Stock, progressive or sport springs for my 5.0 W111 Coupe?

[GGR]

Once my 5.0 engine + 5 speed manual gearbox drivetrain and LSD 3.27 rear axle are ready for install, this will be the time to upgrade my suspension as every thing will be out of the car by then.

Coxracing and SL Market are offering progressive and sport springs:

http://shopping.netsuite.com/s.nl;jsessionid=0a0104471f4323b8e4463748415bb0faa8537a040293.e3eSbNqNc38Le34Pa38Ta38TaN50?c=ACCT1100 29&sc=2&category=5

http://www.slmarket.com/springs.htm

This car will essentially be a driver, so it should retain enough comfort on long distance trips. But I also want to occasionally get the best of my additional horsepower on track days. So, I’m looking for the best compromise. I was told sport springs may be a bit too harsh on long distance trips. Progressive springs look quite appealing to me as I’m told comfort is retained in normal use but sprigs get stiffer when needed. Or should I just keep my stock springs and fit stiffer shocks?

Thanks in advance for sharing opinion and experience!

[winecountryone]

I like the idea of the sport springs but nearly had heart failure when I saw they are close to 900$ set for my 107 SL. They aren't nearly that expensive for the newer cars.....Why do these cost so much? Are there any other alternatives?
If someone had the specs for diameter and rate from old AMG literature,I'm sure these could be duplicated or a matching application be found cheaper.

[alabbasi]

What kind of wheels are you putting on your car? I think these may effect ride one way and handling the other more then springs and shock.

[t walgamuth]

If you can get a bigger sway bar that would be a big improvement front and rear. Then the progressive springs might be a good choice since they will give a supple ride with good support once you lay into a turn. Then be wary of going to a lot heavier wheels. The weight of the wheels should be the lighter the better for both handling and ride. And get the hd or sport shocks by bilstein or adjustable konis. At the track the instantly adjustable konis can be used to dial in the chassis for optimal handling for the conditions and what you are doing with the car.

Are you talking about a chevy motor? If so what will be the total front end weight compared to what you had before? The weight of the engine and tranny combined must be considered.

[JiveTurkey]

Shocks are going to be a big contributor, but most of the "adjustable" types on the market aren't intended for track days. They're adjustable in the sense that you set them to comfort when you install them, and as they age you gradually "adjust" them to a firmer setting to maintain their original performance.

Remember what 'ole Mr. Chapman said, "Simplify, and add lightness."

If you're adding in extra horsepower (read; Weight) then the oem spec shocks and springs aren't going to cut it. Designing a suspension is a long process and while that 5.0 (god help you if it's an American lump of iron, because they're heavy) will make your W111 go disgustingly fast in a straight line it's going to corner like a Jeep Wrangler unless you do some calculations (I don't Jive with math) based on the new weight added to the vehicle.

In short, if you've already decided to go ahead with the engine swap and you're serious about using this car on a track, then install the stiffest shocks and strongest springs you're comfortable buying. The best way to do this is to find the new weight of the vehicle (or guesstimate it before completion) and compare those specs to another production Mercedes that comes close to your custom one. Then see if you'll be able to install those on your car without major fabrication.

[t walgamuth]

The Koni shocks I have on my Miata have a hollow stem with a little flat end which you can turn with a special knob which alters the stiffness drastically. If my car is pushing I can stiffen the rear shocks until it is neutral.

Actually what happens is it eventually is breaking traction at both ends more or less equally. It makes driving the little dear quite an involving task!

[GGR]

Thanks all for all these very useful comments! I need to give more info on my project so that we can be more precise.

My car is currently fitted with all the driving gear, suspension, brakes etc. of a 3.5 Coupe. In short, it's a 3.5 Coupe disguised into an earlier 220.

The 5.0 engine I'm fitting is an alloy block M117. Its weight is similar to the inline six that was originally installed in the car, and lighter than the iron block M116 currently in the car. In this respect, my front springs would already be stiffer than needed. MB offers a wide range of springs for these cars, from the W111 220 to the W108 4.5, with some further variations depending on the options fitted on the cars. So, I'm not worried about finding the right stiffness, I'm more curious about the benefits of progressive springs.

What rims I'm going to use is a good question. It will depend on the brakes. I currently have some 3.5 brakes which are very efficient, given that they are the same as the ones found on the much heavier 6.3. But I can upgrade them if needed with four pot front calipers out of a bulletproof W126 which are a straight fit on my king pins, and 560 front rotors that would need me to modify my front hubs to fit (offset is correct). This option would certainly improve the brakes but would also add quite some un-sprung weight as the rotors and calipers are much bigger. It would also oblige me to fit 15" rims to clear the calipers which I would have to do anyway because I can't find any V rated 14" tires.

If I go for "15 rims I would go for some 215/65-15 tires, as they would keep the correct circumference, and I may have some rubbing issues if I go with wider tires than that. I currently have some very light 6x14 aluminum rims out of a W123 diesels that look like the iron ones and which can accommodate hubcaps. 15” rims and tires will definitely be quite heavier.

Finally, this car will be a (sporty/sleeper) driver. I don't necessarily want to go over the top in every aspect, I'm looking for the best compromise to get a homogenous power/weight/suspension/brakes combo. Track days may only represent 2% of its total use, so it's not the priority. Nevertheless, I would find it a pity if I feel my brakes are too weak and the suspension too soft to get the best out of the power and torque combined with a 5 speed manual and an LSD.

[JiveTurkey]

Originally Posted by GGR

In short, it's a 3.5 Coupe disguised into an earlier 220.

The 5.0 engine I'm fitting is an alloy block M117. Finally, this car will be a (sporty/sleeper) driver. I don't necessarily want to go over the top in every aspect, I'm looking for the best compromise to get a homogenous power/weight/suspension/brakes combo. Track days may only represent 2% of its total use, so it's not the priority. Nevertheless, I would find it a pity if I feel my brakes are too weak and the suspension too soft to get the best out of the power and torque combined with a 5 speed manual and an LSD.

YES YES YES!
This was what I was hoping to hear. I just get scared sometimes because I've seen countless save-able old Mercs that someone has stuffed a Ford (****ers Only Run Downhill) 302 into and those make me sad.

What you're doing is noble (and *****in') and upon completion you will be awarded the JiveTurkey seal of approval.

As far as Wheels / Rims. If the alloy's from the diesel are in good shape you should definately use them. Are you planning to go with Bias-Ply or Radial tires?

[GGR]

Thanks! If you're interested in the engine set-up you can read more about it here: http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1495778-higher-compression-ratio-m117-engine.html

My "diesel" rims are in good nick, and I believe the power of my current 3.5 brakes combined with the very light weight of these rims is a good combo. Unfortunately the best tires I can fit on these rims are H rated 205/70-14 with max allowed speed 210 km/h, When I have good hopes to pass the 240 km/h with that car. Further, the 70 profile is quite high. I don't know if a 65 profile on heavier 15" rims is preferable to a 70 profile on lighter rims.

I have another question. I have all the parts needed to fit the "anti-dive" or "anti-lift" system whatever it is called, found on the rear axle of the W109/112 air suspension cars. A guy in Germany who raced W111 chassis time ago and whom I am in contact with is going to fit that system on his 3.5 Coupe. His rationale is that you can enter bends on the brakes as that systems keeps the back of the car down, while without it you can't because when the car lifts up the camber changes and you have all chances to end up off the track. He quite convinced me to go for it but I wonder why MB fitted it only on air suspension cars. If it's so good, I guess it would have been available as an option on the 3.5 Coupes. And I like what 'ole Mr. Chapman said, "Simplify, and add lightness." So I'm not going to add weight and complication if the benefit is not worth it. On the other hand, I've already been cought by that change of camber trick a day when I had to lift my foot from the gas pedal in tha middle of a fast curve. That was EXTREMELY scary and I think I'm quite lucky to be still here writing on this forum. But that was on a W112 already equipped with such a system and it didn't prevent it, as in fact brakes were not involved.

[JiveTurkey]

Originally Posted by GGR

Thanks! If you're interested in the engine set-up you can read more about it here:
My "diesel" rims are in good nick, and I believe the power of my current 3.5 brakes combined with the very light weight of these rims is a good combo. Unfortunately the best tires I can fit on these rims are H rated 205/70-14 with max allowed speed 210 km/h, When I have good hopes to pass the 240 km/h with that car. Further, the 70 profile is quite high. I don't know if a 65 profile on heavier 15" rims is preferable to a 70 profile on lighter rims.

Less rotating mass is always better even if you have to contend with the sidewall deformation that comes with taller tires. 240kph is about 145 mph (I think) which would be a pretty awesome rush in an old Merc. Are you planning to go with Mud'N'Snows for regular driving with a set of track tires? Or are you going to just use one set of tires?

[GGR]

Originally Posted by JiveTurkey

Less rotating mass is always better even if you have to contend with the sidewall deformation that comes with taller tires.

You're the first one I hear saying this, but I like it. Would save me some work and additional expenses.

I'm planning to have only one set of wheels. The idea is really to go grocery shopping in the morning and have fun on the track in the afternoon (OK, I can add 0.5 psi in the tires and empty the groceries from the trunk before rushing on the track).

Do you have an opinion on that "anti-dive" system?

[JiveTurkey]

Id say the "anti-dive" system's usefulness should be determined after you're further along in your build. As of right now you're mainly familiar with how your car handles in stock (ish) trim. Upon completion of your (awesome) project the cars handling will be significantly altered (we're hoping for an improvement obviously.)

Since you're going to change your springs, shocks, wheels, and tires you might find that the car will handle well enough in it's new form and any effort spent fabricating the stuff you're going to need to mount that system from another car would be better spent doing other modifications.

As for the wheels, I'm glad you dig my theory that taller sidewalls aren't going to be that much of a pain. While the taller tires are going to flex more, they're going to flex in a consistant manner, so it won't take you long to adapt to them. The lighter wheels are a huge benefit because every time you come out of a corner, or lay on the brakes that rotating wheel has to be accellerated or stopped. Objects with more mass are more difficult (obviously) to accellerate or slow. It's a steady parasitic loss that should be avoided.

[GGR]

Well, unfortunately I have to take my decision much earlier. I'm rebuilding the rear axle and it may go in before the rest, as this is a rolling project. If I go for the anti dive system I will have to fit the 6.3 wheel tubes I have. If not, I will stick with to the 4.5 wheel tubes. And given the complication of these rear axles and the work involved to swap wheel tubes, I don't want to change my mind too often.

[t walgamuth]

I suspect the anti dive is necessary on the air suspension since the air bags are much softer than springs. Without it the front end probably would really hug the pavement on braking. And the rear would rise so much the geometry change would be problematic.

Sounds like a great project!

What year 220?

[Tony H]

Here are the wheels I am using: 16X8 600 SL wheels. The tires that came with them are too tall (225/55). I think I will see if 235/50 will fit.
The air suspension cars do not have compensators on the rear axle. I wonder if the combination of the compensator and anti-sway bar might result in peculiar handling characteristics. Has anyone ever installed a rear anti-sway bar on a 108-111-113 car? I bought a 6.3 rear sway bar many years ago with the intent of installing in on my 3.5 coupe but never did.