A question of balance

Why V6 power?

The MXV6 was originally conceived as a one off. A personal challenge. A project to prove what was thought to be true; whilst effective, a forced induction inline-4  just lacked the character and sophistication we knew the car could exemplify. But if we were to replace the engine, what with?


At the time, we were long-term employees at Overfinch; where V8’s were scattered around the workshop and the knowledge and experience of the workshop engineers were there to be tapped. But we couldn’t help feel that a V8 was overkill and would somehow overpower the little sports car (literally and figuratively). We respected the MX5s purity and wanted to keep all that was good about it and enhance it. This wasn’t simply the pursuit of power and performance figures; the result had to feel right.


A sweet, high revving 6-cylinder engine would surely have the characteristics we were looking for? An inline 6 would be too long, so the hunt for a suitable V6 was on. After extensive research, we settled on the Ford Duratec V6; more specifically, the Jaguar S-Type 3.0l.


The Duratec V6 has an impressive pedigree; originally a Porsche design, then Ford, with input from Cosworth. As well as powering humble saloons, derivatives of the Duratec V6 power more premium cars from the Mondeo ST24 and ST220 to the Noble M12, Morgans and Marcos’. The Jaguar version looked like being the best with a forged crank, DAMB tappets (Direct Acting Mechanical Bucket). It is oversquare with a bore of 89mm and a stroke of 79.5mm, so is a high-revving engine that develops max power at 6750 rpm; features that have made it a popular choice among race engine builders.

Mountune will build you a 420hp version for racing. Such engines have campaigned successfully in Sports car racing and substituted the fragile and expensive 6R4 engine in group B rally cars.


This had to be the right engine? It ticked all the boxes plus, almost unbelievably, it was reliable, cheap and plentiful. Building the V6 MX5 wasn’t, however, without its challenges. It’s not the most compact engine with chain driven quad cams and VVT. But it is all aluminium, so it was in with a good chance of being no heavier than the cast iron MX5 lump it would be replacing; so important in keeping the critical weight distribution right.


There was simply no way of knowing if this would deliver on the vision… without building it.


The full build story of our V6 MX5 is documented elsewhere but after several iterations, false starts and much perseverance the proof is here. It works. And by that we mean it delivers on the vision. Light, high revving, sweet, tractable and of course oh so tuneful. It is a balance that suits the car beautifully. It takes everything about the original MX5 and somehow resonates with it; elevating the whole experience to a new level. Not just the performance. It’s quick, sure it’s quick but much more significantly, it has soul.

Engine specification

Jaguar AJ30 / Duratec 30 

  • 2967cc 60deg V6

  • Direct-acting mechanical bucket (DAMB)tappets

  • Dual overhead camshafts

  • 4 valves per cylinder

  • 89mm bore, 79.5mm stroke

  • Variable valve timing

  • 240bhp at 6750rpm 

  • 221lbft at 4100rpm

Tested at 270bhp using Rocketeer Exhausts, Induction, & ECU




Jaguar AJ30 used in Rocketeer MXV6 V6 MX5 engine conversion
Click play to hear the Rocketeer MXV6, V6 MX5

Production MXV6

Third generation design

Every component used in the prototype engine conversion has been analysed, redesigned, improved or eliminated but this time with a view not only to improvement but also to repeatability - batch production.

  • Gone are the ITB’s. In their place are plenums for better drivability, cold start convenience and proper idle control. Due to packaging constraints the ITB’s are compromised. The plenums will breath better and deliver substantial performance and efficiency improvements over the ITB’s

  • The front sub-frame has been totally redesigned to accommodate the engine, but it will also be significantly stiffer, lighter and cheaper to manufacture than the tubular item it replaces

  • Engine mounts are revised to better isolate unwanted vibrations and locate the engine more accurately

  • The sump is now a bespoke aluminium casting and as such is a structural part of the engine as originally intended

  • The adapter plate is completely new; repositioning the starter motor to improve packaging and retain the standard MX5 clutch slave cylinder

  • The new MBE ECU is bespoke to Rocketeer. It’s a ‘plug and play’ solution and is compatible with all existing instrumentation

  • The exhaust has been designed from scratch to improve flow and further enhance the acoustics

  • In fact, the only part that hasn’t been changed since XP1 is the alternator drive pulley.