help with taking timing out on launch

Discussion in 'PSI Superchargers Tech Questions' started by badd57, Jun 28, 2011.

  1. badd57

    badd57 Member

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    blown alcohol top dragster, last year ran 6.60 et and .997 60' bbc 565 with 871 7al msd bird catcher hat nossels only. this year same motor 1471 hi helix, msd 20 amp mag 28* total timing, port nossles, fuel system flowed, 6.95 @203 60' 108 leaves the starting line way to violent @ 3200 rpm 3.89 gears 34.5 hoosiers, got the new msd controler 7730 box, what would be a good starting point to ramp out some timing at the hit. :(thanks
     
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  2. moparchris440

    moparchris440 Member

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    3100 door car here BAE 1471 Lehay box and 6 shooter. 10.5 w's. convertor driven 1.40 first gear 4.10 rear. We take out 15 at the hit and ramp it all back in at 1 to 1.2 seconds into the run. depends on the track. Hope this helps
     
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    Last edited: Jun 28, 2011
  3. bill

    bill Member

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    taking out timing

    has anyone used spud millers air retard to advance timing wondering how it works
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    Badd57, I think everyone has covered how much they are taking out on launch. 10-15* is not unheard of. The big thing you have to remember is the more you take out the more chance you stand of blowing the tires off if you ramp it back in too fast. This is just something you have to play with. Don't be afraid to take a little time in ramping it back in.
     
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  5. Scouder

    Scouder New Member

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    Mike, are you saying 10-15 total left in the engine, or 10-15 taken out from some point? Seems like it could be either or both.

    -Brian
     
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  6. Mike Canter

    Mike Canter Top Dragster
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    I am talking about taking it out.
     
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  7. Alkydrag

    Alkydrag Sr. Dragster

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    Explain what you mean by "violent". How can it be more violent when it slowed down? I think you might be rattling the tires leaving at 3200 with a 3.89 gear.
     
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  8. badd57

    badd57 Member

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    it is rattling the tires, so more higher rpm or lower on the 2 step ?:confused:
     
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  9. Mike Canter

    Mike Canter Top Dragster
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    The trick is wheelspeed/driveshaft RPM at 0.5 seconds (what I use). At 0.5 seconds the driveshaft RPM has to be over 2600 or you are going to have shake for sure. How high depends on the car's traction and track. Normally 3000 is around the top limit for a real good car. So if you are below 2600 you are taking out too much power.
     
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  10. Flyboy68

    Flyboy68 Member

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    Would this be the case on 10.5w tire as well? 2600 and above?
     
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  11. Mike Canter

    Mike Canter Top Dragster
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    Can't tell you that because I have never had the pleasure of tuning a blown 10.5 car. That 2600+ rpm at .5 seconds means we are on a roll and the higher we can get it an maintain traction then the better the ET. I have found if that driveshaft is below 2600 rpm then you are going to have a bad 330'. So in that situation I would think it is close to the same. I do not know about the shake side of it.
     
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  12. overkill69

    overkill69 Member

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    shaft speed

    Mike i've seen shaft speed numbers thrown around a couple times and nobody ever mentions the rear gear ratio. We have numbers from our old car with a 4.56 rear a 1.71 low. Now we are testing with a 4.86 rear and a 1.41 low. I can do the math but I figured it's just a matter of seeing what the tire will take.
     
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  13. Mike Canter

    Mike Canter Top Dragster
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    Yes and no. There is a certain amount of physics involved here in order to accelerate the car down the track. Regardless of what gear ratio we use we still want to car to accelerate at close to the same rate. I agree it is all in what that tire attached to that car will take. You want to be at that max adhesion point on that tire that if you went a little faster then it would start slipping and grabbing. You can slow down and have it safe but that is not going to win. Because of this the race is 90% won by the 330' mark. Beyond that 330' point it is really not a traction issue but a horsepower and clutch issue.
     
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  14. blown375

    blown375 New Member

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    Not being rude or anything but.....you cant go by a number like that just because somebody else uses it !
    like the guys are saying;
    Rear gear , transmission gear and engine torque play a huge role in that !
    Say , Mike has a 3.89 gear in a car with 526" engine and a 1.80 powerglide and I have a 4.57 gear with a 433" engine wih a 1.82 low three speed .... do you think we are both going to be at 2600 rpm @ .5 seconds ?
    you have to figure out what your own combination likes. :cool:
     
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  15. Mike Canter

    Mike Canter Top Dragster
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    I admit that the more accurate way would be to have true wheel speed but believe it or not it works out. Maybe it would be a little off with a 3.89 gear but I don't get to see many of those in PMs or FCs. I would not think that transmission gear has anything to do with these driveshaft RPMs that are desired to accelerate that car. The only think I have seen is if the wrong first gear is used or the motor is down on power then the car cannot achieve those ultimate driveshaft RPMs so it has a bad 60ft and 330' times and goes into shake a lot.
     
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    Last edited: Jul 1, 2011
  16. badbird

    badbird New Member

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    The common thing here is the tire the 34.5 will usualy maintain grip at those shaft speeds and be rotating fast enough not to deform grip and shake,
    it dont matter what power output the engine is or what rear gear you have within reason, a well tuned blower motor will have grunt, these numbers are not cast in stone every chassis responds differently but they are near enough to be a good starting point, 2600 @.05 will work, the thinner tire may be a bit different but id bet it wouldnt be far away from those numbers,
    Its easier to go too far then work back than starting weak and shaking every time,
    That is about the limit of a loaded tire in a decent chassis, if the engine is small or weak it needs a higher numericaly gear to give you the tourqe multiplication to acceive those wheel speeds Converter cars will use different gears to get the same result as the converter multiplys the engine tourqe so you can probably use a deeper 1st gear but remember the tire dont know or care whats driving it, It will still need the same wheelspeed so stay round, a heavy pro mod will like one first gear, a light FC another but the aim in all cases is to spin the tire hard enough so it dont weak shake and slow enough so it dont lose traction completely and spin shake..there is your tuning window.
     
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    Last edited: Jul 1, 2011
  17. blown375

    blown375 New Member

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    I should have elaborated a little more , the subject was "pulling timing" and yes the transmission ratio and engine torque will have an effect how much timing is pulled to achieve the desired driveshaft rpm.
     
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  18. badbird

    badbird New Member

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    if your pulling timing then yes the amount you pull will depend on the power you have the gears you have to get to that number
    I think what mike is sugesting and from looking at what the Op said
    that it leaves way more violent i can only read that as its shaking harder,
    id read that the OP needs more power, less gear, leave at a higher rpm or any combination of those untill it actuly blows the tyre off at the hit then just reduce it a bit at a time untill he has a fast race car that dont break parts Anyhow you reduce shake means everything else is happy for longer,

    your right the post has gone from pulling timing to wheel speed, I think thats cause the two are linked when your pulling timing and i think mike is trying to be sure that pulling timing is the real answer to the Ops problem,
     
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    Last edited: Jul 1, 2011
  19. Mike Canter

    Mike Canter Top Dragster
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    Yes, thanks Badbird, and YES again they are very closely linked. You adjust the launch retard based on the driveshaft speed to keep it in the "RPM window". If too fast then retard it, if too slow then put it back in. On the RPM window I gave listed you can take it or leave but I can tell you it will put you in the ballpark and keep you out of shake and get you going. You have to have a reference because you just can't start adding or subtracting timing and hope for the best.
     
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  20. BigB

    BigB New Member

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    Maybe a dumb question but you guys are referring to drive shaft rpm not engine correct?
     
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