Nova Corner Weights/What To Do With It?

[5448]

I weighed my car with four corner scales to see how far off my weight bias was and to see what I could do to improve it. I used weight plates as ballast and moved them around for different scenarios. The car is a '71 Nova, aluminum head 388, NA, fiberglass hood and front bumper, leaf spring, Cal-Trac car on 28X10-15 slicks. Raced last weekend after rain, and 60 ft's varied from 1.47 to 1.81! Some of this was due to track prep, but the car is also finicky. I would like to improve the hook consistency, and based on the data below, I'm looking for suggestions. The LR weight seems pretty heavy: 130 -150 lb heavier than RR. The battery is in the RR trunk area. The most beneficial seems to be 45-50 lb added to the LR, but it makes the LR-RR split worse.

I tried to copy an Excel file into the message, but the columns don't line up very well. There are 12 different load cases listed. Any help with getting weight off the LR and evening the splits would be appreciated.

Thanks,

Eric



1971 NOVA CORNER WEIGHTS 6/10/2007
TIRE PRESSURE: Front 36 psi; Rear 15 psi
SHOCK SETTING: Front 90/10; Rear 5 (Rancho RS9000)
CAL-TRAC SETTING: Lower Hole, 3/4 Turn preload
FUEL: 10 gallons

VEHICLE STATE TOTAL WEIGHT (lb) LF RF LR RR % F/R % L/R REAR BITE (lb)
NO DRIVER

No Ballast 3035 730 802 795 708 50.5 F 50.2 L 87

50 lb LR Trunk 3086 735 784 836 731 50.8 R 50.9 L 105

WITH DRIVER

No Ballast 3248 809 825 873 741 50.3 F 51.8 L 133

50 lb centered against trunk latch 3298 801 818 906 773
50.9 R 51.8 L 135

25 lb added to battery box (RR) 3272 798 828 885 760 50.3 R 51.4 L 121

50 lb LR Trunk 3297 812 806 915 763 50.9 R 52.5 L 151

50 lb Centered on rear bumper 3296 797 815 909 776 51.1 R 51.8 L 133

45 lb LR trunk 3292 812 808 912 760 50.8 R 52.4 L 152

50 lb between rear roll bar down tubes 3296 805 824 901 766 50.6 R 51.4 L 130

50 lb passenger seat 3296 813 844 882 758 50.3 F 51.4 L 130

100 lb centered against trunk latch 3346 792 808 939 807 52.2 R 51.8 L 133

45 lb LR trunk, 55 lb centered against trunk latch 3345 803 799 948 795 52.1 R 52.4 L 153

[John_Heard]

Do you know if your preload in the cal-trac's is affecting the weights any? It probably won't change a lot, but if you've still got the car on the scales try backing off the caltracs and see if that makes much difference.

I have not been able to even mine out either, it's heavy on the left rear with driver and about even on the front.Doesn't seem to affect it at launch or anything though, so it's something I quit worrying about.

[sunsation540]

it's a pain but put a 1/2 inch spacer in the LF this spring is dead that is why even with you in the car it's not holding up more weight. and dont let the front diff bother you your not going roundy round.. remove the shocks and the bottom bolt in the cal tracks make chassis changes preload last,

[John_Heard]

Good point about the LF maybe being soft. The scale info is interesting but lord knows what's going on in regards to weight at launch and going down track when the car is putting the power down. Not to mention wheelstands.

It would be interesting to find the center of the front end and jack the front up at that point and see how evenly the weight distributes to the rear tires.

[John_Heard]

Just sharing, my car - this is before I took some more weight out of it

LF 882, RF 860
LR 909, RR 821
Rear 1729 49.8%
Total 3472 (w/driver)

Without driver front was about even and LR carried about 50? lbs more. It's always been heavier there for some reason.

[5448]

Thanks for the info. With no ballast in the car, it leaves the line with the LF about 3-4 inches higher than the RF. That is why I think adding weight to the LR may help. Weight on the rear is definately needed for some traction consistency as well. Other than that, the car doesn't pull to one side and drives straight down the track. The idea of the soft LF spring is also a good area to look at; I run Moroso trick fronts, and cut two coils from the RF and 2.5 from the LF to get the nose down near the bumpers on the A-arms. After this, the LF was 1/4" higher, but after racing the LF is 1/4" lower. These are not new springs, so I thought they would have already taken a set.
I did not try taking the preload off the Cal-tracs, just moved weight around.
I will have to borrow the scales again and try a few things; if nothing else, I have some data for future reference.
Thanks for the corner weights of your car, Beyond, maybe the heavy LR is common for 3rd gen Novas. It just seems a little out of whack, since that area of the car has nothing extra in it!

Eric

[sunsation540]

make me screech !!! the left rear has nothin in it ,,.,,, my car is withen 8 lbs before i get in its 100 heavy in lf and 60 lr 1.5 turns in the top right bar adds 50 to the right rear and another 40 to the lf as for the front springs i did mine the reverse one coil off the rt front and 1/2 off the lf cant help to much every car is diffrent i bought scales and the car has been on them 6 times and set there for a week once playing, the anti roll bar moves -15 from the left and adds 25 to the right rear when you lenghthen the right bar. one turn, and it's a A body i have put the wheels 24inches in the air and it drives with 2 fingers start with even rear weights.! in the rear screw the front the preload in the rear turns to a push down track...

[sunsation540]

1008 LF 865 RF 799 LR 797 RR 3470

[John_Heard]

I dunno, I'm kinda skeptical about how much static weight tells us about what the car is going to do once torque is applied and the wheels are in the air.

[5448]

I agree, John, the static weights can be correlated to the launch of the car, but what would be really beneficial is real time data recorded during the run.

For my car, I don't think adding 150lb to the RR is the answer. The car already leaves LF higher, and adding weight to the RR is only going to take that much more off the LF. Or maybe I'm looking at this completely wrong.

I think I'll build some removable bars and move them around for testing.

Eric

[sunsation540]

i"m sure there is someone better than my dip stick that can make you understand this.. but you are not adding weight you are placing the same weight in diffrent places if you put a spacer under the lf spring it pushes down on the RR harder moving weight it also makes the LF the heavy corner to fight the torque rotation left to right making it harder to lift.. further the car only sees the first shock of power on the launch as per corner weights. preload, is a diffrent animal and will cause push any preload in the car will push on the start and top end avoid...mike peaters bail me out...?

[Mike Peters]

Sorry John/Sunsation and John/Beyond. Reading all the #'s in the original post made my eyes hurt. I couldn't follow it all. I agree with everything being said by both Johns. A good thing has been done by putting the car on some corner scales. That is always good knowledge to have. I think there have been several mistakes made here. First of all, the car was weighed with preload in the Cal-Trac bar. Second, the front springs have been cut to different heights. Cutting a spring changes the rate of the spring and makes it stiffer. Also, by cutting the LF to a shorter height than the RF, there is less stored energy in the LF though it is a stiffer spring. Longer, softer springs provide stored energy. I would suggest getting matched springs in front. A spacer in the LF is not going to restore the spring rate and adding the spacer will add more preload to that corner which would make it heavier in addition to the diagonal corner. Match your springs, take out the preload, and scale the car again. Still, this is not going to solve any traction problems you're having 5448. Corner weights are a diagnosis for when the car is doing funky things like pulling to the left or right when launched or diving to the left or right when braking. Adding preload or additional weights to try to equalize corner weights is not a solution to traction problems. Traction is still a result of weight transfer and traction coefficient.

[John_Heard]

Sunsation (Dang I wish more of you guys would post your names so I could remember!) - I can tell you've been around circle track cars and used to moving weight around with the springs. I just don't know how much of that applies to drag racing really.

I do think corner weights are an excellent way to find a collapsed spring, bound up shock, things like that no doubt and it's very good to have a baseline to help diagnose problems if and when they come up. In a perfect world I'd like to see even left/right #'s too, I just don't want to add preload anywhere to get it.

One of the things that's puzzled me on my car is that it has about 50lbs of bite in the LR with no driver and the front's within a couple lbs. Where is that coming from? Common sense would say it shouldn't be there, the battery over the RR should make that corner heavy but it's not. My guess is that I've got a spring that's not perfectly matched to the RR, or perhaps it's a issue that the spring mounts are not even in the car. Without the ability to put it on a surface plate to check everything I'm just guessing at this stuff. But the bottom line is that it launches straight and drives straight, so I'm not messing with it for now haha.

[5448]

Sunsation/Mike/John,

I think I finally get it. Guess you just had to hit me in the head a little harder! I was looking at the weight shifting backwards. I will borrow the scales again and weigh the car with no preload. I also plan on ordering a new set of front springs, since the front has settled further over this past week. The trick springs in the car were five years old, but still seem to be taking a new set after cutting.
Funny how easy it is to open a can of worms! When I first weighed the car, I was only looking for weight bias and a baseline to start making changes from. I also wanted the rear weight of the car to order a set of Cal-Trac split monos. To that end, I accomplished my goal, and I also have a direction to start making some changes.
I will try to make some changes in the next month, and will post my results.

Thanks again,

Eric

[mmsports33]

Now this is coming from a round track guy.....but like John said......you can't live and die by the scale numbers....even in a round track car. Obviously you don't want them way out of wack and you want your percentages to be close but when looking at exact numbers it's really just a reference point.....to let you know where you are at and when you make a change you have an idea of where you went......but there are tons of other factors but it can be a useful tool. Also it has been my experience that you can't "jack" weight to the rear of a car as good as you can to the front.....especially in a "stock" type chassis....tube chassis seem to be a little easier to play with the weights with.........just my .02...........