Technical > Roo Man's Room

Rearend Upright Strap Thickness Requirement

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Countn Carbs:
Thank you guys.  I appreciate all the help and information.  Point taken on ordering the SFI specs and I will certainly do that.  Thank you again.

rooman:
Regarding this part of the spec: " Single plates must be
fully welded to the rear end uprights (#8) and to the upper (#4) and
lower (#16 & #17) frame rails on one side of each plate with 1/4"
(6.4mm) minimum wrap around the upper (#4) and lower (#16 & #17)
frame rails. The other side must be welded with one (1) inch (25.4mm)
minimum skip welds. Double plates must be fully welded to the rear
end uprights (#8) and to the upper (#4) and lower (#16 & #17) frame
rails on one side of each plate with 1/4" (6.4mm) minimum wrap
around the upper (#4) and lower (#16 & #17) frame rails."   the 1/4" wrap refers to the weld and not the mounting plate. That may sound pretty basic but I know of an instance of an NHRA tech inspector telling a builder that the plate had to be wrapped around the tube. As Larry Morgan noted in one of his clashes with the NHRA, "You can't fix stupid"

Roo

THE FRENCHTOWN FLYER:
Countin,

I see by your avatar car you are constructing a FED with a vintage inline six. While the SFI spec may call out 1/4" 4130 plates I think that in your specific case you could logically argue that the the 3/16" plates will more than suffice for the power you are capable of transmitting to the rear end. A good alternative to cutting off the existing plates and welding new - which would induce warpage into the rear housing - might be to weld localized reinforcements (i.e., washers)around the plate mounting holes. If at such time as you decide to install a blown hemi you could consider a further upgrade to the housing.

I'd feel perfectly safe with 3/16" plates.

Countn Carbs:
Regarding this part of the spec: " Single plates must be
fully welded to the rear end uprights (#8) and to the upper (#4) and
lower (#16 & #17) frame rails on one side of each plate with 1/4"
(6.4mm) minimum wrap around the upper (#4) and lower (#16 & #17)
frame rails. The other side must be welded with one (1) inch (25.4mm)
minimum skip welds. Double plates must be fully welded to the rear
end uprights (#8) and to the upper (#4) and lower (#16 & #17) frame
rails on one side of each plate with 1/4" (6.4mm) minimum wrap
around the upper (#4) and lower (#16 & #17) frame rails."   the 1/4" wrap refers to the weld and not the mounting plate. That may sound pretty basic but I know of an instance of an NHRA tech inspector telling a builder that the plate had to be wrapped around the tube. As Larry Morgan noted in one of his clashes with the NHRA, "You can't fix stupid"


Roo

Thanks Roo - this section did actually cause some confusion when I read that..

Countn Carbs:
Countin,

I see by your avatar car you are constructing a FED with a vintage inline six. While the SFI spec may call out 1/4" 4130 plates I think that in your specific case you could logically argue that the the 3/16" plates will more than suffice for the power you are capable of transmitting to the rear end. A good alternative to cutting off the existing plates and welding new - which would induce warpage into the rear housing - might be to weld localized reinforcements (i.e., washers)around the plate mounting holes. If at such time as you decide to install a blown hemi you could consider a further upgrade to the housing.

I'd feel perfectly safe with 3/16" plates.


Thanks FF - yeah the rearend plates are indeed 1/4" - it's the uprights that are 3/16" so it looks/reads like we're good.  Yeah you're right...just a little inline 6 with not much power but plan to run it monthly in our Vintage Drag Racing club.
Also - great article you wrote in this months 12 Port News!!  Looks like an awesome little project and looking forward to seeing more about it in future issues.

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