More power on a 2013 V6 Mustang 3.7...

[Voltwings]

EDIT: His car is classed in DS per the 2019 SCCA Rulebook.

I think this would be the ticket to a fast DS(D-street) classed V6 Mustang:

Bilstein(keep the stock springs per the rules)
18x8" lightweight wheels
255/45R18 200tw tires
Snell SA2015 helmet
CG Lock(for the seatbelt to hold him in place)
Blue Painters Tape or a set of numbers/class letters from Trackdecals.com

Its usually $35-40 to do an autocross event. Sign him up for the local SCCA events and have fun. Once he gets the feel of the car, the power delivery and rotation he can start fine tuning with the adjustable Koni dampers along with maybe a larger front sway bar to get it to rotate more(rules allow 1 sway change in street classes).

Fixed. I'd also worry about a 255 on an 8" rim, maybe a 245 would fit better as far as sidewall stability is concerned?

 

[kevinatfms]

Fixed. I'd also worry about a 255 on an 8" rim, maybe a 245 would fit better as far as sidewall stability is concerned?

You can use Koni Sports in street class. Why would you suggest Bilsteins over an adjustable rebound shock? The monotube damper is an improvement but being able to adjust the damping would be my choice. Strano specifically picks the Yellows for 05+ Mustangs to get it to rotate although he does offer the Bilsteins too. Id call him for advice but both could be a great upgrade for a stock class car.

A 255 fit on my 17x8's on my 2005 before i moved up to 18x9.5's/275' combo. There was a little bulge with a 17" rim but not enough to cause a lack in steering feel versus the 235 section width tires that came stock. I think an 18" or 19"(the performance pack supposedly came with 19's?) with a 27" tall tire would cure most of that bulge that i had with the 17's and a 255 section width.

This is also a newer Mustang and as such a tire sized in 255 is much better sorted(27" tall versus 26" for pre 2005 cars) with aspect ratios than the 245's that came on pre-05 cars. I guess a 245 would work to improve the gearing a bit but id still want more width than a 245 with something that has 300ish hp. Worst case scenario would be to get the stickiest tire on the stock wheels(if they are the performance pack 19's) and see how it does.

 

[Voltwings]

You can use Koni Sports in street class. Why would you suggest Bilsteins over an adjustable rebound shock? The monotube damper is an improvement but being able to adjust the damping would be my choice. Strano specifically picks the Yellows for 05+ Mustangs to get it to rotate although he does offer the Bilsteins too. Id call him for advice but both could be a great upgrade for a stock class car.

A 255 fit on my 17x8's on my 2005 before i moved up to 18x9.5's/275' combo. There was a little bulge with a 17" rim but not enough to cause a lack in steering feel versus the 235 section width tires that came stock. I think an 18" or 19"(the performance pack supposedly came with 19's?) with a 27" tall tire would cure most of that bulge that i had with the 17's and a 255 section width.

This is also a newer Mustang and as such a tire sized in 255 is much better sorted(27" tall versus 26" for pre 2005 cars) with aspect ratios than the 245's that came on pre-05 cars. I guess a 245 would work to improve the gearing a bit but id still want more width than a 245 with something that has 300ish hp. Worst case scenario would be to get the stickiest tire on the stock wheels(if they are the performance pack 19's) and see how it does.

-Quality of a Bilstein shock / strut Vs Koni mostly, have seen lots of sub par Koni results and experiences.

-My comments on tire size had less to do with steering feel and more to do with sidewall stability, if your tire width exceeds your rim width, you basically don't have any preload on the sidewall and it's very easy to "roll the shoulder" in that case. Most 255s have a tread width closer to 9", if you put that on an 8" rim, not only are you not preloading the sidewall, you're paying for tread you can't even use. Granted, we do road racing, not autox, and I've heard the "just stuff as much tire on a rim as you can" thing more than once. Maybe that's just how autox works.

-I know he's probably width limited by class rules, but even a 255 is too small on these cars, we were racing my wife's 3.7 on 275s and it wasnt enough. However, if he is limited to an 8" rim, I (again, for sidewall reasons mentioned above) would probably like to see a 245 instead.

 

[kevinatfms]

-Quality of a Bilstein shock / strut Vs Koni mostly, have seen lots of sub par Koni results and experiences.

-My comments on tire size had less to do with steering feel and more to do with sidewall stability, if your tire width exceeds your rim width, you basically don't have any preload on the sidewall and it's very easy to "roll the shoulder" in that case. Most 255s have a tread width closer to 9", if you put that on an 8" rim, not only are you not preloading the sidewall, you're paying for tread you can't even use. Granted, we do road racing, not autox, and I've heard the "just stuff as much tire on a rim as you can" thing more than once. Maybe that's just how autox works.

-I know he's probably width limited by class rules, but even a 255 is too small on these cars, we were racing my wife's 3.7 on 275s and it wasnt enough. However, if he is limited to an 8" rim, I (again, for sidewall reasons mentioned above) would probably like to see a 245 instead.

Duly noted. Great observations for OP to give to his son. Hopefully he goes down this road instead of the "throw parts at it" phase.