Chassis Stiffening

[EasyE]

I'm coming down the home stretch on my '67 F100 stepside, and after a bit of a snowball with the engine plans it looks like I'll be making ~650 hp. So that's pretty sweet, however when I was pulling the frame off the trailer when it was coming back from powder coat I realized that it is not very stiff at all in torsion....

So to all the guys who are making big power (or even those that aren't), what have you done to stiffen the chassis up to accommodate higher torque loads? Roll cage? Some kind of cross bracing?

FYI, the truck has a police interceptor crown vic front end with sway bars and an explorer 8.8 rear with 3.73s, traclok LSD, sway bars, and homemade caltracs.

Thanks, all.

-Eric

[cep62]

I would think the easy ? way is to " box the frame ".
Basically , you're taking you C chanel and welding it into square tubing.
That'll stiffen it a lot with out doing a frame mounted cage.

[basketcase0302]

[HIO Silver]

Stiffening the side frame rails does not require that it be fully boxed... Figure for example a 16-inch boxed section, open 8-inch section then another 16-inch boxed section. Adjust lengths and gaps as necessary. Leave enough space to access the wiring harnesses and brake line tubes.

3/16th plate will add weight... I suggest cutting holes on the boxing plates and using dimple dies to flare the holes to restore the stiffness.

In terms of torsional twist.... Skip weld the OE crossmembers and then consider doing the same with fabricated tube and plate x-members.

[BobbyFord]

Taking the flex out of the frame will eventually lead to cracking.

[EasyE]

For some reason I didn't get any notification that anyone had responded to this....

And I of course got distracted. Well the short story is the frame is already powdercoated, so I'm just going to put it together and hope for the best at this point.

Welding the OE crossmembers is a good idea; wish I'd have thought of that before powdercoating it.... Crap. If things get squirrely I'll probably just cage it, but hoping it doesn't require that.

[Manny]

Tube crossmembers frame rail to frame rail bolted thru the rail might be your best option if she winds up funny after lots of

[MadMike]

when I was pulling the frame off the trailer when it was coming back from powder coat I realized that it is not very stiff at all in torsion....

Most bare frames will be pretty flimsy. Bolt the bed and cab to the frame and that will stiffen it immensely.
Unless you plan on only drag racing this truck with slicks, I doubt you will have any frame problems.

[EasyE]

I made a square tube frame for the bed sides/floor to bolt to and that bolts to the frame in 8 places, so that should help.

Also, the cab is currently sitting on rubber isolators at all 4 corners. Should I pull those out and just bolt the cab to the frame with a big fender washer in between?

[Ranchero50]

No, leave the rubbers in place. Also, don't weld the cross members. The whole thing needs to flex consistently or you will create fatigue points that will crack and fail. Rivets trump welds on frames.

Even my F-350 long wheel base frame has a surprising amount of flex.