Miata power makes this Porsche 914 extra special

By Zachary Mayne
Dec 9, 2023 | Mazda, Porsche, Miata, Mazda Miata, Porsche 914, 914, Porzda | Posted in Features | From the Aug. 2013 issue | Never miss an article

Photography by Zachary Mayne

[Editor's Note: This article originally appeared in the August 2013 issue of Grassroots Motorsports.]

Transplanting an engine from one car make into another is nothing new. Since the advent of the automobile, imbuing a car with additional power and ending up with something unique has been widely practiced.

Since the introduction of the Porsche 914 more than 40 years ago, numerous copies have received engine swaps–and the new powerplants haven’t been exclusively from Stuttgart. There are a few reasons why Porsche’s mid-engined machine is a popular starting point for a hybrid. For one, they’re still relatively common and also happen to be pretty inexpensive in today’s market. You can buy a decent rolling chassis for a grand or less. Spend a few bucks more, and it’s possible to have a rough but drivable example.

The 914 also boasts an optimal mid-engined layout. However, unlike some other cars with similar chassis configurations–the Fiat X1/9 and Toyota MR2 come to mind–the Porsche has a relatively large engine bay. 

They’re also pretty light. Add in some real power–whether from a Subaru WRX or a NASCAR racer–and the 914 quickly turns into a missile. At the same time, chassis balance remains good. 

History and Hillclimbs

New Mexico car enthusiast Jeff Watson agrees that the 914 makes a great home for an alternative powerplant. In his case, it’s a Mazda Miata engine that powers his lightweight, Arctic Silver track day special.

In high school, Jeff drove a 1968 Dodge Charger, which is a fun, vintage muscle car in its own right. But as he discovered during his first autocross, the Charger was no race car. “I autocrossed that car exactly once,” chuckles Jeff. 

The Charger was soon replaced with an AMX that was built to run in SCCA Solo events and hillclimbs. When Jeff wasn’t studying economics at Boise State University, he was driving that AMX up Freezeout Mountain, where the nearest hillclimb competitions were held–and are still held today. 

After graduating from college, Jeff started looking for a Porsche 914 to race. “The 914 was chosen because it was the most affordable mid-engined sports car,” says Jeff. “I’m one of those people who believes real race cars have their engines in the middle.” In 1981, he bought a blue 914 that he soon turned into a race car, and that example was quickly followed by another.

Porsche 914s became a recurring theme in his car-related life. The saga has recently culminated in the 914 pictured here, which Jeff affectionately refers to as the “Por-zda” thanks to the Mazda Miata engine under the deck lid. 

However, the car is notable for far more than its Japanese transplant. Jeff has infused this car with every ounce of knowledge and skill he’s learned in 35 years of hillclimbs, road races and SCCA events—including his 1992 SCCA National Championship win in a C Mod Lola Formula Ford.

Jeff purchased this 914 in 2004. He’d recently sold a Formula Ford race car and was suffering from project car withdrawals. “I couldn’t not have a project,” he admits. 

He spotted the 914, a ’74 2.0-liter with black paint, in the local newspaper. “It looked good from a distance, but the paint was cracked and the motor was worn out. It wouldn’t do anything more than idle.” The seller was a young man storing it in his dad’s garage. Dad wanted the car gone. 

The 914 ran better once Jeff did some work on the carbs, which were missing the auxiliary venturis. He drove it for a couple of years with the old, wheezy 2.0-liter flat-four before starting on the transformation that would result in a radical, track-only beast. 

The first step was an engine transplant. Jeff says the organ could have been anything from a later Porsche 911 engine to a more modern WRX boxer. “None of this is new ground with the 914,” he admits. “The choice of a Mazda BP is somewhat unique, but engine swaps of all sorts have been done on 914 chassis from the very beginning. The Mazda BP-series motors are light, strong, have good power per displacement, are reasonably priced, and have good parts availability,” notes Jeff. “Very few of those things can be said about a Porsche motor.”

Once a good, running engine was sourced from a junkyard, the next step was making it work in the mid-engined Porsche chassis. For simplicity’s sake, Jeff elected to retain the 914’s original 901 five-speed gearbox rather than try to fit a new one to the chassis. “Kennedy Engineering makes an adapter for the transaxle and flywheel/clutch assembly, so I fabricated a new engine mount bar,” he explains. 

Halving Carbs

Prior to the 914 build, Jeff had become interested in motorcycles, specifically Ducatis. As a result of his motorcycle ownership, Jeff became exposed to the modern carburetors fitted on bikes like the Ducati 916. He decided to install motorcycle carbs on the Miata engine, and settled on Keihin FCR flat slides–the same type popular on race-built superbikes at the time. 

That decision led to a whole new engineering project. “We didn’t have any idea if the carburetors would even work,” admits Jeff. Delivering the proper fuel pressure to the Keihin carbs was one of the big stumbling blocks. 

Since they’re designed to work on a motorcycle, the fuel is gravity-fed to them. “They don’t work like the more common Weber carburetor, which led to a lengthy learning experience tuning them,” he notes. 

Repeated experimentation with a fuel pressure regulator eventually allowed Jeff to determine the right fuel pressure: a very low 1.0 to 1.5 psi. The carbs are fastened to the engine with a custom billet aluminum manifold and breathe through a single large air filter. An electromotive crank-fired ignition system was installed to ensure that the engine has sufficient spark. Jeff used an Innovate LM-2 wide-band air/fuel ratio meter to dial in the maximum horsepower.

The Next Level

Like most projects of this scope, the 914 build has gone through numerous phases. After the Por-zda was driven on the street, Jeff decided to take it to the next level, which meant the project changed trajectory from a fun street car to a far more radical, track-only machine.

Taking a page out of Colin Chapman’s playbook, one of the primary objectives of the build was removing as much weight as possible. In this case, the final weight of the car comes to 1775 pounds with a driver and full tank of gas. 

Ham Fab, a small specialty shop in Edgewood, New Mexico, performed the majority of the chassis and suspension work. Very little of the 914’s original chassis was retained, with the exception of the passenger compartment. An eight-point roll cage ties the front and rear shock towers together in one rigid unit. 

The chassis sheet metal from just in front of the shock towers to the front of the car could then be removed entirely. Normally, this would not be possible since the 914’s A-arms bolt to the chassis near the nose of the car. The solution was having a custom set of A-arms built that are reversed, so they bolt to the chassis toward the center of the car. “The point was to reduce the weight beyond the wheelbase,” says Jeff. “And this also places the suspension loads on the strongest part of the chassis.” 

The front suspension consists of Ham Fab threaded coil-over struts that use single-adjustable Koni struts and 911 spindles. These spindles were installed higher on the strut than the stock spindle placement. The relocated spindles ensure that the 914 can be lowered significantly without altering the original roll center of the chassis. 

An adjustable Ham Fab hollow anti-roll bar is also used at the front. Adjustable camber plates and 911 Turbo tie-rods round out the changes. Brakes consist of slotted 911 rotors that are clamped by four-piston Wilwood calipers, Porterfield brake pads and braided steel brake lines. 

At the rear of the Porsche, much of the original chassis and sheet metal behind the driver’s compartment was removed. A custom cradle was designed and fabricated to support the engine and Porsche 901 transmission. The stock 914 trailing arms were beefed up, while the stock bushings were replaced with zero-compliance Delrin plastic bushings.  

The rear suspension is similar to the front in that it uses adjustable coil-overs with single-adjustable Koni shocks. There is also an adjustable anti-roll bar. Adjustable toe links were installed, which were braced against the chassis to prevent the suspension’s toe setting from changing during aggressive driving.

Custom Body

The majority of the fiberglass body draped over the 914’s custom chassis was sourced from American International Racing. The engine lid came from Jeff’s stash of parts, while the fiberglass Targa bar and featherweight door skins were from Ham Fab. An underbody diffuser was fabricated and installed, and Jeff reports that it has greatly increased the car’s stability at high speeds.

Inside the 914 cockpit, it’s all business–just a grippy race seat, suede steering wheel and other necessary controls and gauges. 

With the build nearing completion, the original junkyard engine was replaced with a more powerful, purpose-built one by Soren Loree from Miata Specialists in Albuquerque, New Mexico. Higher-compression Miata pistons were installed in a stock bottom end. The heads were cut down to further increase the compression ratio, which ended up at around 10.5:1. A set of mild performance camshafts were also installed. The header was designed and fabricated using engine simulation software so that it showcased an optimal design.

“The engine breathes so much better through the manifolds and header,” says Jeff. The crank-fire ignition system mounted on the original Miata engine was simply moved to this one. The new engine pumped out an impressive 165 horsepower at the rear wheels–not bad considering the engine’s tune could still get more radical. 

The cooling system was also upgraded from the small, front-mounted radiator that had provided cooling to the first engine. Ron Davis Radiators made a custom radiator to Jeff’s specs and installed it near the middle of the car, right in the passenger-side footwell. Custom aluminum ducting delivers fresh air. The ducting then continues after the radiator and leads into the engine bay. 

“The ducting reduces the potential for lift and greatly reduces the drag created by cooling,” notes Jeff. “We tried to keep the drag to a minimum.” The cooling setup is also very effective: “The engine never runs above 195 degrees, even on a hot day.”

Future Dieting

While the Por-zda would no doubt be an impressive weapon as a full-on race car, Jeff wants to steer clear of road racing. 

Instead, he plans on honing his driving skills behind the wheel of his radical 914 during track days, autocross events and time trials. Future plans? Jeff keeps it simple when he quips, “More power, less weight!” That will probably mean either forced induction or a larger engine down the line, which could be anything from a V8 to one of Porsche’s larger flat-sixes. 

Though for the life of us, we can’t figure out how he plans to remove any more weight from the car.

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FPZguy New Reader
1/9/18 3:44 p.m.

Beautiful car and well thought out build.  I've taken a similar approach to my 240-Z build.  Although it weighs considerably more (1,875 lbs.) it makes a little more HP with the mildly prepared 280 engine.  Removing weight is the cheapest way to increase overall performance (acceleration, braking, turning).

TexSquirrel New Reader
1/9/18 3:48 p.m.

Very nice!  

Robbie GRM+ Memberand PowerDork
1/9/18 4:32 p.m.

Yes, excellent!

accordionfolder Dork
1/9/18 4:52 p.m.

This is easily one of my favorite cars now. So little dogma, so much pragmatism. 

10/10 would read again. 

Polopharm New Reader
1/9/18 8:18 p.m.

What is the vertical metal square tubed thing to the right of the steering wheel?  My first glance I assumed a shifter. But either way seems to me would be a safety/ tech inspection issue. 

 More power less weight solution - Hayabusa 1300!

Title could be "tube framed autocross car with some Mazda and Porsche bits and pieces"





mistanfo UltraDork
1/12/18 11:24 a.m.

Hayabusa engines might make more horsepower, but the article states that he wanted availability and aftermarket. Sure, it exists (Hayabusas cans make stupid levels of power for not terribly stupid amounts of money), but how available, inexpensive and reliable are they? Also, what kind of torque levels are they seeing? I know my FJR1300 is around 140hp and 99 ft. lb., figure the Suzuki is higher on HP but maybe not on torque (stock v stock)... good for a light car, it would get worse with something heavier.

pres589 PowerDork
1/12/18 11:42 a.m.

When I saw the title I assumed rotary 914 combination.  Was not expecting a BP.  Cool car.

JimMurphy New Reader
1/26/18 5:27 p.m.

After working on an E Mod Solo 914V8 through two frustrating years I traded it for the E Mod solo yellow Jeep.  I wished that I had known Jeff BEFORE I took on that project.  One thing that I would have done IF I kept it was to significantly reduce the torque on the Chevy 350ci V8 by replacing the crank with one from a 265ci Chevy V8 - the excessive torque made it hard to drive AND it broke a lot of stuff along the way.  With its light weight, high torque is not needed.

motomoron SuperDork
6/21/18 12:08 p.m.

In reply to mistanfo :

I've raced a stock Hayabusa powered SCCA C sports racer / P2 sports racer since 2012, and the engines are as reliable as anvils. I'm still using wet sump lubrication, and motors look new, and have perfect compression and leakdown after 2 full seasons. I imagine in a track day environment where you're leaving a few percent on the table they'd go a long, long time, and if you manage to pop one, (checks his watch)...
some kid just totaled their 'Busa just now.


DesmoDog New Reader
6/21/18 5:38 p.m.

Not for nothing but the Ducati 916 didn't use carbs. It was fuel injected just like the 851 and 888 Superbikes before it. The Keihin FCRs were/are the hot ticket aftermarket carbs for the lower tech two valve, air cooled twins used in the Monsters and Super Sports of the day. 

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