Hello,
I have about 100K on my '91C4 and I am currently considering lowering my car with H&R Performance Springs. I wonder if this is also a good time for me to swap out the OEM shocks (still the original pairs) for some new ones?
How long do they typically last anyways with normal street driving conditions? Also what would be a good replacement to the OEM shocks for street/track purpose?

Thanks much for any input.

 

Hi Mike,
I got a '91 with a little over 30k, and had Bilsteins(heavy duty)installed. I've been lowered with Eibach springs for years with the Boges; which worked good, but it feels even better with the Bilsteins.2 front Bilstein stuts and 2 rear bilstein shocks ran about 800 plus installation(worth it).From what i understand they have two types, race and heavy duty(aka sport)for street use that can be adjusted for the track.

 

Thanks Geo,
After a little of looking around on the web, seems like Bilsteins are the way to go. Currently I do feel there is excessive body roll in and out of the corder. Hopefully with the lowered springs and these shocks the roll will be much reduced.

thanks again

 

Ah, yes, the Bilsteins are the ticket!

Please notice when hunting for these bad boys that there is no "sport" option available for the 964. They are referred to as "HD" or heavy duty. The part #s are readily available off of www.shox.com or I can email them to you.

I have recently changed out the springs and shocks myself...what a job! I learned some new words during my latest endeavor.

I used the H&R lowering springs for a 965 (C2 Turbo) and Bilstein HD shocks/struts...the results were astounding! The difference in ride quality didn't seem too harsh...but the handling...what a difference!

Keep in mind, I do track events...and a lot of them, so the 965 springs may NOT be what you want to do, stay w/the 964 springs.

My next adventure is a sway bar upgrade, front & rear.

By all means, if you have any questions, or want some neat/high quality digital pics sent of the upgrade...let me know via my personal email address. I can also refer you to a great website that details changing out/upgrading the shocks, swaybars, brakes...etc. if you're interested. Cheers!

 

Dear Michael,
First thing you need to do is to establish what model 1991 964 do you have. Do you have a 1991 version of the 1990 model or the 1991 model.
The 1991 version of the 1990 model (which is a 1990 model with airbags) was produced for the USA only, between May 1990 and October 31st 1990. The 1991 model fully was produced from Nov 01 1990 thru to July 1991.
The front suspension is the same basically but the rear is not.
I do not recommend you install lowering springs on their own on just the front.
M030 sport option will not lower your 911 anyway, will just make it 40% stiffer in ride.
M030 cannot be installed on pre Nov 1990 model C2s and C4s.
I do not agree with the Bilsteins. As has already been stated, they are HD not sports. I would highly recommend the KONI Adjustables Sports. This is what I use and they are really good.
Anyway, you need to determine what is installed on your C2 by simply checking the date of manufacture. You need to know this before moving forward. Once you have established which version of a 1991 model you have (which by the way as ROW 911s were still 1990 models) then you can check out the alternatives.
Ciao,
Adrian
911C4

PS: tracj use will shorten the life of all the components on your 911. For normal road use the Boges last a very long time.

 

Thanks Adrian,
You have introduced another set of variables that I was not aware of. To my recollection I think my car was stamped Nov 1990 on the door frame.
By the way, what do you mean my M030? I plan to install H&R performance (lowering by 1.5") springs front and rear and also change the shocks and struts (as the OEM have already 100K miles on them)KONI or Bilstein? I guess there is more homework to do.
One last thing. You guys Rock!! I love this board.

Mike

 

Hi Everyone,

I have some input on this discussion regarding the lowering of the 91 C2.

(Hi Adrian !)

First - the best way to tell a "real" 91 is to look at the intake manifold. The pre 91's were aluminum and the later ones were plastic.

My car is a 90 and has airbags - it does not have the glove box on the face of the dash it is under the dash.

As for lowering a 90 C2 - you most certainly can lower it as I have done it with mine and it was manufactured in Jan 90.

I used the M030 spring and Dopke lowering perches. This is a very effective way to get the car down and retain the use of stock springs.

Hope this helps !

 

Tom,

Excuse my ignorance, but what and where is the intake manifold?

Having learnt about cars in 3 different languages I sometimes find new words for old things.

Thanks

 

Hi Riccardo,

The manifold is the unit the sits between the fuel injection controls and the upper side of the heads on the engine. It directs the air to the cylinders.

Tom

 

Just thought I'd "chime in" again in regards to Adrian's comments towards Koni's. Koni's are excellent shocks and would make an excellent replacement.

But I have some interesting info. that may keep you on the Bilstein issue. First of all, Bilstein decided not to call their performance option for the 964 "sport", instead they called it HD for heavy duty. A technician at Bilstein advised me of this and offered up a suggestion that w/all of the progressive rate spring options...they didn't want to make people believe that these were harshly valved shocks, hence a viable "sport" option.

I have talked w/several Porschephiles including Steve Weiner and Windward Performance among others...all seem to concur that the Bilstein HD series shocks coupled w/H&R lowering/progressive/sport springs makes for an excellent setup due to the coincidence that the valving on the HD Bilsteins seems to be "perfectly" matched w/the spring rate that H&R and even Eibach offer.

Now, as a testimonial...I use my car on the track, quite a bit. Understand I have, to date, only one event w/the "new toy", but from previous experience w/suspension upgrades on my previous track car...I can tell you, this is the ticket. It is not an obnoxcious/harsh upgrade, but when you pen it into the corners, it really holds well. The rebound seems to be nice and smooth as well. Just a short sweet and simple testimonial.

Please keep in mind that a lot of posts/replies on here are just opinions/experiences from people in various environments and driving scenarios. The whole idea behind H&R springs was nice ride quality w/performance in mind when you push the car...hence the progressive spring rate idea. Not a bad idea!

All in all, Koni's or Bilsteins...even the M030 factory sport suspension optioned Boges will all do just fine. If you have any ideas beyond that...check out the prices on the Bilstein sport/stage4 coilover option and go up from there!! Geeeeeeez! Now we're talking expensive.

Again, I have nice high quality digital pics that I took while making the change over to Bilsteins/H&R springs, changed the rotors and brake lines at the same time too. You all are more than welcome to email me personally...and I will provide, as I already have for a half a dozen people.

Cheers!

 

Seconds on Jeffs comments, I have a 93 RSA with the H&R's and Bilsteins. In addition, the monoball camberplates and tower brace. The shocks were custom valved by Winward to match the spring setup. The results are incredible stick with a suprisingly acceptable street ride. The last setup I had with the Konis was a 74 carrera. While there is probably no comparison to a 964, on the early chassis they were pretty harsh. Where they shine is on the track after some dialing in. If you are the type to spend the time (and if you have the talent) to properly test and adjust your konis at every track event, I am sure they would perform at a higher level. However if you prefer the "set and forget" option, the Bilsteins seem hard to beat...

PS: I don't know if the additional unsprung weight of the C4 gear would affect the setup. You could check with winward or perhaps Adrian may have more insight on the difference.

 

A couple of point to complicate the situation. Firstly I am an EIBACH/KONI person but I agree that perceptions play an important role here and if you prefer Bilstein and H&R then use them. I always discourage the use of "any" lowering springs on standard boge struts and shocks. I like the ability to adjust my suspension without paying major dollars for complex set ups and very non original set ups which here in Switzerland can bring some conflict with the authorities and resale value.
Now Tom made a point about the plastic intake manifold. Unfortunately this is not a good guide when looking at the type of suspension you may have because I know of many 1990 models which have this plastic intake manifold fitted. Some were done by dealers prior to delivery and others were done in the first few servicings. I will state however that this is not something you can rely on because this action was not uniform. I am also told that even the later 1990 models came out with this plastic intake manifold when they ran out of alu ones.
The only true guide is the date of manufacture plate. Nov 1990 onwards and you have what I call a real 1991 model. Pre Nov 1990 and you have what I call (so do Porsche by the way)a 1991 version of the 1990 model.
Now this only applies in the USA. Officially the 1990 model run was from Sept 1989 to October 1990. May 1990 airbags were installed for the USA only. ROW airbag installation as standard started in April 1991.
I have to make these distinctions understood because otherwise people can be given the wrong info and waste valuable time and money. Very nearly myself some time back.
Option M030 (911) is what is called the Sports suspension option. It was designed for the 1991 Turbo originally because the first Turbos had C2 springs (blue dots) and they were too soft. The ride stiffness is increased by 40% but the ride height is not changed. You can indentify 911 M030 springs by the green dots on the springs. Orange Dots are for the C4 and white dots for the 964 RS.
(There are also versions of M030 for all other Porsches as well so please keep this inmind. Never purchase just Porsche M030 springs etc, always confirm the model they are for).
Now to the comment about unsprung weight. Unsprung weight applies to the rotating mass that the brakes have to stop. Not the actual weight of the 911. To affect the unsprung mass or weight you need to change wheels, tyres, brake disks (arguments over axles rage). Obviously weight changes affect braking but the most immediate impact is the rotating mass that the brakes have to stop.
Suspension changes do not change directly unsprung mass or weight unless you did what I did and changed the wheels. The important thing is to reduce unsprung weight. I used lighter 17 inch Turbo wheels.
One last and VERY IMPORTANT POINT. You can spend heaps of money purchasing and installing suspension upgrade equipment on your 911. It is all TOTALLY WORTHLESS unless you get the correct ride height adjustments and wheel alignment, front and back, castor adjustments etc done 100% correctly. This is really critical guys and let me tell you. When all the adjustments and balances are done perfectly, you will have a mean looking and mean handling piece of machinery. Do this incorrectly and you will have well a piece of crap (sorry for the French),
Ciao,
Adrian
911C4

 

Adrian, good points, my question on the unsprung weight was the different valving setup for the additional weight of the C4 front halfshaft/spindle vs. the lighter unsprung weight of the C2's front assembly. I'm not familiar with the C4 components, but I would assume the valving would be different to handle the additonal mass, particularly for jounce travel.

You're right on about the setup, I've seen some state of the art suspension setups setup so poorly they don't perform as well as the factory equipment.

 

I too would very much like to lower my car (a '90 USA C2, built Feb. 9, 1990). From what I can see (I am the 3rd owner), it is still equipped with the factory Boges and stock springs. The nose sits WAY TOO HIGH, IMHO.

I agree with the comments about doing the shocks and the springs at the same time, but have a couple questions.

As for the Koni's, it appears that the fronts are just inserts that require some metal work to remove the existing insert, and replace it with the new Koni. Is this correct? Is it a big job?

Secondly, my stock shocks have threaded spring perches. Do either the Koni's and/or the Bilsteins also have threaded collars?

Lastly, I expect that the Koni's are externally adjustable, correct? If so, where is the adjustament, and is it relatively accessible once they are installed?

I had a Miata with Koni's, and the adjusment was at the top of the shock tower...very easy to reach. If that is the case for the C2, I suspect the rears will not be very easy to adjust.

Also, do the Bilsteins have any external adjustment?

Thanks in advance for your replies.

Brian

 

Although more costly than Bilstein, you might want to take a look at the 3-way adjustable Moton.