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

Lip Service

Xmas is over, and I've begun my winter mods. Starting with the cheap and relatively easy stuff, I made the car 2 inches longer by moving the splitter forward. Previously it stuck out a measely 2.5 inches and had only been applied for the purpose of protecting my clam shell from cones.  It did a fair job of that, allowing a couple cracks but fending off major damage.

From an aerodynamic perspective, the splitter was far from optimized. Air was leaking between it and the car and the front edge protruded significantly less than allowed by the rules. Furthermore I've been running with the license plate attached across the struts supporting the front. Both that and the air leak interfere with the creation of a pool of high pressure air in front of the car which is what creates the down force.  The new configuration should be a tad more protective in addition to providing more front down force.

I also added some foam to keep the air from flowing between the car and the splitter.

The paperclip corners required an extension...

And for those of you wondering about my mounting system, the basic idea was to not attach it to the (fragile & expensive) fiberglass clam shell. Instead I used Aluminum angle to bracket it onto hardpoints.

And the front is connected to the tow hook hard point.

So with an additional 2" of down force perhaps I can return to using my wing at full height and not get significant under-steer. With the corners already poking past the base of the car I've pushed this splitter as far forward as possible, so if I need to go out to the full 6" allowed by the rules, I'll probably be making my own out of plywood...

Mods For 2013

Winter is upon us, at least from a racing perspective, and soon from a seasonal perspective. The lotus is parked safely in the garage, with a tank full of stabilized gasoline. The daily driver has swapped on it's snow tires, the 7year old oem battery is replaced, and new wipers/fluid. Oil for both our cars, and snow tires swap for her car, and then some where after Christmas, I can begin tinkering, and prepping for next year.

Here's the list of things I do plan to do for sure this winter, all of them relatively small:

• Delete the rear speakers (weight saving)
• Shift the splitter an inch or two forward (more downforce, but more likely to scrape)
• Need longer bolt to extend splitter bracing, not sure how far forward the bolt can handle, or how long a bolt I can find that fits.
• Relocate the battery to behind the driver seat (weight forward, convenience, compliance)
• The braile B106 is AGM, and so this is allowed as long as I can bolt a bracket to the chasis (per rule 3.3.3.B.17), and I locate it behind the rearmost seat per 14.9.A this should be legal, and allow me to leave the trunk lid closed for all but inspection and most importantly allow me to leave the original battery cover in to avoid weenie protests that removing the < 1 lb. plastic cover constitutes "stripping the trunk" (prohibited by omission until X Prepared class). If I put the cover in I need to unbolt the wing support to take it out for inspection of the battery mounting. This also means I don't need to open the trunk to turn the battery disconnect.
• Rear Motor Mount replacement (less motor movement, more power to wheels)
• In May 2013 New Hoosiers 
• The current ones are > 100 runs now, by may they should be around 150 or so)
• It's not safe to order hoosiers before may due to the risk of freezing during shipping, so probably first 2-3 races of 2013 will be on old Ho-Ho's 

Here are the things I'd like to do this winter:

• Pull the transmission, ship it to AZ and have Blackwatch Racing install an OS Giken limited slip differential (LSD) 
• They have tuned this LSD specifically for the lotus Auto-X platform. My car will NEVER be a real contender as an SSM car without this or a super charger.  
• While the Tranny is out, replace the flywheel with a lightweight version made by Blackwatch Racing
• Replace the Clutch with a lighter, stronger version from ACT (the HDG4 kit

And there's some maybe mods:

• The re-ENFORCER from sector111 (improve shift feel)
• I haven't figured out if it's legal to add this shifter mount mod. Is the mounting for the shift lever part of the "Shift Linkage" as and therefore permitted as per 14.10.G and 15.10.Q? This may require clarification... But it's not really important. It's supposed to make the shifting feel a bit more positive and a bit less wishy-washy (many things are good about the Elise, but the shifter feel isn't one of them).
• AC compressor delete (weight savings)
• Removing the AC compressor will save around 11 lbs. I rarely if ever use the AC anyway, except when I'm trying to get the engine to warm up to full temp, and then sometimes I forget to turn it off, which is not so good. I'm fairly likely to do this one.
• AC condenser delete (weight savings) 
• Another 11 lbs reportedly to be had here, but it requires removing the front clam shell. Probably won't do this if I do the tranny, because both will take a lot of time and the weight in the front may not be a bad thing for front/rear weight distribution anyway. On the other hand, this, the compressor and the speaker delete will likely pay for the weight of the wing... maybe I just move the splitter all the way forward :).

The transmission work will depend heavily on how much it costs to put a new roof on the house. That comes first, and so those may get punted to the 2014 list... Meanwhile, I'm going to try to work bunches of billable hours and see how it goes...