Bilstein or Koni ???

[JOHN21BLACK]

Trying to decide which shock insert to use on Boge struts. I have a 1984 911 widebody slantnose. Wt. 2700lbs. Running 23/30 solid torsions, 20/18 Sway Bars. Going to use car 75% driver 25% track. Want to use a sport shock... Any Ideals from you Autocross pros. Thanks

[michael lang]

I installed Bilstein Sports on my car. I read in your other post that you were told to make the front end stiffer than the rear end. I don't know that I would take that approach, with you having 23/30 t/bars, you are basically at the factory equivalent of spring rate. It may not handle as you are hoping for. I also read you might be going with HD in rear or did I misunderstand. I believe it would be more beneficial and will enhance the handling to go with Sports in front and the rear. Chuck Moreland has been my go to when I have needed something for my car's suspension. If you haven't already called ER, it would be worth your time to make that call. One other thing, if your car is lowered, you will most likely need to readjust the ride height as your car will be substantially higher after you install the new strut inserts and shocks.

[JOHN21BLACK]

I think I'm going to stick with Bilsteins sport in front. I have HD in rear already. See how that feels. Still have to have car corner balanced. Should handle pretty well for street.

[Trackrash]

Most guys will recommend having your Bilstiens valved to match your car.

I personally have found that the externally adustable Konis allow for fine tuning at the track.

[JOHN21BLACK]

What does re-valve run? Maybe worth buying Koni sport adjustable.

[chrismorse]

I have heard of numerous guys going with HD front, (lighter valving because of lower spring rate of front bars and Sports for the rear because of the higher spring rate of the thicker stock or improved rear bars).
Chuck, at Elephant, recommends HDs for stock or slightly improved bar thickness, F/R. I haven't seen anyone recommend sport hardness front shocks with HD rears with stock T and anti roll bars???
So, I am kind of confused about what you have and what you want.
Not being critical, just trying to help you get better handling.
chris

[JOHN21BLACK]

I'm running 23 solid torsion front and 30 solid rear. Was told by mechanic to run a stiff shocking front to match torsion. This Is Why I am trying to get some help on what to do.Thanks for help.

[RichardNew]

Talk to Bilstein. The shocks should match your car. They need to know what torsion bars you're running and the weight of the car.

There is no such thing as a dual purpose shock. A track shock is very different from a street shock.



Here's more than you want to know about shocks.

Richard Newton

[Driven97]

A 23mm front torsion is about equivalent to a 350lb/in coil spring, which is more than double the equivalent spring rate of a 18.5mm stocker (154lb/in).

That's why your mechanic is recommending a lot more damping to match.

[JOHN21BLACK]

That's what he said. Back to my original question. Koni or Bilstein sport ???

[Driven97]

I think what people are saying is that we don't really know if either has sufficient damping for such a huge jump in spring rate. The Konis and Bilstein Sports are intended for stock torsions, and have enough damping (Bilstein) or adjustment range (Koni) to handle a bit more. More than doubling the spring rate is more than a bit more.

If you can find dyno curves (preferably F-V charts) for both shocks and let me know your front corner weight (you car seems really light for a widebody, you're 100lb lighter than my '84 narrow) I could make a few estimates and then run the numbers for you. I did a quick google and came up empty.

There's also a little voodoo magic to shocks. Too much is sometimes not enough, and too little is sometimes just right, if you catch my drift. Richard's blog post linked above is pretty good.

tl;dr They may work, they may not, but I'd put dollars to donuts neither will be ideal. If either is close enough to ideal for your use, however, I don't know.

[JOHN21BLACK]

As far as weight that was an estimate. If your car weight is 2600, mine would have to be more like 2700. All steel widebody with Turbo interior, 16x7/16x8, 930 brakes,no a/c. My weight is 185lbs. Some had said I would have to re-valve the shocks. What would that run to do? Elephant Racing recommends Bilstein sport all around.

[Trackrash]

FWIW. Koni's come in different flavors. I was suggesting the sport yellows. They come in single externally adjustable.

The dual adjustable shocks will handle larger torsion bars.
Edit: Not sure if these are still available?

The Koni reds are OK for a fairly stock street car and a pain to adjust.

[racer]

Shock BRAND doesn't matter. Both are excellent. The issue is the revalving of the shocks to suit your new spring (torsion bar) rate. The only real difference may be in price. Need to talk to a shock expert (company) for advice on the cost/timing and availablilty to match your car.

[msterling]

Elephant racing has a suspension builder page HERE. Punch in your info and see what you get. ER suggests a 22/29 TB package and then a 23/33 for the next step. They don't suggest Bilsteins at that level. They have Von non-adjustable shocks and single-adjustable with a few different choices. You can contact Chuck to get his opinion which might be the best idea.

[Trackrash]

Here you go. See pages 8, 9,13 and 31.
http://www.truechoicekoniracingservices.com/2013_TKRS_Catalog.pdf

[JJ 911SC]

Originally Posted by Trackrash

FWIW. Koni's come in different flavors. I was suggesting the sport yellows. They come in single externally adjustable...

Got them, front and back, going on as this winter project

[Driven97]

Originally Posted by msterling

Elephant racing has a suspension builder page HERE. Punch in your info and see what you get. ER suggests a 22/29 TB package and then a 23/33 for the next step. They don't suggest Bilsteins at that level. They have Von non-adjustable shocks and single-adjustable with a few different choices. You can contact Chuck to get his opinion which might be the best idea.

I've waffled about making this post as I suspect it might start a war, but what the hell. Keep in mind this is only my experience and my opinion. YMMV.

I didn't like Chuck's valving at all for AX. His tune had little low speed damping and virtually no rear compression damping at any shaft velocity. The result was a car with poor body control in out-of-phase movements: or when the mass is heading one way and you are turning the wheel the other, like in a slalom. In AX you spend a very high percentage of the time in that situation, where in a road course you don't. I did run his valving for a few track laps (admittedly not my forte) and it seemed fine.

It took driving a properly set up non-911 to see just how bad my car was at AX. Once I knew what was supposed to be happening, I could feel the tenths of seconds adding on to my time every time I turned the wheel and had to wait, and wait, and wait for the loads to transfer and the car to react.

So I went through the trouble of teaching myself about damping, the theory, and got a little help with the math and ran the numbers. My valving was in the ballpark for a street car up front, not sure at all what the strategy was at the rear. I asked Chuck if he'd be willing to give a shot at a more modern AX revalve all around, he declined.

I've since switched brands in the rear only (splurged a little on double adjustables, learning how to dial them in is educational) and I've only done two events so far but the difference is night and day. The car plants and sets much quicker in transition, has a lot more confidence as well when it sets. A lot of the issues I thought were "just 911 things" have been erased. Before, the car had a bit of a water skier effect - you'd move the front, and after a delay the rear would have an exaggerated reaction. I'd have to have opposite lock all ready to go to catch it. No more. It drives like a real car now. Should have done it three years ago.

Unfortunately, I have to wait until next season to see if the seat of the pants translates into real world results. It may, it may not.

So tl;dr if you are interested in an easy to drive and fast AX car, go to someone who knows and specializes in AX for your shock work, not a 911 person.

[msterling]

Matt;

Are you going to upgrade the front shocks too since they are only "in the ball park for a street car"? One thing that I have noticed at the local level autocross events is that many of the modified cars are slower than the unmodified versions of the same car. This makes me think that designing a modified suspension that works well is not so easy. You have obviously worked hard to get there and are willing to innovate but it is no easy task.

I hesitated to recommend any solution to the OP because I don't even know just what he is starting with. I have Koni Sport adjustables on my car but it has stock torsions and sways and is not comparable. Maybe he should ask local guys who track their old 911s what racing shop they go to for setup/mods. We have such a shop around here and I have used them for advice and service with good results.

[Driven97]

Take anything I say with a grain of salt until I win a national championship on a car I setup. I am NOT an expert. In all actuality, my car is still slow. 48th out of 60 at Nationals is not the person to put your faith in. But I'm trying to learn as much as possible with my failures. Goal for next year is top half.

In the end, from what I can tell, it's not that hard to get a decent handling FR/MR/RR car within the constraints of ST or SP type rules.

1. Calculate out your ride frequencies, and shoot for ~2.5Hz F&R.
2. Valve your shocks for 80% critical damping at 0-3"/sec, digressive bleed off to 30% critical above that. The option for more low speed via an adjuster or two is nice if you can get it.
3. Set your static camber for optimal contact at terminal roll. May end up being 2° in a good double wishbone car, might be 4° on a strut car.
4. Start your toe around 0.
5. Start with a big front swaybar.

Do all that and you should have a car that's at least moderately competent and not a bear to drive, assuming there's nothing weird going on like hitting bumpstops, etc. From there, the devil is in the details, and a lot of things are tradeoffs:

Steady state balance off? Change your roll couple either with more / less spring or more / less swaybar on one end.
Power down problems? Add rear toe or reduce rear camber.
Excessively loose or tight in transition? Tweak shocks.
Adjust the end of the car that is not working. Try one thing at a time.

Get methodical, test, take notes, take data. Every car, every driver, every course, every surface is different. There is no single answer, no magic recipe, no secret bullet. The people that put the time and effort in are the fast ones.

And to answer your question - I haven't decided on redoing my fronts yet. While they are not what I want, it's not the biggest fish to fry at this point. Limited budget and all that.