Thanks for checking out my videos!
I always try to provide balanced information, so please forgive the long reply. As an instructor, I’ve been able to ride in and drive many, many Mustangs. I’ve instructed several students with automatics. It is certainly possible to autocross an automatic, but there are a few things to consider…
Fox Body and SN95 Mustangs with OEM automatics have relatively soft shifts that will cost you time out on course. The automatics want to (and often need to) “kick down” into 1st gear when digging out of slow elements, whereas a manual can usually stay in 2nd gear. Every shift costs you time at an autocross, and soft (slow) shifts will cost you more time. A shift kit will help. I’d also recommend a transmission cooler. Check the SCCA Rules to see if those mods are allowed in the Category/Class you want to run in.
You will also have to “time the shift” when you autocross an older Mustang automatic. This isn’t necessarily a bad thing because it teaches you to be early on the throttle. Keep in mind, driving around the delay in the shift, holding the car in 2nd gear by keeping the rpms up in slow elements, or getting aggressive on the throttle early to time/force the downshift will take some getting used to. In some places out on course, an automatic just doesn’t feel as “present” as a manual.
It’s worth mentioning that the AOD my 1992 GT was born with only made it about 60k miles before it stopped shifting into overdrive (the car was modified but never raced) & my 2000 GT (born with an automatic) had shifting issues after 100k miles (I know the original owner, that car was never autocrossed). Most used 87-04 cars will probably have high mileage at this point, so they might have some expensive automatic transmission issues.
Based on my experience, an automatic Fox Body or SN95 Mustang wouldn’t be my first choice for an autocross car. The vast majority of your competitors will be driving manuals. But I never want to dissuade anyone from autocrossing their Mustang. The people I’ve instructed with automatic Fox Body and SN95 Mustangs have all enjoyed autocrossing their cars.
There are Mustang-specific salvage yards that sell manual transmission conversion kits for Fox Body and SN95 Mustangs. I got one from MPS Auto Salvage over 10 years ago, and I’ve been very pleased with the results.
Later s197 and s550 Mustangs have automatics that shift better (and some can be shifted from the steering wheel). I’ve been impressed by how well the s550 automatics shift. I don’t know how reliable they are over time. One of the fastest drivers I know runs a 3.7L s197 Mustang V6 automatic in CAM-C and he does very well at my local events.
The newer automatics will perform better than the older ones, but I still think most people would choose a manual for an autocross car.
I hope that helps.