In the past several years small block Ford stroker engines
have become all the rage. Every machine shop and specialty
parts house advertises some sort of stroker kit selection,
the most common being the 302 based 347 kits, but even
427 cubes are now available from the 351 Windsor blocks.
So when time came to decide on a new engine project
for our resident '67 Mustang (see Project
Cars), we naturally took the stroker option into
consideration. Of course the suggestion was made to
simply step up to a "big block", or at the
very least a 351 Windsor, and possibly even a stroked
one. However, considering our projects are always limited
in the funds department, moving to a new engine class
would mean extra expenditures such as headers, exhaust,
oil pan, distributor, intake, and the list goes on.
The 302 based stroker simply looked better and better
as the cheap way to gain displacement. We ultimately
decided on a 331 cid motor, for reasons we'll explain
in this article.
We knew for certain that we wanted
more displacement. The 302 which we had built (see 400
Horsepower 302) had indeed met it's goal of running
11.90's, however left us desiring for more streetability.
The big solid-roller cam and 750cfm carb atop the single
plane intake meant a high rpm power band and poor low
More displacement will give us
a good increase in torque all across the board, thus
allowing us to tone down the cam. Ultimately our goal
is bring the '67 back as first and foremost a street
car... a fast street car. To that regard we expect it
to run similar ET's, but this time it will be accomplished
by displacement and torque, not over camming and high-revving.
How much stroke is enough?
Undeniably the most popular 302 based stroker on the
market is the 347. Originally created using a 351 Cleveland
crank cut down to 3.400" stroke and a 5.400"
Eagle rod, the 347 is about as much displacement you
can squeeze out of a 302 block without running into
severe strain or accelerated wear. Technically it is
possible to get as much as 355 cubes from a 302, but
this requires custom machining and the life span of
such a motor is very short, making it a seldom seen,
The Scat 331 kit uses
forged SRP pistons. Note the pin hole is just below
the oil ring groove. On 347 pistons the pin intersects
the groove, resulting in increased oil consumption.
Most 347 kits require the piston
to be so short that the piston pin intersects the oil
rings. While a nickel-sized gap behind the ring on each
side of the piston may not seem like a huge issue, in
fact such a gap will increase the oil consumption of
the motor to some level. We spoke to four reputable
machine shops to get their opinions on using the 347
in a street application, and their responses were equally
divided. It seems as if half of the Ford crowd is convinced
the 347 is not an ideal street motor due to rapid wear
on the rings (from the relatively low rod ratio) and
increased oil burning.. The other half feels the piston
pin issue is a non-issue, and refers to the number of
satisfied 347 owners using them in daily drivers.
Several companies are offering kits with custom pistons
which raise the oil ring grooves above the pin hole.
The Coast High Performance 347 kits accomplish this
with a 0.085" shorter rod (5.315")). Naturally
these 347 kits are more expensive, and critics say area
above the piston crown becomes so thin that the piston
is prone to breaking at the ring lands upon the slightest
detonation. We've actually seen this very thing in a
Shortly after the 347 became popular,
the 331 kits started hitting the popularity charts.
Using the same 5.400" rod, but less stroke, results
in an ideal 302 stroker. The rod ratio is nearly the
same as the stock 302, meaning the side loads from a
331 rotating assembly is not aversely different than
that of a stock motor. The 0.150" shorter stroke
means the piston pin is well below the oil rings.
All in all the 331 has recently
become very popular amongst those not wanting to engage
in the "how long will a 347 last" debate.
While it did make us uneasy to give up 16 cubes, we're
hopeful that we can gain the power back from the 331's
better rod to stroke ratio. Continue