Have an FE something.

Measured the depth of the piston through the spark plug hole with a 3/8" diameter wood dowl that was painted white.

Set the crank at 0 deg , based on the timing marks.

Measured #1 hole depth & #4 hole depth with the dowl contacting the piston and used a black sharpe marker to mark the depth at the top of the spark plug hole. Believe #4 piston is at BC when #1 is TC

Performed this measurement serval times.

The difference is 3-7/8", not 3-3/4".
This measurement would place the stroke at 3-7/8",
which is 1/8" > OE, 390 @ 3.784" stroke.


Is there an aftermatker 390 stroker crankshaft with an extra 1/8" throw
to the OE 3.784" stroke.

 

Don't measure between two different cylinders. Always measure the SAME cylinder at TDC and BDC.

 

Also , need to devise a better measuring method.

Using a 3/8" diameter all threaded rod with nut & washer.
Then adjust the nut with the washer contacting the spark plug hole with #1 piston TDC & BTC positions.

Should be accurate within one thread pitch.

 

You have the 3.784 stroke. The method has some inaccuracy built in, due to the angles involved. 1/8th inch is about what to expect when measuring this way.

Besides, with 3.98 stroke cranks from 428s and 410s around, along with pistons that work with the stroke/rod combo, why would anyone add so little stroke?

 

That is what I was wondering, why add only 1/8" additional stroke, it's not worth the trouble and expense, so measured again using the threaded steel rod approach, only picking on #1 piston, rather than #1 & #4.

Using a 3/8" SAE flat washer, 3/8" threaded rod & nut, set the the crankshaft at 0 deg, TDC with the timing marker. The 3/8" SAE washer just fits into the spark plug recess. Bottomed out the threaded rod, contacting the piston and turned the nut until it was just contacting the washer, then removed the threaded rod, nut & washer from the spark plug hole.

Measured the circumference of the vibration damper using a 1/4" wide steel tape.
From the 0 deg mark on the dampener measured 1/2 the circumference and scribed a line on the dampener. Rotated the crankshaft, clock wise, so the timing marker lined up with the scribed line. Then #1 piston was at BDC.

Performed the identical procedure with another the threaded rod, washer and nut with #1 piston at BDC.

Measured the distance from the washer to the end of each threaded rod using a 1/4" wide steel tape. The steel tape is only accurate to the nearest 1/16"

TDC = 5-1/4"
BDC = between 1- 11/16" & 1-3/4"

Noticed the threaded rod when inserted through the spark plug hole to be about 10 deg skewed from the piston bore centerline for both TDC & BDC measurements.

To correct the measurement to be inline with the bore center line, multipled each measurement by the cosine of 10 deg.

TDC (corrected) = 1-3/4" X cosine 10 deg = 5.17"
BDC (corrected) = 1 -11/16" X cosine 10 deg = 1.66"
BDC (corrected) = 1-3/4" X cosine 10 deg = 1.72"

Stroke = 5.17"- 1.66" = 3.51"
Stroke = 5.17 - 1.72 = 3.45"

The stoke is between 3.51" & 3.45".

Therefore, the stroke must be 3.50" ,which corresponds to an FE 360 & consistent with the build stricker on the door jam from the donor vechicle.

 

Gotta hand it to you method wise....too bad it's a 360. That can be fixed.