[DeTomaso] Ford 392 rev limit?

[Daniel C Jones]

The FRPP 392W with GT40 heads was rated at 430 HP (crank) with the
power peak at 5500 RPM.
For maximum acceleration, you generally want to shift 400 RPM or so
above that.  With the
dyno sheet you can figure exactly where to shift (maximum area under
the curve between
shifts).  While it may turn more RPM before running into valve train
stability problems,
it won't accelerate any faster.  Be aware Ford also had a higher HP
version of the 392W
crate engine that used Z304 heads.

> machinists and engine builders have commented that the factory crate
> engines have been found to have, ahem, factory seconds used as parts.

Ford used Scat reciprocating assemblies in the 392W stroker.  Ford
never produced the
engine as factory fitment.

I'll have to check my old FRPP catalogs when I'm home, but I believe
the 392W engines
used the cast cranks with standard I-beam rods and 302 pistons.  In
the Dember 2005 issue
of Popular Hot Rodding ("The Outer Limits", page 73), David Vizard
suggest the following
Mean Pistons Speeds:

 Factory cast iron cranks             3750 ft/min
 Aftermarket cast-steel cranks        4500 ft/min
 Factory forged cranks                4600 ft/min
 Budget aftermarket forged cranks     4800 ft/min
 Typical race aftermarket cranks      5500 ft/min
 High dollar custom endurance cranks  6000 ft/min
 Pro Stock Mountain Motors            7500 ft/min
 Formula One                          7500+ ft/min

They goofed on the formula in article but piston speed is easily calculated:

 MPS = STROKE * RPM / 6
 RPM = MPS * 6 / STROKE

where:

 MPS = mean piston speed in ft/min
 STROKE = crank stroke in inches
 RPM = enigne speed in revolutions/minute
 6 = conversion factor (one-half of one foot expressed in inches)

For a 3.85" stroke aftermarket cast crank (as used in the 392W),

 RPM = 4500 * 6 / 3.85
 RPM = 7013

That just a suggested maximum RPM based upon the crank.  There may be another
area that is the weak link.

Dan Jones

On Fri, Sep 6, 2013 at 8:44 AM,  <cengles at cox.net> wrote:
> Dear Mike,
>
>
> You wrote:
>
>
>
>   "Ford crate engines, like the Pantera, are 'built to a price' and
> typically
>   won't put up with the same level of abuse as a professionally built
> engine
>   of nominally similar characteristics, because there are corners cut
> everywhere, such as cast vs. forged cranks, rods, mild valvetrain and
> cam specs,
>   etc...."
>
>
> FWIW: on the Speed Talk website Engine Forum, the professional
> machinists and engine builders have commented that the factory crate
> engines have been found to have, ahem, factory seconds used as parts.
> It is perhaps not in all the engines, but it has happened often enough
> that the pros have commented on it.
>
>
>
> Warmest regards,  Chuck Engles
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