I FIRMLY BELIEVE THERE IS A WAY TO FORMULATE, MEASURE AND SET UP REAR CONTROLL ARM GEOMETRY TO SOLVE TRACTION PROBLEMS BUT Many have said the "lower control arm should be paralled to the ground".As if this is enough; is missleading. I could accomplish this buy simply changing tire diameters. If my rear control arm is 1/2" lower at the axle, just add giant tires, right. but this would still leave my instant center above the headlights.SOMEONE PLEASE, tell me if i'm full of crap, but: (1) If the lower arm is parallel to the FRAME (not ground), this would cause the shorter upper arm to become pointed toward the frame line and form an instant center (intersecting) point somewhere toward the front of the car. (2) As the lower control arm is lowered down from the frame, the upper arm will start pointing skyward because it's so short and you will finally have no intersection of the 4-link suspension, therefore NO I/C at all! (3) I have been advised to fix my traction problems with raised upper bars, lowered lower bars, stock boxed bars, etc.,but it seems to me that the angle of the lower arm has everything to do with how the rear axle will lift or press toward the ground. There must be some known factors before changing any arm angles (or not changing the stock ones).(4) It appears that many of us have tried various things until something works. This is inefficient and expensive. (5)Why don't us Buick guys come up with a formula and save us money. Better yet, maby an honest vendor could provide the sientific answer and prove it at the track with repeatability.(6) Start with assumptions such as (a) Front springs are softer than stock (b) rocker panels have a given ground clearance front and back (6" front & 6.5" rear for example). (c) Rear controll arms are level (parallel) to the frame or drop 1/2" or whatever.SOMEONE TAKE THIS AND RUN WITH IT!!
There is no clear cut formula for any traction problems.There is more than one way to skin a cat.You can raise the rear upper control arm mount and lower and shorten the ic or lower the rear of the lower control and raise and shorten the ic.The short high ic will hit the tire real hard but for a short period of time The short low ic will hit the tire alittle softer but will load the tire for a longer period of time.These set ups are quick fixes but still need the torque convertor springs and shocks to work together.This takes time and tuning.If you can bolt on one thing and make the car hook everybody would be running the same thing.It all depends on your car and parts selection no 2 cars are the same. Back in the early days of nmca super street Chuck Samuels had a 65 elcamino with a stock rear suspension boxed control arms and aluminum bushings ten dollar kmart shocks and a air bags the car went low 1.30 to high 1.20 60fts and ran 9 teens on a 9 inch tire and used to street race it.The point of this is you don't have to make drastic changes to the ic to make a abody gm to work.Get rid of all the slop and take the time to work with the whole car as a combination
A starting point? What if: (1) I box all my stock arms. (2) Install harder bushings (are there any nonsqueaking hard bushings?) (3) Cut my rear springs until the rear lower arm is straight with the frame. (4) Cut my front springs just enough to put the front rocker panels 1/4-1/2" lower than the rear. (I read that all 67 A-body springs are cuttable). Does this sound like a good start? I have: Soft front springs Stiff rear springs Cheap gas shocks Air bags Sway bar 7/8" (bushed with 1"pipe"inside the arms) My car sits high at about 9 1/2" rocker panel clearance causing 3/4" drop at rear of controll arm. Rear tires are MT Street 28x12 1/2-15 on 8" widened stock wheels. Tires will spin like crazy until front springs fully extend then you get 100% bite.On a 12.40 e.t. I may get a best 60' of 1.85 if the track is STICKY. Torque converter is s/p 3000 from Kenne-Bell, 3.42 rear. John Osborne drove my car at Bowling Green. "Spun tires" on every run.
It's a start I would find an application chart for rear springs and find a rear spring with the same rate as you already have with with a shorter length mcquay morris used to have one you could talk to a good parts house by you and they should be able to find the application chart.This way you won't change the spring at all other than the shorter overall length. What front springs do you have ?if you cut the front spring to much you'll lose the stored energy of a long spring which will help weight transfer that you are lacking.You need to get the weight to transfer to the rear on launch.I would run some sort of adjustable front shock and run it loose at first until you get it to transfer.You can also loosen the front control arm bushings alittle this will allow the front suspension to move freely. As for bushings call global west they have real nice bushings.I would get them for the front and rear control arms. If you can get the weight to transfer the car should start to hook then you can work with burn out tire psi and launch rpm to make it work good.
Gary, You need to contact HR Parts-n-Stuff. They sell a rear kit for the A-bodies and several guys I met in Salem had their kit on their cars. What a difference. They had a mock-up on display in their tent and I was impressed with the engineering. It will eliminate right rear squat without the use of air bags, hard bushings, etc. I think the kit was $350-400. Visit their website and see the set-up for yourself. I don't have their web address but I am sure you can find it easily.
The 67 new stock replacement ElCamino springs were very long; probably 5" longer. Had to use an inside spring compressor and really crank to get'em into the perch. I figure I can lop off 1 to 1 1/2 coils without being close to the short,fat, GS springs. Should still get way more lift than orig. springs.
Be careful cutting those springs. I cut 1 1/4 coils off my FIRST set of Moroso's and had to get another set. I would start by cutting 3/4's a coil at first. Not that the 1 1/2 wouldn't be perfect but I lost my first set that way on my setup. Do not overlook the converter. It is one of the most important parts. But starting off with a solid suspension is where to begin.
Gary, from my experience and knowledge gained from my peers and alot of initial misinformation, I'll try and be as concise and brief as possible. First of all, the theory that the lower control arm is to be paralled with the ground is false, and raising the pivot mounting points on the top of the differential does not work (in the stock style GM mounting positons) as well as lowering the pivot mounting points on the lower/outer axle tubes. South Side Machining figured this out a long time ago, Metco has followed suit as they supply a drop bracket with their lower control arms which is welded in place after it is bolted in. I had a frame shop do this so the alignment could be checked as this was being done, Metco's upper arms are adjustable IN THE CAR, and all of the arms are billet aluminum with greasable fittings. Yes, the are more expensive, and the setup is visible from the back of the car as well making it nessecary to come up with your own sway bar mounting, as the drop brackets lower the bar height from the ground. I found that having the airbags in elininated the need for the sway bar with these arms, however I do intend to install a heim link style bar in the future. Obtaining a pinion angle guage really helps optimize the setup with adjustable control arms, Summits catalog has one,(4.5 degress down works well on mine, I started with as much as 7) the half right way is to measure this from driveshaft to pinion yoke, the true way is to do it with a straight tube out of the back of the transmission (no change in angle from the U-joints) This is easier said than done, as doing it with the suspension hanging unloaded in the air is useless. If the car is on stands and a jack is utilized to return the suspension to its loaded position, or if you have access to a drive over pit, either way will suffice. My 4,000 pound 73 Century with 3:42 gears, no high stall converter, and 26" Hoosiers hits the tires hard with a slight lift in the rear suspension and 60 foots at 1.86. Nothing to rattle the world about, but good considering what it is working with, as far as the front end, eliminate the "binding" stab links in the sway bar with heim joint rod ends, greaseable frame bushings, and run good ol' Moog non a/c springs (they settle after being in the car a while) and some QA1 adjustable shocks at no more than 80/20, Hotchkis is now making a hollow big moly sway bar that is half the weight of the solid one, hope some of this helps. Shane
launch efficiency Shane, Your reply, as well as some others here, are very interesting. I read and reread these. At this point, I see some theory coming together. First, if the I/C (instant center) is supposed to be higher than 50% P/R (percent of rise)for a vehicle with an automatic, that means that a level lower arm is not the best choice except for stick shifts. Second, most racers settle for consistency over efficiency;end of story for them. If we use a formula to measure efficiency (black and white; apples and apples; no BS), and test it under less than ideal conditions (off the shelf street radials and perform like Greg Gessler's stock appearing Buick) we will approach the optimum solutions. I like this formula: Optimum 60 ft time=168/Quarter Mile MPH 132/Eighth Mile MPH My guess is add .20 for 3.42 or higher gears and med stall converter add .15 for lower gears and higher stall converters add .10 OR LESS for race only applications
Chassis/Setup Efficiency Gary, I think you are a little aggressive on your calculations. I've attached a chassis/setup efficiency chart that I've used over the years. On Buick GS's that run down to the 9.75-9.80 range I've always felt that we must improve not only the 60', but the 330' times to be better than this chart to run the numbers. I strongly believe that 330' times are far more important comparisons when you go from one track to another since all 60' clocks are not the "same". On our 3400# and heavier cars the first 330' is critical to achieve maximum et. Some of our fellow Buick racers that dip into the 7's, 8's and even low 9's usually have more cubes or a power adder to achieve that top end charge. Most of us don't have strong of a "back half" of the race track. My Top Stock car has about 650HP, 3450#, 4.10 gear with 9" tires. It has 56% of the total weight on the front tires! Its best overall time is a 9.75@134.8. Incremental times: 60' 1.300 330' 3.927 660' 6.150 @ 110.15mph 1000' 8.091 As you compare to the chart I am .04 quicker to 60', .04 quicker to 330' and .02 quicker to the 660' than the chart but I run right on the 1/4 et. but am 4 mph slower, partially a function of running a stock 850 Holley. Because of an efficient setup I am probably going "faster" than the horsepower says I should go. Sometimes I think we spend more time "engineering" the right setup rather than trying to find out what works best on our cars at the track. My setup is rather simple but consists of a good 8" ATI convertor, T-400, Moroso front springs, Delalum bushings, Koni front shocks, adjustable TRZ upper and lower control arms in the STOCK locations, TRZ antiroll bar and a set or Varishocks in the rear. On a good track I run 25# of air in the 9" Hoosier radial slicks. My best 60' ever was a 1.269 but still only ran a 9.76. Look at the chart, it makes for some good reading. Good luck. Tom Rix
Efficiency Thanks Tom, I like your chart and comments. Efficiency is everything if "QUICk" is your goal. My agressive formula came from THE CHEVELLE ENGINEER I found on the web. I think his figures reflect the best you can expect to achieve with all the goodies. There some things we can use as BENCHMARKS such as ATI converters which are super efficient. Another benchmark is a FORMULA to measure your performance against. I'm benefiting a lot from this website and hope to start getting some progress going by next spring. ATI converters (like yours) are super efficient. My switch pitch is not; but I have a Tazzo to tell me my street performance (2.01 on concrete), no burnout. I intend to continue to do this same thing because I must have less than optimum traction or I can't test any chassis changes! I WANT TO SHOOT FOR OPTIMUM COLD STREET TRACTION. Then I will start adding horsepower and improved converter, etc.
Tom, Nice chart. Very interesting indeed. According to my MPH (125) I'm dead nuts the same as the chart, except 60'. My best is 1.46, the chart says 1.43. I always thought that's where I should be (1.42-1.43). I'm still working on chassis set-up and then I'll focus on my converter. I think I've learned that my 10 sec. car doesn't necessarily like the same set-ups as my old 11 sec. car. More testing ... More testing ... More testing. Never satisfied! Have fun.
instant center calculator :3gears: I found a web site that has an instant center calculator that works.... if any of you guys try it let me know how it works for you- kirkm - www.inductionmotorsports.com
Tom is you turbo 400 stock geared or is it a low gear tranny with lite parts. That sixty foot is what I want and seem to be chasing. I feel that if I could find it I could really be flying the blue car ran 1.41 sixty foot and ran 9.86 @ 135.86. Early in the year I had a smaller carb on it and saw no real increase in the sixty or 330 over my PRO systems dominator.
In my sprayed GS setting the instant center using the "level with frame lower approach" gave me the best hook ON THE STREET. Setup of the car was very simple. I lowered the car to get the rear control arm level with the frame. Used Skylark rear springs I took to a spring shop and had them reheat the spring to get the pigtail on the axle end to shorten up. Total drop was about 2 inches at the rear from a stock GS. I ran 28x13.50 ET Streets on 10 inch wheels with a 5.5 backspace. Tight fit but tucked up in the wheelwell and a byproduct was a killer stance. Used Moroso front springs for a SBC Chevelle and actually had to shim them on my unlightened non air 70 stage1 slightly to get the front about .5 inch lower than the rear with 27 inch tall front tires. QA1 adjustable shocks on the front. Airbag in the right rear set at 10psi. Stock rear sway bar with gas charged plain jane shocks, no front bar. Converter was an ATI 3200 N2O converter which was a bit tight on motor. Otherwise the car was completely stock suspended. No cage, no holes drilled. It's a real Stage1 and my baby so I couldn't bring myself to doing anything crazy to it. On motor the car at 4000LBS with me in it(track scales) I'd set the ET streets to 13 psi in the left rear and 12 in the right. It would put 6 inches of daylight under the tires on a concrete public highway everytime. No pedaling, just do a burnout and nail it. Motor 60 foots were 1.60-1.55 and ET's were in the 11.40-50 range with an iron Stage 1 motor with 10.75 compression. Spray outta the hole was a no go as it wouldn't hook in first gear on the street. At the track the one time I sprayed it outta the hole fearing for my stock rear with 3.90 gears the whole time(why I never did it) I ran 1.45 sixty foot on a 150shot. Ran 10.92 out of gear and lifting about 100feet before the stripe since I refused to rev it past 6000 with stock rods, crank and no girdle. I always had street traction problems til I took initial hit away for extended hit. Taking some rake outta the car to get the static weight balance moved rearward also helped. Lots of front travel also seemed to get the car to "sit" on the back tires which eliminated the hook, move, spin I see so often with 4 bar GM cars sitting up in the back. Anyway, there's how mine worked on the street for 10 years before I retired it for restored Sunday cruising because I was getting faster every year and was beginning to abuse the car in my mind. PS: Fresh tires are numero uno on the list of making a car hook. Tires get old and lose hook alot quicker than you think.
