Custom frame build and suspension options for my 61 F100 Unibody

[61_F1_Unibody]

I am wanting to build a custom frame for my 61 f100 unibody. It came on a 96 crown Vic frame when i got it that was poorly executed. I have considered going the 07 up crown Vic (I have one) or corvette front suspension and a s550 mustang IRS in the back with upgrades to the front and back. What’s everyone’s opinions on this setup. I will be the first to tell you i dont know much about pro touring suspension. The truck will be running a coyote and 6r80 that will be shoved back and down as far as i can get it and still retain leg room and all of the serpentine drive accessories. I watched Mike trenkle’s bad ass wide body foxbody Mustang and got me hooked in Bowling green KY and talked to him a bit thats about it. With that being said i have a few questions.

1. Does wheel base make or break an auto cross truck? I have considered shortening the bed a bit.

2. Is squared tire set up better in a truck or would wider rear tires keep it from being tail happy.



3. Can it be done successfully on air ride?

[Vimes]

I hope you already have a frame guy. I didn't when I started my project. It took me 2 years to find a shop willing to just do a frame, then I spent 3 years on his waiting list. He's just now getting to it, supposedly. Most of the shops I spoke to were only willing to do a complete turnkey, or backed out on me.

I'd do square on the tires for the ability to rotate, plus it puts the same grip at all 4 corners. And, trucks are inherently squirrelly because there's no weight over the rear tires. Getting closer to a 50/50 front/rear balance will help. My own truck started at 58/42. IRS/IFS will help with handling, but you might not do quite as well at the drag strip.

I don't think I'd try shortening it though. That diagonal line would be hard to make look right and it wouldn't affect handling much. And on the air ride, sorry - I got nuthin.

[mikedc]

Another vote to leave the wheelbase alone. It doesn't look especially long for the vehicle body and it's a PITA to change it.

A CV frame retrofit is probably easier. A Corvette & Mustang IRS deal would be better if it was executed well. Depends how much of a challenge you wanna bite off.

Are you building it mainly for autocross or mainly as a driver? If it's mainly a driver then I would lean more towards the CV frame.


I'm not a fan of airbag suspensions in general. They are inherently softer when the ride height is lower and stiffer when the height is up. That's the opposite of how you would ideally want it to work.

[Arrowhead]

Funny I just came to visit this forum after not coming on here for a long time and your post popped up. I'm also building a F100 unibody but not so much for autocross, just something cool to drive. I'm transplanting a Whippled '15 Mustang into the truck and building my own frame. I'm using everything I can off the Mustang as it was a running and driving donor. I have a youtube that been documenting the process if your interested. I'm about 90% though building a custom frame for it that will accept the mustang IRS, IFS, 6R80 and Coyote. I'm using a BMR tubular cradle for the front and building in the mount for the IRS into the chassis instead of using the Mustang subframe. I'm also planning on using the seats, console and all controls.

https://www.youtube.com/playlist?lis...acjujukEukTm_C

There is also a shop in Texas that's building complete frames similar to what I'm doing so you can bolt in the S550 front and rear suspensions.
https://www.instagram.com/cometfab73/
I think they run about $7500 so I decided I'd buy some tools and some sticks and build my own.

Progress so far

[Foot]

Leave the wheelbase alone, that is already a classic body and people will notice it looks funny. Classics are beautiful for a reason: 1. shapes and features, people like. 2. fit for function. 3 well executed. If you mess with a classic design that everyone pretty much agrees is beautiful, then make sure you have a good eye for symmetry.

Squared is best for tire rotation. But you don't even mention turning radius while lowered and deep dish wheels while lowered make turning lock to lock even more important to choose the most narrow front suspension WMS (wheel mounting surface to wheel mounting surface) This is why guys often graft on S-10 or G-body Cutlass Regal Suspensions that are 54 inches wide and capable of achieving a decent turning radius while lowered with deep dish wheels. Beautiful cars, that just seem really well done often have wheel lips of 2 or 3 inches front and 3 or 5 inches in back. Suspensions that are narrow enough to achieve that beautiful look are limited. For example the G body Cutlass Regal suspension is narrow and has a large number of aftermarket control arms and quick ratio steering boxes. I believe the IROC-Z camaro quick ratio box bolts up. if you want 315/30/18 tires, and 18x11 wheels with say 7 inches of back space front and 6 inches of back space rear then you need a narrow track width suspension. It's not as modern as your corvette suspension but having those deep dish wheels is extremely beautiful on a classic car or truck. The rear axle from a 2004 Mustang cobra is 61.5 inches, that might be narrow enough to give you a deep dish wheel in back. I'd go with an axle that gives me a deeper dish in the rear. Mike Maier runs a straight axle and inboard coil over springs and wins autocross events with it.

air ride is about style and this tells me you do care as much about handling as how the stance will look. The air bags will be the easiest way to get the stance perfect, but one of the other guys mentioned it'll be stiff when it's up and soft when it's low and I didn't know that, It's a trade off. If you build it to the perfect stance with regular springs and then find it can't make it up the Taco Bell driveway, that might be a bummer. I see why you might want air ride to get the best of both worlds.