Reply to "Stroking the 351"

> Pro's and Con's to stroking the 351 /// Windsor /// Cleveland

Stroker math is simple :

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

Use a 408C stroker as an example with 4" stroke crank and 6" rod and 4.030"
bore for 408 cubic inches. Assuming zero deck and re-arranging the equation
to solve for pin height, 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. For reference, here are a few production V8's in the same
range:
bore stroke r/s
Olds 400-455 4.25 6.735 1.58
Ford 460 3.85 6.06 1.57
Pontiac 455 4.21 6.625 1.57
Ford 300 Six 4 6.21 1.55
Chevy 454 4.00 6.13 1.53
Chevy 400 3.75 5.56 1.48

When I was mulling this all over, I calculated a few more numbers:

deck height - (rod length + stroke/2) = pin height

9.206 - (5.778 + 3.50/2) = 1.678 r/s = 1.651 stock 351C
9.206 - (6.000 + 3.50/2) = 1.456 r/s = 1.714 6" rod is easier on walls
9.206 - (6.125 + 3.50/2) = 1.331 r/s = 1.750 a bit longer rod
9.206 - (6.200 + 3.50/2) = 1.256 r/s = 1.771 what many circle track racers
run with Aussie 2V heads
9.206 - (6.250 + 3.50/2) = 1.206 r/s = 1.786
9.206 - (6.000 + 3.70/2) = 1.356 r/s = 1.622 popular 351C stroker specs, uses
offset ground 351C crank
9.206 - (6.125 + 3.70/2) = 1.231 r/s = 1.655
9.206 - (6.200 + 3.70/2) = 1.156 r/s = 1.676
9.206 - (6.125 + 3.75/2) = 1.206 r/s = 1.633 forged crank, popular high rpm
drag race combo with 4V heads
9.206 - (6.200 + 3.75/2) = 1.131 r/s = 1.653 pushing the pin height limits
for a street motor
9.206 - (5.950 + 3.85/2) = 1.331 r/s = 1.545 SCAT cast steel or forged crank,
2.75" Cleveland mains and
Windsor rod journals
9.206 - (6.000 + 3.90/2) = 1.256 r/s = 1.538 Popular sprint car combo
9.206 - (6.000 + 4.00/2) = 1.206 r/s = 1.500 400 nodular iron crank or
aftermarket SCAT, Eagle, etc.
9.206 - (6.000 + 4.10/2) = 1.156 r/s = 1.463 pushing the limits for a 9.2"
deck drag race motor

Before I came up with the XE Aussie NASCAR block and the Fontnana aluminum
block, I was considering running a 400 FMX block. The 400 block has a
generous 10.297" deck height which makes it an attractive candidate for
stroking:

10.297 - (6.580 + 4.00/2) = 1.717 r/s = 1.645 stock 400, lots to work
with here
10.297 - (7.006 + 4.187/2)= 1.198 r/s = 1.673 offset ground 400 crank,
198 Mopar slant six rods,
alternatively can use Ford
truck six rods

The limit on a 400 crank is 4.200" but you have to use Chevy journal rods
to do it and the crank has to be perfect to start with. There are also
aftermarket crank and rod combos available now.

The most popular Pantera combos are:

1. 377 (3.7" stroke, 0.030" over):

Offset grind 351C crank to SBC journal, widen crank journal or narrow rods
for 6.0" SBC rods or use Cleveland width 5.955" 351W rods, custom pistons.
Most conservative. Assuming your crank grinder works reasonably, can be
the least expensive. If not, aftermarket cranks may be as cheap. Room to
go to longer rods (6.125" or 6.2"), if desired. Conservative compression
height and rod ratio with room for a standard ring pack. If you go to the
crank section at:

http://www.bacomatic.org/~dw/alex379/alex379a.htm

There's a good picture of a Cleveland versus SBC journal on the same
crank throw. Notice how long it takes a grinder to do the work and
you'll understand why the cheap Chinese stroker cranks are so popular.
It's a lot of time on the machine to do right. The critical part is
getting a good radius where the journal merges into crank throw.
To do this correctly is a lot of time and labor so you really need a
machinist you trust to do it properly.

2. 393 (3.85" stroke, 0.030" over)

Chinese import cast steel/iron cranks with 6" rods and custom pistons.
Also 5140 forged steel and 4340 forged steel cranks are available.
Like a 377 but with more cubes. Pin is still out of the ring pack.

3 408: (4.00" stroke, 0.030" over)

4" stroke crank, 6" rods, 1.2" compression height. Most cubes while keeping
a decent pin height. Most power for a given RPM (best torque) but higher
piston speed.

All are workable. For my 4.1" bore Fontana block, I picked a 3.85" stroke
4340 SCAT forging which yields 407 cubes. For my backup motor using the
XE block, I'm looking at a 4" stroke for the extra cubes. Even the OEM's
are building strokers these days. The Chevy LS7 as installed in the 2006
Corvette Z06 is a 4" stroke in a 9.0" deck height, all with a GM powertrain
warranty.

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's about 0.27" down from the deck. Beware that some 351C stroker kits use
pistons originally meant for inline valve heads that are cut for Cleveland
style canted valve notches. I don't recommend that.

When shopping around for a stroker kit, there are a number of things to keep
in mind. First of all, there's little reason to buy a kit. You're looking
at cstom pistons so the there's little cost difference to picking the proper
crank, rods and pistons for your application versus buying a kit. In addition
to valve notch placement issue I mention above, you'll need to pick whether
you want drag race pistons, oval track or street pistons. The street pistons
will be of an alloy with higher silicon content to minimize thermal expansion.
Oval track pistons will be a little heavier than the drag pistons but more
durable. I went with the oval track/ road racing pistons for my stroker.
Also, the cheapest crank doesn't necessarily equate to the least expensive
kit. You have to figure in the cost of balancing. A friend's internal
balanced crank required 21 slugs of Mallory metal to balance at $40 per slug
wholesale plus labor. Not cheap but he is turning 9000 RPM. For most
applications, 28.2 oz-in works just fine but stay away from the 50 oz-in
stuff. Some crank manufacturers will tell you the bobweight there cranks
are designed for and others, like SCAT, have versions of the same crank for
6.0", 6.125", and 6.2" rods and various lightening options. I used Wiseco
pistons, 6.0" Oliver I-beam supelight rods and a 3.85" SCAT 4340 forging
for 6" rods. We needed no Mallory metal to balance. Quite the opposite,
it took a lot of grinding to get into balance. The SCAT cranks are nitride
hardedned and are difficult to grind or drill so some shops may charge more
for labor. On rods, you'll have material (5140 versus 4340) and construction
(H-beam versus I-beam) to consider, along with fasteners (capscrews versus
through bolt and nut). If you offet grind a 351C crank, you have to either
narrow the SBC 6" rods or widen the journals on the Cleveland crank or use
a 351W rod. Narrowing the rods is cheaper and easier if you're offset
grinding the crank but a wider bearing may last longer. If you're going
with an aftermarket crank, most will use the small block Chevy 2.1" diameter
rod journals and 0.940" width rods. However, the Ford Sportsman and certain
3.85" SCAT and Eagle cranks are set up for 2.311" diameter 351W rods. Don't
get hung up on rod ratio. The effect of rod length is relatively minor.
In talking with Jon Kaase, he mentioned his rule of thumb for rod length is
2" longer than the stroke. He says that has worked well on his engines from
351C's to his mountain motor stuff. All the combos above have a better ring
placement than popular 347 cube stroker kits for the 5.0 due to the fact the
351C has a deck height a full inch higher than a 302.

Be aware the aftermarket "Cleveland style" cranks are not exact Cleveland
replacement cranks. Rather, they are cranks meant 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. The
Cleveland snout has 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.

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.

> This is probably where my next motor will be coming from.

Make sure they understand the ins and outs of the engine you intend to build.
They can't be specialists in all engines.

> while others put importance on that magic 427 cubic inch number.

Of course the 427 Ford never actually displaced 427 cubic inches. The 427
displaces closer to 425 cubic inches but Ford marketing wanted to one-up
the Oldsmobile 425. The 428 actualy displaces 427 cubic inches but Ford
couldn't call it a 427 since the 427 already existed.

> This power level can be reached with a Clevland as easily as with the Windsor,
>air flow and compression are what make horsepower, therefore the formula for 500
>bhp is (1) a high lift hydraulic roller cam,

I picked a hydraulic roller for my application but you could make that HP
target with a flat tappet cam (hyraulic or solid). You have to be careful
when spec'ing hydraulic roller cams as the heavy roller lifters can limit RPM.
Proper valve springs (I used a BBC hydraulic roller valve spring), lobe
design, and lifters (I used the Crane which support higher revs than OEM
hydraulic roller lifters), and lighter valvetrain (beehives with nickel sized
titanium retainers or titanium valves) will extend the RPM range. David
Vizard recently did a very good article on hydraulic and solid flat tappet
and roller cams and when to pick to pick one over the other. Well worth the
read.

Dan Jones