360 Magnum previously run with a 727. Now going with a 904. Which flex plate do I use? I heard at one time the 727 magnum flex plate will interfere with the starter on a 904.
Thanks Doug

Nobody has used a Magnum 360 with a 904?
Doug

I just asked in the race section not long ago about a 360LA/904.
The 360 I asked about will be internally balanced.
In all of the questions and answers, phone calls made to manufacturers, I found out the 360 (internally balanced) uses the same flex plate as a big block, and either the 727 or 904.
I know you asked about a 360 magnum, (externally balanced I assume) I can’t answer if there’s any differences.
Doubt it helps, but it’s what I know.

Wally.

Same flexplate as an LA would use, assuming it's carbed. Make sure your torque converter has the Magnum imbalance weight on it.

LA and Magnum don't have the same amount of imbalance. Magnum flex plates are available to fit neutral balance converters. Just not sure if there is a part that fits the 904 trans.
Doug

You put the imbalance weight on the torque converter, not the flexplate. Use a 904 flexplate and a P5249843 kit to balance the torque converter for a Magnum 360, instructions should be in the kit but you position the included weights, weld them on and done.

The factory built flex plates with the imbalance weight welded on for Magnums. Just cant find the part number. I have welded the converters in the past.
Doug

Doubtful there is a part number for a factory Magnum flexplate that fits the 904 since no 904 was put behind a Magnum 360.

Not even sure that the A500 was either. You can find the weighted Magnum flexplate for the 360 but it goes with the A518 type trans. (98 B2500 for example). Will it fit your application? I dunno.

B&M used to produce an SFI approved flexplate for this swap: 5.9L Mag to 904. Part number was 10241. It was discontinued years ago, but you may be able to find one if you don't want to go through the headache of welding weights on the TC.

Try PRW

Looks like I'll weld them on. I didn't think this was that oddball a combo. PRW doesn't have one either.
Doug