Rearend Upright Strap Thickness Requirement

[Countn Carbs]

What is the required thickness of the vertical straps in the mounting of a rearend?  Mine are 3/16" (purchased from a well-known chassis builder) and I had another chassis builder tell me over the weekend they need to be 1/4" minimum.
I've tried to locate the requirement in NHRA and SFI regs but I'm not having much luck and I could sure use some clarification.

[gregm784]

Money is very well spent on buying a set of SFI plans. 

Here's the part on rear ends

-----------------------------------------------------------------------------
IV. REAR END MOUNTING STANDARDS
1. UPRIGHTS
a. 1 1/4" x .083" tubing (#8) on each side of the chassis with either one
(1) 3/16" (4.7mm) SAE 4130N steel plate per side (no bosses
required) or two (2) 1/8" (3.2mm) SAE 4130N steel plates per side with
3/4" (19mm) minimum outside diameter bosses. 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.
b. 1 3/4" x 1" x .065" rectangular tubing (#8) on each side of the chassis
fully welded to the upper (#4) and lower (#16 & #17) frame rails with
one (1) inch (25.4mm) minimum diameter bosses fully welded into the
uprights (#8).

2. BOLTED DIRECT
The rear end housing must have one (1) 1/4" (6.4mm) SAE 4130N steel plate
welded on each side of the housing. The plates must be fully welded to the
housing and the plates and welds must wrap around the housing a minimum of
180°.

3. BOLTED INDIRECT
One (1) plate required on each side of the housing. The material may be either
1/4" (6.4mm) SAE 4130N steel or 3/8" (9.5mm) 6061-T6, 7075-T6 or 2024-T3
wrought heat treated aluminum alloy (no cast tooling plate).

4. FASTENERS-MINIMUM SPREAD DISTANCE-EDGE DISTANCE
For indirect mounting, all of the mounting fasteners, provided by the
manufacturer, must be used to attach the plates to the rear end/axle housing.
All plates must be bolted to the rear end uprights (#8) using at least four (4)
7/16" (11mm) SAE Grade 5 (Class 9. or better bolts with steel self locking nuts
on each side. The bolt hole minimum spread distance is five (5) inches (12.7cm),
measured from the centerlines of the outermost bolts. The minimum edge
distance for all plates (including the upright plates) is 1 1 /2 times the bolt
diameter, measured from the centerline of the bolt to the nearest edge.
-----------------------------------------------------------------------------

[gregm784]

Same thing in a PDF you can download.

[hemidakota]

I agree with Greg M., the SFI book has so much more in it. Money well spent and all the information you will need. As I recall it only took two days to get the book also. Good luck and most of all Good Times.
Greg S.

[George]

Buy into the SFI.                                  https://sfifoundation.com/

[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.

[fuel749]

Just so no one gets confused if they happen to find out their rear end uprights aren't .083 wall, the spec Greg quoted is the faster 2.2 spec (5.99 and quicker).  The 2.4 spec (6.00-7.49) calls for a minimum .058 upright.

[THE FRENCHTOWN FLYER]

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.

My bad - I thought you meant the plates on the axle itself. Nevertheless I'd say you're good.

Thanks for the kudos. Stay tuned for the second article in the series of four.

[gregm784]

Just so no one gets confused if they happen to find out their rear end uprights aren't .083 wall, the spec Greg quoted is the faster 2.2 spec (5.99 and quicker).  The 2.4 spec (6.00-7.49) calls for a minimum .058 upright.

Oops, i meant to include that in my message. thank you. 

Yes, that is for 2.4C - Top Fuel.

[fuel749]

Just so no one gets confused if they happen to find out their rear end uprights aren't .083 wall, the spec Greg quoted is the faster 2.2 spec (5.99 and quicker).  The 2.4 spec (6.00-7.49) calls for a minimum .058 upright.

Oops, i meant to include that in my message. thank you. 

Yes, that is for 2.4C - Top Fuel.

I won't bash you to hard since the computer I'm typing this on is the one you built me.