RS rear suspension

[911pcars]

Some discussion on the PParts forum brings me here to ask those with more background info than I do. Information posted there runs counter to what I had previously thought.

I was under the impression that all '73 RS cars had the same rear suspension geometry as regular 911s (save for stiffer suspension, wider wheels, etc.).

Was the RSR rear suspension ever used on any RS model? According to published sources, the RSR used a shorter rear control arm in conjunction with a relocated pivot point.

Bruce Anderson, in his "911 Performance Handbook" says:
"Porsche revised the rear suspension pickup points in 1973 on the second series of 2.7 RS Carreras and on the 3.0 RS Carrera."

The phrase, "second series" has me wondering. Was the second series the same as the the few (49 or so) RSs that were converted over to RSR specs for Group 4 homologation or was this a second batch of street-prepped cars (lightweight or otherwise)? Were there a number of factory-built 2.7 RSs with RSR-type rear suspension?

What publication cites the correct information?

Thanks,
Sherwood

[nick-moss]

According to Gruber/Konradsheim (and others) the pick up point was moved and a shorter control arm installed "from chassis 1409 (43 vehicles were already so equiped)" from May 9th 1973. The location was 50mm to the rear and 10mm higher.

As far as I know this suspension geometry was also used on production Turbos and the early RSs had normal 2.4 suspension geometry

RSRs had additional coil over springs to the series torsion bars, which had to be retained for homologation purposes

Edited to correct build number

[andyjboy]

According to the "Carrera RS" book by Gruber & Konradsheim - the most comprehensive information source (but not infallible) on these models, some of the 3rd series had shorter rear trailing arms installed complete with modifications to the cross-shaft & sheetmetal in the rear seatpan area (commencing with chassis # 1409).

Now where's George(K) when you need him ?...

[andyjboy]

SNAP, Nick!

[andyjboy]

I think the revised pick-up points for the RSR rear trailing arms were moved inwards towards the centre of the car (15mm) & rearwards (47.5mm).

The idea behind this was (supposedly) to improve the handling by more closely matching the rear wheel camber change to body roll during cornering.

[911pcars]

Hi Andy, Nick and Kurt,
Thanks for sharing the info. Can you verify the chassis number? One says after #1049, the other says after #1409. Which one of you wants to own up to the typo? :-)

Thanks,
Sherwood

[andyjboy]

It's #1409.

[911pcars]

Thanks

Sherwood

PS: Several sources cite a total of about 1636 RSs manufactured. If Gruber & Konradsheim report RSs with RSR rear suspension began with chassis number 1409, that means there were approximately 227 RS cars with the revised rear suspension (1636-1409 = 227). I assume these were equipped with other RSR features as well (2.8 liter engine, coil-over suspension, etc.).

Several souces also state there were 109 full RSR-bodied Carreras produced.

Does Gruber & Konradsheim describe any overlap between RS and RSR production or was the group of 109 a completely different production run?

[Ernie W]

Info from the RS homologation book.

[Ernie W]

the back page showing photos