There have been quite a few V8 MX5 projects in the last few years. There’s been the well documented video series from Tom’s Turbo Garage with his Project Thunderbolt, not to mention the well established Flyin’ Miata and Monster Miata who both provide kits and parts to install the LS or Ford Short block V8 into the MX5.
The V8 Miata forums are also a very useful resource, with many contributors documenting their own engine swaps with their various build threads. The only fly in the ointment with these resources is that they are predominately US based, where LS or ford V8s are relatively easy to come by, and pretty inexpensive at that. Here in the UK, however, a crate LS3 from the likes of RoadCraft or Parts World Performance won’t leave you with much change from £6000 after VAT and shipping is dealt with. So what would be a suitably inexpensive and relatively easily available V8 over here?
After much research, digging and talk, especially surrounding other UK based V8 MX5 engine swaps, I settled on the idea of the Toyota build 1UZ which is a 4.0l, quad-cam V8 as used in the Lexus LS400 and, to a lesser extent, the Lexus Soarer.
The reasons for this over other options such as the Rover V8 is down to power, robustness but, more importantly, shape and size. One of the challenges with the MX5 is the height of the engine bay. It’s not a very tall space, which is why the LS3 and other push-rod V8 engines seem to fit so well, as they don’t have the height of an engine with overhead cam-shafts. The MX5 engine bay isn’t short on width (with some tweaks and trimming giving another couple of cm each side if you’re happy with a cutting disk and welder), and it’s pretty decent on length, but it’s not that tall.
The 1UZ however, despite being a quad overhead cam engine is surprisingly compact and light. Super7thHeaven did a comparison of the 1UZ and the Rover V8, and found that the 1UZ is smaller, lighter and more powerful.
Ideally, I’d prefer an earlier, non VVTi engine as it’s less complex and easier to make further modifications such as force induction (hey, no harm in keeping my options open!), and with 260bhp in stock form, on the stock ECU, it’s still a notable increase over the 225bhp my supercharged 1800 MX5 engine was putting out.
To those of you who are thinking “wow, a hulking big V8 in a tiny light car, that’s going to upset the handling!”, consider that the standard MX5 engine has a cast iron block, whereas the 1UZ is all aluminium, so the weight penalty is far less than expected, perhaps about 30-40kg, but there are other options for weight loss that I’m considering that should make the end result nigh on identical to the stock weight
So, 1UZ it is, now where to get one?