prodarwin said:
Regarding reliability, I haven't personally turbocharged one, but watching those around me do it, it seems that even with the same vehicle they can range from A) very reliable to B) very unreliable.
I'm not talking grenading-engines unreliable (though that is absolutely possible), or grenading transmissions (almost a guaranteed outcome in certain applications), but more like "little E36 M3 keeps going wrong and costing track-time, autox runs, etc". Intercooler piping is routed questionably and pops off. Overheating problems. Broken exhaust studs, cracked manifolds, wiring issues, etc.
Most of that is the engineering of the kit. If you go the cheapo DIY route, you're going to have to do more of that yourself, and you're going to have those niggling teething pains as you discover weak points. It's no different than building your own track car and learning where the limits of things like wheel bearings and subframes are - or you build a car with lots of support and talk to people who already know.
We've had the IC piping pop off problem. Solved it by going to a different design of monolithic IC piping that has fewer failure points and uses a type of silicone hose that's grippy on the inside. But if you're making your IC pipes out of chunks of metal tube connected with pieces of hose, this will be a problem.
We've had the broken exhaust stud problem. Solved it by going to better locking fasteners and custom-made Inconel studs.
Wiring is almost always an installer problem.
We've seen the cracking manifold problem on other kits. On a Miata GReddy kit, you had to cut slots in the flange between the runners to allow for thermal expansion. Welded-up tubular manifolds crack as a matter of course. Big chonky logs built out of thick wall weld-els, not as much.
Overheating is due to poor coolant routing (the common Miata routing puts very hot water from the turbo right back into the block, bypassing the radiator), the fact that your cooling system has to deal with more heat and the fact that you're putting more heat into the air in front of the radiator thanks to an intercooler. That requires correct engineering, upgraded cooling and good airflow management. All stuff that a good kit designer will take into account but that you'll have to learn about bit by bit as a DIY builder.
It's also mechanical empathy on the part of the operator. We turbocharged our 3.4L T100 shop truck years ago, doing terrible things that would make a Toyota engineer weep. Added about 25% more torque. A single turbo on one bank of the engine. Fuel management by rising rate fuel pressure. No real timing adjustment. Stock clutch. But it held up to towing an overloaded trailer across mountain passes over and over without any sort of failure, mostly because the drivers knew how to keep it out of the detonation danger zone. Not a vehicle you'd loan out, but it was able to do the job if properly cared for.
