notchback susp design and pricing - Ford Mustang Forums : Mustang Forum
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post #1 of 8 Old 07-09-2015, 01:06 PM Thread Starter
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notchback susp design and pricing

Hey guys, I am totally revamping my 93 notch. Turbo 5.3 LS engine, t56 transmission and 03/04 cobra irs, coilovers.

This is a long process, as I have more time than money for this project, and am willing to hold out for those crazy deals. Few years back saw a complete 04 irs go for 800$ for example.

First: What is a reasonable amount to pay for an 04 IRS? I was thinking around 1000$+ shipping?

2) front suspension setup. Will be keeping my eyes out for a used LS swap MM k member. Now which MM control arms do I want? I will be running 04 spindles and brakes, as well as cobra rack.

I will be using this thread as my general question page.

Thank you.

10.5:1 306, gt40s. 3.73s, 2800 lbs.
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post #2 of 8 Old 07-09-2015, 02:17 PM Thread Starter
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Always was reading a few thread son using the 2014 gt500 brakes. they are HUGE. More of a want than a need. But pricing seems to be not much more for the gt500 stuff vs04 cobra brakes. However I think I need to run minimum 18s to clear those calipers though right?
How is tire selection in an 18? I am looking for at least a 10.5" wide wheel in the rear, 11 or 12 would be nice too.

10.5:1 306, gt40s. 3.73s, 2800 lbs.
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post #3 of 8 Old 07-09-2015, 03:21 PM
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IMO tire selection is better for 18s than 17s.

1k for an 04 Cobra IRS would be a good deal. normal seems to be around 1200-1400 depending if they are modded at all.

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post #4 of 8 Old 07-09-2015, 04:02 PM
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I'll be running StopTech ST40s with 14" rotors on my 86. These require 18" wheels. My wheel/tire package choice is CCWs in 18x11 with BFG Rival IIs in 315/18. If you want a 200 TW tire, then BFG seems to be the only manufacturer with tires above 295 in 18". However, if you want to run R-comps and/or can use a TW tire above or below 200, there are more options.

If you have your heart set on an IRS then what I'm about to convey is irrelevant. But, I've lived with an 01 Cobra since new. I put '00R Cobra Bilsteins and H&R Super Sport spring on the car almost immediately, followed by a CAI. It also has a Borla cat-back and 3.55s (stock was 3.27s that year). Otherwise, stock car; even the wheel/tire package. Car dynoed 300/300 RW about eight years ago.

The IRS provides a nice ride. But performance is sorely lacking. Traction is compromised due to the mounting and axle tramp is more than ugly; things can break even with 31 spline shafts. With your turboed car, you will need to put a lot of attention into the IRS to make if live and function. Then you have to consider the build up after the acquisition costs. Even with the best stuff (FTBR comes to mind), the build cost is on par with a full MM equiped stick axle for not much better performance.

In comparison, my 86 is full MM equipped suspension. The 86, with a stock motor, can run circles around the 01 on an A/X course with the same wheel/tire package on both cars. Moreover, because the T/A eliminates the stock quadra-bind, the ride quality is only slightly more harsh than the Cobra and the 86 runs C/Os and 300# springs (the wheel rate comparison is much higher on the 86). For my money without the need to acquire an IRS, I decided build up my 86 with the MM T/A/PHB, K etc.
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post #5 of 8 Old 07-11-2015, 01:30 PM
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I got my 03/04 Cobra brakes (front) for 250 bucks. Granted it was a friend, but ive found kits on ebay for 500 bucks and you can run 17 inch wheels

the gt500 rotors are 15inches, you will need an 18 wheel
like this guy said 18 inch wheels have more tyre selections,

If you plan on tracking the car i would do the SN95 A arms forward offset (cannot wait to install them on my car)

Foxes understeer: narrow front tyres, Front heavy, engine sits over the front axle, not enough negative camber, not enough track width

So running a 315s in the rear is great and looks amazing, however you will hate the car at the track when you cannot turn. So id go for a square setup with the wheels and tyres and run as much front track width and neg camber as possible. The forward offset arms will add more track and more camber so i would choose those. (wish i did instead of the regular fox MM A arms.

Also what qttracer said the weak IRS will hop and with all that torque and power from that GM engine, i would bet its going to happen or you will spin a lot.

question how much heavier or lighter is an LS engine compared to the SBF 5.0?
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post #6 of 8 Old 07-13-2015, 05:06 PM
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I got my 04 IRS for $500 almost 2 years ago, complete minus the calipers. I got a great deal, and needed a totally redone stick axle (gears, axles, diff, shocks, springs, control arms, EVERYTHING) so instead of spending the $2k on that stuff I went with the IRS and I couldn't be happier. I also have MM coil overs, etc, and will eventually put on the upgraded bushings, but wheel hop isn't that bad with a fairly stock 5.0 in my 92.

1992 5.0 5sp coupe, ported GT-40 intake, TFS 170 heads, Scorpion 1.72 RR, TFS1 Cam, BBK longtubes, BBK H-pipe, MSPNP2 ECU, Full Koni MM coilovers, SVE S1 seats, Moda R6 Wheels, full Cobra Brakes, 2004 Cobra IRS, MM SFC's,
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post #7 of 8 Old 07-16-2015, 02:33 PM
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I paid $2200 Canadian and I got:
front and rear cobra brakes with almost new vented/slotted rotors
complete 04 IRS
Eaton Posi locker
Ford racing diff cover
a ton of Drop Engineering support brackets
MM / Koni coilovers
MM rear sway bar endlinks and bushings and adjustable tie rod ends
FTB cross axis joints
the list goes on...

I think its a great deal. I was always thinking about IRS so I just waited, you need to be ready to jump when a deal comes along though.
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post #8 of 8 Old 07-20-2015, 07:36 PM
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Did an A/X driving class last Saturday. It rained about half the time. Ran the 01 since the 86 is under construction. 1st gear was useless due to massive spin and wheel hop. Had to start the courses in 2nd which proved to be better but too much throttle would break the tires loose and wheel hop. This was at the start of the courses. Near the end when I had a decent straight before the lights, still spun the tires. The IRS needs a lot of work with a bit or power, let alone the torque of a turbo car.
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