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03-13-2023 #1Registered User
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- Jan 2022
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- 88
Fabri-cobbling a Autocross Chevelle
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.
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03-13-2023 #2Registered User
- Join Date
- Jan 2022
- Posts
- 88
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.
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03-13-2023 #3