Fabri-cobbling a Autocross Chevelle

[416velle]

Hello all, this is the first post regarding my pride and joy, my 1969 Chevelle that I'm building for autocross! I'm pretty close to driving the thing out of the garage (first time in 3 years), basically axles/differential/fully finishing rear suspension, and some other odds and ends.
To address the elephant in the room, yes this car does have a homebuilt 3 link! I'm in the final stages of mock-up testing and finish-welding it, so I figure now is the perfect time to detail my reasoning and thought process behind some of this along with my goals. Also I just like to build stuff :D

The basics of the setup:
69 Chevelle Malibu
Engine/Trans
-Mildly wild stroker LS3 (13:1 compression, Wiseco/K1 bottom end, ported/milled LS3 heads, ported/rodmod LS3 intake, ported TB, decent size cam), running on corn, brain dyno says 680hp all day.
-F-body T56 (bronze shift fork bushings, serviced synchros, not magnum-ed so I have to go easy on it), Spec 2 disc clutch, American Powertrain hydraulics kit
Front Suspension
-UMI Upper arms, QA1 lowers, Speedtech ATS spindles, ABC Performance sway bar, ridetech TQ Triple adjustable coilovers, Wilwood 14" 6 piston Aero6 brakes.
Chassis
-Factory Chevelle frame with a HPI Customs Frame Brace kit, Fabricated rear control arm crossmember, 5 added bodymounts



Now, the interesting stuff!
Rear Suspension
-Quick Performance 9", Millerbuilt Floater kit, UMI Lower arms, ridetech TQ Coilovers, Wilwood 4 piston FNSL brakes, Fabricated Upper Link and Panhard Bar!

My goals with the 3 link was to address the shortcomings of the triangulated 4 link and allow me to go a little faster in the turns. I'll detail those in specific post shortly.

[416velle]

Here are a couple pics of where I'm currently at.

Now, my reasoning for the 3 link comes down to 5 things.
1-It looks so darn cool.
2-Adjustable antisquat. This car is(will be) lower than crimes against the Geneva Conventions; after crunching some numbers and research, the geometry in regards to squat kind of pops a squat when the car is as low as it sits right now. So I have a LOT of adjustability in the control arms for dialing in the squat, ie. upper arm AND lower control arm mount positions. I will be crunching the numbers and doing the measurements to find where exactly the COG is and where the instant centers are front and rear so i can minimize pitch the leat amount needed.
3-Adjustable Roll Center. This one is my "secret" to handling SIGNIFICANTLY better than a well-set up upgraded factory suspension car. After a LOT of research, pondering, more research, some reverse engineering of suspension systems from HIGHLY competitive companies, I came to the conclusion that having a roll center AT or SLIGHTLY BELOW the axle centerline is really where I want it to be. Factory roll center with the triangulated 4 link is very high, and some companies don't even recommend a sway bar because its relatively close to the center of gravity essentially making it pointless . Well, its science that if you don't have some affinity of weight transfer, you don't have traction in corners! Now I will be able to tailor the roll center to my driving style, traction, track conditions, basically find where the car wants to be at, and actually utilize a rear sway bar for its intended purpose.
4-I just like building stuff.

Some other reasons not entirely notable are; controlled and predictable axle articulation; weight, all said and done the 3 link setup will be lighter than the 4 link, which gives me a cushion for some other things on this car that increase the weight namely the entire rear axle assembly, frame brace kit, 18" wheels, etc.

For anyone that may be wondering; I will be running a 18x11 and 315 tire at all 4 corners, it does not require modification in the rear (just some measuring and sickeningly expensive wheels) but will require some inner-fender work up front if you decide to run those (I'm not because theyre far too heavy :D).

A couple things to brain-dump (like a photo-dump but different);

The panhard bar is a mock-up piece; my parts are a week away and I got impatient. The swiss-cheese looking frame plates are for plug welding, more strength (if it makes me think its stronger, I'm doing it). The cushion-block bodymounts above the crossmember are disgusting from fire yes, they will be coming out and solid bushings going in, I just don't quite know yet exactly how I'm going to "box" the kick-outs to the crossmember. The control arm tie-bars will be installed with some doubleshear mounts to the crossmember, eventually. Yes that is indeed a bodymount where the upper control arm mounts to the frame; I was afraid the force of 700hp on that arm would twist my welds to the frame, so with that in mind if it wants to move at all under load it now has to break my welds, twist chromoly tube, break the eventual boxing to the bodymount kickouts on each side, break the control arm tiebars, AND pork the crap out of the body crossmember which is actually fairly thick metal. Sway bar is not in yet nor is it mocked up because I don't quite know if I want to bolt on or weld sway bar mounts to the axle.

Later this week when the parts arrive I will do a complete mock up of the rear and start to fully weld it.

[andrewb70]

Cool build! Looking forward to the updates.

Andrew

[Hotwire]

Damn man, you literally just did the bucket list I have for my rust bucket!!

[416velle]

[416velle]

Proper panhard bar built and mocked up, coilovers mocked up for clearance, something feels off because nothing is fighting me here!
Waiting on some tabs for reinforcing the crossmember to the lower arm tie-bars, then i can start fully welding everything up, also decided on a strategy for bodymount-crossmember boxing. Rear axle will come out tomorrow for final assembly of floater ends/brakes, paint, and axle measuring.

[David Sloan]

Cool project!
I’m in for updates.

[TitanFox]

Looking good so far. Interested in seeing how those tires fit up front.

[chevelletiger]

I'm also doing something similar as you except a torque arm.
From what Blake at speedtech said ,was ti set the panhard bar 8.00 to 9.00 from the ground.

[chevelletiger]

Looking good so far. Interested in seeing how those tires fit up front.

68-72 chevelles fit an 18x11 315 30 18 pretty easily.

[416velle]

You have to do the measurements on your specific rig, i found a 6.5” backspace fits best but i have thick meaty wilwood lugdrive rotor rubs and hubsaver shims. 18x11s fit wonderfully WITHOUT INNER FENDERS for how low my car is/negative camber settings/ackerman steering arms and no modifications needed, no tapping anywhere at all which is a plus (taiwan fenders so not like i would care too much :3 anyways)

Super low with 2.5° negative camber WITH inner fenders would require the “roof” to be raised right in the meat of the fender lip, and a securing bolt/cagenut to be removed. I had rubbing over big dips even with a 275/17x9.5 5.5” backspace wheel previously.

[416velle]

I'm also doing something similar as you except a torque arm.
From what Blake at speedtech said ,was ti set the panhard bar 8.00 to 9.00 from the ground.

This is good to know, thank you.
I have 4” total adjustment so i guess ill have to think about where to put it at to start out!

[416velle]

Got the rear fully welded and basically final assembled (except for bodymount reinforcement and control arm tiebars). Got the thing on the wheelstands (infuriating) and its like i need a 1-2” shorter spring in the front or something. Maybe this is “lowered” for normal people but its a skyscraper for me, and i dont expect settling to take a full inch out of the neutral height. *sigh* Will call ridetech tomorrow and see what their recommendation is. Or if anyone here has a recommendation? I do remember fighting the thing on the way in because i had to compress the spring by hand to get the spanner nut threaded in.

[Kcrain]

Do you have the weight of the engine in?

[416velle]

Yes, thats whats frustrating. The car is as heavy as its going to get up front with the exception of fiberglass hood and bumper.

[marolf101x]

Do the front shocks have the dropped upper cap, or are they flat like the rear?

[416velle]

Do the front shocks have the dropped upper cap, or are they flat like the rear?

The kit comes with some 2.75" drop caps, I did look to see if theres shorter caps which there are, but they're only 3/4 inch shorter and a pair of springs were cheaper.
So I bought some inch shorter springs, those will give me an inch of wiggle room. 800lb/in, 7" height.
My options if that doesn't fix it are:
-2" drop caps
-run a MUCH softer spring rate
-a combination of everything

The instructions did say specifically "Recommended for use with ridetech Strongarms for proper installation" (I have QA1's) which leads me to believe the lower eye mount point may be lower on their arms, it doesn't look to be the case from the pictures though.

[Olds.PhD]

The instructions did say specifically "Recommended for use with ridetech Strongarms for proper installation" (I have QA1's) which leads me to believe the lower eye mount point may be lower on their arms

Yes, they do:

"Lower StrongArms feature a double sheer lower mount for increased strength. We have also dropped the lower shock mount to increase suspension travel and moved the lower ball joint forward to increase caster settings while keeping the wheel centered in the wheel opening. Injection molded Delrin bushings with 13% Teflon are used to reduce deflection and stiction."

That is in the description of the full suspension kit.

[marolf101x]

I was referencing this. . .

It moves the spring down 0.75"
If you have this you can swap out to the "flat" cap, and the lower threaded spring retainer will move up 0.75", which will allow you to lower it more.
I designed them for an 8" spring. The threads stop short of the top of the shock. That's so you can never preload the spring so far it binds, which will cause spring sag or settling.

The lower control arm should be parallel to the ground at ride height (from center of ball joint to control arm frame mounting bolt should make a horizontal line)
It can run uphill slightly (ball joint higher than frame pivot), but don't go crazy. Remember, everything was designed around the ride height mentioned above.

The 7" spring will help, but I strongly suggest you remove the shock and measure the mounting points at your desired ride height.
The ridetech mount in the lower control arm is lower than the QA1 (difference between the monotube length and the twin tube length, the monotube needs more room to fit the dividing piston and nitrogen chamber)
If you desire a very low ride height you might run out of shock stroke. It'll bottom out mid turn and unsettle the car.
If this is the case you can go to the 3.6" stroke shock.

[416velle]

Thank all of you for the info. I will tonight be measuring my travel from bumpstop-ride height and shock mount-mount/shock travel and compare that to the ridetech instructions. If i can get away with not changing lower arms i WILL, if i get a different set ill go with UMI more than likely because the dropout bottom mounts and if the 2 options of heights it comes with dont work, i can build some to be perfectly what i need.
Headache. Guess thats what i get for running 10 different companies stuff for one car