racing tech questions

[t2000gts]

i've been wondering about these for a while now, and it's about time i figured out wth is going on cuz i need to know for my own car.

1) what effect does tire pressure have?

basically. higher tire pressure all around = bad launch, good top end? lower tire pressure all around = good launch, bad top end? (i'm making these up). and then variations on front/back. and for handling purposes, just oversteer or understeer in a celica.

2) what effect does humidity have?

80% humidity and barometer at 30.26 inches and steady. dew point is 43 F, and temp is 49 F. this would hurt the car? or benefit it? would i be slower or quicker on the same day with a lot less humidity?

3) JEEZ I FORGOT MY QUESTION. @#$%. uh...why does shifting off the rev limiter benefit the automatic GTS? it drops slightly higher (maybe 50-100rpm) on the shift, and picks up speed right after the shift quicker. there's a lot less hesitation on speed that you usually see on manuals shifting normally and automatics shifting slowly. see videos i posted in racing forum.

4) what should pressure in all 4 cylinders on the 2ZZ-GE be? i wanna get a compression check done. 20,000 miles.

5) would 0w30 synthetic oil give or take some hp (obviously not noticeable, but still)? which oil gives or takes hp in what weather?

THANK YOU FOR ANY AND ALL REPLIES. GOD BLESS AMERICA AND NEWCELICA.ORG.

[t2000gts]

also

when car is cold and turned on. the steering is loose and easy. still responds the same (i.e, turning it this much still gets the wheels to turn that much but it turns easier). as it warms up, the steering gets stiffer. when it's warmed up or hot, it's sometimes annoying how stiff it is. i have to put effort to keep it steady in a sweeping turn. especially if i have one hand on the wheel. i don't want either, but somewhere in the middle. is this possible?

link to post with videos: http://www.newcelica.org/forums/showthread.php?s=&threadid=3348

[scapamouche]

I can only answer a couple of your questions, others will take care of the rest, I'm sure.

1. For autox, you want the lowest pressure in the tires that doesn't allow them to roll over. Try using some white shoe polish on the edges of the sidewalls by the tread, then go on a run. If the polish on the sidewalls is scraped off near the edge of the tread, you have too little pressure for your tires. Raise the pressure in small steps until no rollover is seen. Try the opposite if you have no wear until it appears, them raise pressure till it's gone.

1a. Changing pressures front to rear DOES affect handling. Raise front or lower rear pressure to increase oversteer (decrease understeer,) and vice versa. I usually run 45# in front and 28-30# in back when I'm on strteet tires. I've also got extensive suspension mods, too- Teins, Front and rear Strut Braces, front underbrace, rear underbrace and swaybars on the way.

1b. The tire pressure advice above is for STREET TIRES!! I'm no expert in race tires (I know R-1s, Hoosiers and Kumhos all like DIFFERENT tire setups.) ASk someone else. Autxr???

2,3,4. I dunno.

5. In theory, lighter oils take up less power in parasitic losses, but you're right, itis pretty negligible. If it was me, I'd use the same 5w30 in synthetic as I would mineral. Again, I'm no expert.
I can tell you that 20w50 doesn't work too well in a Wisconsin winter- try changing the oil at 20F outside!!! It took me 2.5 HOURS to change the oil in my Nova!! Don't do that!!

[Unity112]

A few things to add. Are you asking about settings for autox, or drag. You mention launching so I assume you are talking about drag racing. For autoxing scapamouche is pretty much on the dot.

1. For drag applications, you want lower tire pressures in the front, and higher pressures in the back. Lower pressures give the sidewall a little more room to deform, therfore giving better grip on a launch. For an autox application, youd want higher pressures in the front, and less in the rear. This, as scapamouche mentioned will help decrease roll over and increase oversteer to an extent. Road Racing, youd still want a little more pressure in the front, but not as drastic as an autox setting, because higher speeds may have different effects on the tire.

2. Humidity is a killer for any car. Too much humidity will hurt performance. I can't explain technacally, but yes humidity will affect performance. Just as 100 degree temperatures affect performance.

3. (dont have an auto)

4. Not sure, I don't have any info on that yet.

5. 0w10 is primarily used in race engines. It gives hp, but doesn't have enough detergents in it for extended use in a daily driven motor. Not entirely sure if this is entirely correct, but it does shorten motor life. Not too sure about the effect of 0w30 though.

[RexPokinghorn]

#4 compression tests should be based on a scale of 100%

You'll want to be as close to perfect compression (100%) as you can be. I'd say 90% and lower is cause for worry.

[t2000gts]

thanks guys! i knew you people in this forum would be able to answer most of 'em :D

one more about tire pressures tho. i launch at 2000rpm (powerbrake) and usually bog. wheelspin almost NEVER happens. i take it wheelspin in this case, if i can achieve it, would be good? what would be best tire pressure setup?

i have two videos of wheelspin issues:

with Injen CAI/TRD Exhaust, bogging at 2000rpm:
http://subzero.mine.nu/celica/autoGTS_cai-trd_ex_qrtr.avi (5.5MB)

with stock airbox + K&N filter, stock exhaust, getting a launch that i can only dream of nowadays:
http://subzero.mine.nu/celica/autoGTS_0-60.avi (7.7MB)

to view both, you need DivX installed, if you don't already have it:
http://subzero.mine.nu/celica/divx_31alpha.exe (569KB) (be sure to run 'Run Me First' seperately after running this prog! it won't install until you do!)