Suspension upgrade, Like Modern! Options

[Randal]

Been thinking about what it would take to build in tubes or whatever to allow a complete Boxster suspension swap out on a 914.

It is likely a big project, but maybe not.

Anyone else been thinking about this? (IMG:style_emoticons/default/sawzall-smiley.gif)

[Chris Hamilton]

Bob, that suspension system on your car looks very nice. Those really look like fantastic pieces.

It is not however a modern suspension system like we are talking about here. I don't see anywhere in the car that the actual suspension geometry has been changed beyond what can be done with basic upgrades on a 914. The trailing arm shape and pivot points are still in the stock locations, and the front A-arms and struts appear to be basically the same geometry also.

The main thing that I'd like to change on my 914 is the curve described by the rear trailing arms as they move on their pivot, and your car doesn't seem to have addressed that point.

[ChrisFoley]

I don't see anywhere in the car that the actual suspension geometry has been changed beyond what can be done with basic upgrades on a 914. The trailing arm shape and pivot points are still in the stock locations, and the front A-arms and struts appear to be basically the same geometry also.

The 935 front end as Bob pictured has valuable geometry alterations in addition to the increased adjustability. Several manufacturers make similar products and they aren't all the same however.
The better ones, such as ERP and what I have from TRG on my race car, have the inboard lateral pivot moved inward and upward substantially.
This improves the angle of the arm on a lowered car and decreases the camber change through the range of motion.
The outboard spherical bearing is also raised in comparison to a stock ball joint, which allows a substantially raised spindle, thereby further improving the camber curve.

Using a threaded body RSR type strut allows 2 1/4" coilovers which saves 1/8" on tire clearance and improves scrub radius compared to the 2 1/2" coilovers required on stock struts.
Additional scrub radius improvements require re-cambered struts such as are on our white FP car.
Unfortunately the "935 type" (Kanna Motorsports (IMG:style_emoticons/default/headbang.gif) ) suspension parts on the white car do not have all the geometry improvements of the ERP setup.
The Tangerine Racing Products camber box setup allows camber angles from negative 3* to 0* so DOT tires or slicks can be used effectively.

The front end isn't where the biggest grip issues lie on a 914 suspension however. Lowering a 914 exacerbates the shortcomings of the stock semi-trailing arm rear suspension arrangement.
The roll couple at the rear is quite high, potentially even above the cg when slicks are used with stock pickups because of the pivot shaft angle required to get a proper camber angle. The camber/toe curves are less than desireable as well.
A combination of raised pickups and de-cambered trailing arms is needed to solve these problems if retaining a stock-type suspension.
The Tangerine Racing FP car sits less than 3" off the ground at the jacking donuts and has the roll couple at about 8-9" off the ground, way below the cg.

All this is a lot of work but still quite a bit less than grafting parts from another car onto a 914 or building a subframe and multi link suspension from scratch. Eligibility for racing or AX classes below "Modified" is retained as well.

[andys]

The roll couple at the rear is quite high, potentially even above the cg when slicks are used with stock pickups because of the pivot shaft angle required to get a proper camber angle. The camber/toe curves are less than desireable as well.
A combination of raised pickups and de-cambered trailing arms is needed to solve these problems if retaining a stock-type suspension.
The Tangerine Racing FP car sits less than 3" off the ground at the jacking donuts and has the roll couple at about 8-9" off the ground, way below the cg.

Chris,

Can you explain why you de-camber the trailing arms? I'm taking de-cambering as removing that 1.5* of camber (or more?) built into the stock trailing arm. Do you then lower the inside ear of the pivot shaft (to lower the roll center?) thus angling the pivot shaft?

Thanks,

Andys