Flexplate and TC for a BluePrint 408 Magnum

Morning all,

Let me try and clear up any confusion on the matter. Even though our engine uses a Mangum block, it's built to be as close to an LA engine as possible. The only thing "magnum" about it, is the block, the weight on the harmonic balancer, and the intake bolt pattern. The REAR Balance, is as LA360 as it could be.

Aftermarket rotating assemblies can be balanced several ways. It's really just adding, and/or removing weight from various places to achieve balance. Be it internal, or external.

In the case of a BluePrint 408 mopar, it's balanced as any external LA 360 would be on the rear.

The balancer we use is a 1970+ LA style, we simply use the magnum weight on it. This cuts down time and cost to the end user when balancing. That's where anything magnum leaves the discussion when it comes to the rotating assembly.

The title of the thread could be edited to "BluePrint 408 stroker flexplate and Torque converter options" as it's not a "magnum" engine.

Now, let's also understand that today, most aftermarket flexplates sold. Carry the rear engine balance weight. That's because most converter companies just sell a neutral balance converter. (Chrysler was the only company from the factory to weld weights to converters, instead of flexplates, that i know of)

So assuming you're running an aftermarket converter, with no weight, you want this flexplate.
Chrysler SB Steel SFI Flex Plate - LA 360 SB EXTERNAL BALANCE - Chrysler Compatible

There aren't many/any oe converters I'm aware of that would have high enough stall for a cammed stroker, and be balanced for an LA 360. So again, you are looking aftermarket (probably neutral) converter.

Here is our balancer that comes with the magnum weight installed. So problem solved there too. Harmonic Balancer - Chrysler Compatible - 273, 318, 340, 360 and 408


As a notable caveat. Since chrysler did balance converters, and not flexplates, if you did somehow buy or find a stock la360 balanced, weighted converter, you could run that with a stock (neutral) flexplate. Beyond the obvious of being a 50 year old flexplate, That would work, from a balance perspective.

Either the converter or flexpalte need to carry the LA360 weight. One or the other. The oe and aftermarket placement just vary on where they put it.

Hope that clears it up!