OK, the weight is not too bad, for a C10.
Here are some thoughts.
Anti-squate is a trade off. The higher mount will have more forward bite, but less 'brake-bite', and the lower mount will trade forward bit for brake bite.
I'll take a guess that on you're "aggressive" laps, you were trying to "go in deep" in the corner. That never pays off on street tires. Braking early, going in smooth, and getting on he throttle early on the exit pays off big time. This may be part of the lap improvement when you were taking it easy.
Roll center will get more and more important. The rear roll center is at the center of the panhard bar. Since one end is mounted to the housing, the rear roll center doesn't drop much when lowering the truck. The front roll center is generated by the IFS geometry. Drop spindles lower the RC the same as the amount of drop. Drop springs have an even greater effect. Tall ball joints usually raise the RC a bit. Let's say the truck had a balanced RC when stock. Lowering the rear 7" probably only lowered the rear RC about 2" (Not sure about the POL bar). Lowering the front 5 1/2" probably dropped the front RC 7" (just a SWAG). So now, you have a 5" imbalance on the RC line ft/rr.
Keep this in mind. Roll center work with the mass (weight) of the truck. The farther the RC is from the weight centerline (usually about the camshaft height) the more the truck will want to lean. (body roll) shifting weight to the outside tire. If the RC was equal to the weight height, there would be very little roll. - BUT, also very little side bite loading of the tire, which can help grip in the turn. Again, it's a trade off. Sway bars can be used to 'fool' the truck about the roll center, but this is a band aid and has other negative effects. ** THERE IS NO SUBSTITUTE FOR GOOD GEOMETRY **
So, what to do. Do the caster mod. you need 6 to 8 degrees. No money spent. Try some tall ball joints. Uppers only. Find a 73-87 front sway bar from a 1Ton dually. Or look for a bigger one from Helwig. You could also try a stiffer front spring, maybe Hotchkis) remember that the bigger bar and stiffer springs are just band aids for poor geometry. You can make it better, to a point. Consider our low roll panhard bar. this will drop the RC, and the truck will want to lean in the rear, but then you can hook the rear bar back up.
OK, this needs to be said. Sorry in advance. There are a lot of parts available for the C10 front suspensions. Some make fantastic claims as to performance/handling/ride quality gains. Lets be brutally honest. The OE crossmember sets the inner pivot points of the suspension. The spindle sets demands on the outer pivot points. So, what can you honestly get from these parts? 1. Maybe some increased Caster, if the arms moved the lower ball joint forward (this will come with more bump-steer due to raising the steering arm). Some have re-worked the upper mount to increase the camber gain, BUT, this approach also increases Roll Center Migration - not so good. 2.Converting to Coil-Overs. This will usually get you a better shock and an adjustable spring mount, BUT most have less suspension travel than stock. Not so great, but, short springs on the OE arms also limit travel. Less travel = Less ride quality. And, if it was done for the quality of the shock, put a great shock on the OE mounts. Why am I saying this? Well, it's not for the hate mail. Be Honest about your build. If you are working with a stock crossmember, do a spring and spindle, caster mod, new bushings/ball joints, and GO. But, if you want more performance than what that will offer, STOP. STOP wasting money on the OE geometry. You will have more $$ invested in the OE crossmember than it costs to step into something that actually works. It sounds harsh, but it's the truth. Write it down.
Spindles 300 - 850
Sway-Bar 250 - 400
Tubular arms 800 - 1200
Coil-Overs 500 - 1500
Rack and Pinion 950 - 1700
Brakes 300 - 2200
So, for somewhere between 3100 and 6500 bucks, you can work over your OE based IFS. And, the crossmember will drag the ground, and the geometry will still suck in comparison to something designed in this century. Take a moment to understand large scale manufacturing. The C10 chassis design really started in 1960 (same IFS geometry as 63) they started selling in 1959. So, parts production started in early 1958, late 1957. That means prototyping happened in early 1957, So, final designs were done in 1956, and concept drawings were done in 1955. Farms, dirt roads and bias ply tires. It is now 2017. This design is 62 years old. Those of you who think it can be tweeked into the modern hi-performance realm should throw out your smart TV in favor of a console black/white, with tubes and rabbit ears.
Sorry to jack the thread, but it is very important to understand the truth of what these IFS designs can, and can not do. Yes, mod them, race them, drive them and have fun, but know there will be a wall you can't get over.
