Looking for input to decide on front coilover shocks. Note that the car has an extra 100lbs on the front suspension due to having an iron block and centrifugal blower kit. Current Z51 front suspension is worn out and sagging. I don't know what spring rate to go with due to extra weight.

 

Hello, I went with silvers 18k front spring rate and 10k in rear with the upgraded swift springs.Your case prolly could use 20k front.
you will not regret getting these wish I did it sooner.handles so much better. Drift a few weekends a season but mostly street thrashing.
Call, or email them. Great company to deal with

 

That stiff? This a purely street racer. I'm only going to do the front for now.

 

What trans, since if M6, then just swapping to an A6 Fe3front trans spring, which will solve the problem of the 100lbs on the front end. Hence z51 Fe3 M6 spring comes tensioned lighter for the M6, and FE3 A6 stronger for the A6 trans since it adds about 100lbs to the front end. If A6 in play on the Z51, then just swap to a FE5 spring for the front end for the extra trans and steel block weight.
Note, Z06 only comes in a M6 so only one type of FE5 front trans spring.

This will solve the spring rate problem for $100, a set of DRM shocks with poly bushings for $575, maybe upgrade the sway bar bushing to poly, and then all you need to do is correctly corner balance the car, and it will be back to a correctly tuned suspension that is going to work from the start.

On coil over system, lets face it and most will never road coarse the car hard enough to justify it/be able to tell the difference on a track, much less even a smaller percentage being able to dial it in correctly as well. And the rub, not only should the springs be adjustable, but the shocks adjustable as well (read your looking at $4K for a system that the shocks are fully adjustable on a system).

 

Decided to go with 550# QA1 coilovers in the front. Turned out great with a better ride and weight support.

 

I'll give another vote for Silver's. Running a 12k/10k setup on my 06 Z51. Fantastic setup, rides better than OEM, had some weight savings from removing the leaf springs, and everything is adjustable. Have almost 45k miles on them, no issues at all. Excellent guys to deal with, and will help dial you in. 18k is overkill stiff for the front unless you are drifting, they recommend a 14k for a street driven car with an iron block/blower. They are much more popular on the facebook groups, lots of reviews.

FYI, they are adjustable shocks as well, not sure why Dano said that. They have a double adjustable setup if you are more serious about track racing.

 

I agree! 10/12k adjustable setup for a C6 is perfect.