On the face of it the two vehicles, the Haynes roadster and the MEV Exocet share a lot of common elements.
Both follow a basic concept - You are taking a donor car of some form, and using parts off of it which you cannot really manufacture at home (Uprights, engine, brakes etc) and transferring them to a new vehicle which different in some way, usually lighter by getting rid of most of the luxuries that road cars come with (Radio, heater, windscreen, roof, padded seats)
The core difference between the MEV and the Haynes roadster is the level of home fabrication which the designers think you can manage yourself.
MEV Exocet The MEV frame comes from serial car designer/lovely nutter Stuart Mills and MEV Limited - https://mevltd.co.uk/kit-cars/mev-exocet and is a more complex frame than you could build alone, featuring curved tubes and a specifically made frame which can bolt directly onto the MX5 roller skate.
Effectively you strip an MX5 down to this level and then bolt the ready made frame to the top using the existing mounting points on the MX5 chassis.
You re-use the MX5 wishbones, suspension, leave the steering rack and drivetrain in place with the bolt holes from the MEV chassis just lining up with the bolt holes on the MX5 base. A few things needs to be rerouted, the fuel and brake lines for example and all of the wiring, and the fuel tank has to be relocated and bolted to the new chassis, but for the most part, its a bolt on. If you had a running MX5 to start with, you’re basically good to go now*
*Okay you’re about 60 hours away from ready but, you get the idea.
The disadvantages of this approach is that you can only use an MX5. You have to specify which Mk of MX5 you’re using to MEV when you buy the frame and the final size (but not weight) of the car stays the same as the wheel base is the same as the original car.
You can however easily apply for an “Age related plate” as you have re-used a lot of the original parts. Your collapsable steering column is already in place and fit for the IVA and you dont have to work out which parts are compatible with each other, and more importantly you don’t need a welder.The most advanced tool “needed” is an angle grinder, though obviously if you have access to a more extensive tool box, it gets easier.
Haynes Roadster The Haynes Roadster is a build by the book kit car, designed to be built using a Ford Sierra. To say you start with less ready fabricated parts is an understatement, the starting point is - Build a table to build your car on:
This is effectively a rigid and solid base which is level and square and a specific size. This size will be used to measure other elements from the center to keep everything square, so its a good idea to mark out a centre line etc early on.
The build table can be a simple frame on the floor, though you’re going to bend over a lot and its hard to get level unless your floor is level. This wheeled frame setup obviously takes more effort but in the long run seems a sensible thing to make.
You then start to cut parts out of 25x25 mm box section to the specifications of the book.
So far this all seemed fine and easy, just follow the book right? Well the issue is that the book requires us to have a Ford Sierra donor car. All of the measurements are designed to hold Ford uprights, to make space for a Ford Pinto engine and gearbox and to hold the rear differential of a sierra. The MX5 donor throws a curveball here, the engine is a different size, the uprights are different widths and the rear diff is a different shape.
What we have now then is “Book spec” - Those elements which are by the book, and “Hope someone on the internet has done it before so we can copy it spec”. We are lucky in that the frame we have is mostly cut to where it needs to be, but not entirely. This saved us many hours of mm precision cutting but means that now we dont know which sections of the frame (Made by Talon Motorsports, no longer in business) are intentionally modified to make them fit, or which just weren’t cut right. We also have a set of ready made wishbones to copy which the original maker made to his own spec (Ill upload the dimensions for these later):
Suffice to say this is a very different build project versus the Exocet, but the plus sides are you can use different parts. The owner of my frame originally is planning a build with a 1 litre engine from a Kawasaki Ninja, but using the MX5 Differentials, uprights and steering column. Mine is a straight MX5 build. Some people have mounted V8 rover engines in them, you need to make mounts and brackets to place everything yourself but the vehicle has no limit other than its physical dimensions on what it can hold.
The downside is time and knowledge. If you don’t know what can fit with what, or which parts you need, you’re going to be doing a lot of googling and looking at other peoples builds for clues. The frame alone to weld up has taken me the best part of 60 hours so far, the whole Exocet build is possible in 100 (So they claim) so this is a long game.
But hey, lockdown, what else are you going to do.
Which one to choose
It’s safe to say the Haynes roadster is more work, harder and you’re battling against the book being 15 years old and based on a car that no one really owns or has anymore. This leaves you needing to research more and find the right parts, but gives more freedom to choose parts.
Sadly most people are unlikely to ever build two cars, but in reality an ideal situation would be to build the Exocet and then once you’ve learned some lessons (lessons I learned, service and overhaul your clutch before you refit your engine), move to the Roadster. The alternative is to hit up someone like MK sports cars or GB sports cars and buy the frame and such from them, and then it’s in theory much the same as the Exocet builds.
So, if you cant weld, buy a frame, if you can weld and are mechanically minded, get the book and do it yourself.