Underdrive

I ran across a neat modification that wasn't too expensive: Underdrive pulleys. When I first saw the name it looked uninspiring. "Under" sounds like less. However just like with weight, when it comes to engine drag, less is more.

When your engine runs it turns the wheels to move the car. That much everyone knows. It's easy to forget that the engine turns a bunch of other things, the alternator, the water pump, the AC among them. Each of those things takes a certain amount of energy that would otherwise be available for turning the wheels and making you go fast. These accessories are turned by a pulley on the serpentine belt, and the size of the pulley for the alternator determines how fast the alternator spins. (of course for a race car, one simply removes the AC all together...)

Spinning these accessories faster of course takes more energy, and slower takes less. This is how an "underdrive" pulley helps. It spins the accessory somewhat slower leaving more energy for the wheels. This also reduces the wear on the accessory somewhat. It also makes the car slightly easier to start, and reduces engine drag on lift.

So why didn't it come like that from the factory? Because factory cars are optimized for street driving at lower RPMs, whereas race cars spend most of their time at high RPM. Since accessories such as alternators and water-pumps are needed to cool the engine there is a limit to how slow you can go. Additionally to spin slower you need to increase the size of the pulley. At some point pulleys would start touching (and that would be BAD), so that's another limit.

I got my new pulleys from Monkey Wrench Racing, and they claim that it's worth about 3whp on a celica that makes 158 peak wheel horse power, which is just a tad less than most Elise's make with the same engine. A stock Elise makes around 162whp. My engine tune from charlie-x adds 8bhp which is around 6-7whp, and this pulley should give me another 3whp... so that should put me in an (unverified) range of about 170-172whp. My muffler and air in take might possibly add a little more, but most folks say the CAI doesn't do anything for power, and muffler changes don't have much effect until you improve the catalytic converter, which is the limiting factor for the system.

What's 3whp worth? Not a whole lot, but the pulleys were only 70 bucks each. I'll probably gain around 0.010 to 0.020 seconds on a 60 second course... but I've lost places by as little as 0.001, so I'll take it. Every little bit helps. Many days 0.02 is enough to move up one place in the pax standings.

Ups and Downs

I've been busy... The first two events were polar opposites. In the first event of the Season I raced well. Very well. I had the best result ever, which made me feel real good about the work I put into the car. The extended splitter allowed me to raise the wing back up 48.5" and the car still drove well.

I will admit one small bit of luck though. It was a cold day and I got a re-run for my last run of the day. The extra heat in the tires may have helped, but since I dropped over 1.5 seconds it probably wasn't all tire heat either. The net result was I beat the entire field and took home another first place trophy. Second season in a row I've had a first place start. I also paxed 33rd in a field of 152 cars... with SSM pax!. SS pax would have put me at 16th. (it's unclear whether or not wing+splitter > than LSD, I may exceed an SS car by now, but probably not by much so perhaps a realistic estimate is probably still above 20th place).

The second race started well. I got a re-run on my first run and I laid in a time that was fastest in the class and briefly the fastest time with doors (i.e ignoring the formula and open wheel cars). But after that I found ways to make one mistake after another, and I never improved on my time. My final run started out good, and I believe I was faster through the first sweeper than ever before, and the slalom was smoother than previous. I got to the next element with more speed than ever before... I was somewhat surprised when the car actually made the turn into the next element without difficulty and that surprise caused me to stop looking ahead. I turned too tightly on the next element rather than powering through and then realized I'd taken the wrong line. The brief moment it took for that regret to cross my mind delayed my breaking point by a few 10ths of a second and I entered the tight slalom way too fast... and I chose to go of course since even if I saved it I would have been nearly sideways and terribly slow or even spun.

Back to my old tricks of loosing my focus when something unexpected happens... (in this case the car behaved better than I expected). The net result was that on his final run David finally pulled ahead by 0.020 seconds knocking me out of the trophies and into 4th place (of 9 cars). We won't talk about my pax standings, but it will suffice to say that I was on par with some of my worst days last year. Although my fastest time once again followed a re-run I don't think I can blame cold tires this time. I know I made plenty of mistakes.

As I alluded to on in the previous post, I did some weight reduction and rules compliance work over the winter. The wing bracing interfered with the ability to inspect the battery and still retain the stock battery cover, so I moved the battery to sit on the chassis just behind the firewall on the driver's side. Hopefully it won't get wet and short in the first rain event!

Items Removed:

Harness bar
Harness
Rear speakers
Excess Battery Wire
Misc battery stuff
70% of S111 battery bracket
Unused battery Bracket
AC Compressor
AC Condensor
Some AC piping that was easy to reach
2lbs of Freon
Sunvisors
Rear view mirrors

Lightness added: AC stuff: 17.4 lbs, Harness and bar, 15.4 lbs, Battery stuff 1 lb, visors & mirror 1.5 lbs, Rear speakers 2.1 lbs... TOTAL: 37.4 lbs

Moved Forward:

Battery 6lbs, 2 ft forward, 8 inches down.
S111 switch (3oz?) 3 ft forward, 1ft up.

Added:

15" battery cable
Copper Battery lug
Aluminum plate speaker hole cover
Foam speaker hole cover
Aluminum battery Bracket.
Cable ties.
OEM Battery Cover.

Weight added, ~2lbs

Net Lightness: ~35 lbs, enough to compensate for the too-heavy wing I added last season (although the wing weighs less, it is also higher up on the car than anything else).

Present race weight (estimate): 1870 lbs

Minimum street weight with no wing, no tow bar, and 1/3 tank of gas: 1845 lbs