Corvette aluminum Knuckle + 73 B-body LCA

I'm setting up my Swinger for autox focusing on weight distribution and unsprung weight. So to that end, I already have a Pentastar 3.6L & T5 to go in and I'm looking to mount a Rack & pinion forward of the front axle.

I was brainstorming about front suspension setups that allow a forward facing steering arm and decent ackermann. So I was wondering if anyone considered using Corvette C4 aluminum knuckles(#13 w/ hub and bearing) and mating it to a 73up B-body LCA?

I located a sample of each to prototype.

aside,,Anyone use Performance Trends Roll Center Calculator? and have an Abody file?

Seems like a lot of effort/research/risk for not a lot of return. Reasoning being, AutoX's are normally on rather smooth surfaces, correct?, and unsprung weight is mostly about bumps, not weight transfer while cornering. Pure weight reduction, is found elsewhere a lot cheaper and easier. Now if Road Race is the goal, everything I have read indicates the OEM Vette bearings don't cut it. It you want sizzle and uniqueness, I'd head to rear with a IRS setup.

What is the lower control arm even from ? F body or something like that ?

No they're off a B body,,,,just not a 72 and older.




So your option for "a lot cheaper and easier" solution to a forward facing steering arm that does not result in negative ackermann and retains the t-bars,,,,is what exactly?? I'm honestly open to any options really

Aluminum is just a side benefit not at all the reason to swap.
Mounting the 3.6L would be a bit easier with the steering gear and drag link out of the way. Since its a good 10" shorter than a small block, it leaves a lot of room up front for a rack.

Well, does the autocrossing are you doing allows such a wide rule interpretation to use such a combination? Most SCCA based classes I've seen are so restrictive to prevent this type of mod.

Rack width and travel to much such an arrangement would be a big concern to me, otherwise you are introducing the potential for as bad or worse bump steer characteristics as the stock rear steer.

FWIW, Firm Feel was working on a pretty trick set up using 73+ B body lower arms and a variety of aftermarket parts. I've seen pictures of it before, but don't recall where. You might try searching around to find something on it and gleen some ideas form it.

I was planning on running it in CAM-T, which looks pretty open. The 3.6l Pentastar will shave a good 200-225lb off the nose of the car and moves the CG back a bit.

The plan was to get the suspension parts modeled and see how the geometry shakes out. It may wind up horrible.

I have the C4 Knuckles already in Solidworks, so I just need to get the B-body LCA modeled up and figure out the suspension points. I was hoping to get a jump start on the chassis side if someone had some info on that.

Having designed a pull-rod suspension from scratch, I'd certainly like to give warning and have very well defined (accurate) XYZ coordinates when evaluating that suspension. Roll center height, roll center slope, roll center migration, bump steer, camber change heave/roll, kingpin inclination, scrub, ackermann/steering angle, etc are all big players.

Seriously?!? You have data for an Abody?
If so that would be sweet.

autox is rarely on a smooth lot. We have the scca nationals going on here right now and it's in an old airport staging lot. Acres and acres of grippy concrete but definitely not a smooth flat surface. The few other places i've run in the midwest are the same or worse.

Classic american muscle has an awesome rule set. 200tw tires, specific weight minimum depending on class, street legal, and a finished interior. That's pretty much it. I'm building a 69 valiant for the cam t myself but staying with factory style parts.

Sorry, I thought you said you were focusing on Unsprung weight and F/R weight balance.

I wanted to see how the +73 B-body LCA compared to a Abody. So to the best of my ability I measured(Calipers)and modeled each LCA in SolidWorks.

http://www.forabodiesonly.com/mopar/attachments/20161228_154608-jpg.1715002081/

At first if you just look at the arms as the B-Body looks a good 1/2" longer. But its a bit deceiving as the differing Ball joint attachment points throws things off. That's why I went ahead and modeled each one separately.

So from this assembly model the two arms aren't too far off in actual length. Less than .25" for sure.

http://www.forabodiesonly.com/mopar/attachments/upload_2016-12-28_15-51-16-png.1715002083/

For this type of effort, I'd probably go with a fabricated tubular lower that is a 2-3" longer than stock, a matching upper arm, and a lot of offset on the wheel to get a good scrub radius set up.

I was thinking a longer upper arm would have been mandatory but after measuring and modeling the A-Body LCA and seeing that it's so similar in length to the 73 B-Body, it's not so cut and dry.

I recently picked up a copy of Auto-Ware FRONT SUSPENSION GEOMETRY PRO. Once I have the stock A-body suspension points entered, it should more easily show changes in RC and Camber curve that different length control arms make.

Very cool post. I'd love to see any numbers yoy generate. Don't let the naysayers stop you. If nothing else you will learn quite a bit.

The C body knuckle is probably a better choice (old kit car setup) or use a stock car type knuckle.

But sometimes it is better to learn these things yourself so by all means build it, test it and try it.

There are stock car circle track modular aluminum uprights, spindles, and steering arms out there. IIRC, Sweet or Coleman. And there are lots of brake setups for those that are usually less expensive than the one made for a specific production car.

To accommodate the rack and pinion, the C-body would need a custom forward facing steering arm that provides enough ackermann without putting the tie rod end through the brake rotor.

Ball joint to Ball joint, 88-93 C4 knuckle is about 1" taller than the tallest C-body.

Kit Car specs says the SAI is 9 degrees. The C4 knuckle I have here is measuring its KPI at ~17 degrees, which seems awfully high. The Googles claims the 88-up C4 KPI is vague but claim to be in 13-15 degree range.

A side benefit is that the C4's front bearing's 47 tooth tone wheel will provide a convenient wheel speed input so the ABS module can output mph to the PCM for throttle and speedometer.

Do it! I assembled a certain '65 Coronet with the late LCA's and it gets you a TON of room between the frame and control arms (something A-bodies dearly need). Biggest hassle is custom made strut rods. A-body LCA's are indeed a little longer than the B-bodies for some reason. We used the late B,F,M,J spindles and steering arms with stock rear-steer setup. Keep in mind that the A-bodies mount the shocks much farther outward than the B-bodies. This will reduce shock effectiveness (going to B arms) and probably require removing the frame extension for the bump stop. I've wondered about those C4 knuckles in the past since my silly brother has at least 2 of those cars and they're easy to see with the nose tilted.

I saw the different shock location. I figured if the math works out on the C4 knuckle and B-Body LCA, i'd fab a shock mount as close to the knuckle as I could get it. Something like this Firm Feel example.