Built SRA or Upgrade IRS

[Quasar Z]

For a guy with both road racing and drag racing experience who trailers his cars “to” and “fro” you don’t strike me as a very technical detail guy. Road racers tend to be a very suspension savvy and have no problem sharing that knowledge and you are telling a guy to replace his IRS with a live axle :dw: Not only that but your drag racing a wet noodle convertible.

What’s wrong with this picture?

Reading comprehension is what is wrong with this picture! Where did I say that I trailer my cars? Where did I tell the OP to replace his IRS with a SRA? You must be reading a different thread, as I mentioned that I brought a couple of Corvette's home on a flatbed (different then a trailer - broke the rearend at the drag strip) and I would encourage you to read my posts in this thread more thoroughly as I never recommended for him to go to a SRA, I just shared my experience and actually pointed him in the direction of the FTBR website. Talk about not being a "technical detail" guy.

Also, when have I drag raced my convertible? It has never been to the track and probably never will be...it is a cruiser that my children enjoy. I have a fast car for the drag strip:coolman:

 

[ac427cobra]

Ok, you got me. I am ignorant about these cars and their storied history of being road race champions:rollseyes I did read "Iron Fist Lead Foot" and will tell you that there are not a whole bunch of successful Terminators out on the road course circuit or autocross track by experience, not speculation. As an owner of an '03 Cobra, I think it is a great car for what it is. It is not even in the same league as the Corvette's that I have owned and raced.

Bringing up the 300 or so 2000 Cobra R's produced as well as Maximum Motorsports? Is MM currently campaigning an '03-04 Cobra, or better yet do you think a good portion of their business comes from these cars? Your two examples are not very good as they represent an extremely small percentage of the Mustangs that are raced. The bottom line is that a heavy, iron-blocked and supercharged car is not the greatest road racer. Will people road race them? Absolutely! Does that mean they are the best car (or even Mustang) for that purpose? Apparently you think so but again, I will respectfully disagree without insinuating that you are ignorant:beer:

Maximum Motorsports did a lot of development on the IRS. Here is a document their test driver reported on the changes to the IRS with their bushing kit:



IRS Questions: Answered by MM test driver Dave Royce.

MM test driver Dave Royce answered these questions after he won the first American Iron event we entered after swapping an IRS into the MM race car.

Dave’s answers may be quoted, or just use them for background information when talking to customers.


Compare driving the car with the IRS to driving it with the Solid Axle with Torque-Arm & Panhard Bar (SATAPB).

1. Were there any differences during corner entry between the SATAPB and the IRS?
A - Corner entry is changed in a way I didn't expect. Like the SATAPB, the car has great initial turn-in. However, once the car is set, it seems more stable from turn-in to mid-corner or Apex. This allowed for harder corner entry and earlier throttle application.

2. How does the IRS compare to the SATAPB during mid-turn, steady-state cornering: In long, sweeping turns? In shorter, tighter turns?
A - Mid corner with the SATAPB is good, but the IRS feels very stable and ultimately allows the driver to use either the throttle, brake or steering wheel to make micro corrections to maintain perfect balance. Long, high-speed turns are always a challenge in a Mustang, and the entry and exit play a huge role in how well the middle of the turn works. However, sticking to the question - Mid-turn is quite good. With the SATAPB, I would have to wait just a little through the middle, and then use the incredible launching capability of the Torque Arm to get great straight-away speed. With the IRS, I was able to apply the throttle just after turn-in and maintain some throttle application throughout the middle of the corner. Specifically speaking about the Talladega/Riverside corner, in the counter-clockwise direction, I could come off Magic Mountain with full throttle, make the right hand turn, stay drivers right, and maintain at least a quarter throttle at turn in. After turn-in, I could start to slowly roll into full throttle all the way to the braking zone for the Bus-Stop turn.

3. At corner exit when can you put the power down? What are the differences between the IRS and the SATAPB?
A - Corner exit changed the most. The SATAPB required a relatively straight car attitude to apply all the power, or risk a sloppy, slower exit. The IRS, with increased mid corner grip, allowed for earlier as well as a consistent throttle application (always desirable). Some corners I would be applying throttle just after turn-in.

4. Compare the two suspension types in transitions- especially quick right-left-right changes such as S-curves or slaloms.
A - The key to a great handling chassis is how it transitions, or handles the weight transfer. The SATAPB would transition well, much better then the OE Mustang suspension, but would have understeer and then oversteer - not much transition between the two, requiring at times, requiring the "Good Driver Award" to keep it out of the dirt. The IRS maintained composure throughout the S's. I was able to run full throttle through the S's, and would often touch the curbs without having to apply corrective inputs.

5. Was there any wheel hop during the standing start?
A - The launch was probably the most surprising to me. I have done zero launches with the IRS, so I was ready for one of two things; either a mild to severe wheel hop, or a hazing of the tires. I was sure it wouldn't just free-spin, as it had decent grip out of the low speed corners, so I put that possibility out of my mind. With this mind-set, I readied the car to launch at about 2500RPM, while rolling on the throttle and letting the clutch out in a rapid, controlled release. Much to my surprise, the car hooked up with absolutely no wheel hop. I believe the tires were hazing, or slightly spinning, but I was able to keep rolling on the throttle until it was time to pull second gear, and so on.

6. Compare the SATAPB and the IRS in how the car reacts to hitting berms, and other variations in the track surface, such as large bumps or dips.
A - I touched on this a couple of questions ago. When hitting "berms" the SATAPB, or more specifically straight axle, as I don't think the TAPB is a major contributor to this change, would usually set the back of the car over or upset the balance to the point where the driver would have to induce correction, obviously slowing the car. The IRS does what you would expect. It leaves the outside tire with full contact, while the inside tire rides over the berm. This was very noticeable in high speed corners where there is a small steep berm that usually must be avoided. I was able to allow the inside rear tire to be on the berms, and not have to lift off the throttle. This provided that extra few inches sometimes needed to keep from sliding off the track at corner exit, as well. On some berms the rear felt a lot like the front, almost a non-issue.

7. Which would you rather drive, a Mustang with IRS, or a Mustang with a solid axle and a torque-arm?
A - IRS, hands down!

8. How was the braking with the IRS, compared to the SATAPB? Was there any rear brake hop?
A - Braking was a little better. The biggest advantage was the ability to do more trail-braking, deeper into the corner No detectable wheel hop under braking was experienced.

9. What were the worst features of the car with the IRS? With the SATAPB?
A - IRS, not enough horsepower. Too much body roll.
A - SATAPB, not enough horsepower. Seemingly difficult to tune in consistent and predictable corner grip. You can tune it for better entrance, better mid-corner, and decent exit grip, but getting all three seems to be a challenge.

10. What were the best features of the car with the IRS? With the SATAPB?
A – IRS, Terrific transition and mid corner grip. Able to roll onto the throttle earlier. The ability to negotiate berms and curbing without upsetting the car.
A – SATAPB, Great acceleration, no wheel hop, substantial improvement over the OE 4-Link.

11. People often complain about wheel hop during acceleration with IRS cars. Was this a problem you saw with the MM race car?
A – With the setup from MM I completely forget that IRS has a wheel-hop issue. In fact I can say there is no longer a need to associate wheel-hop with IRS, at least with the set-up I drove from MM.

12. You have driven the MM race car with both our complete solid axle torque arm system, and our complete IRS system. What would you say to people that are considering either switching to the IRS or to a solid axle, in cars that came with the opposite rear suspension? Assume they were looking at it from a performance standpoint, were technically able to do the work or have it done, and wanted to make their car handle the best they could? Is there a clear winner between the two?
A – The SATAPB is a lot better the OE, but requires the driver to mechanically balance the car during corner exits. The IRS has a more natural balance tendency, and therefore is easier to keep balanced on the edge with the throttle and brake. So the clear winner is the IRS.

13. How would you compare the modified IRS in the MM race car to other IRS-equipped cars you have driven on the track?
A – I would say it’s comparable to any IRS car I’ve driven. It’s better than most stock IRS, including the Cobra.

14. How did the entire MM road race car, in its current IRS form, compare to other road race cars you have driven?
A – The MM road race Mustang was comparable to the GT3 Porsche in a lot of ways. This may be due to the fact that I set cars up similar for my driving style, but it usually is the fast way around the track. The high-speed stability is good, trail braking is much improved, and steering response at turn-in is great.

15. Did the MM products on our IRS cure any issues or complaints you observed when testing any other IRS-equipped cars?
A – Some IRS cars do not allow for enough camber adjustment, and have undesirable bump-steer.

Did the MM products on our IRS cure any issues or complaints you observed when testing any other IRS-equipped Mustangs? (i.e.: Did you notice any benefits from the MM IRS products we added to the OEM Ford IRS?)
A - As compared to the stock Cobra – street set up – it’s night and day. The OEM car seemed to float around in the middle of the corner, and exhibited unpredictable traction or wheel spin. The MM race car, even with “R” compound tires, felt positive in most driving situations. Mid-corner predictability seemed vastly improved.


16. How is the overall balance of the car with the IRS, compared to the SATAPB?
A – The SATAPB had good balance as compared to OE 4-link and the OE Cobra. After two days of testing the IRS with MM upgrades, I think there is no going back. The balance is what one would expect from a well-sorted performance car.

17. Are there any differences in the tune-ability of the two systems?
A – The ability to tune the rear alignment and static camber is substantially beneficial. If we can get the car to launch off the corner as good as the SATAPB does, you definitely have a better package. However, if I was drag racing, I think I might stay with the SATAPB.

I just don't completely agree with their approach to the fix. That is why I developed my own kit without ever seeing their kit because they didn't even have a kit when I developed mine. ;-)

If you're road racing a vert, you clearly chose the wrong vehicle. In the FAQ located on our site:

FTBR Frequently Asked Questions

I state that a good FLSFC is absolutely necessary with a vert.

Spanking Z06's with a Mustang is my absolute favorite past time! :dancenana: There are some Z06 spanking vids in the FAQ if you're interested.



:thumbsup::coolman::beer:

 

[Powershift03]

There are some Z06 spanking vids in the FAQ if you're interested.

Yep! And they are rated R!

:lol1:


:rockon:

 

[Quasar Z]

Just out of curiosity, did you attempt to cure the wheel hop issue? Or, did you decided to swap out to an SRA instead?

Here is a quote of a simple explanation of wheel hop right off the MM web site, and it doesn't matter coupe or convertible....


A major complaint of IRS owners is wheel hop. The undamped compression of the rubber bushings in the rear suspension is the primary cause of wheel hop. That undamped movement is amplified by repeated loss of traction. Wheel hop occurs because the rear tires continually oscillate between losing and then regaining traction. The extremely soft stock bushings contribute greatly to this oscillation because the rubber compresses easily and then springs back, over and over again. To reduce wheel hop the stock rubber bushings must be eliminated.

I actually did. If you read my first post in this thread, I mentioned that I had MM bushings, BF brace, H&R Sport springs and MM FLSFC. The wheel hop was not bad before the addition of the KB but was horrible after. I was going to try the FTBR kit but did not want to go through all of the work just to reduce the hop, I wanted it eliminated. There are several convertibles that still exhibit wheel hop after all of the rear suspension mods...they are just not rigid enough.

I just cannot understand why people get so defensive in the IRS vs SRA argument...it's almost like people take it personally! Kind of like the KB vs Whipple subject. I just enjoy my car and modify it in ways that makes me happy.

 

[Quasar Z]

If you're road racing a vert, you clearly chose the wrong vehicle. In the FAQ located on our site:

FTBR Frequently Asked Questions

I state that a good FLSFC is absolutely necessary with a vert.

Again, I never stated that I road race (or drag race) my car and I also stated that I do have FLSFC's. I did also refer the OP to your site Bruce. If I had a coupe, I would have had your kit on my car.

 

[ac427cobra]

I actually did. If you read my first post in this thread, I mentioned that I had MM bushings, BF brace, H&R Sport springs and MM FLSFC. The wheel hop was not bad before the addition of the KB but was horrible after. I was going to try the FTBR kit but did not want to go through all of the work just to reduce the hop, I wanted it eliminated. There are several convertibles that still exhibit wheel hop after all of the rear suspension mods...they are just not rigid enough.

I just cannot understand why people get so defensive in the IRS vs SRA argument...it's almost like people take it personally! Kind of like the KB vs Whipple subject. I just enjoy my car and modify it in ways that makes me happy.

The reason we get so defensive is because we simply can't understand why anyone would want to put something as archaic as a stick axle in a car that the SVT engineers wanted an IRS. :shrug:

The SRA was developed way back when the Century count was still in negative numbers. :dw: Roman chariots had an SRA in them!

This is the 21st Century. The IRS is so technologically advanced with improved handling and ride comfort they are putting them in almost EVERYTHING that comes from the factory!

Drag racers can certainly benefit from an SRA. But most people drive their cars 99% of the time on the street, not the drag strip.! :idea:

FWIW

:thumbsup::coolman::beer:

 

[Quasar Z]

That's the good thing about this car Bruce...it is mine and I can modify it in any way that I see fit. I am not the first person, nor the last, to put a SRA in a '03-04 Cobra. You would think that people could agree to disagree and move on instead of fighting 'till the death on this subject every time it comes up. I love the SRA in my car...it suits my needs. Why does that offend other people when most of them will never know its there or have to drive it? Plus, it makes all of the IRS cars that much more valuable:-D

 

[ac427cobra]

That's the good thing about this car Bruce...it is mine and I can modify it in any way that I see fit. I am not the first person, nor the last, to put a SRA in a '03-04 Cobra. You would think that people could agree to disagree and move on instead of fighting 'till the death on this subject every time it comes up. I love the SRA in my car...it suits my needs. Why does that offend other people when most of them will never know its there or have to drive it? Plus, it makes all of the IRS cars that much more valuable:-D

Guys that drag race could care less. They want to go fast in a straight line and I say if that yanks your crank, go for it. I used to drag race myself. Then I figured out a 12 second rush was not nearly as much fun as a 20, 30 or 45 minute rush. :-D Not to mention every car magazine said a Z06 was the ultimate track car. I took that as a challenge! :dancenana:

But I'm of the opinion that a VAST majority of the people that are converting to an SRA #1 don't fully understand the IRS. They think it's too complicated to understand. #2, think an SRA is the answer to their problems and #3, don't know the difference between a car that rides and handles good to a car that doesn't. Many people that own Mustang GT's (along with SRA converted Cobras) think their cars ride perfectly fine. And for a stick axle, they really don't ride all that bad. Stick axles now are not like they were back in the 50's or 60's. But it's still a STICK axle! :read: You have no camber or toe adjustment on an SRA. You got what you got and that's it!

If you want a car that rides good on the crappy roads we have to drive on these days, I'll take an IRS. If I'm turning the steering wheel, I'm going to want an IRS following my front tires.

People with SRA's are very passionate about their choice and so are the IRS people. I don't pretend to be smarter than a team of SVT engineers. I've met many of them and I'm personal friends with some of them as well. These guys forgot more about vehicle dynamics than most of us will ever know!

:thumbsup::coolman::beer:

 

[Powershift03]

I don't think anyone here is offended. Rather, Bruce and I are just trying to dispel the rumor that IRS has flaws which can't be cured. We are as impressed with what the IRS can be.. as much as you are happy with your SRA.

:rolling:

 

[Quasar Z]

Then let's agree to disagree on a few small points and all enjoy our Cobra's and the modifications that we feel make them better for each of us individually. Between the scream of the KB, the headers, no cats and the wind when the top is down, the minimal amount of ride deterioration with the SRA is not a factor to me. When I am in the mood for a nice supple ride I drive my Lexus:-D

 

[ac427cobra]

Then let's agree to disagree on a few small points and all enjoy our Cobra's and the modifications that we feel make them better for each of us individually. Between the scream of the KB, the headers, no cats and the wind when the top is down, the minimal amount of ride deterioration with the SRA is not a factor to me. When I am in the mood for a nice supple ride I drive my Lexus:-D

Lemme guess, that Lexus has an IRS!!! ;-)oke:

 

[Quasar Z]

Yes sir, IRS is the only way to go for total comfort:beer: The Cobra is for when I want obnoxious sound and power...my kids really like it. I am more of a Corvette guy but with three boys I needed a back seat and they wanted a convertible. The Cobra has been a lot of fun so farepper:

 

[03Snake04]

Bruce, do you have ANY clunking noises when driving? in 4th gear at 40-50 mph do you tap the gas hard and hear this clunk in the rear or has your mods you advertise fix this? .. i will not be happy if i read more into understanding and building the IRS up and hear this crap still ... the last thing i want to hear again is a buddy riding shotgun ask me "whats that noise? is your exhaust dragging?"

i have yet to read your link, but i will before i do any deciding and jump the gun, i want this sound gone! simply put... it is loud and i feel like the thing is going to fall apart and that just drives me crazy

i was told by the previous owner that the irs has a delrin bushing kit installed? i dont know exactly what that pertains to but thats all i know of, also i do believe from reading his posts by searching his username that he did replace the bolts with 14mm ones .. but i could check if i knew what bolts to look for:shrug:

 

[MAD SVT]

Poly bushings, MM FLSFC's, Steeda brace and bracket..... NO HOP @ 580 rwhp

oh ya... in a Vert with an IRS :coolman:

 

[Quasar Z]

You forgot to mention the roll bar (looks like at least a 6 pt) that you have. I don't want to go that far, plus add drag wheels and tires, to a car that I use for a cruiser. Congrats on having no hop:thumbsup:

 

[03mgtermi]

Dude, just go with the SRA swap. When you are done give me a shout. (I see you live in Texas). I am always looking for some new ass to kick on the track (the kind with twisties) :burnout:



On a serious note.....Bruce's kit gets rid of that slop we all hate so much.

 

[Epikmach]

Sorry for thread jacking, but I have a few questions as well.

I have an 03 Mach 1 that I am considering an IRS swap on as well. The car see's 95% street duty (5% strip duty), which is why I like the IRS for the ride comfort. I currently have MM XD LCA's, PHB, & coil overs installed, & if you want to hear clunking & clanking, ride in my car LOL. I am also very close to installing the MM Tq arm setup that I have sitting in my garage, but I am unsure if this is the route I still want to go? The thing that I love about my current SRA setup is, I can dump the clutch from 5,500 & launch the car hard on slicks with no hop. Could this still be achieved with an IRS, & what are the best 60 ft's people are seeing with a FTBR IRS setup?

 

[SlowSVT]

Reading comprehension is what is wrong with this picture! Where did I say that I trailer my cars? Where did I tell the OP to replace his IRS with a SRA? You must be reading a different thread, as I mentioned that I brought a couple of Corvette's home on a flatbed (different then a trailer - broke the rearend at the drag strip) and I would encourage you to read my posts in this thread more thoroughly as I never recommended for him to go to a SRA, I just shared my experience and actually pointed him in the direction of the FTBR website. Talk about not being a "technical detail" guy.

Also, when have I drag raced my convertible? It has never been to the track and probably never will be...it is a cruiser that my children enjoy. I have a fast car for the drag strip:coolman:

You made quite a few generalized statements with a few that are either somewhat misleading or flat out wrong. This statement below is what prompted me to respond.

As far as these cars being designed to handle curves, I would respectfully disagree. With an iron block, Eaton blower and substantial weight these cars are not really suited to handling. The IRS is very neat and exclusive to the Cobra so I would have kept it if it didn't hop - some people are fortunate and don't have hop, especially with the coupe's.

Do what you want with your car. Ride quality is not impacted much and if you like taking off ramps fast you can still do that. If you are a serious road racer or autocrosser, you probably have the wrong car to begin with in my opinion..

There are so many holes in this statement I could drive a truck thru it! The message you were conveying was you solved your wheel hop problem with an SRA and now life is good. The truth is solid axles can hop just as bad as an IRS and there are scores of IRS equipped Cobra that can solidly plant the rear wheels.

You are certainly entitled to express your opinion and you do make a few valid points. But for some Cobra noob who is not mechanically inclined or not familiar with this car may buy into your story and do something in an attempt to solve one problem while creating a host of others. My remarks were actually directed at those people to jolt their thinking and not do something rash.

This topic will always be the subject of debate as long people skew the facts or post misconception on the merits of this swap without presenting a balanced perspective. In a Cobra there are very few instances that actually justify ditching the IRS for an SRA. Ford did not go thru all that expense and logistic of equipping the car with one for no reason.

Good debate for the up and coming Cobra modder none the less. Hopefully there is one less street driven SRA Cobra in this world as a result.

Russ

 

[MAD SVT]

You forgot to mention the roll bar (looks like at least a 6 pt) that you have. I don't want to go that far, plus add drag wheels and tires, to a car that I use for a cruiser. Congrats on having no hop:thumbsup:

do it... never look back, it added incredible rigidity to the chassis.... i can jack up the whole rear of the car with the jack on only 1 side, and still open and close the car doors.. thats amazing.
I also have a Kenny Brown matrix brace sitting in my garage waiting for install, i plan on welding it to the SFC's, and 4 pts of the cage.

I like my polished exhuast too much to go SRA

 

[03Snake04]

is there a way to get under the car and look at each bushing and be able to tell if it is an upgraded bushing or not, color/softness/shape? i am under the impression the previous owner did install a bushing upgrade, but who knows which ones? is there an easy way of telling? i will put the car on stands and take a look before ripping it out with frustration of the irs

but as i sit right now i am under the impression this car does have some "delrin bushing kit" which i was told it had and still the car clunks bad... something up for sure!

however on a side note i do not have hopping issues... im wondering if my differential bushing are factory still and not the aluminum ones..