Can somebody explain this?

Ok here's the deal.. Last Weds I went to the track and this Weds I went to the track.. Here are my 2 closest times, actually identical, one from last week, one from this week. My best time was 14.22 from last week

Last week: (all 1/8's between 78.00-78.19 in 4 runs)
60' = 2.310
330=6.174
1/8 = 9.336@78.19<---
1/4 = 14.304@100.22

This week: (all 1/8's between 79.03-79.28 in 5 runs)
60' = 2.257
330=6.158
1/8 = 9.330@79.08 <---
1/4 = 14.304@99.00

My highest trap today was 99.92, last week was 100.81

All night my 1/8's were 1 mph faster but my 1/4 trap was on average 1 mph slower! Here are the diffrences in conditions.. Humidity was 85% last week was dry. Last week had just under 1/2 tank of gas this week I had just under 1/4 and removed spare (lots of wheelhop today, probably from the weight loss of gas and spare). Temp was about the same at 45. Last week raced on 32 psi, this week 28 psi. Track conditions overall were a bit slicker than last week.

Anybody have any idea why my mph was 1 mph lower in the 1/4 trap when my 1/8 was 1 mph higher? My guess would be the lower air pressure combined with increased humidity, but it still don't make sense to me..


BTW- for the guy who wanted to know what my friend's Celica GTS ran today with all those mods his best run was 15.1@94.2 with a bad 60' of 2.44.. Not to shabby, should be into the 14's with a proper launch

 

you're saying this week 85% humidity? than from what i see you got better short times this week which resluteed in better 1/8th and the 60" will help your mph there too...but because of the humidity your car ran out of air on the top end ...looks good to me between the two times you showed and the condition change...so what im saying is had you pulled a 2.2 last week you might have gotten a 80mph 1/8th

 

I just checked the weather, 85% humidity vs 44% last week.. Also my wheel hop was nearly rediculas, 1/5th a tank of gas and no spare tire is a no no.. This Saterday is import wars, i'll be hoping to be closer to the 14.0 range..

 

Looks like the weather conditions played a part in the mph for you at the end...and the wheel is probably attributed to a little better traction with the lower tire pressure...you did get better short times...what where your launch rpm's this time vs. last time?

 

My 60' times this week were .257 with no wheel hop, 2.31 a little bit of hop, 2.35 a little bit of hop, and 1 horrible 2.47 in which I got loads of wheel hop where i had to cut power to stop it, very possible I slipped clutch out too fast. All launched between 2200 and 2400 same as last week but this week I didn't baby the gas out the gate as much as last week. Last week no wheel hop at all and I managed a best 60' of 2.24 (the rest were 2.30x) with 32 psi with a similar launch technique, both days were a cold and windy 45ish. My best 1/4 time for last night was 14.304 and best mph was 99.92.

I think next time I go I will keep out the spare and keep my psi at 32ish.. So wheel hop is actually increased when your pressure is lower huh? I think if last night was not so humid with my 1/8's I would of ran very close to 14.0?

One last note, one of my runs I tried shifting at 6100-6200 at torque peak and it ended in my worse run ever by about .2 seconds at 14.475@98.66

 

With less pressure the more your tires will bite into the surface and with IRS you tend to have more problems with wheel hop...or so I have heard...I have never ran a car with IRS down the track only with solid rear ends. I think that you will have to play with tire pressures and launch rpm's a bit...I know for my car I installed LCA's to cure the little wheel hop that I was getting...

 

Another little trick you might try is, if you're going to lower tire pressure in the rear tires, pump up the fronts 7-10psi more than normal. That may increase your mph slightly.

Good runs, you'll hit 13's with a better launch.

Chris

 

Thanks for the tip, my front tires were reading 32 on my pressure sensor and my rears were 28 when i was racing.. My front tires should of at least been at 35. Next time I'll put the fronts to 38-40 and the back 30ish.. That should help, also if the weather is nicer it will help, the tires on the Z suck in cold weather and its been 40-45 degrees on my track days.

 

No problem


There's always a give and take situation with hot and cold weather. The car will run stronger in the cold, but it will hook up better in the warmer weather. What you want ideally is cool weather at a track that has great prep. Every track is different though. I've been to tracks before that simply suck ... I can hook up better on the street. Then again I've been to tracks that are so sticky I almost have trouble launching without bogging the car because it hooks so well. A track like that on a cool day is what you want.

Good luck!

Chris