To STROKE or not to STROKE: 100th Topic (in ENGINE)

[RGR]

One of the main tools I use are dyno sims. The best
use they have is setting RPM range for componentry
like cams and airflow and porting. I recently ran a
very long sim and the main result tested was STROKE.

It seems that for maximum HP (all-out RPM)
the V6 really likes about what a stock 3.8 has
in terms of stroke. Right around 3.39" stroke...
It also seems that for maximum torque, the
truck crank of 3.74" is darn close to what the
computer liked for torque, 3.80" stroke.
1 result even had a 3.74" stroke making
nearly identical torque, just with different
other aspects changed just a bit.

Seems like Ford knew what they were doing!

Anybody have any ideas as to why they chose these stroke sizes ???
I mean theoretical, mathematical ideas, not just "cuz it works best"

COMMENTS GUYS? You are all much smarter now, so hit it!

[tire]

Anything to do with the fact is was copied from Buick? Maybe the answer lies in the Buick engineers? :-?

[RGR]

Quote: Originally Posted by V6PowerStang Anything to do with the fact is was copied from Buick? Maybe the answer lies in the Buick engineers? :-?

nope, but perhaps buick used the same rationale too...

It's because of piston speed in the bore for a given stroke,
strokers have to travel more distance in the same RPM range
so they have higher piston speeds. That limits RPM range
and increases frictional losses, so strokers generally have a
lower RPM range. A huge stroke may only want to rev to 6500
but makes much better torque than the smaller motor below this
range. For streetable motors it's best to use the biggest stroke
and matching components to get the power in by the RPM limit.
A 4.5 may not rev as high as a 3.8 but makes better torque
under the rev limit. This is highly simplified but generally true.

[RGR]

Overall, a stroker will run circles around a stock stroke V6,
under a given rev limit. Under ~6500 RPM I like the extra torque
these babies make. Even more so under 5500, in streetable RPM ranges.
But head and itnake flow is critical, as is camming.

[RGR]

TOP, good topic, from the past

[WhiteStang99]

wow, I missed all these topics back in the day...

[dark]

word. can i get a layman's definition of "stroking" robert?

[RGR]

Quote: Originally Posted by dark word. can i get a layman's definition of "stroking" ROBERT?

The stock 3.8 has a 3.39" stroke on the crank, and a 4.2 has a 3.74"
so using a 4.2 crank in a 3.8 is "stroking " it or increasing cubes through
using a bigger stroke crank. Then you can also offset grind a 4.2 crank,
that offsets the rod journals further from center, giving even more stroke.
It determines how far the pistons move, and that "swept volume" is the
engine's displacement, or cubic inch size.

I adjusted your quote above,

[tedness]

stroke it good.

the v6 will love you for it. also consider blower

[dark]

Quote: Originally Posted by RGR The stock 3.8 has a 3.39" stroke on the crank, and a 4.2 has a 3.74" so using a 4.2 crank in a 3.8 is "stroking " it or increasing cubes through using a bigger stroke crank. Then you can also offset grind a 4.2 crank, that offsets the rod journals further from center, giving even more stroke. It determines how far the pistons move, and that "swept volume" is the engine's displacement, or cubic inch size. I adjusted your quote above,

first off, sorry about the name error, i fixed it

second, thanks for that definition, but my question is, can i stroke my 3.8 up to 4.2, or do i have to get the 4.2 block?

[RGR]

Quote: Originally Posted by dark first off, sorry about the name error, i fixed it No Problem second, thanks for that definition, but my question is, can i stroke my 3.8 up to 4.2, or do i have to get the 4.2 block? YES, you can use your block. Everything fits.

See Pete's 4.2 post at the top of this board, it explains everything!

BTW, i have a 4.2 crank and pistons for sale, waiting to get a buyer!