Having said that, I'd like to point out some positive aspects of putting a turbo on a /6, first as an alternative to a normally-aspirated small block V8 buildup, and also as an alternative to a normally-aspirated /6 buildup.
In the first instance, a large percentage of small block V8 A Body buildups result from obtaining a car with a /6 already in it. In that case, the existing engine must be replaced with a 273, 318, 340, or 360 that must be bought, usually.
If you already have a 225 in the car, that's the first expense that can be avoided, and it can be considerable.
From the standpoint of turbocharging a 170 or 198, I'd personally avoid that option just on the "bigger is better" standpoint. Just my personal preference.
There are some things about the turbocharged /6s that are not self-evident, but are things I have become aware of by reading posts made by successful /6 turbo racers. Some of these factors are cost-related; for instance:
For reasons not clear ro me, turbocharged /6s seem to like rear axle ratios that are the direct opposite of their normally-aspirated cousins, both 6 and V8... that is, they seem to perform better on the drag strip, with 2.76:1 rear gears than, say, 4.10s. Sounds crazy, but that has been proven to be the case on at least two of my favorite F-A-S-T /6 turbocharged race cars.
That accomplishes two things: For one, you have a rear axle ratio that enhances drive-ability on the highway, by keeping the rpm’s down, and doesn’t need to be swapped out for a deep gear when you get to the drag strip.
Secondly, since you already have a “one-size-fits-all” ratio in place, you won’t be needing an 8.75” drop-out-center-section rear end (and, I don’t have to tell you how much money they are getting for A-Body 8.75” rears, these days.) So, you can opt for a much cheaper, easier to find, 8.25” unit that will likely already have a desirable ratio installed.
That’s a considerable saving, right there.
The ‘6 turbocharged engines I have seen described, don’t seem to need to turn a lot of RPMs to make good power. The motor in Ryan Peterson’s car (2,700 pounds) has run 127 MPH, and never sees the far side of 5,500 RPM. It is around 500 horsepower, and runs 10’s with a 727 transmission.
That penchant for high performance at not many RPM’s means that the valve-train doesn’t need to have a lot of valve spring pressure, so mostly stock parts (with the exception of the valve springs, themselves) work very well.
No expensive roller rockers, thick-walled pushrods, or titanium retainers required.
Turbo cams are by nature, MILD, so expensive, hi-stall torque converters are not necessary.
This also enhances around-town drive-ability.
Most turbochargers homogenize the sound waves in the exhaust to the extent that usually, a muffler is not necessary.
More money saved…
A high-voltage ignition system for reliablehigh RPM operation is not necessary. The one on our car is an MSD 6-AL, but I’m betting an orange box would work just fine due to the relatively low-RPM operation.
Headers are a wash; you can, if you want, just use the cast iron /6 exhaust manifold attached to a turbo mounting flange and save the cost of headers, but a lot of folks think that this system can be improved upon with a tubing header.
Engine longevity should be good with the turbo /6 due to the fact that you don’t have to wind it up like a 8-day clock for it to be fast. RPM kills more engines than boost…
Just some things to ponder….