The rear suspension that could have been

[91svtbird]

Let me briefly introduced myself. My name is jes and I've been lurking here for about 7 years and never had much to contribute until now.
Well guess what I came across.

Not something you see everyday!

I guess there were 10 made and the other 9 were destroyed.
I should be getting more info tomorrow.

Most interesting thread I've seen in a while. Thank for sharing the pics with us. Can't wait to see more of them.
I can't help but wonder how they got the exhaust piping past that thing to the rear of the car.

 

[jes_csx]

Thanks.

It looks like the exhaust ran down the center just to the sides of the carrier.
In case you or others missed the link that was sort of buried in my post, I'll do this again.


IRS picture gallery

 

[Fox-4]

the more I look at the Rear end the more I want to take it apart, study it, see what parts that will currently fit it and install it and drive it. lol

 

[68fastback]

Just some comments on some of the IRS pieces I've seen in this thread:

The Carling re-developed IRS for S197 is based on the Klaus Arning T5 IRS that was developed by Klaus when he was an engineer working for Ford in the 1960s. It was intended as the IRS for 1964.5 Mustang. It was shelved due to cost and the fact that it didn't materially improve lap times of what would become the GT350 on the tracks they planned to clean Corvette's clock on, so was shelved. On real-life roads, no doubt it would kick a live-axle's butt, but let's not get on IRS vs live axles. Klaus Arning's son, Ralph Arning, is the Ford ombundsman at the Flat Rock plant -- great guy, as many of you probably know. Duane Carling knew Klaus way back when and decided to resurrect the T5 design (MustangIRS.com) It's more sophisticated than it looks -- the retro fit version is quite light, given it's a retrofit and therefore not a hard-point-optimized native design. Additionally, it holds a pantent on it's rear-steer self-correcting geometry which was licensed by Mercedes for many years until computers got sophisticated enough for Daimler to figure out how to do their own self-correcting design without infringing the Arning patent, at which time they stopped licensing it from Klaus (who, as I understand it, retained the patent rights after retiring from Ford).

Dunno what the more modern unit Jes_csx posted pics of is from but it's very cool, imho. I do recall that Ford did a full mock-up of an IRS for the S197 based on the Explorer IRS because that was the only one at hand that could take the torque of the GT500, so that just might be it (dunno). That could be the IRS that caused Ford to say things like 'it would add $5-10K to the S197' -- comments that, no doubt, were made because they helped justify not doing an IRS because that decision was already made when they talked to the magazines. No way a native-designed IRS done in volume needs to cost more than a good audio head-unit, let alone a couple of Tata Nanos (lol).

The control blade IRS referred to was developed by Dana Australia for the Aussie Falcon. It's actually fairly slick and light for a production IRS that is a non-native design (the car wasn't designed for IRS, like the IRS Cobra mustangs, so it was adapted). Control blade IRSs are a good compromise in that they are relative cost-effective (still considerably more than a live axle tho), relatively light for a stamped unit (tho not as light as a native design or, better still, a native design using lightweight materials).

Yes an IRS weighs more (in general, exotic materials aside) than a live axle and costs more (universally). As far as weight goes, realize that an IRS ads very little unsprung weight (and greatly reduces unsprung weight vs a live axle), so almost all the weight it adds (which for a native/dedicated design is not all that much) and 100% of the sprung portion of that weight (most of it) improves the weight distribution of the car. Better still, move the gearbox back there too! On a GT500 that combination might add 130lbs for a good native design (nothing exotic)but most of that will be sprung weight that improves handling and compliance. Including the gearbox move and an alloy block (ala 2011 GT500) and W/D could approach 50/50. By contrast, virtually all the weight of a live axle is unsprung. This is why, I'm sure you all know, live axles just can't handle as well on imperfect real-world roads (in most of the US, but not all) but can kick butt on the relative smoothness of a road course (set up right, etc) ...and, along with cost, is why it was shelved in both 1964 and 2005.

As far as cost goes an IRS will always cost more, but that difference can come down rapidly with volume. Could the 2013 Mustang be an all-IRS build for that reason? Will the Mustang models 'split' for 2013 with a native-designed IRS determining the chassis hard-points such that a live axle can be easily swapped in via an FRPP kit? That could be a best-of-both worlds strategy that would drive the volumes needed to drive IRS cost down and still give the drag racer the preferred live axle. Better still, push IRS across the all new global RWD platform Ford has been developing and the volumes will really drive cost down and possibly permit lightened pieces to boot. Does anyone think Ford would be developing a Global RWD chassis with at least a 12 year life (thru 2025 or so) and not have it be a native IRS? I personally doubt it can be anything but IRS, but we shall see both what it is and what models share it in due time. I'd expect the 2013 Mustang to be one of them along with a RWD sport-wagon of some sort -- a segment Ford has no presence in but DCX, GM and others do, tho at various price points.

I kinda like the best-of-both-worlds scenario best as long as the hard-points are determined by the IRS, not as the later Cobras were done. The Cobra IRS worked well enough (handling-wise) but added more weight and was weaker than a native design could have been. Still it was an early attempt of one chassis sharing both suspension types, but the hard points were, unfortunately, driven by the existing live axle design. No way Ford wil make that mistake again, imho, in a world-class global RWD platform to underpin several derivative models, etc.

Peace, brethren.

Dana Aussie Falcon contro-blade IRS...

 

[Dave07997S]

I assume you are referring to the front control arms, as the FR500C uses a tubular rear LCA.

From here. The arms are no longer available.


And while the front LCA is indeed a stock stamping, the ancillary pieces are all aftermarket...
- longer ball joints
- higher durometer bushings
- unique caster adjustment bushings and hardware

The stamping itself is an award winning piece developed and manufactured by Multimatic, which coincidentally was responsible for the on-track devlopment of the FR500C along with final assembly. In other words, the arm really is a bit more than a stock piece with stiffer bushings. That is all.;-)

On edit (continued hijack)...Multimatic also did the Mustang rear lower and upper control arms, in addition to the front control arms (pg 5 of the linked pdf).

I was looking for this thanks Tob..also note the coil over rear setup and not to mention the Moton like shock assembly...far from OEM. Oh and not to mention the brakes which are 355mm for the fronts a far cry from the puny OEM units.

The biggest complaint that Porsche and BMW guys are complaining about is the fact the rules are definitely setup for the Mustang to be competitive...yet BMW has won 1 championship and Porsche 1 with Mustang winning 3 since 2005.

Dave

 

[Ry_Trapp0]

Some interesting reading on the 'to be' S197 IRS...
DrivingEnthusiast | Ford Mustang – IRS

Tob

wow, after some reading, i'm not sure if i believe everything this guy has to say.

"Trying to build an IRS out of some backwards stamped-steel components on the cheap does not make for a good IRS."
i believe that ford oz and GM would beg to differ. not to mention numerous other companies. stamped steel is perfectly fine in a production suspension.

"The (Cobra)IRS was finally perfected, but the engines got worse and worse."
"And despite it’s great suspension, the car was a worthless POS because of that damned engine."
wat??? everyone knows how compromised that IRS was, hardly perfected!

"The SVT engineers that came with the Mustang told me that they had already totally rebuilt the Ford GT’s engine once and never could make it work on the track."
i'm not sure about you guys, but i certainly haven't heard of anyone killing their engines because they were open tracking their ford GT.


i won't deny that there is some good info in there though, definitely 'grain of salt' though.

 

[ac427cobra]

wow, after some reading, i'm not sure if i believe everything this guy has to say.

"Trying to build an IRS out of some backwards stamped-steel components on the cheap does not make for a good IRS."
i believe that ford oz and GM would beg to differ. not to mention numerous other companies. stamped steel is perfectly fine in a production suspension.

"The (Cobra)IRS was finally perfected, but the engines got worse and worse."
"And despite it’s great suspension, the car was a worthless POS because of that damned engine."
wat??? everyone knows how compromised that IRS was, hardly perfected!

"The SVT engineers that came with the Mustang told me that they had already totally rebuilt the Ford GT’s engine once and never could make it work on the track."
i'm not sure about you guys, but i certainly haven't heard of anyone killing their engines because they were open tracking their ford GT.


i won't deny that there is some good info in there though, definitely 'grain of salt' though.

It's pretty common knowledge the Ford GT suffered from overheating issues running on track. :read:

 

[09Troublemaker]

Just some comments on some of the IRS pieces I've seen in this thread:

The Carling re-developed IRS for S197 is based on the Klaus Arning T5 IRS that was developed by Klaus when he was an engineer working for Ford in the 1960s. It was intended as the IRS for 1964.5 Mustang. It was shelved due to cost and the fact that it didn't materially improve lap times of what would become the GT350 on the tracks they planned to clean Corvette's clock on, so was shelved. On real-life roads, no doubt it would kick a live-axle's butt, but let's not get on IRS vs live axles. Klaus Arning's son, Ralph Arning, is the Ford ombundsman at the Flat Rock plant -- great guy, as many of you probably know. Duane Carling knew Klaus way back when and decided to resurrect the T5 design (MustangIRS.com) It's more sophisticated than it looks -- the retro fit version is quite light, given it's a retrofit and therefore not a hard-point-optimized native design. Additionally, it holds a pantent on it's rear-steer self-correcting geometry which was licensed by Mercedes for many years until computers got sophisticated enough for Daimler to figure out how to do their own self-correcting design without infringing the Arning patent, at which time they stopped licensing it from Klaus (who, as I understand it, retained the patent rights after retiring from Ford).

Dunno what the more modern unit Jes_csx posted pics of is from but it's very cool, imho. I do recall that Ford did a full mock-up of an IRS for the S197 based on the Explorer IRS because that was the only one at hand that could take the torque of the GT500, so that just might be it (dunno). That could be the IRS that caused Ford to say things like 'it would add $5-10K to the S197' -- comments that, no doubt, were made because they helped justify not doing an IRS because that decision was already made when they talked to the magazines. No way a native-designed IRS done in volume needs to cost more than a good audio head-unit, let alone a couple of Tata Nanos (lol).

The control blade IRS referred to was developed by Dana Australia for the Aussie Falcon. It's actually fairly slick and light for a production IRS that is a non-native design (the car wasn't designed for IRS, like the IRS Cobra mustangs, so it was adapted). Control blade IRSs are a good compromise in that they are relative cost-effective (still considerably more than a live axle tho), relatively light for a stamped unit (tho not as light as a native design or, better still, a native design using lightweight materials).

Yes an IRS weighs more (in general, exotic materials aside) than a live axle and costs more (universally). As far as weight goes, realize that an IRS ads very little unsprung weight (and greatly reduces unsprung weight vs a live axle), so almost all the weight it adds (which for a native/dedicated design is not all that much) and 100% of the sprung portion of that weight (most of it) improves the weight distribution of the car. Better still, move the gearbox back there too! On a GT500 that combination might add 130lbs for a good native design (nothing exotic)but most of that will be sprung weight that improves handling and compliance. Including the gearbox move and an alloy block (ala 2011 GT500) and W/D could approach 50/50. By contrast, virtually all the weight of a live axle is unsprung. This is why, I'm sure you all know, live axles just can't handle as well on imperfect real-world roads (in most of the US, but not all) but can kick butt on the relative smoothness of a road course (set up right, etc) ...and, along with cost, is why it was shelved in both 1964 and 2005.

As far as cost goes an IRS will always cost more, but that difference can come down rapidly with volume. Could the 2013 Mustang be an all-IRS build for that reason? Will the Mustang models 'split' for 2013 with a native-designed IRS determining the chassis hard-points such that a live axle can be easily swapped in via an FRPP kit? That could be a best-of-both worlds strategy that would drive the volumes needed to drive IRS cost down and still give the drag racer the preferred live axle. Better still, push IRS across the all new global RWD platform Ford has been developing and the volumes will really drive cost down and possibly permit lightened pieces to boot. Does anyone think Ford would be developing a Global RWD chassis with at least a 12 year life (thru 2025 or so) and not have it be a native IRS? I personally doubt it can be anything but IRS, but we shall see both what it is and what models share it in due time. I'd expect the 2013 Mustang to be one of them along with a RWD sport-wagon of some sort -- a segment Ford has no presence in but DCX, GM and others do, tho at various price points.

I kinda like the best-of-both-worlds scenario best as long as the hard-points are determined by the IRS, not as the later Cobras were done. The Cobra IRS worked well enough (handling-wise) but added more weight and was weaker than a native design could have been. Still it was an early attempt of one chassis sharing both suspension types, but the hard points were, unfortunately, driven by the existing live axle design. No way Ford wil make that mistake again, imho, in a world-class global RWD platform to underpin several derivative models, etc.

Peace, brethren.

Dana Aussie Falcon contro-blade IRS...

some good info

 

[Ry_Trapp0]

I was looking for this thanks Tob..also note the coil over rear setup and not to mention the Moton like shock assembly...far from OEM. Oh and not to mention the brakes which are 355mm for the fronts a far cry from the puny OEM units.

The biggest complaint that Porsche and BMW guys are complaining about is the fact the rules are definitely setup for the Mustang to be competitive...yet BMW has won 1 championship and Porsche 1 with Mustang winning 3 since 2005.

Dave

the bimmers use coilovers and larger than stock rotors too:shrug: besides, wouldn't the GT500 14"(355mm) rotors qualify as 'stock sized'? lets not pretend that any of these cars use stock rotors afterall.

i'm certainly not saying your wrong about the rules helping the mustang maybe a little too much, all you gotta do is look at the engine to see that.

It's pretty common knowledge the Ford GT suffered from overheating issues running on track. :read:

oh yea, i've read about that. but needing rebuilt engines? maybe in SVT testing, but 'normal' use certainly seems safe.

 

[Dave07997S]

the bimmers use coilovers and larger than stock rotors too:shrug: besides, wouldn't the GT500 14"(355mm) rotors qualify as 'stock sized'? lets not pretend that any of these cars use stock rotors afterall.

i'm certainly not saying your wrong about the rules helping the mustang maybe a little too much, all you gotta do is look at the engine to see that.

oh yea, i've read about that. but needing rebuilt engines? maybe in SVT testing, but 'normal' use certainly seems safe.

M3's have coil overs from the factory, they are just setup for corner balancing.

Once again I think with the 5.0L Coyote motor being in this car from the factory now takes alot of the argument about bending the rules for Ford as the 5.0L engine is now going to be an option from the factory...

Also the M3's BTW are allowed a caliper swap not a larger rotor as they come from the factory with pretty large brakes especially the new E92 M3's at 14.2" for the front and 13.8" for the rear.

The Porsche has to make due with the smaller 3.6L H6 making only 325hp, although in race trim maybe they make 350hp. They aren't allowed the larger 3.8L H6 out of the 997S. Porsche brakes from the factory are almost race ready..what's funny is the PCCB's are not allowed in this series as well for the Porsche. Most people who track their 997's and have the larger red brakes just swap out pads and fluid and call it a day. Granted the factory rotors are done after one race..



Dave

 

[BlackBolt9]

grand-am rules require factory style suspension using factory pickup points.

Yes, we must use the factory suspension mounting points. Everything else that was wrong seems to have been covered by Tob already.

I was looking for this thanks Tob..also note the coil over rear setup and not to mention the Moton like shock assembly...far from OEM. Oh and not to mention the brakes which are 355mm for the fronts a far cry from the puny OEM units.

The biggest complaint that Porsche and BMW guys are complaining about is the fact the rules are definitely setup for the Mustang to be competitive...yet BMW has won 1 championship and Porsche 1 with Mustang winning 3 since 2005.

Dave

Give me an f-ing break. The Porsche and BMW guys are complaining because they are trying to cheat to win and therefore aren't getting the concession from Grand Am they probably should.

We won the championship last year not because we had the fastest car but because we were the most consistant. Our worst race finish was 8th and we were top 5 for all but 2 or 3 races the entire season! The BMW's from Turner could kick our ass at will and would have won the championship if they weren't running engines that were so strung out that they blew up at least twice that I remember. That's 2 DNF's and they finished the championship in 3rd behind two Mustangs that never placed out of the top ten. Cry me a river and how about the Porsche's that were running illegal engines, even got caught once when inspected. Don't hear them crying about that, no the real
problem is those Mustangs :rollseyes

FWIW, they are not Motons, last year was the mandated Koni coil overs. Before that we ran Dynamics, which are made by Multimatic as well. They are not any further from factory than the BMW or Porche Koni's that they were required to run as well. Completely fair between the teams.

EDIT: BTW looking at pictures of this prototype IRS, I don't see a way to adjust and or fix toe. From the reading it appears that it's supposed to be self correcting or something along those lines. Not something I think I would want in a race car to be honest. Something that can move without me knowing for sure which way or how much scares me from a car setup POV.

 

[Dave07997S]

Yes, we must use the factory suspension mounting points. Everything else that was wrong seems to have been covered by Tob already.



Give me an f-ing break. The Porsche and BMW guys are complaining because they are trying to cheat to win and therefore aren't getting the concession from Grand Am they probably should.

We won the championship last year not because we had the fastest car but because we were the most consistant. Our worst race finish was 8th and we were top 5 for all but 2 or 3 races the entire season! The BMW's from Turner could kick our ass at will and would have won the championship if they weren't running engines that were so strung out that they blew up at least twice that I remember. That's 2 DNF's and they finished the championship in 3rd behind two Mustangs that never placed out of the top ten. Cry me a river and how about the Porsche's that were running illegal engines, even got caught once when inspected. Don't hear them crying about that, no the real
problem is those Mustangs :rollseyes

FWIW, they are not Motons, last year was the mandated Koni coil overs. Before that we ran Dynamics, which are made by Multimatic as well. They are not any further from factory than the BMW or Porche Koni's that they were required to run as well. Completely fair between the teams.

EDIT: BTW looking at pictures of this prototype IRS, I don't see a way to adjust and or fix toe. From the reading it appears that it's supposed to be self correcting or something along those lines. Not something I think I would want in a race car to be honest. Something that can move without me knowing for sure which way or how much scares me from a car setup POV.

I just want to point out that this is not how I feel regarding Pcar guys and BMW. I'm just relaying what I hear on the boards as I own a Pcar now and have owned E46 M3's. If you read my post I said Moton like setup with thier external oil resevoir (sp?). I do know they are Koni's...hence Koni Challenge which is now the Continental Tire Challenge or something of that sort.

Whats interesting you mentioned that the E46 M3's would have kicked our butts if their engines weren't so strung out...they have to be to keep up with that 5.0L Cammer motor.:-D

 

[BlackBolt9]

I just want to point out that this is not how I feel regarding Pcar guys and BMW. I'm just relaying what I hear on the boards as I own a Pcar now and have owned E46 M3's. If you read my post I said Moton like setup with thier external oil resevoir (sp?). I do know they are Koni's...hence Koni Challenge which is now the Continental Tire Challenge or something of that sort.

Whats interesting you mentioned that the E46 M3's would have kicked our butts if their engines weren't so strung out...they have to be to keep up with that 5.0L Cammer motor.:-D

That's all and well. I didn't mean a direct attack towards you. I was just giving another opinion from someone who actually competes in the series to counter the Porsche/BMW claims that you posted.

Even if YOU know they AREN'T Motons I thought it would be useful information to let everyone know exactly what the ARE. BTW even thought it is not the Continental Tire Sports Car Challenge we are still required to run the Koni shocks for at least this year again.

Not all the E46's just the Turner cars;-) Kind of funny when they have cars that are unbelievably faster than the other BMWs. And even more funny when they can pull on the "high horsepower Mustang" around the banking at Daytona and Homestead. They were also running 2 seconds a lap faster at Watkins Glen also until it rained then we were faster, you know they say that rain is a horsepower equalizier right?;-) And then Grand Am just says it because the almighty Bill Auberlin is driving And no they didn't need to be strung out in order to keep up with us. They did it for an ADVANTAGE in a series that is really close to spec racing with different cars. How is it fair that we have to run a sealed ECU and engine while the Porsches and BMWs can pull theirs apart and play with them? Also if we make SO much more power why do we not have to run a smaller restrictor plate than we already do? Probably to make the cars even. I do get your tongue in cheek statement though :beer:

What are going to be the excuses this year since the new E92? has MORE horsepower than the Mustang and the Porsche now gets the 3.8L? Oh wait, now they will just vilify the Camaro's and 2010 Mustang instead:bored:

Again this is not an attack at you directly, just replying to what you've written. It's good to know you follow the series, maybe someday you can make it to one of the races and say hi:beer:

 

[91svtbird]

That's all and well. I didn't mean a direct attack towards you. I was just giving another opinion from someone who actually competes in the series to counter the Porsche/BMW claims that you posted.

Even if YOU know they AREN'T Motons I thought it would be useful information to let everyone know exactly what the ARE. BTW even thought it is not the Continental Tire Sports Car Challenge we are still required to run the Koni shocks for at least this year again.

Not all the E46's just the Turner cars;-) Kind of funny when they have cars that are unbelievably faster than the other BMWs. And even more funny when they can pull on the "high horsepower Mustang" around the banking at Daytona and Homestead. They were also running 2 seconds a lap faster at Watkins Glen also until it rained then we were faster, you know they say that rain is a horsepower equalizier right?;-) And then Grand Am just says it because the almighty Bill Auberlin is driving And no they didn't need to be strung out in order to keep up with us. They did it for an ADVANTAGE in a series that is really close to spec racing with different cars. How is it fair that we have to run a sealed ECU and engine while the Porsches and BMWs can pull theirs apart and play with them? Also if we make SO much more power why do we not have to run a smaller restrictor plate than we already do? Probably to make the cars even. I do get your tongue in cheek statement though :beer:

What are going to be the excuses this year since the new E92? has MORE horsepower than the Mustang and the Porsche now gets the 3.8L? Oh wait, now they will just vilify the Camaro's and 2010 Mustang instead:bored:

Again this is not an attack at you directly, just replying to what you've written. It's good to know you follow the series, maybe someday you can make it to one of the races and say hi:beer:

Interesting info on the Grand Am series (sort of what TransAm used to be). Only wish I could see these televised live like NASCAR is. I plan to be at LimeRock Memorial day weekend though. Which team are you with, I'll look you up?

I would love to see the Mustang eventually get an integrated IRS, not just for the track but for street use too. I hate going over those bridge expansion joints and some of the rough uneven bumpy roads here in the NY -New England area.

 

[chuckstang]

Last time I checked, both the challenger and camaro use an IRS and both do not handle nearly as well as the GT500

So how is it fact that an IRS is better for handling than SRA (solid rear axle)?

 

[BlackBolt9]

Interesting info on the Grand Am series (sort of what TransAm used to be). Only wish I could see these televised live like NASCAR is. I plan to be at LimeRock Memorial day weekend though. Which team are you with, I'll look you up?

I work for Rehagen Racing. Daytona race is in a couple weeks and will be on Speed Channel the week after. It looks like all but one of our races will be televised this year, just not a live feed and they are working on trying to get that one televised as well. I try to keep a thread on the series up to date in the Open Track forum if you want to keep up with it. There is also another guy on the boards that works for JBS (another Mustang team) that posts in there as well. I'd be more than happy to show you the cars at Lime Rock, just stop on by and ask for Tom.

Last time I checked, both the challenger and camaro use an IRS and both do not handle nearly as well as the GT500

So how is it fact that an IRS is better for handling than SRA (solid rear axle)?

A PROPERLY DESIGNED IRS is marginally better than a PROPERLY DESIGNED solid axle. For the most part, neither has an advantage on a smooth flat surface since suspension movement is minimal. Hence the reason the Mustang does well on a race track against cars with IRS. Ever notice how the way to fix a poorly design IRS is to run really stiff springs??? It's to limit travel and basically get rid of the problems associated with it.

 

[91svtbird]

I work for Rehagen Racing. Daytona race is in a couple weeks and will be on Speed Channel the week after. It looks like all but one of our races will be televised this year, just not a live feed and they are working on trying to get that one televised as well. I try to keep a thread on the series up to date in the Open Track forum if you want to keep up with it. There is also another guy on the boards that works for JBS (another Mustang team) that posts in there as well. I'd be more than happy to show you the cars at Lime Rock, just stop on by and ask for Tom.
.

Thanks for the info Tom I will be sure to look you up, look forward to meeting you there.


George...

 

[ac427cobra]

Last time I checked, both the challenger and camaro use an IRS and both do not handle nearly as well as the GT500

So how is it fact that an IRS is better for handling than SRA (solid rear axle)?

The Challenger and Camaro don't handle as well because they are heavier! :idea:

Thanks for the info Tom I will be sure to look you up, look forward to meeting you there.


George...

George just look for the guy with no hair! ;-)

 

[BlackBolt9]

Thanks for the info Tom I will be sure to look you up, look forward to meeting you there.

George...

Sounds good, look forward to meeting you George!:beer:

George just look for the guy with no hair! ;-)

Hey now! I have hair for the time being, it's too cold out for no insulation :lol:

 

[jes_csx]

I just remembered something. A few years back (when the hertz was announced) there were 2 Hertz cars at Shelby in Vegas that were "supercharged , 6spd and IRS". We thought they were test mules, but it turned out they were built for Hertz execs. In retrospect it seems likely it was the GT500 drivetrain and IRS that didnt make it.