Active Power or C5 Coilover and 15” wheel questions

[Devin]

Question to all those that have built, own or are building a C5 based suspension or Active Power GT40

I’m scratch building my 40 based off the AP chassis design but with modifications for the various body parts I’ve collected over the years. You all and this forum have been a great motivation and source of info to enable this dream to become a reality. I’ll be starting a build thread soon (on those cold days that make working in the shop difficult) but am sourcing some of the next essential items in between TIG time in the shop.

1. What coilover spring rates (front & rear) are found to be good for overall spirited driving with mostly street use? I’ve ran the spring rate calculators but don’t have a great feel for what overall weight the final build will be, so figured I better ask those with experience.

2. I really love that original 15” wheel and tire look. I know from what Chris has told me that it takes using the rear 12” brakes on all four corners. What are the specs & brands of those that are running 15s for your wheels & tires as well as the brakes that support the necessary clearance on the inside of the wheels? I really want BRMs & Wilwood brakes (DPC56s)...but if Halibrand replicas & stock rear calipers are the only option, I would do those as well (love them on my Cobra). Are you happy with the braking performance from the smaller brakes...I would think they would be fine with the overall weight being so much less than a Corvette.

 

[Terry Oxandale]

Not an Active Power owner, but you could find the Corvette OEM spring rates, and then compare the OEM Corvette weight to what you estimate your project will weigh, and then go from there. Obviously you should be able to reduce the spring-rate if using all the Corvette suspension components (in other words, the geometry that helps determine your spring rate is already accounted for). The unknown, is the rear weight bias vs front weight bias between these two cars.
Brakes: I have 16 inch wheels on my project, and the 12" C4 rotors barely fit inside with aftermarket 4-pot calipers. On the track (albeit short ones), obviously the brakes get hot, but have never had a fade, heat checks, cracks, or even much discoloration with them, on a 500 HP/2200 lb car.

 

[Rick]

I have the QA1 coilovers and springs from Chris. The springs are 350 front and 550 rear. This assumes that you have your geometry set up the same as Chris did on the AP chassis. Not the same as the original corvette setup.

 

[Devin]

I have the QA1 coilovers and springs from Chris. The springs are 350 front and 550 rear. This assumes that you have your geometry set up the same as Chris did on the AP chassis. Not the same as the original corvette setup.

Rick, yes I do and thanks so much for the info on the springs.

Do you know what your final curb weight is just out of curiosity?

 

[Rick]

I don't know the weight yet. I don't have the drivetrain mounted. I am told it should be about 2400 lbs.

 

[Howard Jones]

If I were just starting a build like yours I would make up some straight tubing mock-up shocks with simple holes in the ends and wait for later. You will need them late in the go-cart stage but that could be a few years. Most of us have spent at least three years on ours and up to many more building cars. This gives you a lot of time to refine your shock/spring selection and maybe run across some nice less expensive used pieces. You might also consider holding off on the brakes until you need them. Put out the word for your needs here on GT40's.com and see what you run across. Maybe even save yourself a lot of money.

You will need the final choice of wheels to do the brakes but you can mount used-up tires as roll arounds right up until you begin final body fitment. I wouldn't buy new tires only to have them get old waiting for you to finish many years later. Just try to find some old ones in the correct size for now.

As a reference, I have QA-1's on my GTD with 350F and 450R springs, Works well as a dual-use/street tire car. Don't forget gas and you. So maybe 2500-2600 is a more reasonable number with an SBF and a Porsche weight GB. 250 pounds is a lot to take out of a 2400-pound car. Basically 10% of everything!

Good luck, have fun and post a lot of pictures!

 

[Devin]

If I were just starting a build like yours I would make up some straight tubing mock-up shocks with simple holes in the ends and wait for later. You will need them late in the go-cart stage but that could be a few years. Most of us have spent at least three years on ours and up to many more building cars. This gives you a lot of time to refine your shock/spring selection and maybe run across some nice less expensive used pieces. You might also consider holding off on the brakes until you need them. Put out the word for your needs here on GT40's.com and see what you run across. Maybe even save yourself a lot of money.

You will need the final choice of wheels to do the brakes but you can mount used-up tires as roll arounds right up until you begin final body fitment. I wouldn't buy new tires only to have them get old waiting for you to finish many years later. Just try to find some old ones in the correct size for now.

As a reference, I have QA-1's on my GTD with 350F and 450R springs, Works well as a dual-use/street tire car. Don't forget gas and you. So maybe 2500-2600 is a more reasonable number with an SBF and a Porsche weight GB. 250 pounds is a lot to take out of a 2400-pound car. Basically 10% of everything!

Good luck, have fun and post a lot of pictures!

Good point Howard...probably get a set of those wooden shocks for now but am asking to get ahead on data for future order. The wheels seem to be the longest pole in the back order/custom order process which my last experience was at least 2 months (pre-C19).

Hoping a lot of folks chime in with real world experience to help narrow down my search and selections without making and expensive & non returnable purchase.

Thanks for the insight. The attached pic is a work in progress by the way and just for reference.

 

[Rick]

Nice work on the chassis. One suggestion for you. The upper control arm mounting bolts normally use shims to adjust camber and caster. On mine, I welded the bolt heads from the inside of the footwell so that the alignment can be done without having to hold a wrench on the inside when installing the shims.

 

[Devin]

Nice work on the chassis. One suggestion for you. The upper control arm mounting bolts normally use shims to adjust camber and caster. On mine, I welded the bolt heads from the inside of the footwell so that the alignment can be done without having to hold a wrench on the inside when installing the shims.

View attachment 126647

Love it! Great minds think alike...was planning that exact thing!

Thanks for the tip.

Devin

 

[Terry Oxandale]

Are the upper control arm mounting points (plate steel) being reinforced?

 

[Devin]

Are the upper control arm mounting points (plate steel) being reinforced?

Yes sir, just did this for the rleft side today!

 

[Terry Oxandale]

Great! Looks like you're on a good track. This chassis is looking bulletproof.

 

[Rick]

What are you using for a model to build from? Do you have CAD drawings?

 

[Devin]

What are you using for a model to build from? Do you have CAD drawings?

Rick,

Bought the AP plans from Chris and contained both PDFs and Solidworks files from which I’m modifying for my needs and body work.

There is still a lot of value for me looking at all the pics of everyone’s projects as there is even discrepancies in the AP plans and all the various systems yet to be integrated and installed.

Devin

 

[Joe]

Rick,

Bought the AP plans from Chris and contained both PDFs and Solidworks files from which I’m modifying for my needs and body work.

There is still a lot of value for me looking at all the pics of everyone’s projects as there is even discrepancies in the AP plans and all the various systems yet to be integrated and installed.

Devin

I lowered my drivetrain roughly 1 inch. Once I installed the Kennedy adapter plate I set it so the bottom of plate is flush with bottom chassis Rail.that is the lowest point on driveline.I also made my trans mount out of 3/8 steel for less flex.as few mentioned to me and makes a great point,weld 2 tabs on the front foot box near upper control arm that will later attach to the aluminum walls to take some off the stress off aluminum bends.

 

[Howard Jones]

I like your style! Battleship built baby! You might want to grind off that sharp corner where the lower control arm mounts. That one will hurt!

 

[Devin]

For sure Howard, lots of grinding in the near future. My latest welds aren’t too bad but I definitely will clean and round stuff off as it looks better and safer working around for the future build,

I figured that the AP design might be a little over built but the steel cage around the occupants isn’t the place to save weight or go with a minimal structure. The aluminum and lighter steel will be my “crumple zones” to absorb any potential impact. I like what a couple of guys have done with the anti-intrusion bar in the doors and may look at a lighter version of that being how low these cars are with all the big trucks here in West Texas.