2.8 RSR build - questions

[pjo046]

Hi all

I have a Carrera 3.0 engine and understand that these are well suited to build 2.8 RSR replicas. I also have a 2.2T engine in my garage, and by using the crankshaft from this in my Carrera 3.0 engine I have the basis for a 2.8 RSR.

I like the idea of building a 2.8 RSR, but I would like to keep it affordable. Therefore I would skip mechanical fuel injection and rather go for EFI and PMO manifolds and ITBs.

What would I need to do to the longblock to build an RSR besides installing the 2.2 crankshaft? I have no knowledge on the subject. can I use the conrods from the 2.2 and the CIS pistons from the 3.0 or will I need new parts?

What needs to be altered on the heads and camshafts etc for this engine to perform? As it would be a high rev engine, would the valvetrain require modifications?

[faapgar]

Hi,I have built around 15 of these motors from a 930/02 engine.Carrera 3.0 or 76-77 Turbo case.2.2T crank is cast iron and non counterweighted.You need 2.2E or an S crank.If you use the standard rods your compression will be around 7 to 1.You can have Pauter make longer rods.I have 2 of these built on the shelf and they rev really quick.Fred

[pjo046]

Hi
Thank you for your reply. So then the 2.2T engine is of no use then. Are there other parts in that engine that could be used on a 2.8 build?

Are you saying I only need longer custom rods, and that I can reuse the C3 domed CIS-pistons? Or am I better off changing to custom flat top pistons (JE or similar)?

What is the main benefit of going 2.8 rather than building a 3.0 RSR?

[Geneulm]

I would recommend that you use this sites "search" provision. There are a lot of folks that have used this case for short stroke motors using 2.0/2.2 crank and rods in this case. The same search provision may also show contrary opinions to that which was stated as to what your crank is made of. Further non counter weighted cranks have been used in racing applications for years.

[faapgar]

The only non counterweighted crank used for Porsche I have used is a 356C crank.2.2 911T crank is a boat anchor.Remember it is cast not forged.Fred

[chris_seven]

Surely a 2.8RSR Replica engine should be using a 5R/7R Magnesium Case as this is the factory specification engine.

It was based of the Group 3 engine from the 2.7 Carrera RS. There was an Alusil case homologated in August 1973 but generally the Carrera 3 case was used in the 3.0RS which was homolgated in early 1974.

I am not sure if the 1973 case is the same as the 930 Turbo Case which I believe was used in the Carrera 3.

If you just want a modified engine it doesn't matter but if you are building a 2.8RSR Replica and need an FIA HTP then I don't believe you can use a 3.0 engine in a long bonnet car.

The FIA don't normally like mixed homologation details so 2.8RSR are long hood and 3.0RSRs are Turbo Bodied IB style cars.

The 3.0RSR used a 6 bolt 70.4mm crank which tends to have a torsional vibration at around 7800rpm. This vibration can loosen the flywheel and can be alarming.

If you build a 2.8 litre engine with a 66mm crank I don't understand why a Carrera 3 case needs non-standard rods. I would have thought 2.23S rods would work as they are 2.2mm longer than the standard rod used with the 70.4mm crank which should deal with the 4.4mm reduction in stroke.

If you are not going to use the engine beyond 7500rpm I am not sure the short stroke is particularly worthwhile but at 8000rpm+ it would be good.

This is a modification I have not carried out and if I am wrong I would be pleased to know why and how to modify the rods.

The 911T rods are probably not good enough but 2.2S rods are not bad or an aftermarket rod such as R&R also look quite good.

We make our own 2.0 litre style rods which work with standard bearings and we tend to use ACL Race Bearings which work quite well.

.

I am not a great fan on the 2.0 T Crank for two reasons. The first is that it is, as has already been stated, cast iron so it will not have as good a fatigue life as a steel crank.

The second is that the lack of counterweights will reduce its life at high rpm as there is nothing to help absorb the vibrations caused by high order gas torques which can be quite damaging.

Some people do seem to use them successfully on 2.0 litre race engines but with the higher combustion forces due to the increased capacity more damage is likely to accumulate.

The CIS pistons will be relatively useless as they will seriously restrict the overlap you can use so a 964 profile cam is about as far as you could take this engine without the exhaust valve hitting the pistons.

Pistons won't be flat toped but will need a dome and either JE or Woessner make suitable parts.

I would run a Schrick Sports Cam and use the Carrera 3 carriers.

The T heads could be interested as there may be enough material in the port to have them re-worked to a D Shape Exhaust ports.