Flexplate question

[1968Droptop]

I have a question regarding which kind of flexplate I need for my application. I'm building a 750hp BBF for my boat (max rpm's is near 6.8K). A buddy says to run a SFI flexplate. I can see no differences between a SFI and stock unit, except for the thickness of the plate itself. In a jet boat application the flexplate is only used to start the engine. Why would I need to run an SFI unit, when the only thing the flexplate is used for is starting the engine ? Am I missing something here ?

[Duane HTP]

Yes, Like you said, the SFI Plate is thicker and that is very important. In a car application, the flexplate is bolted to a torque converter. This gives it rigidity. In a boat there is nothing bolted to it to stiffen it back up, and the flex plate will do just what the name indicates, FLEX. This can cause premature starter problems. I know, there'll be serveral that will come on here and say I've run mine that way 10 years with no problem. But, It's by far best and good insurance to run the thicker flex plate.

[mach1alaska]

Yep what Duane said:)

[1968Droptop]

That makes sense Duane, thanks.

[Cas]

I ran into exactly what Duane mentioned with an SFI flex plate that ended up warping. Unfortunately, I thought I was getting a good SFI approved but that was not the case. When I replaced it, I went with this one
CSR Torque Master (http://www.jegs.com/webapp/wcs/stores/servlet/product2_10001_10002_748020_-1)

[Oldsquirt]

...... When I replaced it, I went with this one
CSR Torque Master (http://www.jegs.com/webapp/wcs/stores/servlet/product2_10001_10002_748020_-1)
Same one I chose back in 2002 for my Chevy. Much thicker than any of the
stock ones or most of the inexpensive SFI ones. Much pricier, too, however.
Keep in mind, SFI only dictates the minimum requirements, so not all SFI-rated parts are created equal. For flexplates, I believe they only specify minimum thickness and amount of weld area holding the ringgear to the web.