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:
    56
    655
    79
    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

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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

    19,136
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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

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    1
    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

    166
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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
    655
    79
    You could have been running into a headwind.
     
  8. fdjizm

    fdjizm Drag Queen

    19,136
    179

    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

    166
    1
    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.