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PostPosted: Thu May 28, 2009 7:06 am 
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I recently installed a set of CE ladder bars in my car. Last weekend I made my first passes with this setup. I got the best et, mph and 60' ever so I'm pretty happy. After talking to some guys at the track and doing a bit of research I realized my setup of the bars is far from perfect or good. I got the coilovers and springs adjusted to the proper hieght they had been setup with too much preload in the springs. Then I borrowed a set of car scales and have my car setup on them. So now I have some numbers from them but I'm not sure exactly what to do with this info.

FL:1145# 31.5% FR: 909# 25.1%

RL: 762# 21% RR: 808# 23.3%

Total:3618

These wieghts are the car in race trim with driver in the seat and I'm 200#.

So what I'm asking is what kind of distribution of wieght am I looking for. Completely even on all four tires?

The car is a 1967 Dodge Charger 440 10.3-1 E-heads 4500 converter 4.10 with a 30x9 tire coilover springs are the 150#

Best run was a 11.158 @ 119.953mph 1.539 60'


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PostPosted: Thu May 28, 2009 5:37 pm 
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Yes, you want equal rear tire loading, but NOT on the scales. You want equal rear tire loading during your launch. Presently, your RR is heavier than your LR (on the scales), but, as you apply driveshaft torque, the LR will become much heavier than the RR.

In other words, the driveshaft torque greatly upsets the loading of the car. The only way to achieve equal rear tire loading during the launch is to build some form of asymmetry into the car which will cancel the effect of driveshaft torque.
http://www.racetec.cc/shope


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PostPosted: Thu May 28, 2009 9:58 pm 
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Billy when you scale a car what side to side weight on the rear do you go for.


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PostPosted: Thu May 28, 2009 11:38 pm 
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BillyShope wrote:Yes, you want equal rear tire loading, but NOT on the scales. You want equal rear tire loading during your launch. Presently, your RR is heavier than your LR (on the scales), but, as you apply driveshaft torque, the LR will become much heavier than the RR.

In other words, the driveshaft torque greatly upsets the loading of the car. The only way to achieve equal rear tire loading during the launch is to build some form of asymmetry into the car which will cancel the effect of driveshaft torque.
http://www.racetec.cc/shope


So using scales is a waste of time :?:


Well then my next question is how to build this asymmetry. The only real adjustments are spring/t-bar, shock dampening or the preloading of one of the ladder bars, right?

I'm heading out to the track tomorrow so I'll find out how this is going to work.


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PostPosted: Fri May 29, 2009 7:03 am 
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You'll probably find that it'll go nice and straight with what you got there in regards to static weights. It does seem heavy on the LF, which will also load the RR. I think that's something to take a look at as you have time to fiddle with this. Did you get any numbers without the driver?

What kind of shock and spring arrangement do you have up front?

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PostPosted: Fri May 29, 2009 7:19 am 
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Pegasus wrote:Billy when you scale a car what side to side weight on the rear do you go for.

Page 15 of my site has a spreadsheet for the wheel loads necessary to achieve equal rear tire loading as the fronts lift. In other words, the RR is going to be very heavy as you sit on the line, but, as the driveshaft torque increases from zero to the value which causes the fronts to lift, the RR and LR loadings will approach the same value.

And, this is why I don't recommend this sort of thing. You only have equal rear tire loading at that final instant. Up to that point, you're most likely going to veer to the left. So, if you set the car up on the scales with equal rear tire loading, you lose performance as the driveshaft torque upsets the loading. If, on the other hand, you put in enough preload to give equal rear tire loading at peak driveshaft torque, you could end up with an ill-handling beast.

Obviously, the ideal arrangement would be to have equal rear tire loading on the scales AND equal rear tire loading for any value of driveshaft torque. But, the only way this can happen is for the car to supply a canceling torque exactly equal to the driveshaft torque.

Let me answer this other post and you'll see that this can be done.

SaskCharger wrote:
So using scales is a waste of time :?:

No, not at all! I consider wheel scales a necessary investment for any serious dragracer.
SaskCharger wrote:Well then my next question is how to build this asymmetry. The only real adjustments are spring/t-bar, shock dampening or the preloading of one of the ladder bars, right?

Wrong! You're missing one, but it's at the other end of the car. And, with a ladder, this is about all you have! At the front of the car, I would assume you have identical front coilovers. Now, consider what would happen during launch if the RF coilover had a higer rate spring than the LF coilover. As the front of the car lifted, the RF spring would lose more load than the LF. Since the sum of the RF and RR must always be equal (otherwise, the car would be rolling over), that means that most of the weight transfer is going to the RR. And, if you have exactly the right ratio of RF spring rate to LF spring rate, the driveshaft torque value would not affect the rear tire loading.

Of course, you won't find exactly what you want in the spring suppliers' catalogs, but you can get very close. Read Pages 34, 35, and 16 at my site.

(This same sort of thing can be accomplished with the proper adjustment of a 4link. See Page 19.)

Finally, I recommend use of a traction dyno as a final check on your work.
http://www.racetec.cc/shope


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PostPosted: Sat May 30, 2009 12:56 am 
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Do you have coil overs on all 4 corners? If so what spring weight are you running up front and in the rear?

When you scaled the car,....did you unload the preload on one of the ladder bars? You do this by taking one of the rearend mount bolts out. You don't want any preload in the rear suspension when you're scaling the car. Thats something you add after getting things weighing as correct as you can get.

If you're intrested I'd be more then happy to help talk you through how I would set your ladder bars up. PM me and I'll send you some contact information if you're intrested.

Don

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PostPosted: Sat May 30, 2009 7:21 am 
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Saskcarger, No offense to Billy but he is just going to tell you his theory from his way of thinking.He has some good info on his web sight but it don't work for every car...Your car need to get up on the back tire and need stored energy in the front springs!!!On the other hand Don is going to give you a set up to where to start and where to go from there. Scales are a very valuable tuning tool and when you get right where it works good and has constant short times then scale it and make a note of those corner weights. Then if something goes wrong you will have records to fall back on... :scratch:


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PostPosted: Sat May 30, 2009 11:44 am 
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I appreciate the replys.

Well I took the car to the track last night. It launches straight no pull either way. So handeling was fine both at the start and through the entire run.


Bill I checked out your site. That is a lot of info it's going to take a while to sort through that but i plan to.

The front of the car is still a stock Dodge set up. It has the lightest torsion bars made specificily for drag racing. There is a set of CE 3 way adjustable shocks in the front set to 90/10. I'm pretty sure this is not the hot set up.

The front jumps up quickly and it seems to spin around 60-100 feet a bit. I had both rear shocks at max compression which helped the 60 foot.

Now this is on a friday night street leagl so there is minimal prep to the track and no traction compound.

Car ran a 11.17 @120mph with a 1.61 60' best of the night there were two other 1.6* 60' runs.

Ere are a few vids of the lauches.




http://members.shaw.ca/Lobux/vids/Launch1.wmv
http://members.shaw.ca/Lobux/vids/launch2.wmv
http://members.shaw.ca/Lobux/vids/launch3.wmv

I plan to adjust the the front shock to the mid setting and see what this does.


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PostPosted: Sat May 30, 2009 1:48 pm 
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Location: New Jersey
Back of your car is way to stiff. It don't move a bit...You need to soften it up and get the back of the car to go down so the car points up. This will get the rear planted so it don't spin...It really should short time in the upper 1.50s :mrgreen:

How heavy spring in the back???


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PostPosted: Sat May 30, 2009 4:10 pm 
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So you figure the comprssion settings in the back are too stiff?

They are 150# springs.


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PostPosted: Wed Jun 03, 2009 10:02 pm 
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SaskCharger wrote:So you figure the comprssion settings in the back are too stiff?

They are 150# springs.
springs don't sound to bad,what kind of shocks are they?are they single adj?or double adj?

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PostPosted: Wed Jun 03, 2009 10:52 pm 
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They are QA! double adjustables

I finally got a copy of Morgans Doorslammers so I'm reading late into the night, who knew centers could be instant.


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PostPosted: Thu Jun 04, 2009 7:01 pm 
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lookin at your videos, your tire hook for a instant,then spin...so play with your shocks,stiffen up the extension,to keep them applied longer,sorry i only have qa-1 singles,so i cant give you a setting on the compression.

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PostPosted: Sun Jun 14, 2009 12:16 am 
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AH, good ol' SIR.

Hope to see you there this summer.

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1974 Pontiac Ventura, 455P (9.5:1 comp.), 850DP, 3100 ''Tight'' 10'', 3.73's/28x13.5
Upgrading in June:
KRE 310cfm@.550 heads, 10.5 comp., hyd roller, 3800 tight 10'', better rear suspension.
Race Weight: 3750#'s
2007 best: 11.97 at 110 1.65 60ft.


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