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

Rams Eye New Track Car & Daily Reveal

New track car? You bet! Just picked it up a few weeks ago for a long term test to serve as a dual purpose daily and track car. It's a bit obscure and forgotten about but packs a lot of special features and one of the best AWD systems you can buy. Watch to find out what it is, why it's forgotten, and what I like the most about it (plus how much I paid for it!). Liked this? Make sure to subscribe so you don't miss new videos! Follow Rams Eye The Track Guy on Facebook and Instagram! View this post on Instagram A post shared by Michael R (@ramseyethetrackguy) on Sep 8, 2020 at 4:43pm PDT

GTR vs Evo X vs STI: which has the best AWD system?

A few weeks ago, I made a post explaining  mainstream AWD system types and how they compare , pros and cons, etc. including some simple diagrams to show where the power goes and how much. As promised, this post will focus on specific cars and what AWD systems they use, especially ones that that have more or less been defined by their AWD systems, and the best place to start may be with a bombshell; the Nissan GT-R. Nissan GT-R (R35) The GT-R has built a reputation around having monster traction and very approachable performance, thanks to its AWD system - Advanced Total Traction Engineering System for All-Terrain (ATTESA) - and what it can do for you. But the GT-R doesn't actually use the most mechanically sophisticated type of AWD systems discussed in the previous article, namely a "true" AWD with a centre differential. Instead, it uses a clutch pack to transfer power. RWD-based clutch-type AWD schematic - Rams Eye The Track Guy © The R32, R33, and R34 Sky

Michelin Pilot Sport Cup 2's vs Bridgestone Potenza RE-71R's

I never thought I'd ever run Michelin Pilot Sport Cup 2's on my 2012 Boss 302. The cost is astronomical and they are supposed to last the least of anything comparable. So how did I end up with (nearly) fresh Sport Cup 2's? A complete fluke. I came across a lightly used set with only a few hundred miles and no track time; 305/30/19 takeoffs from a GT Performance Pack Level 2 (GT PPL2). I knew my 71R's were getting very worn before the season started and likely wouldn't last the whole season, even this short one. The price was far better than a new set of RE-71R's, a little more than half, and local Time Attack rules (Canadian Automobile Sport Clubs) recently made 180 and 200 TW tires equivalent, meaning no PAX or PIP point penalty for going with 180 TW tire like the Pilot Sport Cup 2's. I have been very curious about how PSC2's compare to RE 71R's but I stayed away due to their being painfully expensive and, up to last year, their 180 TW rating would

Bridgestone Potenza RE-71R Track Review

2012 Boss 302 on square 305/30/19 RE-71R's at AMP - Graham MacNeil © For better or for worse, I have heard and read so much about RE-71R's. Everyone swears by the grip but complains about the wear. Generally speaking, the pros are: 1. They grip as well or better than most R comps. 2. They don't wear as quickly as R comps if driven occasionally on the street. 3. They work better in the rain than R comps. The cons were limited to overheating quickly when used on track (being an autocross tire) and wearing too fast on heavy cars like mine. In the popular 200 TW category, they are faster than the popular Hankook RS-4's and BFGoodrich Rival S's according to published Tire Rack Tests. According to plenty of reviews, they are also faster than well established R comps like R888R's (which don't seem to work too well on heavy cars anyway) and the venerable NT01's. But I was still hesitant for a while until I talked to a tire tech support gentleman