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Author Topic:   351 Strokers, Optimizing Bottom End & Block ???s
MDF99
Gearhead

Posts: 234
From: Hamilton, Ohio, USA
Registered: May 2001

posted 06-25-2002 04:49 PM     Click Here to See the Profile for MDF99   Click Here to Email MDF99     Edit/Delete Message   Reply w/Quote
These are some general 351 stroker engine theory questions. I'm pretty much in the dark here.

Deck Height: 9.2" vs. 9.5" Which is more advantageous for more HP/Torque and engine longevity? Is there a trade off here? Is it as simple as the 9.5" deck height allows you to stroke for more cubic inches and nothing more?

Aftermarket Blocks (Dart SBF) vs. Ford SVO Blocks: Anyone have experience with either? Has Dart improved over the Ford design in any way? Nope, I'm not planning to buy either one anytime soon.

When I look at stroker kits (like at flatlander racing) they'll list two different rod lengths as options for a particular engine kit, i.e., (6.0" and 6.2" for both the 408 and the 418). Are they for different blocks or what? How do they arrive at the same number of cubic inches with different rods lengths and the same stroke?

What does it mean when a block has siamese bores? Why or when is this advantageous? What the hell's going on here?

What's the bottom line on connecting rod ratios? I think I read that the longer rod is easier on the cylinder walls but you can gain bottom end torque with a shorter rod? Is this true? Where's the trade off w/ rod ratios? What's optimal?

Finally, given your choice of any available engine block, deck height, bore, stroke and rod length; which stroker combination do you think optimizes both power potential and engine longevity as well?

------------------
Matt Fraley
1966 Mustang Coupe; 289, T-5, 9" 3.50
http://mdf99.tripod.ca/289_Side.jpg

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[email protected]
Gearhead

Posts: 935
From: Lakewood, CO, USA
Registered: Jun 2001

posted 06-25-2002 05:29 PM     Click Here to See the Profile for JCQuinn@work   Click Here to Email JCQuinn@work     Edit/Delete Message   Reply w/Quote
Matt

I will attempt to answer your questions as my knowledge allows.

1. You are correct, the taller deck makes it easier to put in more stroke. The deck height also governs your manifold choice. Make sure the deck height you want can use the intake you want to use. A bigger block will weigh more but I don't know if the difference is significant.

2.SVO blocks are whats left after the NASCAR teams select the ones they want. The leftovers are still good, just not the best. I think the aluminum svo blocks are made by someone other than Ford but I don't remember who at the moment. The Dsrt blocks have supossedly been made stronger than the Ford version, I don't know if they are but Dart has a very good reputation. The best part about them is that they use smaller mains which is a weakness of the stock 351 block if you are going after high rev's.

3. Rod length has nothing to do with displacement. It just moves the ring package up or down the piston. Displacement is set by bore and stroke only.

4. Siamese bores means that there is no water passage between the cylinder bores. It makes the block much stronger and leaves more room for larger bores. Downside is less efficient cooling.

5. Many people have chased this rod length thing all over the place. Most production stuff centers around a 1.7 ratio. In general if you have too much airflow, a shorter ratio will help get the air moving quicker. If you have restricted airflow a longer rod pulls the air better and will help make horsepower. This does not seem to be a critical area despite what you may have heard. People have made good horsepower with a wide variety of ratios. The important thing is to have a system that works together. You have to optimize burn rate, airflow, compression ratio, cooling rate, ignition timing anb probably several other things to get an optimal system. Anything near 1.7 will work fine and ratios from 1.5 to 2.0 have worked fine in lots of engines.

6. For reliable horsepower you want a large engine that is light weight and does not go above 6000 RPM. Useage will determine the exact choice and that is up to you. Personally I would take a Dart 302 block with a 4.125 bore and the small main size and run it around 10,000 RPM. It would not be reliable but it sure would be fun.

John Quinn

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steve'66
Gearhead

Posts: 9533
From: Sonoma,CA,USA
Registered: Mar 2000

posted 06-25-2002 05:58 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
Matt,

Are you talking C or W here? W's are 9.48 or 9.5 deck height, and yes the 9.5 give you .020 more room to fit everything. We're using a 6.25" rod in Missy's 408W but as Reher-Morrison says, rod ratio is about 12th on the list of things to worry about. Making sure they stay attached is much more important than how long they are.

Just remember that as stroke is increased the piston speed increases tremendously and better parts are required to keep things from pulling themselves apart. Unless you reduce rpms (which will offset the power capability of the increased cubes).

How's your '66 running?

SteveW

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Daniel Jones
Gearhead

Posts: 898
From: St. Louis, MO
Registered: Aug 99

posted 06-25-2002 07:05 PM     Click Here to See the Profile for Daniel Jones   Click Here to Email Daniel Jones     Edit/Delete Message   Reply w/Quote
>These are some general 351 stroker engine theory questions. I'm pretty much in
>the dark here.

I recently answered a similar question on the Pantera list. Allow me to
recycle my response:

>Deck Height: 9.2" vs. 9.5" Which is more advantageous for more HP/Torque and
>engine longevity? Is there a trade off here? Is it as simple as the 9.5" deck
>height allows you to stroke for more cubic inches and nothing more?

The piston, rod, and crank all have to fit within the block. The taller
the block, the more room you have to work with. The downsides to a taller
block are increased weight, height and width. Assuming zero deck, the
math is very simple:

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

Stroking consists of reducing piston pin height or connecting rod length
(sometimes both) in favor of additional stroke. There are limits, of course.
When considering pin height, you have to leave room for the ring pack. Go
too far and you'll run into oil control and piston rock problems. Custom
stroker pistons often have the oil control ring intersecting the pin hole
(a bridge is used to span the pin) in order to get a workable space. Thinner
rings may be used. As far as what is practical, Dave Williams notes that Ford
4.6L Modular V8's have 1.2" pin heights and that 1.14" pin height pistons are
fairly common in stroker engines. Remember that larger bores and piston to
cylinder clearances will be harder to seal.

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.

Reducing the rod length, compromises the rod ratio (the ratio of the rod
length to stroke, center-to-center). Decreasing the rod ratio increases the
rod angularity which increases cylinder wall loading and friction. The larger
the ratio, the longer the piston dwells near TDC, allowing more power to be
extracted from the combustion event. The more restrictive the induction
system, the more benefit you'll see from increased rod length. Since the
piston speed profile is altered by changing rod length, engine tuning will
also be affected. On the downside, longer dwell time at TDC also requires
deeper valve relief notches in the pistons for the same cam timing and is
more prone to pre-detonation. When choosing between extra stroke or longer
rods, the extra stroke means extra displacement and generally more power.

Keep in mind that, all things being equal, increasing stroke will increase
piston speed and reduce maximum safe rpm. However, it will also tend to shift
the power curve down, so less RPM is required for the same power. Since rod
stress increases in proportion to stroke and by the square of rpm, it's easier
on the crank to make power by increasing stroke than it would be to spin it
higher. Short rods increase acceleration near top dead center which makes
either worse. Gas loads dominate at low rpm, inertia loads at high rpm.
If you plan on running in events like the Silver State open road race where
extended periods of high RPM is required, you'll want to stay conservative on
the stroke of re-gear the transaxle to keep RPM in check.

Stroking can be accomplished by offset grinding the stock crank, altering
another crank to fit, or using a custom crank. Offset grinding requires the
crank rod journal diameters be reduced which, in turn, requires smaller
journal rods (stock 351C rod journals are 2.311"). Modified production rods
(Ford, Chevy, Mopar, Olds, etc.) or aftermarket rods can be used. Aftermarket
Chevy 2.1" and 2.0" journal rods are available from a number of manufacturers
(Eagle, Scat, Oliver, Carillo, Crower, etc.) and come in a variety of lengths
(5.7", 6.0", 6.125", 6.2", and 6.25" and others by special order). Prices
range from $200 to $700. Pistons are typically custom ($500 to $700) or
modified aftermarket ($200+), though some manufacturers like Scat make custom
cranks that use production rods and pistons (e.g. Scat 3.85" stroke crank,
351W rod, and 302 piston for 351W block). Check Circle Track magazine for
aftermarket rod suppliers.

Other stuff to keep in mind. The block or crank may need clearancing to fit
a stroked reciprocating assembly. You have to verify the cam's not in the
way, makes sure the crank, rod, and bearing widths are compatible, worry about
balancing (Mallory metal is expensive), etc.

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.

After studying it a while, I've decided to go with a 4" stroke crank, using
a 6" rod, 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

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
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)

Dave Williams recently did a stroker crank for a customer and worked out a few
possible Cleveland stroker combinations using modified production parts:

351C crank, KB112 pistons, Chrysler rods, 3.64 stroke = 373 CID
351C crank, 1.14 pistons, 6.200 Eagle rods, 3.71 stroke = 380 CID
400 crank, 1.14 pistons, Chrysler rods, 3.88 stroke = 398 CID
400 crank, 1.14 pistons, Olds rods, 4.120 stroke = 422 CID

Jim ended up with a 372 cube stroker using a 3.64" stroke offset ground 351C
crank with 6.125" Mopar rods. He could have used modified Keith Black
hypereutectic pistons (1.14" pin height, designed for a 6" rod 383 cube Chevy
stroker) for an inexpensive package. However, Jim called KB and John Erb
(KB's chief engineer) recommended against fly-cutting the pistons for
Cleveland style canted valve notches. Jim called around and got the best deal
from Lunati on custom forged pistons ($550 with 5/16" deep valve reliefs).

Enough babbling. The popular budget choices for a Cleveland are:

1. 3.7" offset ground Cleveland crank with 6" rod (Olds or Chevy), custom
pistons

2. 3.85" Scat crank with 5.95" Windsor rods or 6" Chevy rods, custom pistons

3. 4.00" Ford, SCAT, or Eagle cranks, 6" rods, custom piston

All are workable. I picked the 4" stroke for the extra cubes.

Dan Jones

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Moneymaker
Administrator

Posts: 27499
From: Lyons, IL, USA
Registered: May 99

posted 06-25-2002 07:29 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
FYI gang:
Dart and SVO or FRPP blocks are cast at the same place by the same company in Milwaukee Wisconsin. As are the GM Bowtie blocks and the Mopar race blocks.
The FoMoCo "sportsman" series blocks are cast by Ford themselves.

------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl

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DRAGSTANG351
Journeyman

Posts: 67
From: FLORIDA
Registered: Dec 2001

posted 06-26-2002 12:56 AM     Click Here to See the Profile for DRAGSTANG351   Click Here to Email DRAGSTANG351     Edit/Delete Message   Reply w/Quote
Hey Guy's

I would like to get some ideas on which way to go with my 351c drag motor...let me start off saying i got a set of C302B heads on the way...thanx to Alex & Dan i have located a couple of jack roush ford motorsport intakes A351,A331...i want to get the heads flowing around 320-340 cfm range and top it off with a 950 HP series carb... this will take care of the top end.

I had planned on buying stock length H-beam rods for $550 and a set of BRC pistons 13.5:1 $599...this is where i could use some good advice on my combo, since i was already going to spring for the new rods and pistons
what would be the ideal stroker for a drag only 351c using my stock crank, what should i offset grind my crank? what rods should i use? i need the pistons compression to be around 13.5:1 / 12.5:1 for nitrous 200HP/shot
I also need a good cam recomendation to top this combo off.

Here are the other particulars about the car...C-4 trans w /8" 5500 stall/ 4.56 gears / 28x10.5x15 slicks 2900 pound car with driver.

any info would greatly be appreciated

thanx guy's

kelly


this is where i could use some

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Moneymaker
Administrator

Posts: 27499
From: Lyons, IL, USA
Registered: May 99

posted 06-26-2002 01:11 AM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
CP or Venolia pistons only with the edge going to CP. I would never use another brand again in any serious race engine. Nobody has a better quality piston. No brag just fact!
Crower or Oliver rods. Yes they cost more, but what does a failure cost you in the long run. I have over 450+ runs and over 200 dyno pulls on a set of Crower Ultralites. They are as new! We put over 450+ runs on our Venolia pistons and I sold them to another superstock racer. The only reason they were replaced is because the block was worn.
I would call Kuntz for a crank as he has some trick Austrailian and other pieces he might be willing to part with. Several differant strokes.
Sorry, but I don't make cam recomendations here anymore as I am not smart enough.

------------------
Alex Denysenko
Co-Administrator and Moderator/ non 65-66 Mustang owner sensitivity co-ordinator

NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Part time secret agent license #0089
Professional Manwhore
The Barry of BarrysGrrl

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DRAGSTANG351
Journeyman

Posts: 67
From: FLORIDA
Registered: Dec 2001

posted 06-26-2002 01:23 AM     Click Here to See the Profile for DRAGSTANG351   Click Here to Email DRAGSTANG351     Edit/Delete Message   Reply w/Quote
Alex

I was hoping you would give me a cam recomendation for my combo...between me and you i would value your input.

kelly

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MDF99
Gearhead

Posts: 234
From: Hamilton, Ohio, USA
Registered: May 2001

posted 06-26-2002 08:42 AM     Click Here to See the Profile for MDF99   Click Here to Email MDF99     Edit/Delete Message   Reply w/Quote
Steve, I've not yet driven my 66, it's some B.S. I'm working away from home for four months on a job for the US Army Corps of Engineers. It pretty much sucks. I fired up and broke in my new engine for 30 minutes the evening before I left. It fired right up and sounded bad-*** . So, it'll be there waiting for me in mid-September when I finish this up. All I've got to work on now is my diesel pickup, pumps, compressors and electric motors and such. I'm looking at a 1970 Mach 1 right now am just contemplating my next engine build. It has a 351 Cleveland in it now. I'm interested in both the C and W.

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Mpcoluv
Gearhead

Posts: 1341
From: Charlotte NC usa
Registered: Apr 2001

posted 06-28-2002 08:31 AM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
As Dan said, I use Lunati pistons in my 372C.
This was before Holley bought Lunati...
Lunati pistons my be crappy now, or great, I don't know.
I did have good service and tech help from them, and they delivered my pistons in about 2 weeks. They were boxed as "Lunati and Taylor" pistons. One thing to look out for is that Lunati shipped 140 gram pins with the pistons. After I complained, they swapped me a set of 119 gram pins free of charge.

------------------
Jim Sams
'69 mustang Coupe
372C

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MDF99
Gearhead

Posts: 234
From: Hamilton, Ohio, USA
Registered: May 2001

posted 06-28-2002 11:09 AM     Click Here to See the Profile for MDF99   Click Here to Email MDF99     Edit/Delete Message   Reply w/Quote
Your 372C sounds like it's a neat motor, what's the rest of your engine combination? I went to college at UNC-Asheville and have a bunch of friends that live in Charlotte, great city!! I miss NC, have a good one.

------------------
Matt Fraley
1966 Mustang Coupe; 289, T-5, 9" 3.50
http://mdf99.tripod.ca/289_Side.jpg

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Mpcoluv
Gearhead

Posts: 1341
From: Charlotte NC usa
Registered: Apr 2001

posted 06-28-2002 01:02 PM     Click Here to See the Profile for Mpcoluv   Click Here to Email Mpcoluv     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by MDF99:
Your 372C sounds like it's a neat motor, what's the rest of your engine combination? I went to college at UNC-Asheville and have a bunch of friends that live in Charlotte, great city!! I miss NC, have a good one.


Well, 4V heads bowl blended, guide streamlined and polished chambers. 10.4:1 compression, Isky custom cam 224/232 dur @ .050, .545/.565 lift 108 LDA. HV oil pump, Price motorsports restrictors with the lifter gallery restriction drilled out to .125. I am currently using Dan Jones strip dominator with a 1" spacer and a predator carb. I just received a Terry Parker Funnelweb intake designed for use with the roush type port inserts. I'll put that on at some time. Terry is a very nice guy to deal with BTW.
Lets see...Tubular automotive headers (poor ground clearence!), and 2 1/2" exhaust with H-pipe and 3-chamber flowmasters.
Waiting in the garage is a canton 7 quart road race pan and pickup and a 8" detroit locker (yes I still have the 8").

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