If you’re looking for:
Part 1: The Rebuild, go here.
Part 2: The Wrap, go here.
Part 3: More Goodies, go here.
Part 4: Aero, go here.
Part 5: Cooling, go here.
Part 6: Fuel & Oil Control, go here.
Part 7: Clutch, Trans, Misc., go here.
Part 8: Roll Cage, go here.
Part 9: Brakes, go here.
Part 10: K24 Swap 1, go here.
Part 10: K24 Swap 2, go here.
Part 10: K24 Swap 3, go here.
Follow Up
In Part 8, we were waiting on a driver net before we could have the tech inspection done. The Schroth net with the new quick release mechanism that we originally ordered was still undergoing testing and its availability was severely delayed. So, we went with a equally good option- Safecraft.
The day after we installed the net, we were able to get an authorized NASA tech inspector to come to the shop and check our work to give it the official “pass.” If you’re planning to have your car inspected, it helps to find the checklist that they will be using so you can make sure you don’t miss anything. Below is the form that NASA uses.
Dyno
The next step was to put the car on a dyno to see how much power it makes. NASA’s Super Touring series is a horsepower to weight class. Super Touring 4 (ST4) must have an adjusted weight/horsepower ratio of 12:1 or higher. We took the car down to our friends at Blacktrax Performance and had a baseline done on their Dynapak dyno. The car made less power than we were expecting, but that was a good thing given the current weight of the car. 202hp/145tq.
To calculate the average horsepower, you will need to ask for the 50RPM data export so that you can get the following data points:
Horsepower at: 250 rpm, 500 rpm, 750 rpm, 1000 rpm, 1250 rpm, 1500 rpm, 1750 rpm, and 2000 rpm GREATER than Max HP rpm.
Horsepower at: 250 rpm, 500 rpm, 750 rpm, 1000 rpm, 1250 rpm, 1500 rpm, 1750 rpm, and 2000 rpm LESS than Max HP rpm.
There are different ways to calculate this based on the engine’s max RPM, but for forced induction engines specifically, they ask to calculate the average horsepower by dividing the max HP plus the sum of the three highest data points by 4.
For us, the average came out to 196 HP. At a weight of 2,200lbs, our power to weight is 11.2:1, which means the car would be classed as an ST3 car. However, there are still some adjustments that need to be considered. There are a list of modification factors that will either add or subtract from the ratio. For us, the following applies:
Vehicle weight less than 2600lbs: -0.2
DOT tires with a section width of less than 266mm: +0.6
Total adjustment: +0.4
These adjustments bring our power to weight to 11.6:1, which is still under by 0.4. We can either add 75lbs of ballast to the car, reduce the average horsepower, or take advantage of another modification factor. Luckily, cars using the Toyo RR tires get a +0.6 point advantage, which is exactly what we need!
Food for thought: Our average horsepower is taken between 7,450-8,200 RPM. Increasing the area under the dyno curve before 7,450 RPM would not be calculated in our average horsepower. Increasing mid-range power might be an area worth improving.
Anyway, we decided to change over to the Toyos, but it wouldn’t be as easy as just replacing the Hankooks that are already on the car.
The Quest for 0.6 points
Tires
The Toyo RRs only come in a few sizes that would make sense for the 111R platform, but none will work with the 16/17” wheel stagger that is currently on the car. We will have to consider the overall diameter, since we’ve noticed in the past that the ABS doesn’t like the front and rear diameters to be too different from each other. The sizes that made the most sense to us were 225/45/15 and 245/40/17.
Brakes
The next obstacle we were faced with is the 15” wheel fitting over the larger “Cup Brakes” that the S240 comes with. We’ve tried a few different 15” wheels that would fit, but they would require a 15-20mm spacer. The best thing to do would be to downsize the front rotors from the Cup 308mm to the Standard 288mm. Instead of putting the standard AP CP5119 2-pot calipers on, we went with the AP Pro 5000R calipers, which maintains a similar brake pad friction surface area as our original “Cup Brakes”. Paired with 2-piece rotors, we saved about 5 lbs per side! We may need to recalculate our power to weight when we’re through with the brakes.
It’s well known that these cars have too much front brake bias, so to help balance that, we will be replacing the rear floating calipers for the standard front 2-pot calipers. This is a common and easy mod as it only requires a radial mount bracket that will allow them to bolt right to the factory upright. If you have an Elise/Exige and plan to do this, keep in mind that one piece rotors are usually the same front and rear, but there is a difference for two piece rotors. To maximize weight savings, they will usually have a larger hat and smaller ring in the rear, since the stock rear pad profile is smaller for the front. If you have two piece rotors, we will need FRONT ones to match with these calipers. The 2-pot calipers are about 7lbs lighter in total and will remove some slop that the original floating calipers have. If you want to maintain a hand brake, you will need to leave the floating calipers attached or replaced it a dedicated hand brake caliper.
Wheels
The wheel choice is still undecided, but the original wheels were sold, so the car temporarily sits on a set of borrowed white TE37s.
If you’re looking for:
Part 1: The Rebuild, go here.
Part 2: The Wrap, go here.
Part 3: More Goodies, go here.
Part 4: Aero, go here.
Part 5: Cooling, go here.
Part 6: Fuel & Oil Control, go here.
Part 7: Clutch, Trans, Misc., go here.
Part 8: Roll Cage, go here.
Part 9: Brakes, go here.
Part 10: K24 Swap 1, go here.
Part 10: K24 Swap 2, go here.
Part 10: K24 Swap 3, go here.