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Here is the first tech question from Nathan regarding the differences on the Kenny's SN95 IRS track cars and the S197 Kenny Brown track cars:

I was just wondering about a few more details on your CSR/OT Cobra packages.

• Are these modified IRS equipped 99-04 platforms superior in handling to the modified live axle 05+ S197 cars?
• I would like my car to be a good all around performance car. I will open track and road course, but I will also swap wheels and tires and head to the drag strip occasionally.
• Where will package prices start and what are some popular option prices?
• What are the turn around times?
• Is your setup too aggressively tuned toward open-track racing for the car to perform well in the quarter mile as well?

 

Thank you for your time,

Nathan

First, regarding the content details -- the IRS CSR-OT (Club Sport Racer-Open Track) can be found at http://www.kennybrown.com/motorsports_csrot - and for a live-axle comparison, my new S-197 CSR-GT/4 (Club Sport Racer GT-4), http://www.kennybrown.com/2009-mustangs/class-2.

As far as handling, I have driven both the IRS and live-axle and they both handle exceptionally well on track. The only real difference is in how they drive, that is, the "line" you take around the track. The strength of a live-axle Mustang is its bite off the turns and straightaway speed. So you want to shorten the corners and lengthen the straights, especially if your engine has a lot of torque. That is easily achieved by using what's called the "late apex" technique -- late braking, diving past the traditional apex, rotating the car and accelerating hard off the corner. My live-axle AGS GT-4 package (Advanced Geometry Suspension) is designed and engineered around leveraging and maximizing the strengths of the live-axle Mustang.

A Cobra with my AGS-IRS (Advanced Geometry Suspension) drives differently. The independent rear affords better compliance on rough surfaces and good mid-corner speed so the late apex technique is not necessary. In fact, it is often counter productive. The only limiting factor of the IRS is the amount of "anti-squat" that can be safely built into an IRS. Anti-squat references the "side-view" geometry forces which is basically the amount of bite (or anti-squat) that the rear axle generates; live-axles (by virtue of their design) can have more anti-squat built in than the IRS.

Which actually answers another one of your questions: If you are going to do both open track and drag strip, the live axle S-197 would probably be the better choice as IRS cars don't make particularly good drag cars. But then again, which IRS Cobra you choose makes a difference as well. For my money the '99-'01 naturally aspirated Cobra with my CSR-OT package makes an awesome track day car. Light, nimble, quick and easy to drive plus with the upgraded IRS does kind of OK at the strip. After all, Kirmie (my green ‘01 IRS Kenny Brown Mustang) was a naturally aspirated Cobra CSR-OT with a little massaging to the 4.6 4-V and if you talk with anyone who was at a track event where I was driving Kirmie, they'll tell you it was pretty much unmatchable.

The '03-'04 supercharged Cobras make big power but the trade-off is a bunch of front end weight, something a Mustang doesn't need for track driving, that negatively impacts balance, braking and turning. The other issue is heat, or more specifically heat soak from the supercharger. The more you drive the more heat the supercharger makes and the harder it is to get rid of. If it weren't for the IRS the '03-'04 Cobras would be potent drag cars which is probably why some "strip-lovers" have converted their '03-'04 Cobras to live-axle.

As far as my packages being "too aggressively tuned for the track to be a good quarter miler" - The same principles and geometry that generates "grip", i.e. getting off the corner at the track, - generates "bite" at the strip. In the end - traction is traction whether at the strip or track. I also should point out that that being an aggressive track car doesn't automatically mean a lousy street car. That's a myth perpetrated by those that don't know how to make a car handle without using stupidly high spring and/or shock rates. The Kenny Brown IRS CSR-OT and the Kenny Brown CST-GT/4 are both track day cars that you can take to the street. In fact we have both a softer and a firmer spring packages for both the IRS CSR-OT and CSR-GT/4 so tuning the chassis specifically for your needs is not a problem.

Regarding costs and build time, that's pretty open. At this stage each car I build is a one-of-one for an individual client specific to his needs and budget. Packages can start as low as 12K and go upwards from there depending on individual needs, the base package, options and budget. Build time can run anywhere from a couple of weeks to several months or more, again depending on the individual package content and delivery of components from suppliers.

Popular options pretty much vary from client to client but ultimately revolve around your specific needs and wants. You can check out the base packages and some options at the above listed addresses.

Which ever path you choose, e-mail us at info@kennybrown.com when you are ready to start and she can set up an appointment for us to plan your project.

Kenny