I pulled the trans out of my 91(727)and the flex plate out of 727 is different then the plate for a 518 I bought to put in the truck,are the flex plate out of the 727 and 518 different,or is the flex plate out of the 727 a after market plate,here is a pic of the 727 plate on the left and the 518 on the right.

 

Flexplates on the 1st Gen trucks were actually known to crack or lose the center bolt section completely. 2nd Gen flexplates were better and there are SFI flexplates available too.

 

My question is the flex plate on the left a stock or after market plate

 

Thats a stock one.

 

I have seen the SFI flexplates available on Ebay and are they as good as a brand new 2nd GEN flexplate? Also, what does SFI stand for? Thanks.

 

http://www.sfifoundation.com/home.html