Rick Titus
November 24, 2015
Photos By: Rob Kinnan, Randy Richardson

For Mustang fans this question is often asked, but never answered—until now. Be warned, this story does not have a happy ending.

Little known fact: While the first-generation Mustang was being transformed from a Falcon to the best-selling new car ever introduced (a record that still stands) a small group of chassis development engineers at Ford were working on an independent rear suspension (IRS) that would bolt right into the new platform. Two of the setups were known to have been built, and the testing was very much in progress. Shelby American crews tested the system in a race-prepped SCCA A/Sedan 1964 Falcon. At the same time, the same group of highly talented Shelby employees were developing the all-new Shelby G.T. 350 Mustang and its racing sibling the G.T. 350R. Long story short, early test reports, though encouraging, concluded it would require more development to work well in the G.T. 350s and Ford management wisely decided that it would adversely impact the introduction price of the Mustang. Remember, Mustang not only sold well on its looks but on its value as well, so in hindsight it was a smart move not adding IRS to the cost of a car that, at the time, had no real competitors.

Fast-forward 50 years to the introduction of the 2015 Mustang, the first Mustang to come with IRS as standard across all model/trim lines, and by far the best generation of Mustang ever built, and now a world class performance sports car. The automotive market and the performance deltas have moved a great deal in 50 years and Ford management, or more accurately the enthusiast group of engineers assigned to the next generation Mustang, felt that in order for Mustang to compete in international markets it was time for an IRS system. In our view, they’re right, and what an amazing car the new Mustang is. But that just stirred the original question even harder; would the first generation Mustang have been a better car with IRS from the beginning?

This is the independent rear suspension built to the original blueprints and installed in Jim Mariotta’s G.T. 350R clone.

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The two cars tested were built identically as G.T. 350R clones from all new parts, with the only difference being the rear axle setup. Both are numbered 98, but the IRS car has a letter “i” added to the number. Jim Marietta owns the IRS car, while William Deary of Jackson, MI owns the live axle version.

That question has burned into the souls of the original team of Shelby G.T. 350 R-model builders who tested the system back in 1964/1965—they refer to themselves as “The Original Venice Crew,” OVC for short. They are the small army of super-talent that built the very first Shelby Mustangs, and were the team and crew on the very first Team Shelby racecars. A team that won the SCCA National Championship on their very first try! A team, I should add, that included this author’s father as its driver—Jerry Titus. Many will remember that the first Shelby American enterprise, once Carroll moved out of Dean Moon’s shops, was the Venice building in Southern California. The original team assigned to the G.T. 350 was made up of an amazing group of people. From lead engineer Chuck Cantwell to lead fabricator Jerry Swartz, and the team had everything from a teenage rookie to a highly experienced racing wrench in the form of Ted Sutton—hard workers each and filled with pride and determination to win. Apparently that question burned brightest in the soul of the aforementioned teenage rookie, Jim Marietta, who went back to school and became a very successful businessman. He’s also the man who brought The Original Venice Crew back together.

Late October of 2014, I receive a phone from long-time friend Randy Richardson of the Los Angeles Shelby American Automotive Club (LASAAC). He tells me that the original Shelby crew are building two 1965 G.T. 350R replicas and they plan to install one of the original Ford Development IRS units in one and track test it against the solid axle car. How cool is that? Talk about a group of folks who have a need to know the final answer. It turns out that teenager, 50 years later, funds the building of the IRS car and pays to bring the old crew back together. Seems Mr. Marietta is a man with a large heart and loyal memory, and if that wasn’t enough, world famous Daytona Cobra Coupe designer Peter Brock, in whose shop the cars were being built, joined the effort to refine his clever R-model rear window and front valance designs. That, folks, is what you call a Super Team.

The team decides it wants the two cars, both K-code models bought off of eBay, finished and running by Valentine’s Day 2015, because that’s the day Shelby factory driver, the late Ken Miles, recorded the G.T.350R’s first race victory at a little race track by the name of Green Valley in Texas 50 years ago. So the hard work begins and the OVC and LASAAC members put in the hundreds of hours it takes to transform streetcars into track ready race cars in just five months. But before one car turns a wheel in anger, Shelby Race Engines has to build and deliver two 450hp 331ci race engines, the project’s lead engineer Duane Carling leads the IRS install, and the rest of the team has a busload of work to do. As the cars near completion the team takes them to MAECO Motorsports, owned and operated by good friend Michael Eisenberg, for final finish and tweaking before heading to Willow Springs for the big reveal. And big it was, as most of the LASAAC turned out for what was a truly a historic day.

The track testing that day was held to mostly light laps for break-in. Former Shelby American Cobra team driver John Morton was on hand, as were Peter Brock and Eisenberg, all damn good drivers, and each did laps in both cars. Feedback was limited to the few easy laps and based on first impressions both cars went back to MAECO for some refinement and service. Then Jim Marietta called and said, “Rick, I’d really like to get you in these cars,” largely I suspect to honor my father. It was an offer I couldn’t refuse. Jim and I met and I learn he’s serious about sorting these cars out, and particularly the IRS car, which he owns. It’s then that I learn that The Original Venice Crew plans to build a limited number of these cars for sale. Turns out Marietta and Brock have visited a company that manufacturers very precise and complete replica 1965 Mustang bodies right in the Untied States. They’re serious and this takes everything to another level.

This vintage photo source by Jim Marietta shows the original IRS setup installed in the 1964 Falcon development car back in the day.
The IRS as installed in our test cars at Willow Springs. Notice the beefy steel bar that mounts the Jag/Dana 44 differential. The original IRS was designed around the then available Jaguar IRS setup and used its center section, but if/when the Shelby IRS clones are built, they will most likely use the much more common 9-inch center section.
It’s always a good day at the track when you get to hang out with, from left to right, Skeeter McKitterick, John Morton, Peter Brock, and Vince LaViolette.
Jim Marietta, owner of the IRS-equipped car, worked for Team Shelby when he was a high school kid. Here he shows one of the original uprights from the prototype IRS setup.
Marietta kept his first paystub from Shelby American, dated March 18, 1965.

So it’s not only about finding out which suspension system works best but it’s now about truly making these cars perform at “track car” deltas. The minute I learn that I’m coming in as a development driver I start making phone calls. First up, longtime friend, Rob Kinnan: “Hey Rob, want Mustang Monthly to beat every other car magazine in the world to an amazing story?” In less than a second Rob replies “We’re in, what do you need?”

My only request, besides insisting that Rob do a few laps in the cars, is that I want Randy Richardson for lead photographer on this one. I asked Jim Marietta if I could bring in a team of test drivers, guys I knew could dial these cars in, and he agreed. The first call is to John Morton, a legend for good reason; second call, Skeeter McKitterick, my racing mentor and one hell of a racecar sorter; Vince LaViolette, the current Shelby American development driver and prototype manger, a former racer and a guy who works with the 2015 Mustang IRS every day; Michael Eisenberg, who makes the older Mustang go faster than it was ever intended to go and knows how to drive them too; Greg Reynolds, current Shelby Mustang vintage racer, who has built one of best handling older Mustangs I’ve ever driven; Bruce Kawaguchi, another super-fast vintage Mustang racer; and finally, Dennis Ambayec, a very good driver that I currently vintage race against and had no prior Mustang seat-time (I wanted Dennis’ first impressions of the two set-ups). Last, but most certainly not least, I requested that Drivers Talk Radio Producer and my Co-Host, Jay Dalton be there to manage all the data recording. Jay and I have tested a huge list of products for FCC competitive claims certification for several major automotive companies. The tale of the tape would tell the story. If the IRS was going to be better we wanted to know in what corners and by how much. The data doesn’t lie.

The solid axle car was the quicker of the two, partially because of the toe-steer that was happening in the IRS setup.
Peter Brock’s original vented rear window design for the R-models looked like this; but when the part showed up at their first race, it had a slightly different shape, with a transitional edge that changed its angle where it went under the roof. The cars we tested used windows of his original design, to see if it was worth anything in regards to lap times. The results were inconclusive.

Marietta wanted the test to take place at one of the Shelby’s most often-used original test tracks, Willow Springs International Raceway in Rosamond, California. Adding to my list of gunfighters, Jim brought in Ted Sutton and Duane Carling. Video and photography staffs were on-hand to represent Drivers Talk Radio, Mustang Monthly, and The Original Venice Crew; so to say the least, record keeping was more than handled. MAECO Motorsports transported the two cars to the track and their crew off-loaded and prepped the cars for a full day’s workout. A brief meeting of the group was held to set goals and standards. Each driver would do six laps in both cars twice, their impressions gathered after each drive. At the completion of the second cycle of laps one driver, in this case John Morton, would do the instrumented testing for segment and lap time comparisons. The cars ran great and the plan was working perfectly up until John got in the first instrumented car and…rain! Not hard but enough to keep the track wet—at one point Morton went out to see how the track felt and returned after just one lap stating that of course the low-speed corners are pretty good but the 160-mph turn eight had puddles that he highly recommended we not try to drive through. Who could blame him: both cars were fitted with dry racing tires so the day was done.

Marietta reserved the track for 10 days later, as we poured over the driver impressions. With a group of this skill level the impressions didn’t vary much, though a couple seemed more encouraging than others, myself included. This was the first time these cars had been brought to the track with the intent of running at their limits and, to be fair, they still needed to be sorted. Ambayec was the first to point out a brake bias issue in the IRS, with too much braking to the rears. Since racing against Dennis I’ve been amazed at how deep the guy can drive a car into a corner before climbing all over the brakes. It wasn’t many more laps before the others agreed that there was too much rear brake in the IRS car. From a handling point-of-view, we all remained troubled at the lack of stability from the rear of the car.

On the other hand, the solid axle car suffered from a bit of understeer, easily tuned out with a little less front sway bar and more shock work. In short, the solid axle car was already very good. So the focus remained largely on the IRS car as all the drivers were going quickly in the solid axle car. Morton set fast time in the solid axle so we now had a delta, but the IRS car still needed work to truly answer the challenge. Typical of Skeeter and Vince, they wanted to return with various springs and shocks, and I even went out on a limb and suggested a 3/8-inch rear sway bar might be worth trying. Not something you’d normally bother with on a live axle set up but somehow I felt the IRS system might want it. Much to my surprise nobody hated the idea. So two wet racecars were put away and the long-standing IRS question would have to remain unanswered for 10 more days.

MAECO Motorsports was in Mexico supporting one their clients in Mexico’s biggest road race, so little suspension work was accomplished short of a rebound adjustment on the rear of IRS car and what was thought to be enough brake basis adjustment. Gray and threating skies greeted us again but this time no rain. Our group in total was a bit smaller. Marietta, Sutton, McKitterick, Morton, Kinnan, and myself, not to mention all the video and photo guys. Both cars were there again and all the drivers drove each just to warm up. Amongst the changes Peter Brock wanted to test was a full-width, under-body, front spoiler. Made of heavy rubber and hinged, he wanted to see if the cars would point into a corner better, reduce understeer and the effects, if any, on water/oil running temps. Skeeter tried both cars with and without the front spoiler and found that point in was about the same, they both picked up just a little understeer without the spoiler, and engine temps went up 10 degrees on both water and oil in both cars without the spoiler. Conclusion, the front spoiler works.

Though the adjustments to the IRS car had been small it was time for Jay Dalton to instrument the cars and collect some data. It was agreed that the shock changes had improved the IRS car but it still remained very twitchy and had not gone far enough. Oddly, the brake bias adjustments had no effect. More were tried and still no improvement. Turns out the car had a faulty bias valve. It was decided that both Morton and myself would set deltas in both cars, with six laps each in each car. Jay had “painted” the track with the GPS and broken the track into three segments.

The engines in both cars are 331-inchers from Shelby.
The interiors on both cars were Spartan to say the least. But hey, racecar! They each had a rollbar but not a full cage.


Segments

A: Included the entrance to turn 1 and the exit of turn 2.
Total distance: 3,481 feet

B: Included the entrance to turn 3, through turn 4 and all of turn 5.
Total distance: 3,281 feet

C: Included the entrance to turn 8 and through turn 9.
Total distance: 2,978 feet

Fastest overall lap time:
(Live Axle) 1.38.00
(IRS) 1.39.15

Fastest Average speed in Segment:
Live Axle IRS
A: 88.08 mph A: 85.24 mph
B: 67.48 mph B: 66.97 mph
C: 100.77 mph C: 97.85 mph

Highest Speed Reached at Entrance to Turn 8:
Live Axle: 165.23 mph
IRS: 163.56 mph

In-Corner Time Comparisons by Segment & Car (seconds):
Live Axle IRS
A: Live Axle 27.00 27.9
B: Live Axle 33.15 33.4
C: Live Axle 20.15 20.75

Weight:
Live Axle: 2,835 lbs
IRS: 2,805 lbs


Conclusion

The live axle car was faster in every segment, resulting in a quicker lap time by 1.15 seconds. Yet despite the segment and lap time differences, every driver agreed that with just a little more development the IRS could turn out to be the better track and racing car. The consensus was that once driven at the limit in racing mode, it would be the better car to pull off that racing line to make a pass. So at this stage of development, the live axle car is still the better of the two set-ups, but what we learned after the test not only encouraged us to believe the IRS car could wage a comeback but truly upset me at the same time. Turns out that the Ford prototype IRS has “passive toe steer” built into it. Reasonable thinking for a streetcar at very low speeds, but not for a racing car! A certain engineer heard the collective reaction to how twitchy the IRS car was and how it wouldn’t take a set, but he continued to think in only street car terms—disappointing to say the least. So the age-old question of IRS versus live axle in the first-gen Mustang remains, in part, unanswered. We agree with Ford’s decision not to put it in the first Mustangs, but for the racing side, we’re thinking otherwise.

Feeling very unsatisfied, the entire team, with Marietta’s support, agrees to continue to develop the IRS system. The first step is to remove the passive steer, and after that we’ll test some springs and shocks just to see how much quicker the IRS setup might go. Stay tuned.

On the second day at the track, the crew made some shock adjustments on both cars to dial them into race duty.
The legendary John Morton belting into the IRS car.
The (considerably slower than Morton) editor Kinnan got a few laps in the IRS car as well, but had to bring it in when the left front tire went down. Bummer, but we’ll get the cars back to the track soon, and he can burn the tires off like they’re meant to be.
Morton and LaViolette with their rides in “The Balcony” at Willow Springs Raceway.
Riverside, California. Using what was later to become Don Pike’s SCCA A/Sedan & Trans Am Ford Falcon as a “test mule” the Shelby American G.T. 350R team put a lot of hard miles on the prototype system.
Check out these cool photos of testing the IRS Falcon with other Team Shelby machines at Riverside in 1965.
Mounted under the Falcon’s rear, the IRS system, which was designed for streetcar use, was neither pretty nor light. Had it proven to be cost effective, you can bet the Shelby crew would have taken a lot of weight off and taken the passive toe steer out of it.