This past fall, I decided that I wanted to get more into track events, as well as get out of a slow FWD track/autox car (coming from an STS prepared Honda CRX). I have wanted a Honda S2000 since I was a kid, as they always seemed like a great street car, 2 seater convertible, VTEC, and twice the power of a Miata, what's not to love? Anyway, I had been watching a Honda S2000 for a couple of months on Marketplace. This S2000 however, was far from the car I wanted as a kid. The car in question is a K swapped, track prepared time attack car. The previous owner had built the car almost to the limit of the Gridlife Club TR ruleset, with the exception of putting the car on a hardcore(and pricey) diet to meet minimum weight.
Those familiar with the Honda S2000 chassis, are most likely to be aware of the fuel starve issues that plague these cars on fast left hand corners. This means that generally to avoid this issue the car has to be run at at least half a tank, however, as this specific car is tuned on E-85, and gets 4 MPG on track, so I need to start a session around 3/4 of a tank of fuel. The best way to prevent this issue is through the use of a surge tank. This would allow me to run significantly less fuel, which weighs around 8 lbs/gallon. Going from 10 gallons of fuel to 4 would save me roughly 48 pounds in fuel weight, however, I expect to add 10 pounds to the car with the surge tank, so a net weight saving goal of 38 pounds was the idea that spawned this adventure.
Now there are a few different surge tanks on the market for a Honda S2000, but due to the fact that I am a fresh college graduate, I did not want to shell out the almost $1000 for a plug and play surge tank kit. In college I was heavily involved on a Formula SAE team, which taught me valuable design and fabrication skills, so why not apply those to a surge tank and design my own system (with help from the internet of course). The design was not too complicated, as in theory a surge tank will be full almost the entire time the car is running, as the fuel tank feeds the surge tank, as well as the fuel rail return. I decided that a hexagonal shape should do, as in my mind, this shape would be easier to mount than a cylinder.
I drew up a surge tank, and sent it to the local laser cutting/bending/welding shop. All in all it cost $125 to get bent and welded up, with the exception of the -6an fuel line fittings, as I had decided that I trusted myself enough to weld them on.
Photo of the surge tank with -6an bungs welded in, with 3 on the top, and 1 on the bottom. The 3 stop fittings will be fuel rail return, surge tank feed (from in tank pump), and surge tank overflow to fuel tank. The one fitting on the bottom is the fuel rail feed.
Now that I had the surge tank welded up, I did a quick pressure test by capping 3/4 bungs, and using the 4th to fill the tank with compressed air. I found that one of the bungs needed a little touch up welding to make the tank hold pressure, and that job was done. The next step was to figure out how I was going to mount that thing. I went back to CAD, this time using cardboard, to build an accurate template which I could copy onto .0625" aluminum to make a mount for the top and bottom of the tank. I had already decided to mount the tank in the spare tire well, as it made the most sense to me. Easy to mount upright, good location to feed fuel lines into the car, and easy to build a firewall to separate the drivers compartment from any part of the fuel system.
This was the upper mount all mocked up, I used 3 rivet nuts to mount it to the frame rail that ran perpendicular to the car, then repeated the process for a lower tank mount, which I bolted through the spare tire well, and used a similar strap as the top uses. I put a rubber adhesive on the back side of the two mounts to isolate vibration of the chassis to the surge tank as well. (Ignore the symmetry of the strap, I fixed it later)
Both mounts shown in picture
With the tank mounted, and sturdy, it was time to start running the fuel lines. There's a slight hump in front of the spare tire well, which seemed like a suitable space to run my fuel lines through, as it would have been the easiest way to route the fuel lines in regard to building a firewall.
This picture shows the area I fed the fuel lines through the chassis (this was only the start of the mess I made of the trunk area). Another important thing to note, is this hump leads right to the fuel sending unit area of the car.
Fuel line routing at the tank. It is still not quite track ready yet, as the line routing isn't quite to my satisfaction, so I will have to go back and route them in such a way that they are not able to hit the fittings on the tank, it would really suck to break one of those off at the track. In addition, with the fittings I used, I made it incredibly easy to bypass the surge tank system, and re connect the factory fittings to the fuel tank in just a couple of minutes. This shows my confidence in all of this working well the first time at the track...
Now I still had to mount the fuel filter, as well as the fuel pump for the surge tank. For the in line pump I went with a Walbro 255, as I have only really heard good things about these pumps. Reliable, and quiet. After sourcing some more E-85 compatible fuel line, I had finished up the plumbing on the surge tank. All that's left next is to wire it up, give it power, and cross my fingers that it works as expected.
Surge tank fully plumbed up
As I am still waiting on some wiring components, I decided it was time to check off one of the other upgrades for the season. An AiM Solo 2 DL lap timer. This AiM not only gives lap times, but it can also connect to a vehicles CAN BUS to get data off the car as well, which will be very useful while analyzing data. This meant that I had to build an adapter harness from the ECU to the AiM. Thankfully, there was already a thread on S2Ki that explained in detail how to do this, and what was required. I followed that guide, wired everything up, and was ready to go into the ECU settings to enable a CAN BUS output.
Photo of the harness I made to run from the ECU to the AiM.
At the point of plugging my laptop into the ECU is where I started to run with issues. The Hondata Kpro that this car runs on would connect to my computer, then loose signal. In addition, it would not populate the tune that was currently on the car, and it would not let me upload the identical tune which the previous owner gave me. I spent days and days researching this issue, and decided it must be a hardware problem, so I pulled the ECU back out of the car, to give a closer inspection, and I found the issue.
Note the burned up area around the silver sticker on the Hondata daughter board. I have no clue how this happened, or when, but when I looked at pictures I had right before I pulled the ECU out of the car, that daughter board was burned up before I touched it. Bummer.
Anyway, I sent the ECU to Hondata to get fixed. Once it is back I plan on finishing up my AiM configuation, mounting the AiM, and testing my surge tank when I shake the car down before my start of the season.
