One of the things I’ve learned from endurance racing is that the best way to improve the performance of a car is to swap or boost the engine. Ha! Well, if you look at the most successful teams, that’s what they’re doing. Well, not me. My car is 100% emissions-legal in California and will remain that way (so I can park it on the street, flat tow it, and drive it to work when my other car has issues). So if I’m not touching the engine, what can I do?
- Reduce weight
- Increase grip
- Improve aerodynamics
In the last few weeks, I’ve removed over 200 lbs from the car. I’ve also added a few things. Let’s take a close look at the changes.
- -104 lbs doors. Original doors weigh 72 lbs. I bought doors at Pick-n-Pull and gutted the shit out of them. They are now 20 lbs each.
- -38.5 lbs passenger seat, bracket, and harnesses. Not necessary for endurance racing.
- -29 lbs battery. I replaced the 34 lb lead-acid batter with a 660 CCA lithium-ion unit that weighs 5 lbs.
- -? side windows. The original windows have been replaced by white plastic. Not sure what the difference is exactly.
- -12.5 lbs carpets. It’s a lot louder in the cabin now.
- -12 lbs tow hitch. I keep a tow hitch on the car for carrying extra tires, but since I’ve got a support vehicle for this race, I don’t need it.
- -9 lbs rear seat frame. I used to mount the fire extinguisher and cold box on the rear seat frame. The fire bottle is now mounted to the floor, which is lower and lighter. The cold box is similarly mounted to the floor.
- -6 lbs rubber gaskets. The hatchback had a lot of unnecessary rubber. I don’t need to be weatherproof.
- -4 lbs night racing lights. No reason to carry 4 extra lights for a daytime race.
- +X lbs cold box. The previous cold box was a cold therapy unit I got on eBay. This one is much larger so that it will remain cold during long endurance stints.
215 without taking into account side windows or cold box.
How much faster is the car minus 200 lbs? Optimum Lap (see previous post) says only about 1 second over 3 miles. But it also reduces fuel consumption by 2%.
I also had a plan to remove the rear hatch, which weighs in at 39 lbs. That’s not a lot but it seems unnecessary. So what happens when you remove it? Does it negatively affect drag? Well, I decided to test that the old-fashioned way: yarn. The hatch comes off pretty easily, just 8 bolts. Decorating the car with yarn took a while longer. After I was done, I went for a test drive with a video camera mounted to a pipe sticking out the back of the car. What I observed was the dreaded station wagon effect. Back in the 1960s and 1970s, station wagons had rear windows that rolled down. Unfortunately, the low pressure zone at the rear of the vehicle caused exhaust fumes to swirl into the cabin, causing carbon monoxide poisoning. Clearly, 39 lbs isn’t worth carbon monoxide poisoning! Eventually, wagons were installed with wind deflectors that redirected the air spilling off the roof to go down the back of the car. While this solves the carbon monoxide problem, it also generates both drag and lift.
My next thought was to make the back of the car a bit higher. In addition to purchasing extra doors at Pick-n-Pull, I had also bought an extra hatchback. I cut the top half off and gutted it. Since it was now a lightweight metal skin, I mounted it with a few strategically-placed zip ties. More yarn and another test drive later showed that the station wagon effect persisted. The half-hatch isn’t enough to block the back draft. And why should it be? I’ve just re-created the rear of a 1970s station wagon.
My next thought was to make a lightweight hatch with the half hatch and a sheet of plexiglass instead of glass. I decided that before I did that big job I would do a smaller job: replace the side glass windows with plexiglass. To remove the side windows, I used a guitar string garrotte. I was able to remove the window without breaking it, which meant I could used it as a template for cutting the plastic. Although I cut the plastic without any problems, it cracked when I drilled it. Grrr. After experiencing how fragile and persnickety plexiglass is, I said “fuck the lightweight hatch” and put the stock one back on. I also decided I would replace the glass windows with opaque plastic rather than clear plexiglass. Not every project is successful.
I’ve run a lot of tires on the Yaris from Hoosiers to Douglas. In endurance races, I often opt for a medium tire that has decent grip and wear. But for this race, I want to have the stickiest rubber possible. Most people will tell you that the cheater 200 TW tires are Bridgestone RE-71R and BFG Rival S. The other tire that’s just as fast is the Federal 595 RS-RR. Not a lot of people run the RS-RR but I have in the past and it was within a couple tenths of the RE-71R at Laguna Seca. But it’s a lot less expensive. In order to get as much grip as possible, we are going wider on the rim, from 7″ to 9″ and tire from 205 to 225. Hopefully that extra width will mean the tires don’t overheat as sometimes happens. On the rears, we’ll go with 205/50/15 RT615K+ or RE-71R on 15×7 rims.
How much more grip will we get with wider tires? I have absolutely no idea, but let’s say it’s 2.5%. So 1.025g grip instead of 1.0. That results in another second.
In the right context, there’s a lot to be gained with aero modifications as they can reduce drag and increase downforce. Unfortunately, it’s not that easy to measure. By most accounts, an air dam is a good thing as it both reduces drag and increases downforce. So I made an air dam using some plastic made for edging a garden. I don’t really know what values to put into Optimum Lap to determine the theoretical benefit. It could gain us 1 second. Or less. Or more. The only way to know is to test. Thankfully, there is a test day before the Lemons race.
10 thoughts on “Winning B Class: part 3, performance modifications”
Hey, you racing this weekend? I’ll see you there! Also, dry dremelling holes in the plex. Or get a “plastic” bit. The sharp edge on most bits cause the cracking…
Yes, racing this weekend. See you there. Thanks for the tip on the plexiglass. I still have some, so I may try that.
I hope you mean lexan, not plexiglass.
As far as I know, plexiglass is not acceptable in any racing series.
For side windows?
Yep. Plexiglass shatters and leaves sharp fragments.
Lexan does not do that.
ChampCar specifically mentions that Plexiglass IS ALLOWED for rear windows (9.3.2) and even part of the side window (220.127.116.11). Neither Lucky Dog nor Lemons has any wording about Plexiglass for side windows. They only talk about front windows. WRL and AER have blanket statements about replacement of glass with Lexan/polycarbonate only.
This surprises me. Perhaps it’s fallout from the great lexan wars in chumpcar’s past.
Aero, if you’re data logging, coast down on front straight? Or road leading to track? We had a wing on the MR2 that decomposed during one of my stunts that added som much drag I dropped 2-300rpm at end of front straight.
If I was only concerned with drag, then some kind of coast down would be appropriate, but there’s also downforce to consider. I’m going to be looking at the top speed on the main straight as well as the corner speed in T2.
Have you noticed how many Lemons cars are sporting splitters and big wings? What happened to cars with stuffed animals hanging out of them?
If you remember the Z600 hamster we had a huge double wing in back and a big splitter in front and it absolutely made a difference at Buttonwillow carousel and T-hill T1 and a couple others. Seemed really stable confidence-inspiring.
The Metro-gnome also had big aero and Alex had it set up to oversteer when slow and understeer w/ fast w/ the aero. Heard it worked,