Bilstein Sport of Bilstein HD??

[garrege]

I've got a stock '69 and i'm planning to upgrade the suspension with new 21/27 bars and bilsteins.

It doesn't appear Bilstein Sports are made for the rear, only HD's are offered on the pre-'72 cars.

Three questions :

1. Am I getting into trouble if i use Bilstein Sport in the front and HD in the rear?

2. Should I settle for HD's in the front and the rear because the thicker (21/27) bars will make the ride firm enough already?

3. Is it correct to assume Bilstein Sports should feel the same in different applications? In other words, Bilstein specifically valves them to feel the same on a BMW, Audi, VW and p-car?

I've always had Bilstein Sports on my other non-porsche cars and I love them. So I'm assuming i would love them on the p-car too. In general, i want a sporty/firm ride; the factory set-up feels like a cadillac.
I'm trying to be semi-conservative with the 21/27 bars because it won't be a track car.

I guess i could always buy the HD's for the rear and then if i don't like them, send them back to Bilstein in San Diego to re-valve to Sport specs.

thanks,
geoff

[Flieger]

1. Dampers must be matched to the spring rate. If the wheel is underdamped or overdamped, it will ride harsh, just different kinds of "harsh". If you use HDs front and rear, your rear may be bouncy and you may experience the rear end bouncing and switching between under and oversteer in a corner. Sports are a better match for the rear weight distribution. That said, your torsion bar setup is a little more front stiff biased than stock due to the relationship between diameter and spring rate.

2. The ride's "firmness" is set by the springs, not dampers. Custom valving is always the best choice.

3. I do think Bilstein valves sports for their intended (Porsche) make, though probably not to feel exactly the same on a BMW.

I believe you can use the later Sports on an earlier car. You need to make a little clearance for the top dust cover by trimming it or replaing it with a rubber bellows. You also must get a bushing sleeve for the 12mm bottom bolt on the trailing arm because the later diameter is 14mm. I am not an expert, so I hope a knowledgeable person will chime in.

[stout]

I'd start with the revalving, so you only have to do the job once.

I'd also buy a matched set from a good Porsche shop that knows what it is doing and have them sent for the revalving by that shop. Let them know your specs and how you will use the car and on what kind of surfaces. A torsion-bar 911 with revalved Bilsteins can be surprisingly good in terms of ride quality AND handle better.

I've spent quite a bit of time in 911s with revalved Bilsteins on road and track (and even in the same 911 Carrera 3.2 on the same day on the same track back to back with Bilstein Sports and custom-valved Bilstein Sports. The difference was dramatic, and that 911 absorbed bumps like a 10- to 20-year more modern car -- and while the move up from there to remote-reservoir shocks was even better, I didn't feel like it justified the large jump in price. I'm sure there are several shops that know what they're doing with revalving Bilsteins, but two I have first-hand experience with are Smart Racing Products and S Car Go. I'm guessing ol' Dave at TRE knows what he's doing, but I've never sampled his work personally.

Hope this helps!

pete

[garrege]

...your torsion bar setup is a little more front stiff biased than stock due to the relationship between diameter and spring rate....

Actually, I'm not sure you're right about the front biased. I got this grid off pelican which seemed to be trusted, but it's baseline is a SC/Carrera which has a 24 rear versus my 23. Using the same calculation as the grid, the rear 23 should have a diameter measurement of 279,841. A rear 27 is 89.9% stiffer than a rear 23 (531,441 / 279,841).

If someone was upgrading a SC/Carrera to 21/27, you are correct, that upgrade would be more front stiff biased.

Does this grid look right to everyone else?

The other points are sound advice, thanks guys.

[Flieger]

To me, the chart seems to indicate that 21f 27r torsion bars bias tthe roll stiffness towards the front with more understeer as a result.

I am a little weary of interpreting and converting the chart for an extrapolated torsion bar stiffnes relationship function.

I guess what I was getting at was that you would want a damper at least as stiff as a Sport in front due to the change in relative torsion bar sizes.

Cheers

[mjmoran]

1. Am I getting into trouble if i use Bilstein Sport in the front and HD in the rear?

YES

2. Should I settle for HD's in the front and the rear because the thicker (21/27) bars will make the ride firm enough already?

NO

3. Is it correct to assume Bilstein Sports should feel the same in different applications? In other words, Bilstein specifically valves them to feel the same on a BMW, Audi, VW and p-car?

Don't know.


i could always buy the HD's for the rear and then if i don't like them, send them back to Bilstein in San Diego to re-valve to Sport specs.

Bingo! Better yet, contact as stated above and get the set matched to your bars. Rennsport Sys in Portland, Elephant Racing and others will do this for you. Steve at Rennsport would be your best source for all the answers...