Solid Axle vs IRS

[N/Angel]

Guys, I know there's endless topics about this on SVTP but I want the opinion of you guys that actually track the cars.

My car is a 2003 GT coupe, completely gutted, rollcage, 32V/Eaton engine, T-56, 4.10, T2-R, 9x17 Wedsport wheels all around with 275/40/17 Kumhos right now.

as for suspension/steering, this is what I have:

MM Offset/Delrin A-Arms
Steeda Offset steering rack bushings
03-04 Cobra steering rack
Steeda bumpsteer kit
MM steering shaft
Steeda front swaybar with aluminum mounts and HD endlinks
KW Suspensions Variant 3 Coilovers with KW balljoints
Steeda tubular subframe connectors with x-brace
Steeda aluminum upper control arms
Steeda aluminum lower control arms
Steeda rear swaybar
Steeda rear shock tower brace
Bilstein HD Quadshocks

now, last time I drove the car (4 years ago before the engine blew) it ran pretty good and handled "ok", I never thought about it much and was happy with what I had.
since then I have met my boyfriend who owns a performance shop and is a hardcore trackguy with countless laps on Hockenheim and Nürburgring.
he laughed at me when I said I want my Mustang to handle good enough to be fast around turns.
the car is finally back up running since Monday and the first thing he comes to ask me is how on earth am I wanting to drive fast if there is no way to adjust camber in the rear. his words, if I want to go fast around turns I should get an IRS.

now I have refused driving an IRS Mustang because I was always afraid that I might want one, lol.

so basically, my question is, is it possible to make the solid axle handle as good as an IRS can be made to? probably not, but is it worth spending a couple of thousands on an IRS swap or should I at least give it a try to get some sort of watts link or torque arm/panhard bar or 5-link setup and see if we can live with that?

the car needs to be stable at high speeds and stick around turns even with the much lighter then stock rear now that it is gutted.

just asking for ideas and opinions, not looking to start arguments

thanks :beer:

 

[Jimmysidecarr]

A Torque arm and a Watts link will transform the car.
They are almost as fast as an IRS car on a smooth track.
One trick I remember that some of the NASA CMC guys use, is to use one very worn out upper control arm, along with a tight one, as kind of a "poor mans three link".
There are much better set ups though.

If it's not a street car, you can also add about a 1/4 degree of negative camber to the rear axle housing before any binding occurs in the diff from axle gears to diff case interference.

If you are as good of a reader as I think you are, you will find valuable set up information for live axle 79-04 Mustangs on Corner Carvers(best to just read and not post over there :nonono and also the road race/autocross section of the Corral has some good posts.

Before you post on Corner Carvers read all the rules carefully, it's best to just search and read over there though, they can be pretty tough on new people, and asking questions that have been already covered at length will cause a melt down.

I'm an IRS guy so I am not a live axle set up and handling expert.

One thing I will warn you about is NOT using heim ends on BOTH ENDS of all four control arms! This turns an already bad Quadra-Bind Mustang 4 link into a locked up nightmare, some heim ends are OK but never ALL.
The geometry is wrong and it can not articulate through suspension travel without binding badly.

There could be some good posts on here too, that I may not have seen because I am usually reading about IRS stuff.:beer:

I did a search for "road race torque arm set ups" in the svtp google search and was going to give you a bunch of links.
But my right click is broken on my mouse, so I cant.

 

[99COBRA2881]

Pick your poison. Both rear ends need work to perform well on the race track, both are poor setups in stock form. If you already have an IRS develop it and get the car on track already.

I have been around the IRS my entire time of open tracking and now SCCA road racing and I like its predictability. Also having the added weight on the rear end of the car isnt a bad thing.

Anthony
SCCA ITE #26

 

[98 Saleen Cobra]

uh oh lol.. Here's something that I'll throw out since I'm bias to SRA.. Look at the guys that run the fastest in AIX racing.. A47 and Griggs Cars.. Guess what they have?? A IRS is a great setup too though no doubt.. The ride quality of both when highly modified is about the same a little bit better with the IRS though.. EDIT: One thing that I forgot to mention.. Griggs can camber the rear of a SRA for you..

 

[99COBRA2881]

The guys that are fastest in AIX have the HP to make them fast regardless of which rear end is under the car.

 

[N/Angel]

A47 and Griggs Cars..

Griggs can camber the rear of a SRA for you..

I wish A47 had a rear suspension available...

How does Griggs camber the SRA rear????

 

[Jimmysidecarr]

I wish A47 had a rear suspension available...

How does Griggs camber the SRA rear????

Actually anyone with an Oxy-Acetylene torch can camber an axle housing, once they look up how and jig it up so they can measure what you have now and also the changes.

You heat up a golf ball sized red spot on the top of the tube and when it cools it shrinks and pulls the top of the tube in.

Repeat as needed, measuring all the way through.

Soild rear axle camber and toe. - Corner-Carvers Forums

(got a new mouse, LOL! right click works now.)

I think I'd rather buy a junk yard IRS and rebush it.

 

[98 Saleen Cobra]

Both will work for you needs like plenty have said.. :beer: If you already have a SRA I would just stick with that and go from there. If you want an IRS get the FTBR full kit ect and go from there.

 

[wheelhopper]

I have never tracked a straight rear axle car. My thinking would be that you can make a SRA work rather well, cosidering Ford still uses it with great success on their current crop of GT500s and Boss Mustangs. The AIX guys also do just fine with them.

I run an IRS in my '90 GT and I love it. It balances the car out nicely and adds 3" of track to the rear of the car. You're not going to get a whole lot of negative camber out of it. The most I have seen is -1.3. That may sound like a lot to Mustang guys, but the BMWs and Miatas run much more than that, and I can tell you on a twisty track TTE Miatas eat up my TTD Mustang.

One draw back to adding the IRS is that you will not be able to use the car for AI or CMC, if that is in your future plans.

It should not cost you thousands of dollars for the swap. You could probably find a Terminator, drag racer, that would be willing to trade you straight up. If you have both cars together the swap could be completed in a day.

Honestly if I was you I would probably install a torque arm/pan hard bar set up and call it a day. The main reason I installed an IRS was because I had it sitting around for a year and needed to add discs to the rear of my stock fox body, in order to track it. Since I already had the IRS, it was cheaper than buying a rear disc conversion.

 

[Krwy]

I have had a built, 3-linked SRA, and my current MM PHB SRA combo on my Mach. The only real advantage that I see the IRS has is over uneven terrain. My Maximum Motorsports 3-link car was unbelievable. I have also driven an IRS car, it was good, but it takes a lot more $$$ to build and stuff a IRS under a SRA car. I would say build the IRS if you already have one in the car, or already have one sitting on the floor of the garage. With your SRA GT, open the Maximum Motorsports catalog and order their rear 3-link kit. Griggs also builds really good quality race proven parts as well. I have seen plenty of NASA AI cars and AIX cars going very fast with the SRA. Ford still builds the SRA, and the Boss 302 Laguna Seca still runs the SRA and is an awesome car on track.

 

[wheelhopper]

I disagree by saying it takes more $ to make the IRS work. You can get the FTBR kit for the about the same $ as buying a torque arm and panhard bar. Both rear set ups can benefit from an aftermarket diff. and some may say that a serious OT IRS needs a rear diff. cooler, but I know of several IRS cars that don't have the cooler and do just fine. It comes down to what you have in the car already, IMO.

 

[Jimmysidecarr]

The OP is in Switzerland and has a GT with an SRA.
Unless there are junk yards with wrecked 99-04 Cobras over there, she is going to want to maximize the SRA and not start fresh with an IRS that would need to be rebushed.

The maximum motorsport catalog I believe will be her best solution, freight for that stuff will be reasonable, freight on an IRS will be steep.

 

[N/Angel]

Actually anyone with an Oxy-Acetylene torch can camber an axle housing, once they look up how and jig it up so they can measure what you have now and also the changes.

You heat up a golf ball sized red spot on the top of the tube and when it cools it shrinks and pulls the top of the tube in.

Repeat as needed, measuring all the way through.

Soild rear axle camber and toe. - Corner-Carvers Forums

(got a new mouse, LOL! right click works now.)

I think I'd rather buy a junk yard IRS and rebush it.

thanks for the link, I will show it to my boyfriend, lets see what he thinks about this idea :beer:

I have never tracked a straight rear axle car. My thinking would be that you can make a SRA work rather well, cosidering Ford still uses it with great success on their current crop of GT500s and Boss Mustangs. The AIX guys also do just fine with them.

I run an IRS in my '90 GT and I love it. It balances the car out nicely and adds 3" of track to the rear of the car. You're not going to get a whole lot of negative camber out of it. The most I have seen is -1.3. That may sound like a lot to Mustang guys, but the BMWs and Miatas run much more than that, and I can tell you on a twisty track TTE Miatas eat up my TTD Mustang.

One draw back to adding the IRS is that you will not be able to use the car for AI or CMC, if that is in your future plans.

It should not cost you thousands of dollars for the swap. You could probably find a Terminator, drag racer, that would be willing to trade you straight up. If you have both cars together the swap could be completed in a day.

Honestly if I was you I would probably install a torque arm/pan hard bar set up and call it a day. The main reason I installed an IRS was because I had it sitting around for a year and needed to add discs to the rear of my stock fox body, in order to track it. Since I already had the IRS, it was cheaper than buying a rear disc conversion.

yes it will be a couple of thousands because, first I need to buy an entire IRS assembly and have it shipped over to me, then start adding bushings and braces and what not to improve it, by the time it is all setup I'm sure I would have spent quite a bit of money

I have had a built, 3-linked SRA, and my current MM PHB SRA combo on my Mach. The only real advantage that I see the IRS has is over uneven terrain. My Maximum Motorsports 3-link car was unbelievable. I have also driven an IRS car, it was good, but it takes a lot more $$$ to build and stuff a IRS under a SRA car. I would say build the IRS if you already have one in the car, or already have one sitting on the floor of the garage. With your SRA GT, open the Maximum Motorsports catalog and order their rear 3-link kit. Griggs also builds really good quality race proven parts as well. I have seen plenty of NASA AI cars and AIX cars going very fast with the SRA. Ford still builds the SRA, and the Boss 302 Laguna Seca still runs the SRA and is an awesome car on track.

Maximum Motorsport 3-link kit? time to look at the MM website, never heard of it

The OP is in Switzerland and has a GT with an SRA.
Unless there are junk yards with wrecked 99-04 Cobras over there, she is going to want to maximize the SRA and not start fresh with an IRS that would need to be rebushed.

The maximum motorsport catalog I believe will be her best solution, freight for that stuff will be reasonable, freight on an IRS will be steep.

thank you for pointing this out, I was just going to reply that I doubt I'll find a junkyard IRS around here.

 

[Krwy]

Example of a MM package

Torque-arm Package, 1999-04 Mustang GT, Standard-Duty Torque-arm, Non-adjustable rear lower control arms [MMTASS-8] : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!

Griggs rear kits

Griggs Racing Products

 

[N/Angel]

does the torque arm sit lower then the differential? my car is pretty low already and I'm trying not to add anything that makes it even lower.

has anyone ever tried the Steeda 5-Link-2 Kit? or the Fays2 Wattslink?
there's a 2011 GT (I know very different) with a Fays2 Wattslink that ran the Ring and said the car is good for a 8 Minute lap with an experienced driver and a bit more suspension tweaking. wonder if the wattslink would get my car to a similar level?

I don't really want Griggs, a Griggs equipped 99 Cobra took 14 Minutes for one Nürburgring lap, so either the driver was terrible or the suspension simply doesn't work for this track. either way, for that kind of money I'm not willing to experiment what the reason was

 

[dtheo]

The new Boss has straight axle and performs well, nuff said.

 

[N/Angel]

The new Boss has straight axle and performs well, nuff said.

that's what I keep saying :beer:

but what is it that makes the Boss handle so well?
it can't be just a bare solid axle like it came stock on my GT...

I tried to find pics of the Boss rear suspension but no luck.

 

[Krwy]

Boss 302 rear suspension

As for the Griggs equipped car on the 'Ring. He must have been a novice driver. Griggs makes serious hardware. Griggs SLA front end is serious stuff. I would say Griggs would cater more towards a race built Mustang, while Maximum Motorsports (fantastic parts, don't get me wrong) has a more street oriented parts line-up. Either choice between a Griggs rear and MM rear would be light years ahead of the stock 4-link quadrabind set-up.

 

[98 Saleen Cobra]

A 99 Cobra has an IRS so unless they ditched that for a SRA they didn't have a full griggs rear end with a Watts link and a tq arm.. As for the tq arm and how it sits you have nothing to worry about when it comes to rubbing it wont.. My car is literally low as hell and griggs cars sit even lower with zero issues. If you want the best for a SRA Griggs is hands down the best.. If you want the best for the front Griggs and Agent 47's SLA's are hands down the best.. MM doesn't really compare to those two. You are going to pay a pretty penny for either one though..

 

[David Hester]

I used a modified Griggs torque arm and panhard rod for years. No binding and launched off corners great, no real dive on braking either.

and yes, it does hang down, but rarely dragged on anything...if you stay on the pavement. :nono:
yes, that is a nine inch Ford