Suspension Upgrade for Challenger

I'm planning out a 1970 Challenger build with a 440/512 EFI stroker, and a GV 727 auto. I wanted to know what suspension upgrade system would work best. Whatever system I go with, I know I will be going with a US Car Tool chassis stiffening kit.

This is my current (possible) list of upgrade parts:

Borgeson P/S Conversion Box 1-1/8" Sector Shaft
Firm Feel E-Body 1.18 Dia Torsion Bars w/ dust boots and adjustors
Hotchkis Geometry Corrected Tubular Upper A-arms w/ protective boot kit
Hotchkis Sport Sway Bar set
Hotchkis Geometry Corrected Sport Leaf Springs
Hotchkis Tuned 1.5 Adjustable shocks
Hotchkis Adjustable Steering Rod Kit
Hotchkis Adjustable Strut Rods
Firm Feel Fast Ratio Steering Arms
Hotchkis Pivot Shaft & Bushing Kit
Doctor Diff. Strange S60 Rear End w/ 35 spline axles, TrueTrac Carrier, 3.23 gears, 1350 large aftermarket yoke
Baer Front and Rear Pro + Brake Kit

It's either all this, or an RMS AlterKtion front end and Street Lynx rear. My goal is to make this handle as close to a modern car as possible, like a 2015 Challenger (they recently did many suspension upgrades), so that it can keep up with (or at least come as close as possible to) modern cars on a track or the street. Money isn't my main concern here, I just want to know what system will give me the best performance. What has the best turning radius, the best stability, the least body roll, and which can handle at speed the best.

Also, is there anything here I should add or discard? Anything that might work better?

Fast ratio arms AND a borgenson box will make for some serious fast ratio steering. Faster than current production cars I believe.

Borgenson is roughly 14:1
Fast ratio arms make a 16:1 stock ratio 12.7:1.

Im going to take a wild guess estimate without calc'ing anything out that you'll get 10:1 or something steering. Is there some modern car you've driven with that ratio to compare to?

Why 3.23 gear ratio with Gear Vendors? That would seem like really lugging the motor on the highway.

What tire size you running back and front?

Make it a trifecta, LCA stiffening plates, 11/16" TR, 4 link triangulated rear suspension and US frame connectors, wait that's four stellar solutions, Oh well. Not.

You have your mind made up, go for it, the vendors need the cash flow.

I drove a 2015 Challenger R/T Scat Pack, I believe it has a 12.3:1 ratio, and even that was very nice. I wonder if 10:1 may be too fast...? Does it make the car harder to turn if it has a higher ratio (may be a stupid question but I'm new to suspension and steering)?

As for the gears, what ratio would be better for a GV?

I haven't decided on the tires, I don't even have the car yet. I'm in the process of building up the cash to buy the car, and I'm planning out the build in advance so that I know exactly what to do and what to buy once I have it. What size tires would be ideal for a good mix of speed and handling, and to accomodate 17" or 18" wheels?

Sounds like you've got a really good plan going. With our bits you'll have no problem out handling a new Challenger. We handily had all the other cars covered at the autocross at Carlisle this year.

I'm sorry, I don't know what you mean by trifecta, LCA stiffening plates or 11/16" TR, would you please elaborate?

Probably 18" rims since high level performance DOT wide 17" tires are disappearing.

Think 275 wide in the front as a starting point. In the rear, I don't know what people can fit in there with a low stance. I'm sure 275's will fit. I'm thinking 295's with fender lip and offset hangers?? And I you mini tube and relocate springs you can get much wider.

Steering ratio does not make the car go faster or slower. It's the driver's preference and whether he can make the car go faster or slower with certain ratios.

I have a 14:1 box with a 13.5" wheel and I like it, I just need to work on NOT driving one handed all the time.

Good info, thanks. And I know it won't make it go faster or slower, I just want to know if it'd be harder to steer with a 10:1 ratio vs a 12.7:1

It was a bland way of saying you don't have a nice plan going. The 4 items I mentioned are what the novices normally list in their goal to achieve "modern handling" and my disdain for all of them, cited here many times, in length. Your request is common. A little research here would make you painfully aware of that initial goal and my position. Very few in one sitting make the changes you are contemplating, and those that actually do, years later the cars are still on jackstands. If you are contracting the work, they should be making the suggestions to you. My suggestion is, your car is probably in really good shape with only a few of the long list upgrades. You need to do a bit(?) more research here, narrow down your goals, tweak the car as you go, and learn the process. And I seldom follow the herd.

The new challengers have electric power steering with a couple different modes to change the driving feel. Be hard to simulate that with a normal steering box, i would think.

too bad you are so far away Dan, I'd love to get whooped by your challenger!

True, but I wasn't planning on trying to replicate it exactly

Harder to steer, if you are using power assist, no. However, what fast ratio steering does is make a car feel "twitchy" and very sensitive to inputs at higher speeds. At 75 mph highway speeds, it may feel like you can change lanes by flicking your wrist. Generally speaking, the higher the speeds the car is used at, the slower the steering speeds tend to be. Uber fast steering ratios are great for autocross, disasterous for top speed events.

In that case, I may want to just go 12:1

I'll share a few comments based on running a similar car (Challenger, 496 EFI, 5 speed/20% OD, 3.23 rear) on the road and HSAX course a little bit.

In terms of stiffening, the frame connectors are a start. There is benefit in reinforcing and stiffening the K frame also. Firm feel did mine with gussets, plates in failure prone strut and LCA mounts and full welding. Torque boxes help and also believe plating the LCA's helps.

The 3 speed auto + GV + 3.23 should put the gear ratios about where you want them as long as your cam is not too wild (what cam?). The ~20% overdrive will be a "top speed" gear or close. For cruising you could handle more OD with the stroker or lower numerical axle ratio. For sustained hard running (road race, Silver State classic ect.) you will need a low slip converter and good cooler to keep transmission temps reasonable and keep the transmission alive.

It will be a seriously fast car. I would not personally want super fast steering in that application. The stock ratio with a smaller steering wheel would be my choice. Also the fast ratio arms limit header choice.

Brakes sound good. I run a Cobra based kit with 13" in front and 11.7" in the rear. I started with Bear front only and drums in the back. Not the best. Hard to balance and I burnt up the drums at a track day. I installed the Dr Diff rear disc kit and a huge improvement. With the brakes you choose, need to check piston area, especially on the front. The Cobra based kit has smaller piston area vs stock Mopar and needs more hydraulic pressure. I wound up changing to a 15/16" master + dual 8" booster to get my setup to 100%. Hydroboost is another option.

Good luck!

Your car sounds pretty great too! If I may ask, what EFI system did you go with?

As for the cam, I'm not sure yet. I know I want to build this engine and car so that it is possible to get 20 mpg on the highway, and Chryco Psycho over on cuda-challenger.com said he could design me a cam grind that would work for that.

I solved the fast ratio arm and header problem, I found headers that will clear them.

Thanks for the advice!

On the EFI I run 1'st generation FAST XFI (port injection). The FAST stuff has worked and held up well for 10+ years... the overall fuel system worked well when I switched to pump in tank. External pump did not work so well.

Which headers are those? Are they big enough to not hinder a 512 cubic inch motor?

They're TTI 2" headers with 3.5" collectors, and I was planning on using 3" reducers to hook up to the 3" TTI exhaust I selected. They're rated up to around 600 horsepower

I've got 285-40-18s on 10" w/ 5.5" BS for the back of my Challenger w/ stock spring locations and rolled lips, so 275 would definitely fit. I _think_ 295s would fit but I would 3x check the BS measurements as it will be tight. They would for sure fit with the offset hangers and rolled lips.

What would happen if I decided to ditch my idea and go with coil-overs and power rack and pinion all around? Would performance be about the same as with all the Hotchkis and Firm Feel stuff I listed?

Also, out of curiosity, would it be possible to ditch the rear leaf springs and go with a Street Lynx coil over kit but leave the rest of the suspension parts? How would that affect performance?

You can go all out and take out the stock suspension stuff all you like, but I think you will find the same reaction from many here:

These cars had a good setup from the factory that just needs some updating.

Updating is less expensive and less work than it is to slam additional suspension setups under the car that are designed like a Ford or a Chevy.

Lots of people love their RMS setups, so clearly they make a good product.

The issue for many on this section is that coil-over setups don't seem to perform better than the updated stock setups and require more money and more modifications to install than the updated stock systems. So the basic answer to your second question would be: Yes, performance would be about the same for more money.

Many people are against a 4 link on these cars as well - if you look through this section, there are a lot of discussions of 4-link versus OEM or 3-link setups.

Most recently the coil-over versus stock, 4-link versus 3-link was debated in this thread: https://board.moparts.org/ubbthreads/ubbthreads.php/topics/1869049/sons-71-duster.html#Post1869049

Personally, if I was going to go all out on a suspension package for an E-Body and I truly decided that I wanted to do away with the stock stuff, I'd go for an Art Morrison Full Frame, a Schwartz G-Machine Chassis, or a Roadster Shop Chassis, which are all available for an E-Body.
But there is a LOT of cost there - and I'm not sure that the cost is worth the performance (just to end up running Corvette spindles!).

Thanks for the link. I looked into the G-Machine, it looks very cool but it comes with a coil-over setup. Could I ditch that and put in the Hotchkis parts instead? And I'll look into the Art Morrison frame

Nope, once you go with one of those frame/chassis setups, you are looking at GM stuff.

Hotchkis makes OEM-style replacement stuff for Mopars - torsion bars and strut rods and swaybars that replace factory stuff, but are better.

I doubt that any of their stuff would be compatible with the GM parts used on those setups, but I suppose you could ask.

I don't know why you would, though, those are three very reputable names in the AutoX/Pro-Touring world, I'm sure whatever they sold to you will be great for handling, even if it will be super expensive.

My personal problem with all of that is: How much greater would it be than the Hotchkis or Firm Feel stock-style stuff attached in a factory way for a lot less money?

Good point. I think I'll just stick with the stuff on my list

Another thread on this forum has been following a Valiant with torsion bars, he has been doing pretty good for himself without the expensive coil over conversion.

https://board.moparts.org/ubbthreads/ubbt...tml#Post1743045

Both can work for you, just depends what you are looking for. I don't really buy the cost argument on the coil over vs stock type set up, if you are starting with a stock front end that you have to replace everything on one of the bolt in coil overs kits may be cheaper in the end, but you have to buy the whole thing at once.
Both drive good but I would give the edge to a alterktion over a stock set up on the street, they certainly are much easier to adjust and have more suspension travel, brake kits may be cost a bit less as they use more common spindles.
All out handling I would guess may just end up coming down to the tires and proper setup more than what front end is used in the car. Just my 2cents

I was worried about this when I purchased the borgeson steering box, since I have FirmFeel quick ratio pitman and idler arms. For me, this combo works very well. The steering in center area is still slower than for example in my bmw m5, or 07 320d. I have taken my car to 150+ mph, no "twitchy" feeling of any kind.

I do have tubular uca:s with 7deg caster set in.

I am currently building a Challenger for a customer in a pro touring style. I have widened the wheel tubs 2 inches in the rear to fit a big back tire in it. Ordered a Hotchkiss TVS for it. The rear springs will be moved inside the frame rails to get maximum tire in the back. One thing I have wanted to do is box the LCA's. Any pictures of that? I don't want to block access to any important areas on them. I will also be bracing and fully welding the stock K member. This is a great thread chock full of info!

LCA braces are shown here, they do not block access

www.AREngineering.com makes ready made plates with holes in them.

I made this in 1998 with 3 pieces 1" strap.

Well add this to this to your info base, 99% of time LCA boxing here, is pointless, and is mainly monkey see monkey do.

https://en.wikipedia.org/wiki/Monkey_see,_monkey_do

"Monkey see, monkey do
From Wikipedia, the free encyclopedia
Monkey see, monkey do is a pidgin-style saying that appeared in American culture in the early 1920s. The saying refers to the learning of a process without an understanding of why it works. Another definition implies the act of mimicry, usually with limited knowledge and/or concern of the consequences.[1]"

Thanks Goody and AutoX! I will be doing that as soon as I am decide to take a break from the body. As for JCC, what's the deal? Not on positive comment on this thread. I think he needs a hobby besides sitting at his computer and typing nonsense!

The one strap I put on the end near the ball joint I would not put there again.

The one under the sway bar connection I probably would to support the extra forces of a really thick swaybar bar on the LCA sway bar tab.

The strap at the very back of the LCA I would definitely put on again. The two halves of the LCA like to slightly move apart and it puts slack on the pivot/bushing point. Now I've noticed there is no side to side slack, but over 35 years there is slack between the OD of the LCA pivot and the LCA stamped ID. I don't know if this is from wear or original tolerances. I think both contribute, but I was not like that way in 1997.

"Nonsense"?

"what's the deal?"

If you asked a real pertinent question, I would respond in kind.

I missed the memo on only "positive" comments being allowed.

Have another banana.

Do you have pics of your brake setup? I have a very similar front setup (same PBR calipers, Baer branded kit) and it is calling for the calipers to be rear mounted. How bad was it to install the rear discs? And the booster? How much vacuum? My 360 doesn't make much.

BTW: just another Hotchkis TVS customer here (minus the subframe connectors) and love how it handles now with a proper alignment. It is definitely the best bang for the buck. I am proof it can be done on the cheap as everything was bought with a discount online, discount at a show, or someone had an open box product that they decided not to install. Definitely wasn't one click shopping, but I saved serious dough. I run the FFI Stage 3 with fast ratio arms, and 1.18 torsion bars. I have the old RCD Bilstein shocks out back, and just switched to QA1 sing adj up front and you can't tell by the ride I have big t-bars. Also am running an aluminum headed small block and fiberglass hood on my Challenger.

Might as well put the LCA plates on, not a whole lot of other things you can do to a car for $25.

I also run a Bear 13" kit on the front purchased ~10 years ago. I first installed it with the iron master supplied by Bear and a reman OE 9" single diaphragm booster. The Bear hoses did not work as supplied for rear mount calipers - too short. I wound up using them as a pattern by cutting them in half and using a piece of poly tube slipped over the flex part to join the halves. That way I could adjust length and orientation of the ends. With T bars out, I tried full jounce, full rebound and full left and right adjusting the hose length and orientation until it worked. I used some hose clamps to lock the poly tube in position and sent the mock-ups off to Inline Tube. A week or so later they sent back a set of perfect hoses.

Maybe/hopefully Baer or Dr Diff have the hoses figured out now.

With that I had good functional front brakes... but not enough line pressure for max effort stopping. As I got more serious about track use, that needed fixed. First was the 8" dual booster. I got it from Mancini, however Dr Diff sells them also. Straight forward installation... at least no harder than a stock booster. Working on the linkage under the dash is not my favorite but as the saying goes, just nuts and bolts. The back of the dual booster is a bit larger diameter so the hole in your original firewall re-enforcing plate will be a little small... either hog it out or get the new plate that fits (which I did). The dual booster was better but still not 100%. More pressure needed. I added a Dr Diff 15/16" master and it is good now. With sticky 200 TW handling tires, I have all the brakes I can use.

That took care of the front. My rear drums I burned up at a track day and switched to the Dr Diff Cobra based rear kit (mock up pics attached). As advised by Dr Diff, one axle shaft needed slightly lengthened to get contact with the thrust button and provide effective adjustment for the tapered bearings. I welded a hardened washer on the end of the shaft and machined it down based on test fit to get it dialed in.

The system works great with EBC yellow pads. Front and rear are balanced and great stopping capability on a road course with repeated laps.

PS: You asked about vacuum.... I have ~13" at idle after tuning. Before tuning it was under 10". Works fine for around town driving. Also, mine is manual transmission so while braking in gear, probably 20+" vacuum. If yours is lower, probably need a vacuum pump or hydroboost.

How is dust and noise with the Yellow stuff pads?

The EBC yellow pads have no noticeable noise in my application. Dust about the same as the carbon mettalic I ran previously... wheels need a good wash after a track day but not too noticeable with street driving after break-in. During break-in the abrasive surface coat on the pads does make noticeable dust. They are a bit hard with first brake application on dead cold rotors and warm and bite well during the first significant stop... and hold up well with repeated stops.

I believe the EBC "red" ceramic is recommended for best cold bite and minimum dust... but not what I needed for sustained track use and higher temp performance.

Great info! Thanks!!! I've got a couple tricks left in tuning my motor and that, hopefully, will gain me a few more inHG of vacuum. Also, I'll still run the 13" calipers to the front (not real big on separating the UBJ just to switch the spindles) because it seems like no big deal getting the proper hoses made.