whats my Horsepower gain with these mods?

A fatter exhaust system helps performance and reduces heat build up that hastens the demise of the exhaust manifold. a 2 1/4" will benefit from a good turbo type muffler.

The next best thing is buy a high output coil and a good ballast


Fancy, expensive ignition systems are a waste on these engines because, with their long stroke, it is not safe to run them fast enough for them to make any difference. A modified cam will give a lot of power increase per dollar, but don't get crazy with this because you quickly start losing low end performance as the cam gets more radical.

The 170's relatively short stroke allows it to rev high and the 170 is the engine to use if you will turn over 6,000 rpm frequently. a 170 CID slant six HyperPak would deliver a comfortable 182 hp, and turn 8000 RPM if you kept the cam lobes lubricated.

If it's performance you're after, another thing you should seriously consider is swapping the rear end to a shorter ratio- 3.23 was standard, though 2.79 was an option for highway mileage (unlikely with a 170) and 3.55 was an option for performance. Both these two are not uncommon in the 7 1/4" rear ends which are standard behind /6 cars.with a 3.55 rear end, and while the tradeoff is a lower top speed, the reason it was used was to leverage the slant six's torque. It's amazing how many people think right away of hot rodding their engines when a rear end ratio swap will make such a greater effect on their seat-of-the-pants power.
~~~~super 6 swaps~~~
Get both the intake and exhaust manifold together and the throttle linkage is different, so be sure to get everything between the gas pedal and the cylinder head. The Carter BBD is a good 2-bbl carb, easy to rebuild and tune, and will give great performance. This is also how to spot the super six; the air horn is bigger than a 1bbl, so the old air cleaner won't fit. If you're not sure what it looks like, go pop the hood on any 2bbl V8 mopar, where it's the standard item. (The carburetor was somewhat different from the one used on V8s).
The 170 had a shorter stroke than the 225, but the same head and valves. Low end torque was less, but ultimate power was the same. In addition, with the lower block height it was a sturdier engine, and with the shorter stroke could rev higher with less chance of an rpm failure. The Achilles Heel was the cam lobes.