AP Racing 8350 Brake Kit (Evo 9)

This took a lot of consideration on my end, but I decided to downsize from my Evo 10 Brembo + Girodisc brake setup to the AP Racing 325mm 8350 front caliper/rotor kit from Essex. Essex claims 14lbs unsprung mass decrease – 7 lbs each front wheel, compared to the stock Evo 9 setup. My current Evo 10 setup in any case is marginally heavier/about the same compared to that, mainly due to the two-piece floating rotors saving some weight. I also know that my old Evo 9 setup was about 4lbs per front corner lighter than stock, so this shouldn’t be too much improvement from that setup.

In any case, 14lbs total unsprung mass from the front is quite an improvement. Some weight is saved through the rotors, which will be 25mm smaller than the Evo 10s – so a few pounds saved there. A lot of the weight is also saved via the front calipers, which are much smaller and lighter than the stock Brembos. Even just the 4lbs difference I felt going from Evo 9 to Evo 10 brakes was immediately tangible when I first switched setups, so I am excited to be going back, and then some. I fondly remember my previous setup with the 17×9.5’s as the liveliest setup I’ve ever had on the Evo 9, and the car felt lightning quick in transitions.

These calipers should also be much stiffer than the factory Brembos, improving the feel of the brakes. The new strut tower brace I plan to add has a brake master cylinder brace built into the brace itself, which will also aid in feel. New stainless steel lines were added to these brakes, but no feel improvement is expected from that. These calipers have a much smaller area for the bleeders, making it impossible to get a flared wrench on the part – a standard 12pt wrench will work better here. The caliper pistons are actually slightly smaller than the Brembo’s, so in reality brake balance may be shifted more to the rear – not necessarily a bad thing, especially considering the weight changes I’ve been making. They use stainless steel pistons (which I’ve used in the past) to allow for much slower heat transfer (though it holds heat better as well). With it though, no titanium shim will be used moving forward. These also use anti knockback springs, which have just enough force to prevent the pads from going back into their housings.

The rotors are, apparently, also an improvement over what I was currently running. The hat is a much flatter design and the material is more oriented towards racing. These also sport vanes that will pump out hot air, and are directional. With 60+ vanes, more than most aftermarket options, cooling should be relatively efficient. The J hook slots on the face of the rotors have also been designed to normalize heat distribution across the rotor.

Finally, the brakes allow for a much thicker (20mm) brake pad. These pads are much, much thicker than stock, and thus will go a lot longer before needing replacement. At some track events, I could almost see the decrease in pads due to heavy braking zones. I chose to run Ferodo’s 3.12 pads, which are a highly, highly praised track pad with even mu across the temperature range. They also have strong bite, though I’m unsure how this compares with the Raybesto ST43’s notoriously strong bite. Regardless, it will take some getting used to.

All-in, I am hoping that this system performs similarly to the Evo 10 system. It’s possible that it doesn’t brake as strongly as the larger 350mm & piston setup, but again, not necessarily a bad thing. The biggest pro, aside from the weight decrease, was the fact that I would not have to rebuild the calipers (sometimes more than once per season). The dust boots, even with titanium shims, were basically toast after the first track day – so why even bother having a system that will inevitably introduce crud around the pistons?

The biggest downside of this system, I think, is going to be heat management. Going from 350s to 325s means losing a pretty significant heat sink in the rotor. The OEM brake heat shield had to be ditched with the bracket & the upright both not supporting it. Even the ducting I began to use, which did actually improve the temps, did not fit the new setup. They don’t fit against the back of the upright, and in any case, the majority of the air would hit the bracket anyway. AP Racing does not recommend using ducting with their brakes, but still. I will be keeping the OEM control-arm mounted air guides, though I did shave the ends to fit with the brake ducts better. At least, the ducts will not be blocking the air guides any longer. Temperature tape was used to cover the more sensitive bits in this area (bushings & abs sensor), since they are no longer protected by the OEM heat shield.

The install was relatively straightforward. In place of the side-mounted Brembos, mounting brackets installed. They did actually need to be ground, due to the design of the SSB uprights that were installed on the car first. The rotor then slides right into place, and the calipers get axially mounted to the brackets. All hardware is included. The brake lines were swapped, the pads slot in, and that’s it. For a stock upright, this is a fast change, as no grinding will be needed. The pads maybe sit 1mm inboard of the rotor, but I think no big deal there. Easy stuff, compared to the uprights install.

That’s a lot of writing, but all-in, hoping for similar performance, improved longevity and feel, only marginal heat increase, and continued weight balance improvement, chopping off 14lbs in the front. On initial drive, the brake felt firm, but also felt like it took a long time to stop. I am going to have to bed these in before I make any real judgment there. Also a plus in my opinion, it lets me drop back down to 17″ wheels…

2 thoughts on “AP Racing 8350 Brake Kit (Evo 9)

  1. Pingback: Mitsubishi Evo 9 MR OEM Brake Air Guides (MZ555004EX) | QL Motorsport & Car Journal

  2. Pingback: 2022 Preseason Updates | QL Motorsport & Car Journal

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