> I have read that a good choice is a rod to stroke ratio near 1.55:1 and more
> than 1.250" in compression height. source
Those guys are just down the street from me. They don't know Clevelands.
Big port Cleveland heads are fine with short rod ratios. Jon Kaase's
rule-of-thumb is 2" longer than the stroke. So a 6" rod is good for up
to 4" stroke.
> I was not able to find any information about these pistons on the internet
> so I could not find the compression height for them.
deck height - (rod length + stroke/2) = compression height
9.206 - (6.000 + 3.85/2) = 1.281
NBon-custom pistons will likely not be zero decked so the compression height
will be slightly less. Make sure the compression ratio is what you are after.
If dished, make sure it retains a quench pad. Also make sure the valve
notches and top ring are properly located.
> Anyone with any ideas about these kits
My crank was on back order from SCAT for 9 months. I didn't buy their kit
but be aware a lot of these outfits do not understand the issues with our
particular engine. Most of the kits sold are simply pieced together by
retailers who don't actually build engines. They slap some parts together
and hope it all fits. I've seen all sorts of problems from generic retailers,
Ford specialists, and even the manufacturers themselves, including SCAT who
I've had to educate concerning the differences between 351C's and 351W's.
Here's a previous post where I tried to summarize the issues...
Dan Jones
Many of the kits are simply Windsor-based kits with the crank mains turned
down to 2.75" and canted valve notches cut into the pistons. This can lead
to a series of problems. The 351W has 0.3" taller deck height and uses a
longer rod, so piston skirts which clear the crank throws in a 351W application
may not clear in a 351C application. Also, many in-line valve pistons have
the ring lands located too high to safely cut canted notches in. If your
pistons have in-line valve reliefs and canted valve notches, I'd check them
very closely (top ring location and minimum crown thickness). Also, many of
the kits use light weight drag race pistons which are not the best choice
for street or road race applications. Oval track pistons are somewhat heavier
but have the material thickness required to last. Often the pistons in the
kits are designed to be down in the bore so they work in a decked block
situation. Unfortunately, this kills the quench if you don't deck your block.
Often, the compression ratios aren't right for your cam and cylinder heads.
This isn't just a Cleveland problem, either. A friend just got a custom
$2100 billet crank made for his 5.0L-based stroker by a company that does
NASCAR cranks. It had the same problem as your kit, only the engine builder
didn't discover it until after they had balanced the reciprocating assembly.
Seems the crank manufacturer didn't know 5.0L blocks are 8.2" deck heights.
They are used to building NASCAR cranks for 9.5" deck height blocks and
longer rods. Now the crank has to be sent back to have it's OD reduced.
After that it will need to be re-balanced with expensive Mallory metal.
I've made several previous posts on the specific issues involved in
putting together a 351C stroker. I've cut and pasted some of that info
below. I don't have the time right now to edit it all so expect some
duplication and typos. Anyway, here goes:
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 custom pistons so there is 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.
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.
> what will be the best buy stroker kit?
Piece one together that fits your needs or have a trusted engine builder
do it for you. I've seen several of these kits now that are not put
together properly for a 351C.
> 383, 393 or 408 to fit the cleveland engine, 4v heads and high revs (7500
> rpm) (4340 crank).
Be aware that 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 also has benefits when it comes to valve train life.
7500 RPM and increased stroke combine for some pretty serious piston speed.
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 with 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). The 377 is best for high RPM, the 408 the
worst. Keep the 408C below say 6500 RPM and it should live. Premium
components will make any of them live at higher RPM.
If you plan to spend a lot of time over 7000 RPM, most engine builders will
go to neutral balance. The longer stroke cranks are usually set up for
28.2 oz-in and can require a lot of expensive Mallory metal to balance.
A friend went through this. His crank required 21 slugs at $75-$100 per
slug. When he damaged that crank, it was cheaper to go to a custom machined
crank that had the bobweight he needed (no Mallory metal required) though
the crank itself was 3 times as expensive as the previous crank.
You'll want strong and light rods for something like that. The best bang
for the buck I found were 6" Oliver Superlites ordered through Callies.
More expensive than the typical Eagle or SCAT rods but worth it in your
application. Have the pistons custom made to your specs. Assuming you have
quench heads, you'll want a corresponding quench area on the pistons (most
of the kits don't do this) and the upper ring location will be determined by
the canted valve notch. We went with custom Wiseco pistons for my stroker.
In the Dember 2005 issue of Popular Hot Rodding ("The Outer Limits", page 73)
David Vizard suggest the following Mean Pistons Speed for cranks:
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)
As an example, take my 3.85" Fontana stroker:
RPM = 4800 * 6 / 3.85
RPM = 7480 RPM
If all goes well, my cam will peak around 6500-6600 RPM. Shifting 400-500
RPM above that is around 7000 RPM which is still comfortably below the max
safe RPM. If all goes well with the Fontana build, I may try a 4 inch stroke
for my backup motor.
Note that Ford's high nodular iron cranks are similar to the aftermarket cast
steel cranks. Also, keep in mind application is important. You can get away
with a lot in a drag race motor that may get all of 20 miles a season that
you can't in an open road race engine. Also, the crank strength is meaningless
unless you have rods to match (weak link).
In another article, Vizard published a series of tips for getting the most out
of a stroker engine. I've listed them below with some comments:
1. Select as long as a rod as possible to minimize the frictional losses from
side loading and cut the engine's mechanical noise.
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. As an example, take a 4" stroke crank, using 6" rods,
for 408 cubic inches (assuming a 0.030" overbore). 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 my 408C stroker is better than the
popular kits. Rod to stroke ratio for the 408C is:
= 6.0/4.0
= 1.5
That's at the lower end of OEM production V8's:
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
Jon Kaase's rule-of-thumb is the rods need to be 2" longer than the stroke.
He said that has worked well on everything he's built from 289's to 700+
cubic inch IHRA mountain motors. For those who don't know, Kaase was
Dyno Don's crew chief back in the 351C Pro Stock days, designed the
aluminum SCJ Ford Motorsport heads, and won the Engine Masters Competition
with an XE block 351C stroker.
2. Select the lightest reciprocating components for the bottom end.
This ends up being a function how light a rod and piston you wish to choose.
Lighter pistons are thinner and may not last as long. Lighter rods tend to
be more expensive. I went with 6" Oliver Superlite rods which are more
expensive than the typical Eagle or SCAT rods but stronger. Even with the
Wiseco oval track pistons, the required bob weight was low enough that
substantial material had to be removed from my SCAT 4340 forged crank to
bring it into balance.
3. Use an effective crank damper
There are three basic types of dampers used in automobile applications.
The first (and most popular) is the elastomer balancer. Elastomer balancers
are steel (or iron) rings bonded to a rubber ring and are essentially a
non-linear spring with high internal damping. The rubber ring is susceptible
to heat and aging. Elastomer balancers are tuned to a specific frequency and
its harmonics. They works very well if you know what frequncies you wish to
damp. OEM applications use elastomer dampers. NASCAR and Trans Am teams run
SFI-spec elastomer type balancers pretty much exclusively but they have access
to equipment that tunes the balancers to their reciprocating assemblies.
Production engines are likely matched well but when you start changing
components (cranks, rods, pistons) you will change the problematic
frequencies. David Vizard recently did an article in which he expained how
they measure (using an expensive machine) the amount of crank twist when
testing different balancers.
The second type of damper is the pendulum damper. The pendulum damper was
invented by aeronautical science pioneer Fred Lanchester in the early 20th
century. Inside a pendulum damper is a weight held in place by a loose
fitting pin. The pin rolls and the weight swings like a pendulum. A positive
feature of a pendulum style damper is it adjusts itself as RPM increases since
the pendulum has a higher frequency in a higher centrifugal force field. The
Rattler damper is a Lanchester-type damper. The only data I've heard on the
Rattler was by a former Ford engineer who said the manufacturers of the
Rattler presented some data in an SAE paper. He said it was only fair and
they didn't present any high RPM data.
The third type is a viscous (or fluid) damper. For an engine that sees a
heavy load at a fairly constant RPM, viscous type balancers are prefered and
they are widely used in applications like diesel truck, marine and industrial
engines. They operate over a wide range of frequencies with the dampening
increasing at higher frequencies and with increasing mass. However, on an
engine that sees constantly changing (and a high rate of change) RPM, the
internal, free-wheeling damper wheel in a fluid damper lags behind the crank
as the rpm change, and heats up the silicone fluid it runs in. For extended
service, a viscous damper gets very hot and the fluid will in time break down.
Crankshafts have a primary resonance frequency in torsion, and a good rubber
damper tuned to that frequency can be very effective. To counteract crankshaft
torsional vibration, any damper needs mass. More mass means better damping.
Some harmonic dampers (Ford Motorsport, for one) have a weight that bolts to
the damper that you can remove for zero balance but most have the weight cast
in. Sometimes you can machine the cast-in weight away but most just by a new
balancer. Most external balance flywheels will have the balance weight
welded on. You can grind it off prior to internalling balancing the
reciprocating assembly.
4. Use an oil pan that keeps the oil away from the bottom end rotating assembly
as entrainment will cost big power and may lead to failure.
The Pantera flat bottom pans are quote good when fitted with scrapers and
trap-door baffles.
5. Go for as high a compression ratio as possible as it will off-set the
engine's reduced mechanical efficiency due to it's greater piston friction.
The compression your engine will tolerate will be a strong function of the
chamber design (closed chambers good, open chambers bad), the quench distance
and the cam profile chosen.
6. Use cylinders heads with valves as large as possible as there are a lot
more cubes to feed.
Typically not a problem with 4V or most aftermarket Cleveland heads.
Big displacement really wakes up a big port 4V head.
7. Be sure to tighten up the cam's lobe centerline angle (LCA) from whatever
was optimum before by about 1 degree for every 16 cubic inches of capacity
increase.
8. Increase valve lift at least the same proportion as the increase in
displacement.
9. Make sure the induction system has enough flow capability to handle the
extra cubic inches.
Investing in heads that flow well in the lift range you are interested pays
off more with increasing displacement.
10. Try to keep the induction system cool as this makes more difference with
a stroked engine.
The most popular Pantera 351C stroker 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.
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
9.206 - (6.125 + 3.50/2) = 1.331 r/s = 1.750
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 crank, 2.75"
Cleveland mains and Windsor rod
journals.
9.206 - (6.000 + 3.90/2) = 1.256 r/s = 1.538
9.206 - (6.000 + 4.00/2) = 1.206 r/s = 1.500 400 nodular iron crank (or
aftermarket)
Dan Jones
