reinforcing firewall?

[rodjr]

Just curious about adding plywood to firewall, I have one of the rpm bodies and my firewall needs some reinforcement. The firewall is concave (in about 1/4" at the center of the outside of body ) and has a shallow valley glassed in the inside outer edge, then a hump about 1.5" wide then back down across the center. Is it supposed to be concave on the outside? If i set a piece of ply on the inside as it is, it will only touch at the 1.5" wide portion near the outside and i will have an 1/8" gap across the center. if anyone has wooded a firewall on one of the rpm bodies i would love to hear how you did it. If i grind the hump out and try to force everything flat it is going to take considerable effort and may cause distortion around the outside edge. If i force only the lower edge flat i will have a shallow bowl for a firewall. I am stumped.

 

[RPM]

Are you referring to the lip on the front of the cowl, that the original hood set into?

 

[butch27]

I built mine up with roven woven fiberglass.

 

[rodjr]

Are you referring to the lip on the front of the cowl, that the original hood set into?

No not the lip on the outside, I am referring to the surface of the inside. It does appear to be manufactured this way on purpose, I just don't really know how I am going to get it flat. If I run a straight edge from side to side on the outside face of firewall, I have 1/4" - 3/8" gap in the center.

 

[rodjr]

I should add that if I place the straight edge horizontally across the very top of the outside of firewall, the cowl body line also has this gap. To put it another way, if I were to place a 1/4" thick strip, 2" wide, in the center of firewall from cowl to floor, my straight edge would go right over it horizontally.

 

[one finger john]

pics or it aint so .....

 

[akzale]

I have an RPM body and didn't notice this issue! I sanded down the inside of the firewall, and glassed in a straight piece of 1/2" marine grade plywood. Set about 50 pounds of weight on it and let it set up for a couple days. The front of the firewall is as straight as can be! I'm well pleased with the way it turned out and the quality of the RPM body!

 

[rodjr]

I wish I could do pics, but I don't own a digital camera, and I don't own a cell phone, and I really only have internet at work and the library. I guess you could say I am a bit old school.

 

[rodjr]

Really i am overthinking it, my best bet is to just remove the existing firewall and glass in a piece of ply, that actually will be pretty easy.

 

[one finger john]

You could just glue and bolt the plywood to the back of the existing, glassed in firewall and address the concavity that way. Unless, of course that bows the body out or warps the body in some other way.

Don't you have friend that has a digital camera? It is 2015 you know. And a few pics are worth a thousand words.

 

[PotvinGuy]

Can't imagine RPM would make it that way. I think you have a reject. I'd cut the whole firewall out and replace it with a plywood panel and glass it in. But I'd call Ron at RPM and see what he thinks first.

 

[rodjr]

Yes, I will talk with Ron when I next call for more parts. I did not really think to bother him with it, I figured when I ordered it that any $ 400 body would certainly require some work. No big deal, just want to get it flat.

 

[rodjr]

best i could do, i have never posted pics before. i notice that the dash has about the same bow to it, and with 3 corners of the body touching the frame the drivers rear has to be forced down about 1/4" - 3/8" to touch the frame. I assume this is fairly normal? Edit: Never mind , thought i figured out the pic thing but it did not work.

 

[rodjr]

Tried again, hope it works.

 

[T-Test]

I cut a piece of plywood to fit the inside of firewall and not touch the edges where it was thicker. Bondoed the plywood onto inside firewall with the bucket standing up, resting on the firewall and placed cement blocks on the plywood to keep the firewall flat on concrete surface to fix my body by MAS. I then fiberglassed the edges with cloth and resin to fill in where the plywood did not touch the edges of the body on the inside of the firewall. Hope this helps. Bruce

 

[Zandoz]

What T-Test said! Or there are other options. On mine I'm planning on covering the fiberglass firewall with 3/16" sheet of aluminum diamond plate. On the inside, above the firewall transmission cut out, I'm going to run at least 1 piece of extruded aluminum T-slot all the way across the firewall...sandwiching (and flattening) the fiberglass between the diamond plate and the t-slot.

 

[butch27]

I think all bodies are like this because of a mold release line there.

 

[bobs66440]

I think all bodies are like this because of a mold release line there.

My Spirit fire wall is perfectly flat. I was able to bond a piece of 3/4" plywood to the inside for mounting the gas pedal, fuse box, etc. without any problems. Maybe you can just get a flat replacement firewall, cut yours out and bond the new one in. It would probably end up being less work that way.

 

[cooter]

Mine looks like that also. there is enough flex in firewall that it will mate flat with ply wood if you stand it up on firewall and set cinder blocks on top of plywood reinforcing till bondo cures.

 

[cooter]

View attachment 11501 Tried again, hope it works.

looks like mine