volkswagens-for-life

Are they the same thing? Are bilsteins an upgrade or downgrade over stock z51 shocks?
Thanks

LongBeachC4

Z51 shocks were made by Bilstein with special valving to deal with the higher spring rates.

volkswagens-for-life

So are they bilstein hd's? Lesser, greater, or just completely different?

c4cruiser

Bilstein shocks also came with the Z52 option (87 and 88 cars only). The Z51-specific Bilsteins have a different valving compared to the Z52 shocks. If yor car has the Z51 suspension, I would definitely go with Bilstein z51-specific shocks.

Vette Brakes has both the Bilstein Sport shocks and the Bilstein "Xtreme" shock which is a special order and I think can be had with custom valving. Might want to email or call them to see what they suggest.

volkswagens-for-life

Maybe I'm not conveying my question accurately.

Where does the z51 shock stand in the suspension world. As in, is it an excellent oem shock, are there better options for handling, are they comparable to a bilstein HD, or are they really in their own world?

c4cruiser

Bilstein is a great shock for C4 Corvettes; they were OEM on anything but the base suspension cars. The earlier C4's that had the base FE1 suspension used Delco shocks.

The "HD" designation could be something entirely different and you should really ask the shock vendors what the differences are in valving and rebound rates compared to the Z51 shock. What one vendor calls a Bilstein "HD" shock may be called something else by another vendor.

Are there better shocks available? Yes, but expect to pay large amounts of money, especially when you get into the world of adjustable shocks like the QA1's or Koni's. Penske makes a set of fully adjustable shocks for C4's that are in the $3K range.

One thing that Bilstein can do is rebuild your existing shocks to either match the OEM specs for your car or they can be custom valved for any specific application like autocross, track/HPDE, or even competition use.

leesvet

The Bilstein IS the upgraded performance[/I], shock that GM offered for the Z51 & Z52 suspension packages.

short answer, YES, Bilstein IS the best that GM offered.

the 'base' shock or hd shock was some generic brand with a gm label.

vader86

The modern names don't correspond to anything from 20 years ago.

Heavy Duty is probably very similar to the Z51 shock, but you'd have to ask Bilstein. When I swapped out the shocks on my 86 Z51 I believe the model I picked was the HD, but its been so long I've forgotten.

GREGGPENN

Z51 versus “HD” shocks are the same quality/class of shock. Both are made by the same company, Bilstein.

As a couple of members have claimed Z51 shocks are a better option (aka “upgrade”) from the stock shocks, I contacted a Bilstein rep to ask this question. I wanted to know if my car would ride OR handle better if I moved from the HD shocks to the Z51 shocks. His answer was “No”. You’ve seen the reason in this thread. Shocks are valved to “mate” with the spring-rate. Z51 springs are stiffer. Basically, Z51 shocks aren’t as “stiff” but their rebound stroke is stiffer. They compress a bit easier but stretch more firmly. I gathered that the Z51 spring provides more stiffness so the shock doesn’t have to. Conversely, the stiff spring requires “firmer” rebound control – to stop it from bouncing. That’s why the counter-stroke has to be firmer than the “HD” shock.

Don’t confuse the actual “HD” moniker to mean anything. Bilstein made a shock for the base springs and another for the Z51 springs. (They also make FX3 adjustable shocks.) When I contacted them, I was looking to compensate for the larger 11” rear wheels I’m running. They replied that the ZR1 cars (also equipped with 11” rears) also came stock with the “HD” shock. If anything, I would be better off with the next size larger rear sway bar…but not Z51 shocks. So, I replaced mine with the ”HD” shock as Bilstein recommends. (FWIW, this information came from an 1989 Z51 C4 owner that still works at Bilstein.)

volkswagens-for-life

Interesting... so it seems that unless I change a lot of aspects of my suspension, the z51 would handle the best due to its valving and control that are based on the OEM z51 spring rates.

So unless I redid the entire suspension setup, I'd probably end up with a worse handling car. Not that i"m planning on altering my suspension one bit, it was just a question that I just had to know.

GREGGPENN

<playing sound of angels attaining wings and relevation>

batchman

You should note that z51 setups vary some with year.

I can tell you that the 1988 z51 package (springs, shocks and bars) was an awesome handling setup.

You don't mention the year of your car so no further help here.

Cheers,
- Jeff

c4cruiser

According to his profile, he has an '87 coupe with Z51.

leesvet

according to what I have seen, the 87 Z51 was a soft yr where owner whining forced GM to use a softer spring to provide more 'comfort' to the driver instead of rock solid feel at high speed.

Having an 87, that is what motivated me to install some 84-85 z-51 springs with a rate that was so stiff and fast that most of the "shock" is transmitted directly to my spine...

It feels very stable at speed, hardly has any roll, even when thrown sideways, and it holds the road very well...BUT, I understand why folks complained about the ride quality in the early days. It is more like a buck-board than a fine automobile that has a well designed suspension. Its harsh, putting it nicely. It handles well, but its tough to live with on city streets...

So, based on MY experience with 87's and Z51 packages, I would say that a rear spring rate of NO MORE than 320 lbs( +- a few) would provide a good solid feel to the car yet allow the driver to sip his/her cappuccino between pot-holes during the commute. 230ish would go a lot toward street civility and a comfy ride. The IRS goes a long way to compensate for soft springs (if you want the family car ride quality)and will still allow the driver to make some emergency/panic moves without severe consequences..

The 411 lbs/in spring that I am running now......is like a 2x4 on edge....Kim Kardashian could sit on the tail and not move that suspension more than 1/4"....
There is EVEN faster/stiffer springs for the C4 ! IIRC, there is a 499 lb/in spring that moves about as much as an "I"-beam .

....and yes, mine came with and will always have Bilsteins.
I had a brief experience with KYB, but that was a mistake. I tried "cheap" and paid the price...

volkswagens-for-life

^I have KYB on my daily driver... never again!!!



Thanks for the input guys. Yes its an 87 z51. Not going to touch the suspension as I love how it rides and handles now, I was just very curious. Thanks for the input.