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October 28, 2006
Lime Rock - The Line
Every time I make it out to Lime Rock, it takes a session or two to get comfortable, so this will be my cheat sheet to remember for next time. Start out with the 315 35/17 Kumho's at 30 psi rear and 32 psi front. Make sure data logger is turned on. Big bend - I was braking at the imaginary #7 marker last time, and running a late apex. The car is just too heavy to do the double apex line. Downshift to 4th and track out to the rumble strips, and bring it over to the right for a very late apex at the esses. Hug the left side of the track (almost no track out for the left hander), and an aggressive late apex for the right hander onto noname straight. It goes off camber at the kink. There were 3 levels of braking cones set up for the uphill corner. I was braking at 2.5, and sliding the car into the corner. If the car was straightened out early, I could get on the gas sooner, without worrying about the back end coming around as I crest the hill. Hadn't picked out a brake marker for West Bend, and could work on a more aggressive line tracking out to the rumble strips. Downhill corner, hard on the brakes early, to set the car up for accelerating through the apex and keeping the rear tires weighted. Late trail braking made the car want to rotate in the corner, which gets hairy with the cold track and hard tires. This was around 4200 rpm in 4th gear (3.70 rear, 1:1 4th, and 25.5" circumference tires). Next time I need to focus on the line for big bend. It's very easy to become distracted with the dirt around, and be too late turning into the apex. Also must stay towards the outside of the track before turning in, rather than creeping in early.
Posted by Z28tt at 1:10 PM | Comments (0)
Lime Rock Park Time Trials
Morning came quick at 5am, with my alarm going off upstairs, which Zip (the wonder lab) heard, and prompted her to try and snuggle up with Dave downstairs in the Aerobed. We actually left before 6am, fueled up, and got to the track around 7am, registered, and through tech very quickly. Apparently Dave's SLP catback needed 3 tries to pass sound (and my unmuffled-only turbos, boomtubes with deflector passed easily). So much for consistency... My first session the track was very slick. I couldn't put any more than 1/2 power down until the car was perfectly straight, or the back end would swing around. The stock cheapo pads got fade about 5 laps in (my PFC race pads were down to their backing plates, and I didn't want to buy $150 pads for one event, as these single piston brakes are getting tossed in the trash), but that was also on the old Indy brake fluid, not even bled. Shawn gave me his old performance friction pads for the 2nd session, we bled them, and pedal was better. Still soft, but not fading. I was using the imaginary 7 brake marker (they go to 6) for big bend. Winter mod is definitely some big brakes. No question this time. The DL90 data acq box was working great (I think, I haven't analyzed anything yet, other than sector times), and laptimes were around 1:05's to 1:07's. Those old Kumho's really need some heat to start working. I need to throw them out, even though there's plenty of rubber left. 3'rd session in the afternoon the track was much warmer (about 65 in the sun, but 34 in the shade, according to my temp gun in the pits). This time I was able to consistently drive the car at 90-95%, and start working on my line, brake points, etc... Data showed most laptimes in the 1:05's and a single 1:04.
I grabbed tire temps in the pits (which is a little late, but I still wanted to see). The FL, RL, and RR tires were 130-135 degF, and the FR was about 10 degrees off. I wonder what my cornerweights are, and if I should adjust them. Time to put the car on the scales, and square it up. Inside to outside edge on the front tires were around 10 degrees hotter, and 5 degrees on the rear. I also checked the rotor temps, which were 450 on the FL, and 480 on the FR (5-10 minutes after I came in). The back of the pads were 380. Tires were set to 34R and 36F cold, which worked up to 40 (too much possibly).
The time trials finally came around, and we're all grouped in the staging area, inside of the downhill corner when I heard screeching, looked over, and a Scooby or Evo just lost the back end, came around 160 degrees, and with a very loud thud, hit the inside tire wall (and moved it over about a foot!), 100' away from us. The entire drivers side was flattened in about 6", but the 3x tire deep wall with thick rubber barrier did a wonderful job of absorbing the impact at 80ish mph. This put about a 30 minute delay getting the car off the track, and I had a chance to talk with one of the Evo guys. Kyle's running 59's consistently, with only about 300 hp, 2900 lbs (no interior), and lots of suspension work. He's got the Race Technologies AX22 data logger, and we'll exchange files to see where the differences are, and how he makes up all the time. My friend with an '07 Z06 had followed him one session, and noticed he's on the gas hard before the apex, while he has to wait a bit longer before feeding in the power. Once I finally got out for the time trials, I tried to warm the tires up, but the car was just all over the place. I did get to start pushing it, but under braking and turning, I'd just end up sliding it into the corner, so scrubbed off too much speed. 1.08.xx, for 2nd place in the Tuner Over class. I'm a bit dissapointed, as I was running 1:04's 2 years ago with less suspension work and was hoping to improve it, but I think those 5 year old Kumho's seemed to need a good 5 laps to get up to temp. There's always next year, which will have new tires, a rear differential instead of spool, a wing, plexi hatch, side & nose skirts, glass hood, real brakes, and 3x the boost.
After reviewing the data from the Race Technologies DL90, speeds through BigBend were 63 mph, up to 74 before braking for the single left hander, around 55 through the esses, up to 105 on no-name straight, down to 68 for the uphill corner, up to 95 before braking to 72 for west bend, up to 95 down the hill, and braking to 70 for the downhill corner, and hitting 135 on the front straight. The car was accelerating around .35 g's in 4th gear, and decel was .8g's before big bend, and .85 g's before the uphill corner. Cornering g's peaked at 1.35, but 1.10-1.20 is more realistic as an average.
Third Session - 1.1mb
Z28tt Car Setup File- 1kb
Posted by Z28tt at 1:01 PM | Comments (0)
October 25, 2006
Moser 35 Spline Axles
The 9" rear has 35 spline Moser Engineering rear axles, with a 5x4.75" bolt circle. Centerbore at the brake rotor is 2.772" and necks down to 2.758" for the wheel. The torque rating is 9600 ft-lbs per axle.
http://www.moserengineering.com/Pages/axletech.html
They originally came with ARP studs, 2.5" long, M12x1.5 thread, .505 knurl, .484 drilled hole, Moser p/n 8255, $17.50/10. The interference fit is .021"
Replaced with GM late model ARP studs, 2.5" long, M12x1.5 thread, .509 knurl, .315 knurl length, 100-7708, $16/5
ARP Techline recommended a .005 interference fit for steel flanges and .007-.008 for aluminum. Moser had a .021 interference. Corner-carver mustang guys use a 15.5mm (.610) reamer for the .625 knurl and .015 interference fit.
I ended up drilling the hole with a 1/2" stubby, with the hand drill (the belt on the drill press kept slipping). The holes measured .500 to .503, and I gave it a shot (.012 interference based on my measured .512 knurl OD, with the garage calipers). The studs pulled right in, no binding, nice and straight on the drivers side. I did the passenger side with the axle still in the rear end housing, and the studs went just as smoothly.
Posted by Z28tt at 5:37 PM | Comments (0)
October 23, 2006
Getting ready for the EMRA Lime Rock Park time trials
Things to complete before Limerock:
Order & Replace rear wheel studs
Install front single piston caliper brake ducts & racing pads
Wire TPS sensor into data acquisition box
Install camcorder
Fabricate side exhaust baffle
Load truck and trailer (cold weather gear)
Clean windshield
Top off oil
Top off rear end fluid
TIghten dipstick
Wire 300+?!!
Turn up boost?!!
wash/wax?!!
Tap out dent?!!
Posted by Z28tt at 3:52 PM | Comments (0)
October 5, 2006
Sound Testing
This afternoon I drove over to my old place of employment, and we used the nice spectrum analyzer to check the sound level for the upcoming LimeRockPark time trials. From 50' to the side, it's at 75 dBa at idle, and 92.5 at 5000 rpms. From the rear, it's 83 at 2500 and 87 at 5000. Inside I get 95 dBA at 5000. LRP's limit is 83 at 50' and 1000 rpm shy of redline. My next option is to put a deflector plate aiming the exhaust at the ground, to see if that helps. If not, then a muffler, or just short shift it.
Exhaust summary: iron manifolds, turbos, 2.5" downpipes, 3.5" y-pipe, to ovalized tubing, and out the side with a 1.5"x8" boom tube.
I also drove a full tankfull today - 17.1 mpg on the highway at 80 mph (well, whatever 2000 rpms is). Much better than the Durango!
Posted by Z28tt at 7:57 PM | Comments (0)