that Aaron should be very proud of.”

owner: Aaron Couper, 42

engine: 3.8-liter Jaguar inline six-cylinder, bored and polished; AE 9:1 0.030-inch-over

driveline: 1967 Jaguar XKE four-speed; Toyota truck differential

suspension: Independent double A-arm with generic coil-over dampers front; four-link with

brakes: Triumph Spitfire rotors and MGB calipers front; Austin Mini brake booster; stock

wheels: Superlite 15x6-inch

tires: Bridgestone Potenza 165/50R15 front; Continental 175/55R15 rear

numbers: 0-60 in 5.5 sec. (traction limited); 1/4 mile in 14.2 sec