Firstly, please excuse the phone pics. I brought my camera but forgot my memory card in my laptop. Oops. So anyway, it’s been a super slow burn on this project because life. But a lot of headway has been made since dropping the car off at Eimer Engineering. Chris at Eimer Engineering is familiar with S2000s and works on Dai Yoshihara’s race cars, so he was the right person for the job. This build also requires a lot of ‘trying things out to solve packaging problems as everything is custom and Chris is a willing partner to do these experiments. Here’s where we’ve gotten so far on making all the custom parts fit.
A goal of this project is to stay stealthy, so keeping the stock rear section of the exhaust was a goal. Won’t this hurt power you say? The combined flow area of the two pipes (assuming 50mm diameter each as I didn’t physically measure them) going to the stock mufflers is only about 15% less than the 3” mid-pipe, so it is a bit of a restriction, but a good compromise to stay stealth. For reference, the stock 60mm diameter mid-pipe is about 38% less flow area than my 3”/76.2mm turbo-back mid-pipe. The team at Eimer Engineering had to cut the stock exhaust where it splits from the mid-pipe to the twin exhausts and makes the transition from the 3” pipe to the stock rear section.
The stock exhaust actually has a nice Y-split which is better than many of the aftermarket offerings for the S2000. As we’ve seen many times, the Honda engineers really maxed out performance given their OEM constraints (budget, piece price targets, etc.) and it’s been hard for the aftermarket to improve on the stock Honda designs.
Here is the transition piece going from the 3” round to the oval profile of the stock exhaust before the split. As you can see, the area of the stock exhaust before the split basically matches a 3″ diameter pipe.
The exhaust from the turbo to the rear exhaust section is all 3” diameter stainless steel. It eliminates the resonator in the stock mid-pipe and also the little stubby side tube that acts as a Helmholtz resonator. We’re going to give it a try and see how loud the system is. We went to a larger diameter pipe and cat and eliminated the resonator which will increase the noise level relatively speaking. But we also put the turbo on there which acts as a muffler. It might be about the same loudness as stock. The major changes being we removed the stock mid-pipe resonator but added a turbo.
This is a GESI GEN2 Advanced G-Sport UHO (ultra-high-output?) cat and its EPA compliant for 2017+ vehicles. It’s 400-cell with a 3” diameter inlet/outlet and 4.5” diameter body. There is a model that’s only a 4.0” diameter body and rated for less power which makes sense. Smaller diameter = less flow area = higher restriction. You can see why I went with the 4.5” body. GESI makes a GEN1 model line for vehicles up to the 2016 model year that’s a 300-cell count. Interestingly enough, they are rated at the same power as the GEN2 with the 400-cell count. One would think the 300-cell would be lower flow restriction. Anyway, I decided to go with the 400-cell as it should be a little cleaner and still flow plenty for my 500 crank horsepower target. I had to get a new cat because my stock one is toast. Everyone who tracks an S2000 knows the stock cat breaks apart after enough track days.