Chassis reinforcement for RSR style duct

[Andy Somogyi]

Hi all,

I'm installing a center mount radiator with an RSR style duct behind it in the front of my 76 912 (swapping to water cooled).

One thing that bothers me is the in the front bottom of the trunk area, there is a double layer box section (see in red).









How important is this for structural support? This is the area that I'll be cutting away to clear the RSR style duct.

Now, under the new radiator, I'll be fabricating a cage out of 7/8" chrome moly tube, this will attach to new brackets inside the bumper, to the side of the tub, under the bumper brackets, and to the torsion bar mounts. This cage is designed to protect the radiator from curb impacts.

My question, is do you suppose this new cage will compensate for the loss of structural support from cutting out the front box section?



Here's the general idea of what I want it to look like when done.




I've got a build page here if anyone's interested

https://www.facebook.com/ArrowBlau/

[Bill Verburg]

Originally Posted by Andy Somogyi

Hi all,

I'm installing a center mount radiator with an RSR style duct behind it in the front of my 76 912 (swapping to water cooled).

One thing that bothers me is the in the front bottom of the trunk area, there is a double layer box section (see in red).









How important is this for structural support? This is the area that I'll be cutting away to clear the RSR style duct.

Now, under the new radiator, I'll be fabricating a cage out of 7/8" chrome moly tube, this will attach to new brackets inside the bumper, to the side of the tub, under the bumper brackets, and to the torsion bar mounts. This cage is designed to protect the radiator from curb impacts.

My question, is do you suppose this new cage will compensate for the loss of structural support from cutting out the front box section?



Here's the general idea of what I want it to look like when done.




I've got a build page here if anyone's interested

https://www.facebook.com/ArrowBlau/

You can cut that area and weld in this, it's a copy of the duct used on the original RSRs
RSR front valance duct

[Andy Somogyi]

Originally Posted by Bill Verburg

You can cut that area and weld in this, it's a copy of the duct used on the original RSRs

RSR front valance duct

I’m doing a variation of that idea. The real RSR duct cuts into the spare tire area, and I’m not willing to lose the spare tire. Also my duct will be a lot taller as the radiator core will about an inch below the hood.

I’ve laid out where the spare tire fits, and I’m fabricating the duct around it.

The thing is I’m still not sure how safe it is to cut through that double wall section right in the lower front — I’m not sure how structural it is. But in any case, I’m hoping the radiator cage will compensate.




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[Cory M]

I think most of the critical support, between the forward control arm mounts, is in the pan further back. People have been welding in ducts, like the one Bill linked above, on these cars and racing them hard for 50 years now. Don't overthink it. If you want to stiffen the area up weld in some tubing and do some seam welding, that would be stiffer than the bolt on cage.

[Andy Somogyi]

Originally Posted by Cory M

I think most of the critical support, between the forward control arm mounts, is in the pan further back. People have been welding in ducts, like the one Bill linked above, on these cars and racing them hard for 50 years now. Don't overthink it. If you want to stiffen the area up weld in some tubing and do some seam welding, that would be stiffer than the bolt on cage.

I think you're right. I made a super simple model (just a tub with struts and control arms) in Autodesk Inventor, and there was very little loading in the front section. I think they probably just put it there for impact protection.