carreracoupe997

My car is an '86 951. It is for track use only. It is running Bilstein Escort Cup coilovers w/ 400/200 springs (no torsion bars), Weltmeister torsion tube/spring plate bushings(hard black poly). and solid T-tube and Trans mounts. Here is my question: I have rebuilt the lower control arms using Rennbays extended pin ball joint and bronze bushing for lowered cars. I want to replace the lower control arm bushings and rear trailing arm bushings. Monoballs would be preferable but I CAN'T pay $550 for the front and rear set PLUS the cost of the castor blocks ($300 more) So..... 1) What can I do? 2)anyone ever use the Weltmeister spring plate bushings before? (i sanded them so they fit perfect and will rotate freely with no play) Any advise on low-buck 951 suspension info and tricks would be appreciated. Thanks

Steve

87944turbo

Racer's Edge sells delrin. You can find them on Paragon's site or RE's site.

The delrins are roughly half the cost of spherical bearings, but of course do not have the ability to pivot in multiple axes like the sphericals and therefore run the risk of binding. You can find delrin bushings for the front of the control arm, both inner and outer spring plates, and the trailing arm bushings.

Weltmeister also makes a red polygraphite bushing for the front of the control arm, but specifically advertises that it is not for track use. However, there are people out there using it on track and the reviews seem mixed. They can be had for about $45.

For the caster block, I am sure there are quite a few people tracking with the 968 caster block. A new pair is ~ $160. These have a lot less rubber than the 951 block, but are a far cry from a true spherical bearing. Unfortunately there is no middle ground choice here, it's stock, upgraded stock, or spherical.

Of course it is always good to talk to someone who completely understands how all of the parts will work together as a system to get the best results. As for parts Paragon Products (http://www.paragon-products.com/) is an RL sponsor and can provide what you need. GL and welcome to Rennlist!

carreracoupe997

Thanks, I was afraid I would have to go that route(spherical). BTW, I jut got my manual steering rack with intermediate shaft in ($100).

rlm328

Where?

DanR

how does this set up work? Is it very soft? I am running similar setup but with 600/800 springs.

carreracoupe997

answering rim328, I just googled 944 manual steering rack and came up with an auto recycler in PA.

now answering DanR, works great as the 944 needs to transfer rate to the rear when accelerating for good grip however I have seen photos of my car at Road Atlanta and I have too much lean on the tight stuff. Will try to correct with 968 MO30 sway bars. If that doesnt do the trick then will move up in spring rate. BTW, this has nothing to do with spring rate, just set up so I thought I would share. Tire temps across entire tire run within 3 degrees. I have ground Control Camber plates and run 2 3/4 degrees left and 2 right.

Van

I agree - interesting choice of spring rates. I run 400/700.

Light weight rear springs don't do anything to "help the weight transfer to the rear" - your acceleration force is what does that... I.e. a 500 HP car will transfer more weight to the rear than a 150 HP car... All light weight rear springs will do is let the suspension compress more and cause your wheel alignment to change more under acceleration.

Having not driven your car, I'm not going to say your spring choices work or don't... But I think your choice puts you in the minority of track drivers...

Van

I've put your spring rates into my handy-dandy 944 spring rate calculator. Your car has a front wheel rate of 331 lbs/inch and a rear wheel rate of 79 lbs/inch.

If your car weighs the same and has the same weight distribution as mine, your suspension frequency is about 2.01 CPS (cycles per second) for the front, but only 1.05 CPS for the rear.

According to the book Advanced Race Car Suspension Development by Steve Smith, typical race cars shoot for about 2 CPS.

Also in this book, is the formula for weight transfer under acceleration:

Wt x CGH x G
WB

Where Wt is total vehicle weight; CGH is center of gravity height; G is the acceleration force; and WB is the car's wheel base measurement.

carreracoupe997

Thank You Van for the great info. As the car is apart I will do the calculations and come up with the correct spring rates. Thanks again!!!!

Steve

Van

You're welcome. I'm not trying to tell you what to do... I'm just trying to encourage you to do more research.

For what it's worth, DanR's springs give him a 2.43 CPS front frequency and a 2.15 CPS rear frequency. I've ridden in his car and enjoyed it. I imagine he and I will be doing lots of comparing this season.

Van

Sorry for beating a dead horse... But I just found this website: http://www.racing-car-technology.com.au/

Check out the suspension frequency video! It's good stuff. Just note that his calculations are cycles per minute - mine were cycles per second.

carreracoupe997

BTW, since I was talking earlier about my rear trailing arms I gave my rates backwards...my bad. Rear is 400#. Sorry for the confusion and thanks for the help.

Van

That gives you a much better (matched) set of spring frequencies:

85 CPM for the front and 91 CPM for the rear.

According to a book I was reading last night, Competition Car Suspension, by Allan Stanifroth, you want about 10% higher frequency in the rear - since the rear will always trail behind the front that hits the bump first...

So, I'm more inclined to think your car DOES feel pretty balanced. (Does that mean I'm more inclined to think your handling assessment earlier was correct?? )

That also makes more sense about your camber settings and tire temps. With stiffer springs, you'll be able to run less severe camber settings and still achieve the same temp range.

PorscheDoc

Same here, I run 500/650 no torsion bars. Occasional street car, so I didn't go too over the top with the rates.

xsboost90

450f/525r and it feels very balanced w/ 245's all around.