More than 800 Honda Accords roll out of Honda’s factory in Marysville, Ohio, every single day. It is a traditional car factory in every sense, a plant that's dominated by speed and efficiency.
Next door, however, is a new plant tasked with doing something that Honda hasn’t had to do for a decade: build a truly low-volume sports car. Around 100 staff are tasked with the build of just eight to 10 Honda NSXs per day in what is, compared with traditional car making, a relatively labour-intensive, methodical and surgical build process. The factory is cutting edge and purpose built, there are no walls and every single build stage is open to view.
So, here’s how Honda builds a supercar:
The metal that constitutes the NSX's aluminium spaceframe is delivered to the factory already shaped, but the frame itself is welded on site. That necessitates nearly a dozen jigs like these, which are in turn fitted to one of three robotic welding booths.
The weld booths are robotised to ensure consistency; and Honda claims its NSX chassis are welded to within 0.1mm accuracy. That means that, unlike other supercars Honda declines to mention by name, no post-welding machining is necessary; say, around the suspension components. The way the NSX spaceframe comes out of the booth is the way it's built.
Here’s a completed welded spaceframe. A carbonfibre floor and roof panel is yet to go on. This is all aluminum bar the A-pillars, which are steel. That complicates things - it means they have to be bolted rather than welded in place, and they are coated to resist corrosion. Honda took a late decision to use steel because it couldn’t get good enough forward visibility with aluminium A-pillars, which have to be wider to provide the same strength.
To make sure each body has been assembled to within tolerances, more than 2700 points of data from 500 different locations on the body can be measured by this coordinate measuring machine. This static one in the middle of the factory is accurate to within of 30 microns - less than the width of a human hair. Honda also has two portable ones that can take to the factory floor, measuring to within an accuracy of 50 microns.
Once checked, the bodies are off to be dipped before they're coated and painted. There are six tanks like this, none of which look like ones you'd want to fall into. It's a pretty industrial-looking process - the noisiest in the factory - but Honda claims most of the liquid is recycled.
Most of the NSX’s body panels are painted by robot, with around four gallons of paint - in up to 11 coats - making it onto the body. Some bits are painted by hand, such as the front grilles, which arrive finished as black plastic, but are then painted black again, mysteriously.
While the body is being painted, the hand assembly of each chassis begins, in the kind of order you might expect. Electronics and hardware first, with the interior coming towards the end.
Every nut and bolt is tightened to a pre-set torque by a wrench that's wired up to a computer. So if anything goes wrong in future, Honda will know where, when, and to what torque setting anything was tightened; and whether other cars might be affected in the same way. Even so, every bolt into aluminium is hand-threaded for the first few turns, to make sure there’s no cross threading in what is delicate (for a metal) material.
The NSX’s engine is also built in the US, but not in the same plant as the car. It’s a similarly labour-intensive process though, which culminates in each 3.5-litre, twin-turbocharged V6 sitting on a test rig undergoing a 45-minute test/running-in cycle.
Honda uses as few robots as possible in the assembly area: in fact, there’s just one, used to apply sealant. Even here, where the body is dropped towards the engine, and then the engine is raised on a table for the last few inches, the process is controlled by hand. There’s only 3-4mm of clearance either side of the motor, and it takes 62 minutes to install the engine in the chassis.
After the mechanicals comes the body fitment. Honda starts with one door, then fits another panel and chases the gaps around the previous panel, and so on. “It’s like laying tiles,” says a manager.
Honda has filed for 12 patents around the NSX’s build process; six of which are in quality control. After the body has been fitted, the car is pretty much finished; from this point on it's a serious proofing process.
Wheel and tyre alignment and ride height are checked on this jig: the car’s only raised to make it easier to work on. First-generation NSXs were exceptionally sensitive to being out of alignment.
How do you calibrate the accuracy of your wheel alignment machine? With a rigid test chassis like this, of course. You won’t knock it out of alignment very easily.
After being aligned, every NSX has its corner weights tested, to make sure everything is where it ought to be. Assuming everything was put in the right place and it’s the right ride height, it will be. If it's not, something quite serious has gone wrong.
Each NSX is raised on a ramp for an underbody check. It’s unlikely there’ll be any damage under there, but this is a chance to make sure nothing has come undone during the dyno test. Every single car is dyno tested on rollers: first there's a run-through to check power delivery, then to calibrate the speedo, then to check brake pressure and a final one to test park-brake strength. It takes around two minutes.
Then it's into an extremely shiny room, where the paint is inspected for imperfections, however small they might be. During the build, when assembly workers are reaching over the car, they put soft leather covers on the bodywork, which, in theory shouldn’t even put the finest micro-scratch into the paint. After the paint check, it's into a water spray booth to check for leaks, and then the completed NSX is out of the door.