Some open critique on a technical/design basis:
I think they are all basic, but the last one with the blue piping is the best of the pack in my opinion.
Engine bay#1: Its just a pipework nightmare. Looks cluttered and messy, terrible for lag (although in practice the difference probably isn't all that huge from something with super short piping, its mostly theory that gives you a bit of a benefit in practive, but won't transform the whole response of the car just from reducing the pipe length). There is just no need for pipework to be that complex and messy on any turbocharged micra. 2" inlet pipe diameter is perfect, no need for anything more than this on a turbocharged micra. But there is definately still not a need for 3 (three!) of those hugely long alloy pipes to be up high in the engine bay like that.
Has front mount cooler by the looks of it - that's a great feature.
Engine bay#2: Terrible because it covers the cam cover. Pain for changing plugs and leads and absolutely not necessary. But that's not a major big deal, its easily removed. Don't like the evil looking bend down from that nice "TURBO" labelled pipe.
I can't quite work out the 3 or whatever air/oil separators that this setup has. What's the go with that?? A bit complex/cluttered to me. But mostly that harsh hacked bend looks terrible for flow - would create a lot of turbulence.
The intercooler looks pretty decent. Again would need to weight up how much boost its running, could be a bit laggy if only running low boost, if running high boost then looks good, but still be good to measure the pressure drop etc. Again front mount cooler - great feature.
Engine bay#3: This one looks the best of the bunch to me. Nice smooth inlet bends, the 3" diameter would help overcome the large number of 90degree bends, however I would much prefer to rotate the front of the turbo so its pointing downwards and then adapt piping and/or intercooler to suit the way the turbo is exiting - this would save about 3 of those bends. This is a very similar situation to what my car currently suffers from. I have a similar little group of 3 90deg bends coming out after my turbo exit, and that's what I'm going to fix up soon. Just mostly so I'm happier with the theoretical design, not sure how much I will notice any improvement in real life, but I'm positive some difference will be noticable. There's nothing wrong with having intake pipe larger than your exhaust, I would say the problem with this one is more that the exhaust is just too skinny full stop. The engine dictates the ultimate restriction in flow out of the exhaust regardless of the diameter of the intake pipe. You could have 5" inlet piping and the engine wouldn't put any more pressure on the skinny exhaust, the engine and ports in the head can only flow so much. 2" inlet diameter is ample on a typical T25 micra setup, but no harm having 3". The exits on a T25 are only 2" to begin with, so not much point expanding into 3" if the turbo is only 2" haha. My car uses 2" inlet piping everywhere and made 137kw@wheels.
This car has a front mount aswell, again that's a good feature.
Nice air filter positioning - easy to access and maintain, in a reasonably good path of oncoming air without sucking up too much dirt etc.
Has this car got an air/oil separator? If not, then it should have. That would be another improvement.
This car looks like its suffocating the wastegate exit very badly. That's no good, most cheap dump pipes just do that though. Good area for improvement. It looks like a pretty restrictive dump pipe when you combine the blocked wastegate dump with its narrow diameter.
The problem with turbo dumps being too skinny is that you're just restricting outright top end flow. Skinnier diameter exhaust piping increases gas velocity, its just that it won't have much of a top end outright flow ability because you use the full capacity of the small pipe pretty soon. On a turbo setup though, there are no downsides in having a larger exhaust dump diameter - there's no reason not to, the turbo acts as a restriction to give some back pressure, so behind that the pipe should be as fat as possible.
Again, depends on the aims of the car. If its meant to spool up quick and only run low boost, then it probably works great. But obviously for a big boost setup, it could definately be improved.
I think what most turbo micra's suffer from is the 90deg bend into the plenum and then the micra's less than perfect intake manifold. A side entry plenum is a good bonus to add into the equation.
Things that I'm not happy with on my own car would be:
- stupid three 90degree bends just after the turbo exit, going to get that fixed ASAP.
- I'm going to try a slightly narrower but higher cooler design and remove those 90deg bends all in one go and see how response is affected.
- New intercooler to also have smooth end tanks - the current one is just garbage, but it was built a long time ago before the market was flooded with great value coolers.
- Position of my air filter isn't good. I'm going to look at what I can do to either relocate it or build a heat shield surround for it.
Things I would go for in the perfect design:
- Front mount intercooler.
- Intercooler size only big enough to cool effectively without being too big to give excess lag.
- Intercooler to have very smooth end tanks.
- side entry plenum chamber
- 2" mandrel inlet piping is sufficient and gives you more room in the engine bay.
- decent fat diameter exhaust dump pipe, preferably double dump to merge wastegate gasses as smoothly as possible which minimises turbulence post compressor.
- smooth flowing manifold
- Minimal length of pipe possible while still allowing front mount intercooler (this what I'm revising on mine soon so my pipework is shorter).
- Tidy and simple air/oil separator solution without messy pipes going everywhere. And definately to have an air/oil separator, its a bad idea to have a turbo setup without one.
Hmm that's about all I can think of for now. Its great to see so many turbo'd micras appearing all over the place. There must be quite a few around in the world now.