340 Flex Plate Question

[kend]

Are the internal balance and external balance flex plates the same? I've had two different answers to this question today and now I'm more confused.

 

[bbrroowwnn]

good question! I know the dampers are definitely different.....my guess would be the flex plates for auto trans are the same due to there rather light weight.......However, flywheels for manual trans I would think would be different because of their heavy rotating mass....I'm also interested in what others have to say....

 

[70aarcuda]

ok....let us clear the air....the same OEM flexplates are used with internal and externally balanced engines because the OEM converter has the weight on it...So they are the same from the OEM..aka Chrysler...this is in relationship to the LA engine....

Aftermarket flexplates...B&M is probably the most popular flexplate for externally balanced engines...as the flexplate are engine specific cause they remove the weight from the converter and put it on the flexplate....so then they are not the same....this allows the converter to be neutral balanced. The newer B&M externally balanced flexplate actually does not have any weight on them...the older ones due....but have a section that is removed from the flexplate...so removing from one side is the same as putting weight on the other side...

So with a 340 steel crank you want a internally balanced flexplate...OEM or Aftermarket solid no cut outs...Like B&M

https://www.summitracing.com/parts/bmm-10230/overview/make/dodge

the 72/73 340 with cast crank is going to need a externally balanced flexplate...

https://www.summitracing.com/parts/bmm-10235/overview/make/dodge

This is the mopar performance flexplate that can be used on a steel crank 340

https://www.summitracing.com/parts/dcc-4529751/overview/

and then the above MP flexplate can be used on a 340 cast crank as long as the weight is on the converter...see the confusion...

 

[jeffnmo]

Well put, that should clear things up once and for all!!!

Jeff

 

[kend]

It does for me, thanks!! It also explains the two different answers I got, so they were both right. That's some handy information right there!

 

[krazykuda]

There are 4 basic flex plates for the Mopars...

There are two different crank bolt patterns, symmetrical and offset...

Then there are two different torque converter bolt patterns, 10" and 11" diameters...

Figure out if your crank is symmetrical or offset, then match the torque converter pattern...

Mancini Racing