Some questions on underbody stiffener plates for 67 convertable:

(1) Mine's gone. Should I replace it? Is it worth all the added exhaust hassles?

(2) If I do replace it, how do they mount? I've seen photos of replacement plates with six large holes. Are there some sort of rubber mounts? I've got the six threaded bosses on the underside but the threads are pretty much gone. I will either need to drill and tap oversized holes or use nuts and bolts.

yes replace the stripped welded nuts and put the reniforcement panel on.convertibles flex more than coupes there could be long term damage to the way your doors close do you want to take that chance? if your running duel exhaust run the pipes thru the pan close to the drive shaft.

Any info on how to bolt it up? Any special washers or rubber needed? The stiffeners I've seen in catalogs don't seem to come with hardware.

When I got mine ( a 69 400 vert.) that stiffener plate was missing....Also mine has two straight pipes w Glasspaks, then to 71 model T/A tips, but there was no problem installing the stiffener plate...it cleared even my 'aftermkt'pipes...But you `ll want it there to stiffen the body , eliminate twisting...I got mine new repro from Ames ,not sure what i paid ( 2 yrs ago),but I think around $85.00, this plate is often missing because its removed for tranny work...and often not replaced...its the same piece for 67-69... You can sometimes find these on EBay , but usually at the same cost as new...Mine did not come w bolts ,but those 6 bolts you can just match one to the hole and buy them at hardware store..no bushings,its supposed to be rigid.
its called " convertible under body stiffener plate " or such....

Bjorn

if you get the bolts from a hardware store make sure there at least a grade 5 or grade 8 bolt

also i have a drawing of the plate installation if you need it. it shows the bolt and washer asy. as part # 3872454 you might be able to get from GM, not sure.

Sure. I wouldn't mind seeing a drawing. Can you e-mail it?

no problem send me an e-mail at firebird69racer@yahoo.com

Here are a few pix of mine on my 67 Drop Top. Another lister posted them on his site, but this should give you a good idea? Second set down on the left.
http://community.webshots.com/user/frazel

I'd say put it back on. You'd be surpized at how much the body will flex on a vert, especially behind any power!

Brett - 67 Drop Top 455!

Great pics, 1stgen. That helps a lot. Thanks. The plate is a lot smaller than I was picturing. I was envisioning something that covered most of the underside.

I'm jealous how clean your bird is underneath. Not much road salt there in the great northwest? Mine's actually not that bad for a northeast car but I still get a rust shower every time I crawl around underneath.

Brett,

What mufflers are you running? Looks like they tuck up there pretty good.

And yes, those are great pics. I've been trying to figure out where the x-brace goes. I've heard I may have a little more trouble trying to fit an x-pipe through it as opposed to an h-pipe like you have.

Jed

Bob S. There's a plate on Ebay now. It was only $20 yesterday I think. Sorry I didn't get the item #.

Robert

Thanks Firebob. I'll probably cough up the 90 bucks to get a new one from Ames or Classic Industries. I just crawled under there again and the half assed exhaust I rigged up with Pep Boys 45 bends off the header collectors will be tough to get to work with the plate. I plan to get some cast iron manifolds and a real exhaust system and then I'll go with the plate. Thanks all for the help.

The pan on my 69 vert was there when I bought it. The car could even be stiffer so get the pan. I just bought the long branch manifolds from ames and went to a custom shop for a price (I like to go to shops that race cars, they seem to like muscle cars) $400-$500 depending on if the x-pipe will fit, h-pipe is cheaper. That's probably less than you can buy the parts for from catalog. Pete

Thanks... actually, I've driven the car for two years now, rain and all, and just haven't gotten around to cleaning it up on the underside.

I have Hooker Super comps with 3" collectors into 2.5" pipes with an "H" crossover, and under the X-pan, into flowmaster mufflers, that dump before the rear end.

I may run the pipes out the back some day... but it's got a nice deep rumble to it right now that cammands attention! Lol...

Anyway, hope the pix helped - Brett - 67 Drop Top 455!