ET and MPH Issues

Discussion in 'Drag Racing Tech Discussion & Timeslips' started by TheDarkPath, Sep 9, 2019.

  1. TheDarkPath

    TheDarkPath forum member

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    Hello everyone,
    I went to the track Friday night (HRP in Baytown, TX) and was able to make 7 runs throughout the evening and night. It had been about 7 years since running the car so I had a lot of rust to knock off myself but my first pass in ~96 degree heat was a 12.306 @ 107.15. That was the fastest pass ever in my car (previously a 12.39 @ 108). As the temps dropped over the evening down to ~86 degrees, I was hoping my times would improve at least slightly. Instead, they worsened netting a best of 12.46 @ 105.5 after that first pass. I was under 1/8 tank of gas as the night drew on and I thought maybe due to being low on fuel, there was some fuel slosh going on and my car was leaning out or something on launch and during the pass so I filled back up to 1/4 tank but the higher ETs and lower MPH continued with a last pass of 12.47 @ 105.5.

    Unfortunately, I didn't have anything with me to data log. The car hasn't seen a lot of miles in the last few years so I am thinking maybe I had some old/dirty fuel down at the bottom of the tank (was a fairly fresh topped off tank of fuel in the last few weeks but hadn't been under 1/8 of a tank in a long time) and may have dirtied the fuel filter. I am going to do a once over on everything, change fuel filter, clean air filter (K&N style on C&L Street CAI), and I now have a laptop setup to data log. Is there anything else I should check? The spark plugs have less than 3000 miles on them.

    [EDIT] What specific items should I make sure to enable for data logging?

    60' time on first (best) pass: 1.690
    60' time on 12.46 pass: 1.721
    60' time on 12.47 pass: 1.732

    I have MT ET Street Radials on 15x8 Racestar wheels in the back, 15x4 Racestars i the front and felt like I was launching well.

    First Pass:
    Last Pass:
     
    Last edited: Sep 9, 2019
  2. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
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    Perhaps the engine was getting increasingly heat soaked over the course of the evening.
    What mods do you have, and what's your race weight?
     
  3. TheDarkPath

    TheDarkPath forum member

    187
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    I thought about heat some but I was getting the car pretty well cooled down in between passes (upper intake, intake pipe, and heads all cool to touch).

    Race weight with me in it was 3380 lbs.

    Mods are: UDP, BMR (Swaybar del, LCA, adj. UCA, adj. PH bar, springs, A Arms), Tokico D-Specs, C&L Street CAI, 4.10 gears, Race Star wheels, Pypes Offroad H, Spydershaft, Circle D 3600 stall, and a Dyno tune that made 300 rwhp / 318 rwtq.
     
  4. fdjizm

    fdjizm Drag Queen

    19,179
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    Was it gaining less over time from 1/8 mph to 1/4 mph?

    I usually subtract the numbers to see if there is any actual loss in power or just the weather.

    I usually pick up between 25 and 26mph from the 1/8 to the 1/4.
     
  5. TheDarkPath

    TheDarkPath forum member

    187
    3
    My previous best in great weather but with a damaged o2 sensor (found out later), I gained 21.81 mph between 1/8 and 1/4 (86.89 vs 108.7).

    Best pass Friday night, I gained 19.4 mph between 1/8 and 1/4 (87.75 vs 107.15).

    Last pass Friday night in cooler air than first, I gained 18.9 mph between 1/8 and 1/4 (86.68 vs 105.58). Lost over 1 mph in the 1/8 vs first pass.
     
  6. TheDarkPath

    TheDarkPath forum member

    187
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    Here are my slips IMG_20190907_012843.jpg
     
  7. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
    56
    714
    91
    You could have been running into a headwind.
     
  8. fdjizm

    fdjizm Drag Queen

    19,179
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    Your 60 ft was the best on the first run, would explain being slower on all the following runs. 60ft is where it all happens. I don't see much wrong with the slips here.

    Maybe your car was just really feeling life on that first pass lol
    BTW, not good to go much under a 1/4 tank while racing, you can starve the engine if it's low enough.
     
  9. TheDarkPath

    TheDarkPath forum member

    187
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    I have typically run a hight ET and higher MPH when spinning slightly off the line if I recall but I guess I just saw more of a drop than expected with better air from first to last run and got worried.

    As far as the fuel level, yeah, I will be sure to have slightly above 1/4 tank next time. Will also be setup to data log just in case.
     
  10. jam07GT

    jam07GT forum member

    59
    0
    [QUOTE="T

    Race weight with me in it was 3380 lbs.

    .[/QUOTE]

    Just wondering, have you done anything else to lighten you car besides the race stars/skinnies, sway bar delete, driveshaft, and a-arms?
     
  11. TheDarkPath

    TheDarkPath forum member

    187
    3
    Just wondering, have you done anything else to lighten you car besides the race stars/skinnies, sway bar delete, driveshaft, and a-arms?[/QUOTE]

    For weight reduction, the off-road H pipe saves quite a few lbs. For track days, I empty the trunk and remove the passenger seat. I also have a rear seat delete and removed the belts and buckles. I also weigh about 130 so that helps.
     
  12. TheDarkPath

    TheDarkPath forum member

    187
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    As an update here, there is definitely something up with the car. The transmission started slipping into neutral randomly when I would come to a stop at times. Giving throttle would get back into 1st gear. Found out the transmission was 2 quarts low on oil. Fluid wasn't burnt looking or smelling. Cycled some oils in and out eventually removing about 3 quarts and adding 5 new quarts. No more issues since with it dropping into neutral.

    With it feeling better, I went back to the track last night and in perfect, mineshaft air, it ran even worse than in 92 degree heat. 1.70 60', 1/4 ET was 12.43, MPH 106.25. After a long cool down, followed it up with a 1.71 60' and 12.57 @ 105.22.

    I data logged the second pass. I noticed a shudder in 4th gear at the top of the track. Data log showed transmission slipping all the way down the track until mid-4th gear where it locked up and caused RPM to drop by about 300. That was the shudder I felt. Comparing slips with past runs, last night in perfect air, I lost time and MPH at every step, 60' to 330 to 1/8 to 1000' to 1/4.
     
  13. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
    56
    714
    91
    Your 60' (1.7), 1/8 mile ET (7.9), 1/8 mile trap speed (87), and 1/4 mile ET (12.4) are right where they should be. The issue is the low 1/4 mile trap speed (106 instead of 109). This suggests that your tranny is slipping after it's shifted into 4th gear 'cause you're only gaining 19mph in the second 1/8 mile.
     
  14. TheDarkPath

    TheDarkPath forum member

    187
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    Here are some of my historical passes. First one was in 2012. Didn't race for 7 years. Next 3 were on a hot night in September (90 degree air). Last 2 were Friday night in perfect air.

    Screenshot_20191103-125402.png
     
  15. Dino Dino Bambino

    Dino Dino Bambino I have a red car

    Age:
    56
    714
    91
    Column E in your spreadsheet is exactly where you should be so that proves my point. Something's going wrong once you pass the 1/8 mile mark.
     
  16. TheDarkPath

    TheDarkPath forum member

    187
    3
    I agree with you, car feels sluggish in the second half of the track. The RPM drop in 4th gear when the TC locked up is also concerning. I need to find someone to look at the transmission - have a bad feeling it's hurt.
     
  17. ponys197

    ponys197 forum member

    214
    5
    You need to have the tune adjusted for the converter in the trans. There are several values that can be changed to have an affect on how the 5R55S shifts and fills . I would also do the 3rd and 4th Servo upgrade. I can tell you that the shift from 3rd to 4th in the 5R55S is a big RPM drop and you can't tune around it. If you log it - you will see how much it drops between shifts. Check out this link on the tuning needed - https://www.mercurymarauder.net/for...Racer-Torque-Converter-amp-TC-Lockup-Schedule
     
  18. TheDarkPath

    TheDarkPath forum member

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    Looking at the datalog, the TCC Desired Slip is showing 1020 all the way through the pass until 4th gear at 5246 RPM when Des Slip goes to 0 correlating with Actual Slip dropping almost to 0 which is also where the RPM drops by about 300.
     
  19. 07gts197

    07gts197 forum member

    800
    30
    Thats because your torque converter is locking up, which its supposed to do. I dont know much about the 5r but in thr 4r70w the torque converter locks up in 3rd and 4th. My guess is that it would lock up in 4th and 5th in a 5r depending on throttle input and other factors like ac compressor clutch cycling etc.

    Not much help but I wanted to add that what you datalogged is normal and the problem lies elsewhere.


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