At 08:19 PM 2/24/2000 -0500, Andy wrote:
>My friend has a 95 Lightning and he says he wants to stroke the engine.
>what is stroking the engine
> can I do it to my 4.7 5spd 3.92 2wd ?
>about how much does it cost ? is it worth it ?
Ohhh boy :) hehe
Stroking means to increase the piston stroke. Can be sone several
ways. Either taking a compatable crank from a larger engine, and cutting
the main and rod journals (along with counterweights, oil seals, etc.) down
to the size you want, or by offsetting grinding the crank and use longer
rods, or simply using longer rods from another engine and cutting the big
end to proper size, and using a compatible piston. The benefit of that is
better mechanical advantage. The rod is at a better angle to push down on
the rod journal to produce more power. A side affect advantage is less
cylinder wall loading due to a better rod ratio, which means you can run
with a thinner cylinder wall, thus increasing cubic inches even more than
just increasing the stroke. A disadvantage, severity depending on amount
of stroke change, is limited RPM range. With a longer stroke, the rod
becomes "heavier" as it swings around. Push it to hard and you have
problems. All depends on the block and amount of increase of stroke.
For racing purposes, if your racing a real short, tight track (circle track
racing), a short stroke is preferred, you can rev up faster. For a long,
high speed track, a longer stroke is desired, along with heavy crank and
strong light rods.
Price? If you go with an off the shelf kit? Too much. Plan to get
poked. If you do it yourself, it's very economical, depending on the
engine and desired stroke. For instance, with a Ferd 302, as an example,
you can go at it several ways, depending on desired cubic inch result you
want. I apologize for the Ferd content, I'm more familiar with Ferds than
Mopars.
For a 315 stroker (from 302 block), you would offset-grind the crank from
its existing 2.123 rod journal diameter to the 2.0468 2.3 Pinto size. This
will allow you to stroke the crank about .076". This will bring you out
from 301.6 cubes to 309.2 cubes if everything matches up right. That'd be
a standard size Pinto journal. Next, you take a set of 2.3 Pinto
rods. The big ends will have to be narrowed, along with the rod
bearings. This is really trivial if you have the equipment. One nice
thing is it lets you choose your own bearing widths and rod side clearance
- something you're pretty well stuck with on a standard production
engine. The 2.3 rods are substantially beefier than plain old 5.0 rods,
and they're even bulkier than the SVO rods. Next, the small ends have to be
honed just a bit to fit the V8 pistons- the nominal pin size for the 2.3 is
.911", the pin for the V8 is .913." Finally, you select a piston with a
fairly deep dish - TRW makes some -and you turn the rim of the dish down
from 1.60 nominal to around 1.42, depending on your stroke, deck height
variation, etc. With a .030 overbore, you're looking at 313.8 cubes. With
.040, 315.4 cubes.
Another way is to turn down a 351 Cleveland crank, but it's not
economical. Take one 351C crank, chuck in a lathe, turn OD of
counterweights down to 5.9", turn rear seal diameter down to 302
size. There's some hand work required on the counterweight ends for piston
skirt clearance. The oil slinger flange in back may have to be modified
depending on whether you have a 302 or 5.0 block.
Have crank cut down from 2.75/2.311 rods and mains to 2.25/2.045 rods and
mains. Take two sets (8) Pinto 2.3 rods. The pin ends need to be opened
up to .927 Chevy size. The bearing ends need to be narrowed to fit the V8
journal size. This is a primo chance to properly set the rod side
clearance, ordinarily there's nothing you can do about it. I recommend
having the rods sized for *pressed* pins.
One set of eight Keith Black 350 Chevy pistons, intended for 6" rods. These
have the right pin height to match up with the Pinto rods and Cleveland
stroke. They have a large valve relief in the deck - I don't know how
they'll clear Ford valves. I don't expect any trouble, but it's simple to
fix if needed. The entire reciprocating assembly must be balanced. It's a
simple no-heavy-metal balance, no problem. Anyone who's paid sharp
attention will notice we're cutting almost a quarter inch of metal off the
rod journals, allowing strokes from 3.25 to 3.75, with displacements from
330-ish to 380-ish (if you were seriously crazy). Yes, you could offset
grind a Cleveland crank down to 3.25 and build a 331. No, it's not a
workable deal - the shops I've talked to want lots more money (on the order
of 3x) to offset grind a crank, than just to whittle it down. By the time
you add in reducing the OD, fixing the rear seal, etc, you're right at the
same price as the forged SVO crank. You'd be crazy to run a carved
Cleveland crank if the SVO is in the same price range.
Want to get 450 cubes from a 351 Cleveland block? Use a 400M Crank. Ferd
engines are so versatile.
Hope that answered your question. I don't know about Mopar engines, never
fooled with them. Time for some aspirin.
Mike
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