When do I use an S.F.I. Flex plate

[MObarracuda]

I’m 30 days away from starting my stoked 340 and A500 combo in my ‘67 barracuda fastback. The engine has all edelbrock up top for intake and cylinder heads and is dumping into cast 340 exhaust manifolds. Should make 380-425hp....I think. This engine is in my street cruiser.

When would it be appropriate to step up to the S.F.I. Rated flex plate? Is now the time or is the stock flex plate adequate? I have a flex plate from a ‘67 273 and ‘68 318 or should I order a new solid SFI flex plate?

What would you do and why?

 

[70aarcuda]

By rule book a SFI flexplate is required went you run faster then 10.99.......

Depending on your torque converter as to whether it used 5/16 or 7/16 thread bolt...your stock one would need to be redrilled to fit the larger thread.....not much meat there...

I just bought the MP SFI flexplate for the 408 going in 71 Duster....I have one of those shown in the picture but did not like how much it weighted...

 

[Demonracer]

Personally, I'd run a new SFI flex plate just for my own piece of mind. JMHO

 

[daves66valiant]

That’s the same one I ordered. Fits 10” and 11” converters. ARP bolts and blue loctite

 

[n.y.340 dart]

Fresh engine fresh trans why not fresh flex plate?

 

[Plymouth 65]

I always use solid flex plates for my builds. Never had one crack, can't say that about a stock one! 65'

 

[MObarracuda]

Thank you all....I have never seen a SFI rated flexplate and I didn’t know if it mattered. Plymouth 65 post brought it home for me. The design of the OE flexplate allows for movement and there is no way to know if the metal has started to fatigue.

Just ordered one for me as an early Christmas present. Thanks for providing your opinion it really help! Merry Christmas everyone.

 

[MObarracuda]

By rule book a SFI flexplate is required went you run faster then 10.99.......

Depending on your torque converter as to whether it used 5/16 or 7/16 thread bolt...your stock one would need to be redrilled to fit the larger thread.....not much meat there...

I just bought the MP SFI flexplate for the 408 going in 71 Duster....I have one of those shown in the picture but did not like how much it weighted...

Quick clarifying question....when you say there is not much meat there. Are you referring to the stock 5/16 bolt or the metal block welded to the torque converter if it were to be inlarged to accept the 7/16 bolt?

 

[1969reddart]

I pretzeled up and snapped the flexplate on a stock 340 car. Use the SFI plate.

 

[MObarracuda]

Just recieved my new flex plate. It is much more substantial than the stock version. When I get a chance I will weigh the stock flex plate for comparison. Here are the photos of what came in the box and spelling doesn’t count....looks like a part not a pares. I made sure the serial number on the flex plate matched the certification sticker.