:
: I have been talking to a number of different
: people lately with regards to my turbo
: project, and I have found that quite a few
: are suggesting using a 170 over the 225. I
: thought I would pose this question here. I
: am quite intrigued by the 170's ability to
: rev to the moon, but does this overcome the
: size difference of the 225? Then of course
: there is the 198, which actually has an even
: higher rod ratio than the 170. This motor
: will be done properly with a large
: intercooler and fueled by propane, so it
: should handle lots of boost. What are your
: suggestions?
: Tom

: I've been pondering that a bit myself - mostly
: "on paper" and with Desktop Dyno.
: I could use some guidance from people who
: have some real experience building all out
: performance sixes. As near as I can tell,
: the biggest effect you're going to see if on
: the shape of the torque curve, if you're
: building for a specific horsepower. Here's
: how my line of reasoning goes: 1. The amount
: of power an engine makes is directly
: proportional to the rate at which it can
: combine air and fuel.
:
: 2. The above rate is equivalent to how many CFM
: of air the engine can pull in, assuming the
: fuel delivery can keep up, which it almost
: always can.
:
: 3. All slant sixes use the same cylinder head
: design, and can use identical intake and
: exhaust systems with identical flow rates.
:
: 4. Since the bore and number of cylinders is
: the same, both a 170 and a 225 would need
: the exact same piston speed to pull in a
: given CFM of air. This means they would
: place similar stresses on the internals and
: demand equally tough bottom end components,
: whether you're talking a 225 turning at
: 6,000 RPM or a 170 screaming at 8,000 RPM.
: All of the forged crank /6's use the same
: pistons and bearings, and I don't see any
: reason to assume that one motor has
: considerably stronger connecting rods.
:
: So, for equal amoutns of horsepower, a 225 and
: a 170 should be able to use indentical
: bottom end components, identical headwork,
: and identical intake and exhaust systems.
: The only difference would be the camshaft,
: and wilder grinds normally aren't
: significantly more expensive. The only other
: component I can think of that might have to
: be different for different engine sizes is
: the ignition - high RPM is murder on breaker
: points.
:
: The result is that in theory, for equal
: horsepower, the cost should be almost the
: same whether you're using a 170 or a 225!
: The biggest reason to choose one or the
: other, therefor, would be the powerband. A
: 225 is going to make its power at
: significantly lower RPM, which is often good
: for something the size of an A-body. It'll
: feel more like a mini muscle car motor. A
: built 170, by contrast, is going to wind and
: scream like a European exotic or an Integra
: Type R. This might make for more fun if it's
: been stuffed into a featherweight kit car, a
: rail dragster, or something tiny that was
: never meant to have slant six power, like a
: Plymouth Arrow.
:
: Ok, am I on the right track here, or totally
: off base?

: Really curious to see DD response to this. From
: my searches - the 170 hp is not drastically
: less than the 225 - seems to me the turbo
: and high rpms will do much better there and
: the overall would be better (safer than the
: 225's hugh stroke)