Skip to main content
HOME   |   ABOUT   |   NEWS   |   TECH ARTICLES   |   AT THE TRACK   |   REVIEWS   |   VIDEOS   |   CONTACT ME

2012 Mustang Boss 302 - Heartthrob Flowpack Axle Back Exhaust




A few weeks ago, I started the car up and realized that I forgot something so I ran back in to grab it and when I walked out, I noticed that there's a lot more vapour pouring out of the side pipes than the rears (as the car was warming up). I read many articles that said Ford designed the side pipes for noise and they flow very little compared to the rears. It certainly seemed like there's more flow through the sides than the rear (although I do have the side baffles completely removed). After that, I decided that I wanted an axle back exhaust. I'm obviously not expecting any power gains (nothing more than a couple hp anyway) but I was ready to turn up the decibels!

I decided on the Heartthrob Flowpack kit (the picture above is of a Mustang GT from Heartthrob's website, not mine) and bought it from American Muscle. I was very pleased with shipping. It shipped on the same day despite ordering in the afternoon and it only took one week to deliver despite being in Canada. I wasn't too pleased with the packaging though and its condition. I have ordered my fair share of aftermarket parts and most parts are packaged to not allow movement inside the box and provide support for the shipping box to keep it rigid. The box was damaged; sort of bulging where the ends of the exhaust pipes where and one of the tips was very, very slightly bent. The deflection was less than 2 mm (around 1/16") and can't be seen unless you are under the car. The quality of the packaging is probably Heartthrob's fault but for $279.99, it was just about the cheapest available with "mufflers." The condition of packaging though is either American Muscle's fault or UPS. There is a chance it could have come that way from Heartthrob but American Muscle would still be partially to blame because they shouldn't have let it ship that way if that were the case. Anyway, it didn't bother me that much so I'll move to the important bit: what they're like.


Pros:
  • The noise is phenomenal. It adds a nice subtle rumble at idle that is very nearly as quiet as stock at idle and slightly louder under light load. It makes the exhaust note immensely deep and much louder under load just off idle, though, and all the way to redline. It is intoxicating. After installing it, I tried to find excuses to go out for a drive.
  • The noise out of the side exhausts is barely changed. I was worried the car would sound better overall but the noise would sound a bit distant while driving since more flow would come out the back and less out the sides compared to stock. That wasn't the case.
  • It is lighter than stock. Much lighter. According to my bathroom scale, it weighs 22 lb. less. While that isn't much on its own, it adds up quickly if you have plans to put the car on a diet.


Cons:
  • It isn't the nicest looking. If looks are a priority over noise and budget, you're better off buying a different one. It won't surprise you, though. It looks like it does on the website, not better or worse. You can go to any online store that carries it and compare it to nicer looking ones and see if you are satisfied with the looks. I will post pictures in another post as well.
  • It is made of aluminized steel as opposed to stainless.
  • Drone. There is a range of about 200 rpms between the 1,750 and 2,250 rpm markers on the tachometer where there is drone. The bad news is: it is bad. The good news is: it is a very narrow range that is very easy to avoid. It is really nice and quiet above and below that range in any condition. It is even very quiet in that range on the highway on flat, straight roads but if you are in 6th gear and you want to accelerate in that range or the road changes and you start going uphill, it gets bad. I simply downshift to 5th if I find myself in that position.

As for power, Heartthrob has a dyno sheet on their website that shows a gain of 8.5 hp on a Mustang GT - 363.9 hp stock vs 372.4 hp with the axle backs - which would work out to almost exactly 10 hp at the crank. Although it isn't a huge gain, I took that with a grain of salt and didn't base my decision on it. Now that I have installed it, the car feels like it pulls very slightly stronger. I don't believe that, if it does add any power, it would be noticeable from the driver's seat. If I tell myself that enough, I'm sure I will be convinced that the car pulls just as strong as stock but for now, it's tough when it sounds that much better! If it does add about 10 hp as the dyno runs claim, great. If not, that's to be expected from just an axle back.

If you would like to look at the dyno graph, go to this link: Heartthrob 2011+ 5.0 Flowpack Axle Back Dyno. The graph looks a bit odd with a large torque spike early on in the graph. However, the graph torque range is narrow (only between 300 lb-ft and 350 lb-ft) where most dyno graphs show 0 lb-ft as a minimum. The minimum rpm shown is also high at 3,573 rpm where most graphs start close to idle, at 1,500 - 2,000 rpm. These factors make make the normal torque curve appear as if it has odd spikes.

Overall, I am very happy with it. I don't think it's for everyone because of the drone and less-than-polished looks but I would buy it again. I will have to wait and see how the aluminized steel construction fares. Check back for pictures and videos comparing this exhaust to the stock one and an installation guide!


Comments







Does An Aftermarket Grille Really Increase Airflow?
I put a Saleen S281 grille to the test to answer that question.

Stock Suspension S197 Mustang With Square 305/30/19's
What you need to fit a proper size square tire setup.

How Limited Slip Diffs Make You Faster on Track
What you need to know about how they put power down and pros and cons.

Can Telemetry Explain Schumacher's Talent?
A comparison between Schumacher's and then team mate Herbert's data.






Cayman GT4 Track Review
The first Cayman with proper (911-challenging) power.

Is an EcoBoost Mustang any good on Track?
Two days at the track in a Mustang short 4 cylinders.

2016 BMW M4 DCT Track Review
It's quick (properly quick). But is it fun?

Can a stock Golf Diesel handle a Track Day?
Not your every day track beater.




🔥 Most Visited This Week

Falken Azenis RT615k+ Street and Track Review

Last year, I picked up a 2009 Lancer Ralliart to do a long term test with it as a dual duty track/daily. One of the first things I knew I was going to do was put a decent set of tires on it. The car came without OEM wheels which was actually good because I didn't have to hesitate about getting a good set of aftermarket wheels to support going wider. Thankfully, my friends at YST Auto Halifax  set me up with a great set of Superspeed RF03RR wheels. The Wheels I had never even heard of Superspeed but I trusted the good folk at YST Auto who mentioned some customer cars running on track with them. These wheels are rotary forged which is basically a prerequisite to be taken seriously in this market populated by companies like TSW and Fast Wheels. The wheels looked like a high quality, well finished wheel and each had a "QC" check sticker on. Just for appearances? Maybe, but I found no defects. The wheels seemed easy to balance (didn't need many weights) and at 18.1 lb. f

Michelin Pilot Super Sports vs Firestone Firehawk Indy 500 - Street Review

I've been a huge fan of Michelin PSS tires and exclusively bought them for the Mustang over the last four years. So how did I end up here? This year, I was hugely interested in trying an "R-comp" tire. I had my eyes set on Bridgestone Potenza RE-71R's for two simple reasons: price and reputation. Although not a true "R-comp" tire on paper, it performs like one by the account of every single test and review I've read (down to wear rates...). They seem like they're easily the most affordable (from a big brand) R-comp tire and combine that with a reputation for having tons of grip, it was an easy top contender. I had my concerns, though. For one, I'm told and have read that they are an autox tire, not really designed for high speed, pressure, and temps associated with open track. For another, the Mustang is a heavy car (as far as track cars are concerned) being roughly 3,800 lb. (including driver), which will amplify the unwanted open track load

Winter Car Maintenance Tips

It's this time of the year again and I thought I would share a few winter maintenance tips that can be overlooked but they can keep a vehicle running better and more safely. 1- Tires They're the only components that connect your vehicle to the road. Regardless of the capability of a vehicle's drivetrain and suspension or how strong the brakes are, they will handle only as well as the tires allow them to. Always get snow tires and not summer or all season tires if snow stays on the ground. If you only get rain but no snow where you live, all season tires are a great choice. Check tread regularly to make sure the grooves are deep enough. Tires have wear bars which indicate  when the amount of tread left is unsafe for driving. Snow tires have two wear bars; one for dry/wet driving and one for snow driving. If the tread is at the taller wear bar (the snow wear bar), the tires are not safe for snow driving but may still be used in the rain or dry. If the tread reaches the

Limited Slip Differential Types Compared

BMW M2 equipped with an eLSD - BMW © A few weeks ago, I posted about traditional clutch-type limited slip diffs (LSD's) and how they work. You can read about those in the previous post: How Limited Slip Diffs Make You Faster on Track . But as you might know or have learned from reading the article, they aren't without their faults, which means engineers are always working to get around those limitations. You may not be surprised to learn that something like the Ferrari 488 GTB doesn't use a traditional limited slip diff, but it's not limited to super cars, far from it. Cars like the Golf GTI, the Civic Type R, various Mustangs, Corvettes, and BMW M cars, and even the Lexus RC F and GS F, all avoid a traditional limited slip diff in favour of one of these technologies. To keep things simple, I'll focus on two wheel drive vehicles. The vast (vast) majority of principles apply to all and 4 wheel drive vehicles, but there are some subtle differences that I'll