Project S2000: Part 19 – Ram Air!!! Plus Hot Air Testing!


More pressure and lower temperature should equal more power right? We’ll examine that in three ways. The easy way is to look at the increase in engine speed vs time I have plotted in the graph. As you can see, the engine speed increases faster over the same time period with the duct installed which means more power. How much more power? We’ll use some math to figure it out.

Power is directly related to the mass flow of air into the engine. The mass flow of air is related to air density. Air density is directly related to air pressure and temperature. The air pressure increased from about 95kPa absolute pressure to about 96 kPa. So that’s about a 1% increase in air density. The intake manifold air temperature dropped from 327 deg Kelvin to 319K. So that’s another 2.5%. Multiply the two gains together and we get a gain of about 3.5% in air density and therefore power. The car was making about 250 crank horsepower after tuning with the Hondata KPro, so in theory, the car is now making about 259hp when doing 130mph with the addition of the extra cool ram air.

Using the datalogs from the KPro and my own little virtual dyno spreadsheet, I calculated an approximate wheel horsepower. The calculated power data are the jagged lines and I drew in the smoother lines by hand to approximate the horsepower value. It looks like the duct gained about 4whp, or a bit over 2% gain. It doesn’t quite match the theoretical, but the real world is never ideal. For sure though, there was a gain in power. I’ll call the ram air, cold air, NACA duct a success.

Edit: A fourth way, more info from my datalogs.  Without the duct: air temp = 54degC, timing = 26-27 deg, MAP = 95.1kPa, injector = 10.1ms. With duct: air temp = 46-47degC, timing = 28 deg, MAP = 96.1kPa, injector = 10.2ms. So, more fuel was sprayed (= more power) as shown by the injector time and the lower intake temperature allowed 1-2 degree of timing (= more power).

Being that it was very very hot, the conditions were great for testing the effectiveness of my vented hood. The last hot weather testing day I did was at Chuckwalla where the peak ambient temperature hit 92 deg F. In that weather, my oil temperature peaked at 117 deg C. On this day at Autoclub, the ambient temperature was 102F. With the vented hood installed, the oil temperature peaked at 117C, or the same as with the stock hood with the ambient temp at 92F. So the vented hood kept the oil temperature the same even though it was 10F hotter outside. Oh, and the coolant stayed rock steady at 190F. I’ll call the vented hood a success too!

On the drive home on the highway, I noticed small changes due to the ram air duct and the vented hood. Even though it was well into the 90s in temperature, I actually reduced the A/C from full cold. So it seems the vented hood was helping pull more air through the A/C condenser improving its effectiveness making for colder A/C. The other effect I noticed, though maybe I was just delirious from the long day at the track in the heat, was the throttle response seemed snappier at highway speed. This would be expected with a ram air setup as it would force more air into the engine, improving throttle response as a result.

The Nitto NT01s kicked ass as usual. I got a little sideways once trying to stay in front of a Ferrari F430, but the NT01s are very easy to catch due to their progressive nature. I could pretty much stay with any car in the corners short of the Vettes and CTS-Vs running on Hoosiers slicks. Once on the straights at Autoclub however, well, Vettes, CTS-Vs, Ferraris and GTRs have a lot of power.

Yup, I’m still on the original set of StopTech Street Performance Pads from when I installed the brakes a few years ago. I think I’m at 6 track days, 25k miles, five dozen auto-x runs, and there’s about 7mm of pad left (more than half). For sure, my brake ducts are helping. After a very thorough cool-down, my front rotor temps were down to 160F while my rears were still at 360F.

Speaking of the rears, they are getting a bit thin. I’ve been meaning to order new ones for the past half year or so. Maybe I’ll finally get around to it. I was planning on doing rear brake ducts for this track day too, but I ran out of time.

So it has only taken me until Part 19 of this project to do my second power modification. Everything else has been to improve reliability, drivability, and handling performance. With all of the cooling modifications, I can track the car regardless of how hot the weather is without fear of overheating anything. The oil barely tops 240F and the coolant doesn’t budge from the thermostat setting. Remember, cooler is better within reason. Cooler coolant and oil keeps the engine cooler. A cooler engine keeps the intake manifold temperatures lower for more power. The S2000 comes with piston oil squirters, so cooler oil keeps the pistons cooler which reduces the chance for detonation. The oil stays so cool, I can track it on standard weight oil without fear of viscosity reduction. I actually had Motul 300V 5W-30 in for this track day which is a little lower weight than the standard 10w-30, and it should last a really long time as Motul oil is not very stressed at 240F. So now I don’t even have to change the oil as often. The StopTech brakes combined with my brake ducts can take anything I throw at them while using street pads! It’s definitely nice to be able to just hop in the car, track the heck out of it, and go home without having to do much prep. Fear not however, more modifications are in the plans shifting the bias of the car more towards a track car.

P.S. If anyone is interested in getting a carbon fiber version of this NACA duct, sound off in the comments and check the option to stay notified of new comments. I might have some made.

Hmm… need a smidge more negative camber up front. Next time… Photo by Caliphotography


  1. Hey Moto IQ , first thing you guys are the one of the best at building track cars and I love all of your upcoming projects. Im in need a a NACA vent for my 2011 BMW 335i and this vent looks perfect. By any chance can you guys get another one made and I will pay before its even made, really need this vent.

    1. Appreciate the comment! This NACA duct was designed specifically for the S2000 hood shape and airbox location. For your needs, you can probably go with something generic? Pegasus Auto Racing Supplies has some NACA ducts that could work.

  2. Would the NACA duct have water issue when it rains? I’m also looking for a brake duct kit for an AP2 that comes with the dust shields already with the hole for easier installation. WASP Composite seems to be the only one that made such a kit with the hole directed towards the center of the rotor as it should be. Unfortunately it doesn’t seem like they sell the kit anymore. Any ideas/recommendations? Many thanks!

    1. Personally, I wouldn’t use the NACA duct in the rain. I’m not sure the stock airbox has any water drainage provision. It’s easy to swap hoods, so I only put on the track hood for the track.

      As for brakes, if you track, I’m a huge proponent of going straight to the StopTech BBK. Of course, that means you need new wheels to clear the brakes. If you want to keep the stock brakes, you could just remove the dust shields. I haven’t had the dust shields o the S2k in ages and I went around 100k miles on my old Nissan without dust shields. You will need to figure out a way to mount the end of the hose. I just zip-tied it before.

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