360/380HP Magnum crate engine FLEXPLATE balance question

I just bought a 360/380hp crate engine, hydraulic roller Magnum based.
It came with a B&M flexplate for a neutral balanced converter. Part # 10236
This is a 360 flexplate for use with 727 transmissions.

I just had a little look, as I'm putting the engine in a 904 based transmission car, and it lists a different flexplate for 360 with zero balance converter. Part# 10239
So searching I found the diameter is about 1" bigger for the 727 flexplate, and it sometimes contacts the starter. Fair enough, but that's not the issue IMO. lol
The 360/380HP crate engine is Magnum based, and literature says it's externally balanced, but a DIFFERENT external balance than a cast crank LA 360!!!!!
So, I need to find the correct flexplate I'm guessing, and let the guy I bought it from know he was running the WRONG flexplate!!!!
Anybody run a 360/380hp crate engine (Or 300hp version) with a 904? What flexplate did you use???? Thanks!

ATP Z-332 flexplate is the only thing I can find, and not sure if it's right yet!!!

Mopar typically put the imbalance weights on the converter, not the flexplate. Check your converter for this, the PO might have very well done it like that.

The flexplate you mention requires the weights on the converter too, unless you had your magnum internally balanced.

I believe 360 LA externally balanced engines had weight on the torque converter. The B&M flexplates allow running zero balance converters on the externally balanced engines.
The 360 Magnum is different, balanced differently, and unless I'm wrong the 360 Magnum flexplate has the weight welded to the flexplate and had a ring around the edge which served the crank sensor....

So..... I believe the needed B&M flexplate is discontinued. Part# 10242 for 360 Magnum balancing.
I've talked to a dozen guys with 360 crate motors who run the (incorrect??) B&M flexplate, they had no idea Magnum 360s and LA 360s were balanced differently!!!

B&M #10241 for a 904 trans to 360 Magnum. #10242 for 727

I had a few of the 300hp/360 Magnum crates external balanced and used the 10242 scalloped flexplate with my 727, no weights on converter.

Yup, I think that's correct. Most guys are running the NON Magnum 10236 and 10239 flexplates. It's actually an incorrect balance, the 10242 (727) and 10241 (904) are the proper flexplates for the Magnum engines. Crazy

I’ll be right back after I get a pic of mine

Mine

I’m thinking of getting a couple of 318-904 plates and cutting the half moon out myself

205994??? Who's Flexplate is that?

Discontinued B&M, bought 25 years ago

Looks to be the same as a 10236 but a different part# !? That's an oldie I guess!

I had a regular production 360 that was originally external balance.
Had a big weight tacked to its converter.
Changed the thing to internal balance stroker, knocked the big weight off the converter, and swapped out the balancer.
Ran smooth as glass.

Could be, I was looking for a 360 LA flex for a 904 trans. It was $150 and change, one for a 727 was $85 but it was bigger diameter and had both hole positions. My idea was to chuck in lathe, cut the 1/2” off but not sure what the balance difference would be. A good math guy could figure that out I suppose. Then I could get the one for a 318-904 then cut the 1/4 moon out. Many ways to skin a cat

Was an everyday question at a former job, back when dinosaurs roamed the earth.

5.9 magnum and 360 LA are absolutely, positively not the same external balance spec.
The magnum had a lot lighter piston and rod assy.

The early 5.9 magnum started with a weighted converter and a zero balance flexplate with one offset hole like we are accustomed to, but was
later changed. I forget the changeover year. I want to say 1994 or 5, but that's probably wrong.

After the changeover year, the factory went to a balanced flexplate as shown, and the converter was then made zero balance, and the one-offset hole was done
away with, making the converter bolt pattern symmetrical.

A late style flexplate like ATP Z332 could be used, if the converter is, or is changed to symmetrical bolt pattern/zero balance.
https://www.rockauto.com/en/moreinfo.php?pk=2746860&cc=1366590&pt=8608&jsn=938
https://www.rockauto.com/info/4/Z-332_2.jpg

B&M doesn't really care about that business anymore, as we've seen.....

This is a 2001 Magnum lockup converter, no weights on either side. I didn’t remove flex-plate so not sure if that’s where the offset is. It had the firing square holes on out side.

The offset is indeed on the flexplate, because the 6 bolt pattern on the crankshaft is asymmetrical.
Flexplate only goes one way.

This was almost an admission of several decades of engineering oversight....

In hindsight, flexplates could have been made balanced in 1973 because of the crank bolt pattern, but were not.
Instead the weight was added to the converter and the converter also had asymmetrical bolt pattern.
The complexity and slightly increased difficulty of assembly and service was really unnecessary, they could have done all cast cranks the same as a 2001 5.9 magnum all along
if they'd figured it out sooner.

Once the flexplate contains the imbalance, then the converter can be built to neurtral and bolted on in any of the 4 positions.

^^This^^ lol
I cannot believe how many guys I've talked to run an LA 10236 or 10239 flexplate on the MoPar Magnum based crate 360s.
I was given a B&M 10236 flexplate with the engine I bought- 360/380hp MP crate engine. It's what they ran when they couldn't get it to "run right". They swapped to a dual plane intake then gave up. Thankfully lol
I found a 10241 flexplate. The 10236 will sit on a shelf!!