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Dusterbd13-michael
Dusterbd13-michael MegaDork
10/26/21 7:14 a.m.

A project im building in my head has a very similar frame rail width to the crown vic, according to google. 

This is a challenge build that is destined for vir and other road courses after the challenge. 

The base car is a unibody, with no aftermarket suspension options. Its similar to a first gen mustang if that helps conceptualize it.

Theres some stuff i can fabricate to theoretically make it suck less, but not a lot. has recirculating ball steering, unobtainium wear parts, and very small brakes that will be almost impossible to upgrade for track work. Additionally, there's the shock towers in the way. 

Which leads me to a subframe swap. The crown vic looks like it may be a good option, but ive never embarked on anything remotely like this. 

It appears that the vic subframe has separate rear control arm mounts,  and the upper mounts sandwich the frame. Which in my application means that i need to build new rails, right? With sleeves to keep the frame from crushing when I tighten things down. Right?

As far as the subframe itself, is there any junkyard brake upgrades for track work? What about springs and shocks? This being a challenge build initially, budget is very constrained. Id also like to enter the ultimate track car challenge with it in tbe exact same form i run the challenge in it, so that adds a new dynamic. 

 

Anyway,  im not even sure what i need to know beyond what ive asked, as im in a whole new arena. Im sure the amount of stuff i dont know that I don't know is staggering, and will come back to bite me. Hence this thread.

DeadSkunk  (Warren)
DeadSkunk (Warren) UltimaDork
10/26/21 7:31 a.m.

Just a thought that I had when looking at the Crown Vic front suspension on the Georgia Tech Insight a few years ago. A Crown Vic is a heavy car with brakes sized to suit that weight. If you build a Challenge/track day car will it need brakes bigger than stock Crown Vic units? What do you think your planned car might weigh? The Insight was pretty light, especially with the engine at the rear and I would think the front brakes were oversized if anything.

And don't underestimate your ability to pull this off. Think everything through, ask a million questions and then start building.

Mr_Asa
Mr_Asa PowerDork
10/26/21 7:34 a.m.

The cop cars had upgraded sway bars, not sure about the corner springs though. 

I started a thread a while back that gave a lot of good info 

https://grassrootsmotorsports.com/forum/grm/learn-me-crown-vics/177044/page1/

¯\_(ツ)_/¯
¯\_(ツ)_/¯ PowerDork
10/26/21 7:37 a.m.

Given that you're aiming for track work with, presumably, a bunch of power... why not start with a subframe that was intended for more performance in the first place?  Yes, cost is a factor but some stuff comes to mind that might be cheap and more performance oriented out of the box.  How about a GTO, for example?  Or maybe a C5?  Is Darth Nader still around for some measurements?

Dusterbd13-michael
Dusterbd13-michael MegaDork
10/26/21 7:37 a.m.

In reply to DeadSkunk (Warren) :

Car is estimated to be 3200 without driver. Thats my napkin math. Won't know final weight until it's built though. But good call on "needing" brake upgrades until its proven i need brake upgrades. 

Im also glad you have that confidence in me. Im not sure i do, but....

Dusterbd13-michael
Dusterbd13-michael MegaDork
10/26/21 7:40 a.m.

In reply to Mr_Asa :

Ill be reading that over lunch 

Dusterbd13-michael
Dusterbd13-michael MegaDork
10/26/21 7:42 a.m.

In reply to ¯\_(ツ)_/¯ :

Honestly, self contained suspension, and the ease of rail width matching. And it matches track width and bolt pattern. But if it turns out to not be worth the effort, ill go back to hunting. 

¯\_(ツ)_/¯
¯\_(ツ)_/¯ PowerDork
10/26/21 7:52 a.m.

Assuming we want to stay on the Crown Vic stuff for now, then, my vote would be to find one that you can hack the entire front of the frame out of and use what you need- or at least, cut out the section from the main subframe mounts to the control arm mount.

dps214
dps214 Dork
10/26/21 7:55 a.m.

Google says the front rotors are somewhere in the 12-12.5" diameter range which isn't giant but isn't small either. Depending on power level that could be enough just with decent calipers, pads, and some cooling. Probably good enough to not need to worry about upgrading immediately.

Stampie
Stampie MegaDork
10/26/21 7:55 a.m.

I remember looking at the Crown Vic and talking to Gumby about it but decided on an RX8 front subframe. Should be lighter than a Crown Vic and it's double A arm construction.  The RX8 had electric steering rack which is problematic. I'm just going to depower it. The NC Miata has conventional rack in the same subframe IIRC

Mr_Asa
Mr_Asa PowerDork
10/26/21 7:56 a.m.

In reply to Dusterbd13-michael :

Not sure how much will be relevant, but I did start it with the intention to talk about a future hat car.

Dusterbd13-michael
Dusterbd13-michael MegaDork
10/26/21 8:25 a.m.

In reply to Stampie :

My concern with that subframe is exhaust clearance. After fighting that in the miata, im definitely concerned about fitting it with a wider engine plan. 

However, anyway you can take a few measurements and maybe a napkin drawing of the mounting points? Weight reduction is definitely appealing. 

DeadSkunk  (Warren)
DeadSkunk (Warren) UltimaDork
10/26/21 8:55 a.m.

In reply to Dusterbd13-michael :

Look at the pictures of the front suspension in my Corolla build thread and you can see how I ran frame rails to maximize width. The frame rails are directly under the bushings for the upper A-arms. Just looking at Stampie's picture , I think I could do the same thing with RX-8 suspension bits, and nothing says you can't spread the suspension out further to create room between the rails if needed. You would just have to watch what it does to bump steer if you moved the pivot points any significant amount.

iansane
iansane HalfDork
10/26/21 10:04 a.m.

In reply to ¯\_(ツ)_/¯ :

TIL how cheap c5 complete subframes are...

RacetruckRon
RacetruckRon Dork
10/26/21 11:53 a.m.

I can measure C4 subframes and provide pictures if needed.

STM317
STM317 UberDork
10/26/21 12:02 p.m.
iansane said:

In reply to ¯\_(ツ)_/¯ :

TIL how cheap c5 complete subframes are...

Along these lines, I'd think you might need to budget for some coil overs too in a lot of cases. I can't see the stock transverse leaf spring being very good unless the nose weight of the new vehicle was close to the donor weight.

Stampie
Stampie MegaDork
10/26/21 4:19 p.m.

31.5 inches between front bolt holes.

27 inches between the inner "towers".

31.75 between rear bolt holes. 

Dusterbd13-michael
Dusterbd13-michael MegaDork
10/31/21 6:23 p.m.

In reply to Stampie :

How much room between the rear "wings" where the head pipes  for a v8 would pass between the k frame and the oil pan? I found  a local complete drop out for a c note....

Stampie
Stampie MegaDork
10/31/21 6:33 p.m.

In reply to Dusterbd13-michael :

21.75 inches but could probably trim it to get another inch or notch it to add much more. Rear crossmember is removable and I probably won't use it. 

Dusterbd13-michael
Dusterbd13-michael MegaDork
11/2/21 9:31 a.m.

It appears that the RX8 subframe may be a good match. We've got about a 30 in Centerline on the front frame rails that the control arms so I'll have to add a little more material on both sides to give it a better landing pad

Stampie
Stampie MegaDork
11/2/21 10:04 a.m.

In reply to Dusterbd13-michael :

If it doesn't work out let me know first so that I can delete all my post about it.

Dusterbd13-michael
Dusterbd13-michael MegaDork
11/2/21 10:57 a.m.

In reply to Stampie :

Will do. Looks close. 

 

Any idea about brake upgrades?

pres589 (djronnebaum)
pres589 (djronnebaum) UltimaDork
11/2/21 10:59 a.m.

Will you need better braking than factory?  I would think your vehicle weight and the RX-8 are within a couple hundred pounds of each other.

I don't race like you do, so you know better, but these events never seemed really big on braking power, mostly just control to avoid lockup.  So 2 cents with my comments/questions here.

Stampie
Stampie MegaDork
11/2/21 11:22 a.m.

In reply to Dusterbd13-michael :

The automatic base model RX8s came with smaller brakes. That's actually what I wanted because I like to run 15 inch wheels and I'm a lot lighter than a RX8. The other models had larger brakes and are much more common.

Dusterbd13-michael
Dusterbd13-michael MegaDork
11/2/21 11:50 a.m.

In reply to pres589 (djronnebaum) :

The hpde and track day goals will put a lot of heat in them, so its more of an "eye toward the future" thing. But at the moment, based on weight at 2017 challenge and google of rx8, they're almost exactly the same. Id actually expect the spring rates to be close enough to try too!

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