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 Post subject: chassis question
 Post Posted: Sun Nov 30, 2008 8:00 am 
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This may seem like a stupid question but my Vega has never lifted the front tires,it seems to me that at the performance level it is at that most cars are lifting the front skinnies,so I don't know if the chassis is right for not lifting them or wrong because it won't.

 The chassis is ladder bar rear with strange single adjustables,I think the rear was 4* neg. last I checked,the front is factory a-arms with comp. eng. 3-way adjustable shocks set at 90/10,its got screw limiters,and the factory front coils have been cut 3/4 of a coil.

 I launch the car between 36-3800 rpm with a 10" converter built for nitrous use,it has 1.80 trans. gear and 4.56 in the rear....its best 60' is a dismal 1.40 and I think the car weighs around 2900 lbs.


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 Post Posted: Sun Nov 30, 2008 9:59 am 
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How much travel do you have in the front?

George


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 Post Posted: Sun Nov 30, 2008 12:16 pm 
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I think there is about 2 inches under the screw limiters


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 Post Posted: Sun Nov 30, 2008 12:54 pm 
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I have several thoughts on this.  

1)  The converter is wrong unless you're going to spray it every time you run it.  Been there, done that with the Studebaker.  Ya just can't have it both ways.  On motor that thing needs to stall up around 6kRPM and since it's a N2O verter it's probably down 700 or 800 RPM less than that.

2)  Unless you're running quarter mile, it's likely that you don't have a low enough gear in that thing.  Me, I'd like to see a 5:14 or at least a 4:86 depending on tire roll out.  It would be good to have the finish line RPM somewhere near the shift RPM.

3)  Those short times are telling me that you lileky have tire spin also.  The 3500lb Studebaker had the fronts up about 3 inches leaving last time out with the s**t box truck engine in it even with short times in the 1.65 range.  So the question here is, how are the tires?

4)  How much adjustment do you have on the front ladder bar mount and what hole is it in now?  Also, is the chassis loading and unloading leaving the line, ie, back end up and down in the first car length or so?  George asked about front end travel.  What he's looking for is help to get it up as it likely needs to have the fronts up off the ground for about 20 to 30 ft to get all you can out of it.  

And, what is the approximate HP of this engine?  How much are you spraying on it?

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 Post Posted: Sun Nov 30, 2008 1:01 pm 
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The height of the center of gravity (C/G) is what causes wheelstands.

If the C/G is high or travels high during launch the front tires can lift off the ground as you accelerate. If the front travel is too fast it can jerk the front tires off the ground very briefly and right back down.

The correct C/G height depends on how fast the car accelerates off the line. A P/S car needs the weight as low as possible. A 9 sec car fairly low and a 11 sec car not so low. It is all about the right balance between C/G and acceleration.

If you are hooking good and front tires stay on the ground then your C/G must be low for the accel of your car off the line.

Rick


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 Post Posted: Sun Nov 30, 2008 3:50 pm 
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Hey Ken,

 1)The converter is wrong for n/a but I knew that ....do you think that is what is causing it,it is stalling less then 7-800 low, it will only go to 3800 on the brake,I know I can't have it both ways but it is performing pretty good now even though that verter is in there.

 2)I am running quarter mile

 3)the tires are new this season so they have 1 pass and maybe 50-60 street miles,at the track I aired them down to 6 psi on the 9.99run....the are Hoosier quick time pro's, I had someone standing beside the car who said it seemed to spin a couple of revolutions and then leave


 4)The ladder bar is in the middle hole now,I don't know what you mean by how much adjustment,it has one hole above and below.

   I don't know if the chassis is loading and unloading,I guess I can't feel that.

  I can back the adjusters all the way out for more travel

  I am guessing the engine hp is around 620-640,and I have not sprayed it at all but it has 175 jets in it now,it is a 200-400hp plate kit



 Rick, I don't know where the C/G is or how to figure it


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 Post Posted: Sun Nov 30, 2008 4:37 pm 
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What is the angle of the bottom of the ladder bar with the driver onboard?


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 Post Posted: Sun Nov 30, 2008 5:11 pm 
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Scott Smith wrote:
What is the angle of the bottom of the ladder bar with the driver onboard?


Yeah Scott, I was thinking of the bottom hole.  

And Jeff, it would be good to get all you can as far as front lift is concerned, especially since your friend saw two rounds of tire spin at the hit.  If you're limiting front lift then you're depriving the rear tire of that energy in the front springs, ie, front end up = more weight on the rear tire.

Without the happy gas I'd venture to say that you need to have a stall up around 5800 or so to get the most out of it.  Hitting the tire a little harder at launch may help get the front up also.  Dunno exactly though as I've not had much experience with a ladder bar setup since back in 1991 but that stall you have now is way below what I would be looking for.

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 Post Posted: Sun Nov 30, 2008 5:48 pm 
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Jeff, What front end do you have in there...Stock??? When I had my Vega I had to put 250lb springs in the front and crank them up to get the front to "ride height" .  If you can do this it will store energy in the font and with the release of the brake it will make it easier for the front end to lift...Now I had a BB in mine so it needed to get on the back tire to prevent tire spin and constant short times...My vega was tube frame with a strut front end and weighing in at 2400 lbs  =;

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 Post Posted: Sun Nov 30, 2008 7:14 pm 
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Hey Barry,the frontend is factory a-arms,urethare bushings,totally rebuilt in 04


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 Post Posted: Sun Nov 30, 2008 7:27 pm 
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Hey Scott & Ken,

  The car is on jackstands right now about 18"in the air with the trans out it but the way it sits on the stands is the car has a 4* downhill grade rear to front and the ladder bar is 2* uphill rear to front,I don't know if this helps with the car disassembled......by the way the rear springs are 110#   ??


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 Post Posted: Sun Nov 30, 2008 8:51 pm 
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Working with what you have I'd put the ladderbars in the bottom hole and loosen the front to 3 inches of travel and try that.  You need to take a look at the toe in (out) with the front jacked up that 3 inches because I've seen it go toe out a bunch and make the car practically unsteerable.  (Ask me how I know)

Without a converter change or spraying it at the hit that's probably about all you're going to be able to do.  I'd say move some weight to the rear from the front like the battery but you probably already have it there.

George


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