Originally Posted by Spectre722
I assume however, that since the projected horsepower is the same with this turbo for both the 1.6L and 1.8L engine that a 1.6L may not make 140 rwhp with this turbo.
Quoted HP numbers are somewhat fungible, with there being quite a lot of variance from one dyno to the next, and from one car to the next.
In general, an otherwise stock 1.6 and an otherwise stock '94-'97 1.8 will probably put out fairly similar numbers on a non-intercooled Shanghai S kit. Neither engine has a knock sensor, so you need to be conservative with the timing. The later engines have a slightly lower static compression ratio and slightly larger fuel injectors, so all else being equal, they will tend to be able to support slightly higher pressure ratios before becoming knock-limited for a given spark advance, but this is definitely a gray area in terms of safety margin in the absence of competent engine management. If you're going to tune on the side of safety, I would expect the difference in power for these engines post-turbo to be roughly comparable in magnitude to that of their naturally-aspirated selves; around 10%, give or take.
That said, the ultimate power limit for any stock Miata engine (90-'05) is about the same, being a function of the OEM connecting rods tending to fail at around 250 WHP for all years. It takes a bit more boost to get the 1.6 engines to that point, but if fuel and ignition management and intercooling are brought up to task, they can get there.
If you are starting from scratch, then a 1.8 car is always a better platform to build from (it already has the 7" ring gear, for instance), and if you are electronically inclined, the '99 and later cars are the best of the lot.
That said, if you already own a 1.6 car in good condition with a strong engine, and have some degree of investment already in it, there's no reason why it can't be turbocharged. Worst-case, you'll have to buy a new exhaust manifold should you ever decide to upgrade.