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Quick background - I come from the Z car platform, having owned, maintained, and in some cases modified four separate generations of those cars. Still have a turbo 370z and an insanely modified/restored 300zx. In 2025, my wife convinced me to test drive a C63S and I absolutely loved it. Picked up a 2021 with 26k miles, selenite grey with a red pepper interior, joined this forum, and here we are.
As I am chronically incapable of not at least lightly modifying everything I own, I started looking at intakes and tune information for this platform. One of the big differences between Z car forums and this one is that every aspect of every mod for every Z car seems to have been tested on the dyno and I can't say the same for the C63s. Probably a number of reasons for that, including less need to mod the car to get performance to match the appearance.
Anyway, doing my part here for those who are researching the same way I do. I picked up Weistec Intakes and a Renntech Flash Tune. Intakes seemed to be a decent design, closed box with better diameter tubing running to the turbos, and Weistec claims they help prevent the smaller stock turbos from running out of breath quite as early. Renntech tune was the choice because packaging was convenient, seems to be reliable, and none of the variation in user experiences that I saw when researching Eurocharged and some of the other options for the platform. I'll add some pics of the intake install, comments on the process, and plan is to take the car up to a local speed shop I use regularly and get it dyno tested sometime next week. I didn't think to do a "before" and "after" so apologies for that, but it'll at least let you know where I wound up.
Ordered the intakes during a Christmas sale and they showed up a few weeks later. Packaging was solid and professional. Parts do not come with installation instructions, so you'll have to pull them from Weistec's website. Obligatory link: https://www.weistec.com/carbon-fiber...9Ys2oBQDsboSyF
Instructions are pretty basic and assume that you're mechanically inclined or have done this kind of thing before. Most is very straight forward, so I'll only note the surprises.
1) Here's how the car looks with no intakes.
Intakes Out
2) Step 3 of the installation involves re-routing part of your electrical harness underneath a hardline on your passenger side. This was a mild pain in the ***. My best guess from analyzing the photos vs my engine bay is that there is a slight change in PFL vs FL cars with a sensor location. The sensor bung, highlighted in red in the image below, made this a very tight fit. Re-routed
3) PCV unit is glued into the intake couplers. This is covered in other posts, but the important part that I didn't catch elsewhere is that it's glued mostly around the bottom of the connection. I worked at this with a small hose pick and was able to get it free. Drivers side was much worse than passenger in glue qty.
4) I did not take pictures of this part because I was too busy trying to figure it out. The stock intakes mount on ball studs. Weistec replaces those with rubber mounts that have threaded studs on both sides. One side threads into the engine block, other side is used in your intake, and a castle nut threads on top to hold the intake housing in place. Drivers side was fine. Passengers side was not fine. In the image below, I highlighted the area I'm talking about. Basically, the rubber mount that replaces that stud tends to sit at an angle. The aperture on the intake which is meant to accommodate that rubber mount stud does not give good access to allow the castle nut to thread onto the stud. I spent a good hour+ on this before my wife took pity on me and gave me a hand. It took an immense amount of manipulation to try and get the stud to poke through the aperture to where I could thread on the nut. Even so, I eventually replaced the castle nut with an otherwise identical flangeless nut to make this happen. 0/10, did not enjoy this part.
5) Last surprise is that the original recirc lines do not have a connection point on the intakes. I did not find this anywhere in the instructions or description of the product. Not a big deal, but consider it an FYI. Here's a picture of the finished product. Excuse the dirty bay, I was all out of ****s to give at that point.
I also didn't mention how hard I had to fight to get the passenger turbo coupler on. Par for the course with a tight bay, but RIP my knuckles. Anyway, finished product looks decent. Impressions: Not much change from a sonic perspective except the disconnected recirc lines do provide the occasional BOV-like noise. Certainly not enough HP difference for my butt-dyno to detect. We'll see what an actual dyno shows. Hopefully my speed shop has a readout from a stock C63S so I can get a baseline to compare against. I should have thought to get my own baseline, but did not.
Renntech Tune is very straight forward. You pay them a mildly exorbitant amount of money, they send you a very beautifully packaged dongle that plugs into your OBDII port.
Step 1: Have full battery. Check!
Step 2: Press start button twice, foot off of brake so car enters one of the accessory startup modes. Check!
Step 3: Make sure selector switch on dongle is set to Tuned and not Stock. Check!
Step 4: Insert dongle. Wait for red light to turn green and pray it does not turn other colors or blink. Check!
Step 5: Enjoy.
This is a noticeable change. Still feels completely stock in Comfort mode, but more aggressive in Sport/Sport+. Haven't tried race yet. Doesn't run out of steam up top quite as quickly. Maybe the intakes are playing their part here.
According to this, this is no where near what power gain Renntech claimed on their website.
I did the Renntech tune on an otherwise stock car back in 2022 and although I didn't dyno it, my Dragy registered slower 100 to 200 km/h (60 to 130mph) times.
They blamed in on heat soak, even though I tried doing the Renntech tune runs first then followed by the stock program runs. On the same road, same outside temperature, and just minutes apart.
I repeated the tests on different days and sent them data logs. In general it was about 0.2 to 0.6 secs slower with the tune. Insignificant, I know, but for the amount of money paid, expecting a slight gain, it was not worth it.
You do know the difference between HP and WHP, correct? This is actually almost identical to what Renntech advertises, and a big jump over the stock hp on these cars. Sorry you had a bad experience, I don't question that at all, but my results are exactly as advertised.
If you're not aware, a Dynometer measures performance at the wheels - that is, after deducting all 'parasitic' losses from your drivetrain. Add 15 - 20% to this number, and you'll have 'crank' horsepower, which is what Renntech advertises on their website.
This is the Renntech dyno vs my dyno. You'll note that Renntech actually promises lower results than mine.
I'm not sure how much of this is due to dyno differences (I can't tell what kind of dyno Renntech was running on), how much is SAE vs STD (Renntech does not note their methodology), and how much was due to the intakes. These charts are supplied as data points only. I'm also running 94 octane (Sunoco)
Last edited by JoshLarson; Mar 21, 2026 at 10:05 AM.
Reason: Added octane level of fuel
That’s funny my first car was a 74 260 Z. Then I bought an 09 370 Z and twin turbo’d it, I did all the work myself but now I have this car and I’ve done all the work too. But it would be nice if there were more people DIYing stuff because actually this car is not that difficult to work on. We’d all have a better idea on the effectiveness of the aftermarket parts. It’s such a great feeling to take your car on that first test drive after you install the part and enjoy the fruits of your labor!
That’s funny my first car was a 74 260 Z. Then I bought an 09 370 Z and twin turbo’d it, I did all the work myself but now I have this car and I’ve done all the work too. But it would be nice if there were more people DIYing stuff because actually this car is not that difficult to work on. We’d all have a better idea on the effectiveness of the aftermarket parts. It’s such a great feeling to take your car on that first test drive after you install the part and enjoy the fruits of your labor!
Similar background and perspective on it for sure. Yeah, one of the things that surprised me on this car is the lack of DIY and info on mods. Granted, this car doesn't need much (or really anything) but if you've done it, you know how addicting it can be.
You do know the difference between HP and WHP, correct? This is actually almost identical to what Renntech advertises, and a big jump over the stock hp on these cars. Sorry you had a bad experience, I don't question that at all, but my results are exactly as advertised.
If you're not aware, a Dynometer measures performance at the wheels - that is, after deducting all 'parasitic' losses from your drivetrain. Add 15 - 20% to this number, and you'll have 'crank' horsepower, which is what Renntech advertises on their website.
Thank you for your educational lesson young man. This is not my first car, nor my first attempt at modding. I've been in this game longer than you been alive most likely.
Perhaps your graph was not clearly labelled then. Are the blue and red lines both modded runs? I was assuming one was before and one was after, in which case your gain is only 0.2% and not 15%... But if they are both after the tune then I guess we really don't have a baseline.
Thank you for your educational lesson young man. This is not my first car, nor my first attempt at modding. I've been in this game longer than you been alive most likely.
Perhaps your graph was not clearly labelled then. Are the blue and red lines both modded runs? I was assuming one was before and one was after, in which case your gain is only 0.2% and not 15%... But if they are both after the tune then I guess we really don't have a baseline.
As noted in my very first post, my plan was to dyno after the mods. I'm not clear why you would think this car would dyno at 600wtq/550whp before mods. Had I seen a .2% increase, I would have been at least slightly displeased.
You are correct, I do not have a baseline for this car, although I've dynoed multiple cars in the past on this same dyno, both before and after. It reads reasonably close to other Dynojets... not at a heartbreaker level for sure, but not unreasonably high. The shop is called RT Tuning and its fairly well known in PA.
Last edited by JoshLarson; Mar 24, 2026 at 03:40 PM.
Reason: Unnecessary snark
It takes literally a minute to swap between stock tune and renntech tune with the flip of a switch on the module, so I'm sorry, I just assumed that's what you did, when I saw 2 lines each each on the chart. Would've been nice to compare though.
The reason why I hesitate to mod this car is because traction becomes an issue. At its stock rating I don't spin the wheels excessively from a stop light however tuned I'm fairly certain the wheels will just spin. Is this the case? How much faster would you be from 0-60 or the quarter mile? After seeing these numbers I'm tempted however...traction.
I don't have good numbers for you. Once the weather warms up, I'll try to better characterize the launch performance, but I haven't had the right combination of stoplights and warm tires to really give this a shot, or taken it to a track.
I realize its anecdotal, but if I punch it on the highway or something similar, it's an absolute beast and the extra power is very present. I can't believe how well this car moves considering it's quite the fatty.
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