Great synopsis. For years I thought the fast way 'round was a 100% neutral handling car. It was fun, a lot of fun. But I couldn't even touch the throttle or the rear started to swing "wide"

After many years of practice I learned the fastest way around a turn was to take a different line, turn early, start to straighten it out and get on the throttle all the way as soon as you can, and then it's 100% balanced , but only at Full Throttle! When I learned to take 75% of the turn with the pedal down, my times dropped another couple seconds, at a time when I didn't think there was any left, and I ran with the "big dogs"and even beat a few! But that took many years of practice. Maybe 200+ autocrosses.

Ever do a slalom? I learned to drive them as above. Car was 4 wheel "drifting" 75% of the time, on the gas. With that amazing LT1 just screaming. Watch Danny Pop drive today. Honestly he's got slicks, 12 inch rubber, and 600HP. That thing is a beast and he is very good with it, And very smooth, being a beast. Personally I think if it slid it more he could be even faster. Smooth is fast, but not the fastest. For that you need to be just a little bit over on the ragged edge. One of my main comrades now runs his own Driving School, Andy Hollis. He and his wife won 7 National Championships.Same for Jerry Fink.He actually builds race cars now. Me? I turned teacher.

Honestly that was work driving like that. Worked up a sweat and was very nerve-wracking. You were always throwing the car around and straightening the wheel to keep it from understeering. It was actually more fun to drive, when it was a little more neutral. Lots of guys drove my car in "race-mode" and they were surprised how badly it understeered. At the time I didn't know how to explain, I just said "you don't know how to drive it" LOL!

For a street car, that probably will never take turns more than 85% of it's potential, I'll not set my vette up that way, I'll go more neutral.Your driving "style" becomes as important as the cars "setup" and they need to mesh.

 

Taking a fast curve on a mountain road with a huge drop off on the side, in a 50+ yr old car makes me more nervous now than it used to. I used to enjoy auto cross. Good action and not much chance of major damage.
Or, maybe I've gotten a bit smarter in my old age.

 

It's FLAT around here in NJ. Any curve with a drop-off makes me nervous! LOL And I can't even imagine being in a Hillclimb race, We went up the Rocky mountains in a Bus doing u-turns all the way up and I closed my eyes. Looking out the window and straight down for a 1000 ft is not for me!

 

Leigh, A few observations on your excellent analysis.

My 78 550 springs are 1 inch lower than stock BUT coupled with 255/45/17 Ultra High Performance Summer only tires, poly upper and lower control arm bushings, spreader bar, Bilstein HD's, rides BY FAR better than most C3's that I have wrote in over the the last 40 years. It rides firm but not harsch at all and in fact, is relatively smooth....amazing!

Most people who ride in my 78 set up the way it is today, love the L-82 355 power but always comment on how nice my C3 rides. I am curious what you would predict is the reason for such a great ride considering the spring frequency you spoke of above for the 550 springs. Both my stock 2012 Lexus IS350 F Sport and my stock 10 C6Z06 ride much harder and harsher than my 78. Rear Suspension is 360 composite, Competition Heim Jointed Struts, 3/4 inch GM Style Rear swaybar, same tire as above

I agree with your comment that adding the driver to the BB C3 adds 75% of driver weight to the rear bias and makes those C3's closer to a 50:50 weight distribution but that same phenomenon applies to the SBC C3 like my 78 with a driverless weight distribution of 48% Front:52% Rear. With the driver added, the SBC C3 in my case now has a weight distribution of 46/47% Front:53-54% Rear which is almost ideal for road racing in a front engined vehicle, in general.

This rear bias of my 78 is the reason GM used a very small 7/16 rear bar on the SBC since the car has a fairly pronounced rear weight distribution combined in the later 70's with the massive front bar of 1 1/8 inch at that time. This front bar was probably the biggest one utilized by GM during that era, which was fantastic. Thie BB C3's probably needed as you stated a much bigger front bar to control the roll rate of the motor better like a 1.25 front bar with that 9/16 rear bar and much higher spring rates, front and rear.

Lots of variables but for street driving not too complicated....All C3's with stock suspension and tires were designed by GM from the factory to understeer, not oversteer, as a GM mandate after the Corvair Fiasco. If a C3 is oversteering with a factory suspension and tire, then something is wrong with the suspension or driver. Getting a C3 to oversteer, of course, is possible if provoked like any car and removing the rear stock sway bar from a stock sport suspended C3 will provoke more understeer but these cars were setup, built, designed from the factory to understeer to start.

 

Sounds like you brought up shocks. So today is shock tuning day.

I'd say you found the perfect shock valving for those springs. By luck, or design, or trial & error. And I notice you do not have adjustable shocks! So kudos to you. Your experience may convince me to try the stiffer 480/550 springs even though the fps numbers say I would not like them because they are so stiff. Wish that I could go for a ride with you and see how great the 550s really can be.

There are four valving circuits in a shock and extremely few models let you adjust all of them. Low & high speed, bump & rebound. And shock tuning is oh-so-important for controlling the springs and getting a good ride. It is much easier if you go with soft springs and soft shocks, you actually have a pretty wide range of what is tolerable, ride wise. But only if you stay on the loose side of the equation. If you tighten them up so to make the handling more crisp (it tightens the immediate transient response) it becomes more difficult to make them ride well and you can go over-the-edge of the see-saw. When you introduce a stiffer spring into the equation, the "Ideal" zone becomes even more narrow and difficult to achieve. The spring rates that the shock has to slow down are everything. It's mainly the spring, but also the sway bars, they are actually just another spring, and the compression of the tires, then the bushings, and then any thing that flexes under pressure. You get the idea. Weight is a big factor in how much pendulum force the shock has to control. So you can see how many variables are involved, and how difficult it must be for a Shock Manufacturer to get the "ideal" compromise for a non-adjustable shock. Why do you think a company like Bilstein makes two versions for our cars with two "fixed" setpoints? The HD & the Sport models?

So basically I think your combo must have been really close to that they tested when they developed the shocks, and that's why they work so well. They probably used a fully loaded later model C3 with a little more weight, etc. They might/probably won't ride quite as well in a 200lb lighter car. Or with a different rear spring, or tire, etc & etc. They should still be "good" but maybe not "great" like yours.

That's why I advocate adjustable shocks for street use for those wanting to achieve the ideal ride/handling compromise for their setup.

I have had 3 sets of tires and 3 sets of shocks on my Caddilac CTS. It has the rare factory FE3 handling pkg they put together for the early CTS-Vs, it's in the 08 body with a V6 and a stick. It is the only model that gets a stiff PS rack valving, without that insane varying assist. They did so much shock tuning on that car, even at the "Ring in Germany, that they absolutely "nailed" the ideal ride/handling compromise. (It has 0.9fps springs btw.) But the shocks were done so well to such a fine level of that ride/handling see-saw tip that it is very easily upset. I mean like when the temperature changes 15 degrees and that lowers or raises my tire pressure by 2 psi. It doesn't ride as well that day! It's very noticeable. I kid you not! I changed the tires to a different brand and it rode much worse. It was tuned for the tires. A second tire brand, wound up somewhere in-between. Then the shocks wore some due to mileage and it became like a different car. With a little wear, and a little more "bleed" in one of the circuits, it would "crash" on certain size bumps, it felt like it had no shock at all on that bump. The handling hadn't changed, just the ride. New shocks brought back the ride. I got a third set of tires, and couldn't get the original as-designed tire model anymore, The ride went away again. I changed the shocks to the very slightly softer FE3 versions, without the load-leveling Nivomat rears, and the ride came back. It is not quite as crisp on turn-in, and I can't hang the tail out quite as easy on the throttle as I could before, it has a little less oversteer, and that was just with a shock change! (And yes I do frequently drive my stick shift Caddy like an autocross car.) It's just that good! It drives more like an M3 than a Cad. That car was just tuned to such a fine-edge that it took almost nothing to change the ride/handling balance. I drove a Camaro with the exact same drivetrain, and needless to say, it handled great! They just didn't have the ride part as well done. I took a CTS-V home for a day, and evaluated the Magna-ride shocks. You know what? I didn't like them, not at all !!. It rode great! Better than my car. The valving stiffens up almost instantly when you turn the wheel and it handles as good as my car but not better. But I just didn't like the huge differential between almost not tire feel and stiff shocks with tire feel. And it had lost an incredible amount of steering wheel "feel" that I did not know how to correct. Maybe I would have gotten used to it, maybe not. But that is what kept me from buying the car. And one other thing, the stick shift was terrible. It was solid, just totally not in character with the rest of the car. But a coupe CTS-V stick supercharged certainly had it own set of cool qualities!!! (That unfulfilled desire is turning into an LS6 C3!)

My race car was the same way. But with adjustable shocks it was much easier. But my spring rates were so custom (850 front!!) that the stock range of the adjustable Koni Reds had almost no effect. So I had Truesports Motorsports re-valve them to fit my car and it's springs, tires etc. I could not believe that they were actually the same serial numbered shocks when they came back, but they were. It handled way better and it rode way better. And the adjustment settings had just the right amount of adjustment. Nirvana!

I have not learned very many expert tricks about shock tuning, but I do know a few. The initial high speed movement affects ride quality severely. And also transient "crispness". The low speed valving affects the handling balance more, because that lasts a little longer than hitting a railroad track. How slow/fast do you want the car to take time-wise, before it settles on it's springs/swaybars in a turn? You can't really feel the tires as well while the springs are giving-way during the cars "roll" And this was only a fraction of a sec on my track car. What you "feel" is the car takes a "set". Stiffening the shocks low speed bleed during this time can greatly stiffen the car during the roll, slow it down, and help you "feel" the tires better. Hence you can push them harder during this time and are faster. But it rides horrible BTW. Some people even intentionally set the rear tires a little stiffer than the front, this helps the rear "oversteer" just for a moment during this rolling/transition phase. This is a common FWD car tactic. Others do just the opposite and make the front stiffer. That's what I did. I felt I had plenty of power to move the back, and mine was on-demand, it was that control switch was under my right foot! Hah! I had 4 wheeled steering in my '70 before they invented it in the 80s/90s! LOL

I mentioned before that I want to try soft/stock springs and stiffer bars. The problem with this is both of them are springs. And if you get to the point where the sway bar is way stiffer than the spring, then you can only get the "perfect" shock tune for one or the other, or you need adjustable high & low speed shocks. You may have heard of the "head toss" problem when the bars are way stiffer than the shocks. When that happens the shocks are not controlling the bars. The factory F41 pkg is relatively close to 50/50 bar /spring roll rate. S it is easy for the same shock setting to control both. The Gymkhana pkg leans a little more strongly on the bars even with the F41 springs. I just have no experience with the stiffest sway bars and the softest springs, in a C3, and if it is too "far",or if it will be a problem, or if fancy shock valving can cure it. I may be experimenting there, definately pushing the envelope. Stay tuned.

Maybe one thing I should mention is that a stiffer spring requires a stiffer shock. This is sometimes not obvious. Too far soft and too far stiff on the shock settings ride worse than "just-right" Big stiff springs & swaybars and soft KYBs? You might feel like it crashes on every tar strip. Or it might even go into "pogo" mode. Or hunt up & down all the time. Too stiff shocks just feel like rock-hard. Instant quick response, but no give or compliance. The old push on the bumper test and it should settle in one bounce is a really good shock test. But only for one speed, a shock dyno test covers all the speeds.

The other shock adjustment is bump/rebound. A stiffer bump adjustment very very quickly destroys the ride. So some adjustables like some Konis, just p[re-set-it and let you adjust only the rebound. But there are two bump valved Konis; Red & Yellow. Street & Sport. Just like the Bilsteins. The difference is the Konis let you adjust the rebound and this has an enormous effect on handling. A wide range of softness & stiffness is provided and they go from very "loose-goosey" to rock hard, on the street red ones. They are really designed for stock strength springs. The yellow ones start with a firmer bump setting, and all their rebound settings are a little higher. They are designed for slightly stiffer springs. Miss the spring rate they are designed for and they do not ride well. No cushy street ride available here on the Yellows, They are always firm. It is primarily the bump setting that does this.

I already have the QA1 single adjustables. But have not tried them yet. They seem to be really good, have good reviews, and can be more easily adjusted with a **** vs the Konis which needed to get taken off. And they can be adjusted where the Bilsteins can not, and I wasn't sure, without driving your car, how good they are, and if my planned changes would ruin the "balance" anyway. But I am concerned about the QA1s adjusting method, it changes both the rebound and the bump together. If the bump/rebound split is set "perfect" for my car, then great. I have heard I can have them re-valved if needed, so that is my plan "B". They also have a "ride" oriented model that divorces the bump/rebound settings. Here they set the bump for a good ride, and then the adjustment works on the rebound. Sounds like Koni Red. That is plan "C" Plan "D" is the double adjustables, and then even have 3/4 way adjustables. So lots of options if I am not happy the first time.

 

Also, don't forget that the type of course you compete on matters in determining your setup.

 

I don't think Koni makes a Yellow for these cars...their catalog only shows Orange (STR.T) and Red (Classics/single adjust).

 

I don't think they do. Not anymore anyway.