[DeTomaso] stroker kit????

[Mad Dog Antenucci]

As usual, excellent points Dr. Dan....I'm not pointing any fingers at anyone except maybe myself on those 3, 393's that didn't work for me....
   
  Your right, engine failure #1 was a snapped cam shaft!  Engine #2 was a lifter...and the same builder built all 3 strokers. I'll leave it at that except to say none of those motors were ever raced at more then 5500-6000 RPM and as you and Gary point out that may be the weak link....running above 5500........then again russ Fulps tells me he doesn't generally have any problems with the 393-400+ strokers he builds for racing and/or street. 
   
  MD
   
  
Daniel C Jones <daniel.c.jones2 at gmail.com> wrote:
  > My experience with the three 393 Cleveland Strokers was not good. They all
> felt from day one like they were going to grenade....Allot more vibration

Mad Dog, can any of those failures be attributed to the increased stroke?
As I recall, these engines were built by a different engine builder and
the one that had the block I sent you was blamed on a broken camshaft.
If you felt vibration, there was something wrong from the get go which
I doubt can be blamed on the 3.85" stroke. I've driven a 4.1" stroke 418
that was nice and smooth and made 556 HP on the dyno under 6000 RPM.
The piston speed at 6000 RPM of that engine may be the same as a 3.7" stroke
engine at 6600 RPM so the stress on the rods is similar but the rest of the
parts (valvetrain in particular) benefit from the reduced RPM.

Rod stress increases in proportion to stroke and by the square of rpm.
While we often speak of RPM, it's really the piston speed that counts.
Increasing stroke means increased piston speed at the same RPM so, all
other things considered, the maximum RPM the short block can sustain will
be decreased. A stroker offsets this since you can make power at a lower
RPM level which has benefits when it comes to valve train life.
Short rods increase acceleration near top dead center which is a little
harder on the rods but helps flow in large port cylinder heads. Longer
rods are easier on cylinder walls but the trade-off is in pin location
and ring pack. Gas loads dominate at low rpm, inertia loads at high rpm.
Excessively high piston speed will exceed the mechanical limitations of the
materials. Excessive side loading will create increased friction on the
bore and the pin/rod and rod pin on the crank. The load on the crank is
a function of the RPM, the weight of the rods and pistons, the stroke, and
the balancing/counterweighting. Reducing RPM, reducing stroke, reducing
piston and rod weight will all help, as will a stronger crank.

Longevity is dictated by the power the engine makes, the strength
of the components, piston speed (a function of RPM and stroke), rod
to stroke ratio (side wall loading) and rin pack (narrow ring packs
don't seal as well, tend to rock at TDC) and the RPM you turn, not to
mention tuning factors (pinging, additional thermal loads due to running
lean, etc.).

> If I don't expect to rev 7500 rpm.. and seldom see 5500 rpm.. then I can
> go with the 393 and make sure of my 4V heads and ITB? :)

Yes. For lower RPM like that, I'd jump to a 4" stroke for 400+ cubes.

> What type of parts should I be looking for and would it basically fit the
> 351C without much modification? I just don't want to run into unexpected
> issue where the machine shop has to do a bunch of other things to make it
> all work out...

You gotta do your homework. A number of small issues, no major shopw stoppers.
Most of the inexpensive aftermarket cranks are not true Cleveland dimension
cranks, rather they are listed as "Cleveland style" because they use the 351C
main diameter ut in most other regards are Windsor. They are cranks originally
designed to go in Ford Motorsport hybrid blocks (or other race block) which
combine the 2.75" Cleveland mains with a Windsor architecture. The Cleveland
snout is longer than the Windsor one. Most aftermarket "Cleveland style"
cranks use the Windsor snout. Cleveland cranks have a "snout ring" ahead of
the #1 main, to space the lower sprocket out to clear the journal. Windsors
have a collar on the back of the sprocket and are machined flat ahead of the
journal. When using a "Cleveland style" crank in a 351C iron block, a Ford
Motorsport spacer (part number M-19009-A341C, required with 351 SVO crankshaft
when used in production iron 351C engine), will fix the problem. The spacer
is not a press-fit and you can push it on by hand. There are true Cleveland
spec aftermarket cranks but they tend to be custom order. Also, RDI stocks a
hybrid 351W/351C timing set from Dynatech to match the Windsor crank snout in
a Cleveland block. Some have reported balancer fit issues but Dave Williams
said my Romac balancer fit snugly on my SCAT 4340 crank as did the FRPP
balancer on a friend's stroker.

The Cleveland #3 (thrust) main is narrower by approximately 0.009" (as
measured by Jim Sams). Most aftermarket cranks with 2.75" diameter mains
use the narrower Cleveland thrust width which allows the use of Cleveland
main bearings but ask before ordering. The main bearing spacer kit that
allows 351W blocks to use 2.75" diameter cranks uses the 351W thrust width
which requires a special thrust bearing (available from Ford Motorsport).
The cast iron 2.75" diameter main Ford Motorsport Sportsman cranks have the
351W thrust width to match the spacer kit. The 4000 series SCAT "Cleveland
Style" cranks have the Windsor snout but have 2.75" diameter mains and take
351C bearing, including the thrust bearing.

Most aftermarket cranks use small block Chevy 2.1" diameter rod journals and
0.940" width rods. However, Ford Sportsman and certain 3.85" SCAT and Eagle
cranks are set up for 2.311" diameter 351W rods.

SCAT offers their cranks in versions to use with 6.000, 6.125, and 6.200
inch long rods, the difference being in the OD of the counterweights.
My engine builder wanted to external balance to 28.2 oz-in and suggested
ordering the 6.2" version, even though we are using 6.0" rods. That way
he wouldn't need to use any expensive Mallory metal for balancing (could
grind down the counterweights as needed). The tech at SCAT (Brian)
insisted this was a mistake. He said that the 6.0" version would likely
need to be lightened. Furthermore, he said the counterweights are cam
profiled on a CNC machine and that turning them down on a lathe would ruin
the balance and not have the desired effect. Dave mentioned he had to spend
a lot of time lightening the crank throws to get the crank into balance.

Canted valve Cleveland heads require uniquely positioned valve notches
at the edges of the pistons. The limiting factor for Cleveland stroker
pistons is often the valve notch in the block and pistons. Cleveland
blocks are usually notched at the tops of their bores for valve
clearance/shrouding which can place a limit on the top ring placement
(needs to be below the valve notch at TDC plus rod stretch). The depth of
the notch varies from block to block but on my Aussie XE block, it was about
0.27" down from the deck. If running quench heads on pump gas, you'll
probably want a dished piston for anything over 3.7" stroke. If so, don't
use a circular dish. A d-dish is better and a mirror image of the combustion
chamber is better yet. Wiseco will do a mirror dish if you send them an
image. You need a flat pad on the piston where the quench pad is on the
head to maximize the quench effect.

> If I believe correctly.. a stroker basically has a longer stroke and that's
> via a modified or different crank that's larger in diameter... mm longer
> rod?...

Stroker math is simple :

rod length + crank stroke/2 + piston pin height = deck height

Of course, you can rearrange the equation anyway you want to solve for a
particular variable. The deck height of the block is fixed so you have to
juggle the other parameters to keep the same stack height. You could shorten
the rod but it's best to increase the rod length with increasing stroke to
preserve the rod to stroke ratio. A good rule of thumb from Jon Kaaase is
to keep the rods 2"+ longer than the stroke. What is usually done is to move
the pin up on the piston to offset the stroke and rod length increases. An
example of a 4" stroke, 6" rod, and 4.030" bore for 408 cubes in a 9.2"
deck height Cleveland block. Assuming zero deck, the stack up works out to
be:

piston pin height = deck height - (rod length + crank stroke/2)
= 9.2 - (6.0 + 4.0/2)
= 1.2 inches

331 and 347 cubic inch strokers are popular for 5.0L Ford V8's these days.
5.0L V8's have a deck height of 8.2", so plugging the pertinent values into
the formula yields:

deck height - (rod length + stroke/2) = pin height
8.2 - (5.4 + 3.4/2 ) = 1.100 inches
8.2 - (5.4 + 3.25/2 ) = 1.175 inches

so you can see the 1.2" pin height of a 408C stroker is better than the
popular 5.0L stroker kits.

Rod to stroke ratio for the 408C is:
= 6.0/4.0
= 1.5

A r/s of 1.5 is on the low end of production Detroit V8's (slightly less
than a Chevy 454 but slightly more than a Chevy 400), so should be fine for
a hot rod motor.

> Would i need a custom piston or a normal forged 351C piston would be fine?

Custom pistons will be required due to the pin location.

> And then of course i'll need new main and cam bearings... piston rings...
> etc for my typical engine rebuild right? :)

Yes. You have the freedom to specify the ring widths and style with your
custom pistons. The block or crank may need clearancing to fit a stroked
reciprocating assembly and you have to verify the cam's not in the way as the
rods swing around. The 351C bottom end is roomier than a SBC so these are
not generally big problems.

Dan Jones
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