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Advice on starting line hesitation.

Discussion in 'Gen 2 Prius Main Forum' started by tnthub, Jun 23, 2007.

  1. tnthub

    tnthub Member

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    After being on this board for awhile I know that many of you folks are well versed in Prius specific things so I have a pre-emptive question before I head out early Sunday AM to Maaine's largest single automotive event.

    The Show, Shine, and Drag will have a line of traffic a mile long at the gates by 7:00am tomorrow morning and I have made appropriate arrangements with a local dealer to "test drive" a "gently used" 2004 Prius begunning this afternoon at close of business today. Included with the Prius will be a couple of magnetic door banners for: Maine Hybrids and I hope to generate some interest and respect for hybrid technologies as well as pass out business cards for my wife who specializes in prius sales.

    I will be driving in the drag portion of the event with only one time trial prior to the beginning of eliminations so any advice on the initial hesitation issue with the prius would be greatly appreciated.

    For those of you who do not know, I have a long record in competitive bracket racing with 45 event victories, 22 runner up finishes, and two track championships. I have a weather station to compenste for environmental variables and easy to change dial indicators so I do not need to mark up the windows with shoe polish.

    In bracket racing the performance of the vehicle is not important but the consistency of the performance is critical. Vehicles are handicapped according to what the driver predicts the elapsed time will be and the start is staggered so that in theory if each driver reacts to the start perfectly and each vehicle runs exactly the number predicted, the cars will arrive at the finish line at the exact same time. If a car goes quicker than what is predicted it loses. If both cars go quicker than predicted, the one who breaks out by the least amount (closest to the dial), wins. The other very large variable is the driver...

    Driver reaction time is not counted as the elapsed time of the vehicle so many races are won/lost on the starting line, however if the driver starts too quickly he/she receives a red light and automatically loses.

    I can drive and I prectice often on a "practice tree" in my office as part of a regular schedule.

    Now the question...

    When I put one foot on the brake and one foot on the gas, depressed all the way, the Prius has a hesitation before it moves. All cars have this but the Prius is far more pronounced than others. This is called the "vehicle reaction time" and needs to be accounted for by the driver so the driver can know when to press the gas or relase the brake as the case may be.

    There are three yellow bulbs and a green at the start. Each light is 0.500 of a second apart. The car needs to physically moving at the exact point the green light comes on so the driver needs to react in advance of the green for a "perfect light".

    In my regular vehicle I idle at 1500rpms and press the gas when the third bulb comes on solid yellow and that provides me a reaction time usually between 0.510-0.530 seconds which is good enough to often provide me an advantage of .01 to .02 over a competitor.

    In a normal rental car, I often have to press the gas/release the brak either as the second bulb goes out or when the third bulb begins to come on.

    The Prius however seems to have far more of a delay.

    Is there an easy way to compensate for this hesitation? Is there a way to prevent the ICE from shutting off or starting up at a prescribed rpm point?

    Remember, speed and ET is not important except in terms of being absolutely consistent every time.

    I will have probably 28 pounds in the front times and 45 pounds in the rear as weight still transfers front to back in a front wheel drive vehicle at launch. There is 8-12 inches of rollout between the stage and pre-stage beams which are the two beams that establish the start of the race.

    This is a 1/8 mile track so it is only 660 feet which should be ook for a car with a stock transmission as stock vehicles generally become more inconsistent after the 1/8 mile mark than before (in my experience).

    The winner of the "general" race lines up against the winner of the "fast 32" for the money. I believe my chances are as good as anyones and I would dearly love to see a Prius lined up against a dragster for the final round.

    Any advice would be greatly appreciated. :)
     
    #1 tnthub, Jun 23, 2007
  2. ServoScanMan

    ServoScanMan Member

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    Congrats on your many wins in drag racing. I was the crew chief for my sons Jr Dragsters. My oldest is the 2001 NHRA Pacific Division Champion, IHRA runner up National Champion, and 2 Time IHRA National Champion plus many other races.

    I never thought about bracket racing the Prius. If the Prius is very slow at reacting then perhaps you can leave on the 2nd bulb or leave when the 2nd bulb goes out. The newer LED trees should make this easier. It's going to be hard to know how to dial in your reaction time with just one time trial.

    Good luck and let us know how it turns out!
     
    #2 ServoScanMan, Jun 23, 2007
  3. usbseawolf2000

    usbseawolf2000 HSD PhD

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    First, I will just make a statement comparing Prius to a regular car. In Prius, having the instantainence 28 hp available from the battery is like having the ICE idle at ~2,000 RPM. I would say, every launch is perfect in Prius.

    To improve your launch further, how about try having the rear window defogger on. I thought that would keep the ICE running. I don't think you can set it to idle at specific RPM. You may want to turn on the AC at full blast also. Right before the light turns green, turn both off using the buttons on the steering wheel.

    Another idea is to turn off the car and power it on right before the launch. The warmup process will keep the ICE running for some time. You can use that window as well. This approach can polute more since the catalytic converter might not be ready for a full throttle ICE.
     
    #3 usbseawolf2000, Jun 26, 2007
  4. Marlin

    Marlin New Member

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    I seem to remember there's some sort of service mode you can put it in that keeps the ICE running. It is often quoted here for use in emission testing where the ICE must idle for an extended period of time.
     
    #4 Marlin, Jun 26, 2007
  5. efusco

    efusco Moderator Emeritus
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    Couple comments then one suggestion.
    Although there is a sense of hesitation w/ the Prius it actually starts moving and reacts faster than any conventional vehicle b/c the electric motor provides instantaneous torque. There IS a delay for the ICE to start and a delay in getting the HP from it...and that's what you're feeling. What you want is the ICE power available sooner.

    I don't know what the exact conditions are where you'll be racing, but if you have the opportunity to get your prius up to 20mph you can drop into B-mode at/above 20mph. That will force the ICE to run and it won't shut off until you take it out of B. There's no reason you couldn't just run the race in B-mode...since the accelerator will, presumably, be floored the whole time there'll be no difference b/w B and D. This should give you ICE available power instantaneously when you hit the accelerator.

    I would NOT recommend running the defrost and such as that will drain your HV battery.

    Some people have experimented with force charging the HV battery (in D steping on the brake and accelrator to get the SOC up into the Green range). But most found little actual benefit despite the fact that it should offer a theoretic benefit of extra electric power and torque.

    Experiement a little with my B-mode suggestion before the race so you know how the car will react.
     
    #5 efusco, Jun 26, 2007
  6. Danny Hamilton

    Danny Hamilton Active Member

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    Ok, I'm not certain on some of these technical details, so hopefully somone else will confirm or correct anything I say here. This is just how I thought things worked:

    First, I thought Toyota redesigned the Prius somewhere around 2004. In the old version, the A/C wouldn't run without the ICE, but the new version has an electric compressor running off the High Voltage battery, so turning on the A/C or the rear defroster aren't likely to force the ICE on.

    Second, I thought that holding the brake and the accelerator down at the same time caused the Prius to charge the High Votage Battery. I thought I read around here somewhere that once the High Voltage battery is fully charged (or at least as charged as the computer lets it get), that the ICE shuts off while holding the brake even if you are holding the accelerator at the same time.

    I would think that for the sake of consistency, this would be the state youd want to be in. The battery has a maximum charge so you have a consistant voltage available for MG1, and the delay between flooring the accelerator and ICE turn on should be pretty consistant. I'm not sure what the delay is betwen flooring the accelerator and voltage sent to MG1 (to get the wheels moving) and MG2 (to get the ICE moving) but I'd expect it to be pretty consistent. The only other thing I can think of that might be helpful would be to have the temperature of the ICE, the Catalytic Convertor, the High Voltage Battery, and the DC Power Switcher as consistent at start time as possible, since the temperature of these things affects the computers decisions on ICE usage and electric power draw.

    If you really want the ICE running before starting, and you aren't going to mess around with diagnostic screens, I thought that having the heat on full would keep the ICE running.

    Even if you floor it while at a complete stop, I doubt the tires will slip at all with 28lbs and a nice clean track, however, keep in mind that if they do, and if you have a Prius with the old traction control firmware, you could end up with a car that doesn't want to move.

    Note: I see that Evan has already mentioned the Force Charge and the Defroster while I was typing this.
     
    #6 Danny Hamilton, Jun 26, 2007
  7. TheForce

    TheForce Stop War! Lets Rave! Make Love!

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    I have experimented with keeping the throttle at around %75 while holding the brake and then releasing the brake while slowly pressing the throttle to %100. When I mean slowly I mean around 1-2 sec from %75 to %100. This usually keeps the wheels from slipping and killing the engine. This way of launching seems to "feel" quicker but I havnt had a chance to have myself timed at a track.

    I have forced charged before and if you hold down the throttle %100 the engine stays on but at a very low RPM. Almost a dying feeling. This was before I had my can-view so I dont know if it was at its max SOC or not and I dont know what RPM it was at either.

    As soon as I get some time off I'm going to do some experimenting.
     
    #7 TheForce, Jun 26, 2007
  8. Sarge

    Sarge Senior Member

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    <div class='quotetop'>QUOTE(efusco @ Jun 26 2007, 01:18 PM) [snapback]468377[/snapback]</div>
    Hmmm... given that the OP indicates the objective is consistency rather than speed, wouldn't it make more sense to drain the HV battery completely to try to take it out of the equation as much as possible?

    I.e. crank up the A/C, defroster, headlights, fog lights, radio, etc... - everything you've got - to bring the SOC down to purple bars, which should get the ICE running constantly (?). Then just floor it and go for it.

    The car will be slow, but at least it should be consistently slow! :p

    Of course, I am not sure if he will be doing the Prius a disservice with the lackluster speed, but hopefully it will at least help him win... :huh: :lol:
     
    #8 Sarge, Jun 26, 2007
  9. V8Cobrakid

    V8Cobrakid Green Handyman

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    ah.. how to get the prius off the line... first off, disable trac. the limiters on the electric motors will kick in if needed.. but you can spin wheels if they slip.

    1. put the car into ign on mode.... not ready... not accessory .. but ign on ( two presses without a brake pedal )

    2. press down on the gas twice

    3. shift to N

    4. press down on the gas twice ( remember... these are full presses.. don't half #$% the pedal push )

    5. shift to D

    6. press down on the gas twice

    7. hold the brake pedal down

    8. start the car

    the engine should kick on, and blink a little red prius on the mfd... you're in vehicle diagnostics mode.

    Don't charge the battery before your run. it heats up the system and causes electrical lag from the battery... because it's warm.

    don't hold the brake and gas at the same time.. it doesn't really help at all. at first you're braking the system, then you let it go.. remember.. you're not running that engine in neutral.. it's turning your electric motors. and when you let off the break.. that electric motor has to change how it's turning... so you're making more work.


    the best advice on your side would be the vehicle diagnostics mode. reducing the chance that the car will take power from you on acceleration should help. ( slippery pavement... slippery lines ) i know it helped me when i did races. solo2 scca races i believe.. so i was cornering.
     
    #9 V8Cobrakid, Jun 26, 2007
  10. hobbit

    hobbit Senior Member

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    I wouldn't try full-bore acceleration in inspection mode. Proper
    control of the normal-mode system on dry pavement should be fine.
    .
    Forget fooling with the accessories. Leave them off. Leaving the
    shifter in "B" will keep the ICE running once it's running -- nobody
    really knows why but that's how it works. That will keep you from
    having an ICE-start delay off the line.
    .
    Going into force-charge mode [brake & accel pressed] will cause the
    car to LEAP forward once you release the brake. You'll probably want
    to experiment with an accel setting of something less than full [as
    noted already] for optimum launch torque.
    .
    Now, please riddle me this: Why would lower front tire pressure give
    any better acceleration? I would think that higher pressure would.
    .
    _H*
     
    #10 hobbit, Jun 26, 2007
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