Can/should I use this stock flex plate?

I would like to use a stock flex plate from an original 1971 Mercury Marquis 429 2v. The flex plate is pristine with no damage and it looks almost new. The application is: 499CJ, mild comp cam, 9.3:1, with a TCI C6 in a 4000 pound Torino. What do you guys think?

Run it!

If its in good shape (no cracks in the center), why not?? Be sure to run the spacer ring with it too.

Yes, I do have the spacer ring and no, there are no cracks anywhere. I am concerned that this engine this flex plate came off of put out a lot less HP than the current engine at about 460 max, which it will never see on this street cruiser. Just wanting to make sure I'm not missing something.

How much do you value your feet?

While the stock flexplate is generally fine for less than 600HP/6000RPM, why even risk it with SFI certified flexplates being so cheap?


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I don't think I have ever saw a stock flex plate fail but I have first hand experience with a cheap Sfi piece. Maybe I'm just unlucky but I do still have my feet.

I bought a brand new SFI flexplate  from Hughes Performance, and had problems. It didn't run "true", and it was oblong...out of round. What a POS. It made for a nice shiney piece of scxrap metal.
It was Made in China

Purchased a new one from Ford Racing, and its been spot on!!
But before all this, I was running a factory stock unit and going 10-teen's and 10.20's with it!!

Stock 429 flexplate...

Probably one of those cheap Sfi units ^^^^^^

cool40 wrote:Probably one of those cheap Sfi units ^^^^^^  

Nope.  Read the comments in the video.  They didn't have an SFI, so they decided to roll with the stock 429 flexplate.  850HP, 7th run...kaboom!

I'm sure somebody on this board or the other one know all the finer details.


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That's comparing apples and oranges dude! Look at the application. Mild cam, low compression. I say run it I trust the factory iron up to 500 ish.

Carl wrote:

cool40 wrote:Probably one of those cheap Sfi units ^^^^^^  

Nope.  Read the comments in the video.  They didn't have an SFI, so they decided to roll with the stock 429 flexplate.  850HP, 7th run...kaboom!

I'm sure somebody on this board or the other one know all the finer details.


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I didn't see where it said anything about stock flex plate in the comments I found but wtf ever. I seriously doubt the OP would have problems with one in his application but maybe he should buy a cheap Sfi flex plate and even a Sfi blanket or shield to protect him?

Carl wrote:Stock 429 flexplate...

First off you don't use a flex plate on a dyno.....that was a flywheel and you should learn the background of the video before posting it.

dfree383 wrote:First off you don't use a flex plate on a dyno.....that was a flywheel and you should learn the background of the video before posting it.

I use flexplates on the dyno.  Lots of people do.

Lots of people also say flywheel when they mean flexplate, so hard to say what they were really using, unless you know something about the engine in the video. And it's a public video. If they don't want people sharing it, they can change the privacy settings.

cool40 wrote:I seriously doubt the OP would have problems with one in his application

I agree, but I'd rather have a new SFI flexplate than an old used one with an unknown number of miles, and unknown history.  I use them all the time, and have never had an issue.  To each their own.


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I've put more than 750 hp through a stock flex plate hundreds of passes in a car but you're right again Carl! Maybe I should go buy a lottery ticket!

Carl wrote:

dfree383 wrote:First off you don't use a flex plate on a dyno.....that was a flywheel and you should learn the background of the video before posting it.

I use flexplates on the dyno.  Lots of people do.

Lots of people also say flywheel when they mean flexplate, so hard to say what they were really using, unless you know something about the engine in the video.  And it's a public video.  If they don't want people sharing it, they can change the privacy settings.

cool40 wrote:I seriously doubt the OP would have problems with one in his application

I agree, but I'd rather have a new SFI flexplate than an old used one with an unknown number of miles, and unknown history.  I use them all the time, and have never had an issue.  To each their own.


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Yeah I do know something about the video and it was a flywheel borrowed from Kaase.....

Lots of people are stupid too, But whatever

Using a flexplate on the dyno, SFI or not could go very wrong, real fast. It could turn into a wobbly piece of sheetmetal. Flexplates get some of their stiffness strength from having a torque converter bolted to it and the nose in the crankshaft pilot bearing.

Thanks to all for your helpful comments. I'm going to run the stock flex plate in this cruiser application.

Doug Rahn wrote:Using a flexplate on the dyno, SFI or not could go very wrong, real fast. It could turn into a wobbly piece of sheetmetal. Flexplates get some of their stiffness strength from having a torque converter bolted to it and the nose in the crankshaft pilot bearing.

^^^^^What this guy said!!!