2.8 Build
 

I am planning on building a 2.8 RSR engine but would like it to be a streetable engine with occasional DE and autocross. The actual engine build is a way out but if I can get some engine builders comments, I can plan ahead.

Here is what I have so far:

• Case is a 2.4 7R with shuffle pins, oil bypass mod and case savers.
• I have Dilivar studs but may be convinced on others.
• Crank is a 2.4 std/std/std 6-bolt
• Flywheel, PP, clutch may be stock but open to ideas.
• Rods to be Carrillo.
• Pistons/cylinders to be Mahle 92mm RSR 10.5:1.
• Oil pump to be late model SC.
• Cams to be '73 S but may be convinced on others. Would like 4-bearing cams but need 4-bearing cam towers.
• Latest oil fed chain tensioners.
• Heads are real NOS RSR heads with 43mm intake and exhaust ports, 49mm intake valves and 41.5mm exhaust valves. I might be convinced to sell these heads but what would I use instead?
• Aase HP valve springs.
• SSI HE with 2 in 2 out sport muffler

I have a set of 50mm high butterfly MFI RSR intake manifolds and a modified MFI pump but both need rebuilds. I will be sending these to Eurometic before too long.

Just to get things started, I have considered 46mm PMO carbs and a twin plug dizzy with dual 3-pin CDI. I can worry about EFI and Tec3R engine management later. Such as Jenvy ITB but not sure what size. 46mm maybe with their manifold and tall velocity stacks. Not sure what size/brand fuel injectors for the EFI.

Other items:

• Dual master cylinder setup from 901 Shop.
• Fuel Safe 17gal tank or even the early ST style 100liter steel tank now being replicated.
• 915 trans with TBD gearing. Thought of airport gearing. Suggestions?

You folks may have seen my build in progress on this thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/316408-post-pics-1973-carrera-rsr-replicas-here.html

Please, any suggestions/comments?

Sounds like Toms RSR clone engine or Mike Moore's RSR clone are very similar engines to what your thinking about. Both were 10.5-1 and based on 3.0 liter engines. One was carbs the other MFI. I think Mikes was actually a 2.8SS but I cant recall. I would look up Toms build as he had alot of engine data from his dyno. ITs a good start atleast.

Why not add a turbo pump to the mix vs the SC pump? I would also ask why not use a 3.0 liter engine as the base vs the mag 2.7? Would save on alot of the machine cost or are you doing it to resemble the real deal RSR engine?

Martini RSR engine build

http://forums.pelicanparts.com/porsche-911-technical-forum/246563-another-rsr-clone-project-dyno-day.html

GL ... sounds like an interesting build.

If you really have the ultra-rare 2.8 RSR heads, you should use the Mahle 92mm RSR P/C's with that for reasonable CR for pump gas.

Cams will depend on the car's weight, how you use the car, and what gearing you will use.

SSI's are too small for RSR heads; you will need an 1 5/8" heat exchanger of some kind.

Could be a real neat engine if its ALL done properly. :) :)

Good luck!!!!

The guys at Rothsport are very helpful and will be able to advise on an appropriate set-up. As are Elgin who can do you a custom cam rather than running something off the shelf that with spec that has been around for 30 years

Thanks for the inputs thus far. More to think about.

Here's a quick glance at a NOS RSR head. Never been used. They have the old-school copper valve guides that should be replaced with bronze. And I think the seats may be too soft since we don't have leaded gas any more. Also, the plugs are 12mm. Who has the proper spark plugs? Smart Racing used to have them listed but they are kaput. I should have bought some back then.

http://forums.pelicanparts.com/uploa...1416354464.jpg


and disassembled RSR high butterfly stacks. Missing one bypass screw.

http://forums.pelicanparts.com/uploa...1416354638.jpg

No problem with putting good guides in those heads,......we do this all the time using our own P-B ones. :) The seats are just fine; don't touch them!

12mm plugs are available in limited heat ranges from NGK. Bosch 12mm ones are all very cold race plugs and not for any kind of street use.

Tall butterfly intake is very rare (if its original factory stuff) and very valuable. An aftermarket bypass screw will make it functional if the TB's are not worn out.

Steve's operation can also advise too:

__________________
Steve Weiner
Rennsport Systems
Portland Oregon
(503) 244-0990
porsche@rennsportsystems.com
Rennsport Systems | Porsche Performance Systems and Support

Indeed - Steve was very helpful when I stuck PMOs and web cams on my 3.0 many moons ago. I think he helped me with the suspension setup too.

I wasn't aware Steve sold Jenvey/Rothsport ITB kits or custom ground cams though.

I certainly do. :) :)

Elgin does some custom profile cams for us that work very nicely. :)

I also have one new set of Mahle 92mm RSR P/C's left.

Jerry Woods Enterprises bought Smart Racing. Last year Craig Watkins retired from the Flying Lizards and bought back the smart alignment stuff back. To my knowledge most of the other products are still available under the JWE brand.

Get some good rod bearings. Pelican has the good Clevite 77 bearings that have been recommended by Auto Associates in CT.

I'd suggest if you're set on the SC pump that you might as well instead get the Carrera pump which has the better venturi tube with the integrated strainer. The older, separate strainer assembly is prone to breakage and I don't believe they are available new any longer? I think URO makes a new strainer but their parts are crap. Also you can't go wrong with the 930 pump (currently a 996 Turbo pump if buying new) for your application. Just need the shorter pump driveshaft and some clearancing of the case for the larger pump body. The only caveat regarding the pumps with the integrated strainer is you need a dished sump plate like the one from Rennwerks or Mainley.

Nice choice of springs. Can handle the higher lift cams w/out excessive spring pressure. Too much spring increases wear and steals some power.

Trans gearing ultimately depends on your priority. Willing to sacrifice some driveability (as in highway use) to optimize it for the tracks you run? Then you can choose your gears specifically to get best use of power/rpms for the speeds you typically see at your tracks.

Thanks for the comments.

So far:

• Heat exchangers with 43mm tubing. (1 5/8")
• 930 oil pump or Carrera pump over the SC pump. Dished sump plate.
• 3.0 case as baseline over the 2.4/2.7. Problem is the head spacing on the 3.0 is 83mm whereas the 2.8 heads are 80mm.
• PB guides and the seats should be ok.
• Need to get part numbers for 12mm spark plugs. Street use and race use.
• Elgin, WebCam custom grinds. GE40 maybe?
• Clevite 77 rod bearings.
• Trans gearing TBD.

I also need help in sourcing the proper intake valves. 49mm x 9mm x 110.1mm. I have SM sodium exhaust valves but still need the intake valves. Should I get sodium intake valves as well, or will the standard non-sodium valves be ok. What are your thoughts on valve brands? SM brand is difficult to find in the US.
http://www.sm-original-germany.com/en/
http://www.sm-original-germany.com/fileadmin/PDF4Download/VM_Cat/VM_single/Porsche.pdf

Any other comments?

The high butterfly will be sent out for rebuild. I do have a modified MFI pump with a 3.0 space cam. It needs rebuild too. Maybe after I get the stacks and pump rebuilt, I'll sell them in favor of finishing the body, paint, more parts, engine parts, trans parts, ITB EFI. Thoughts?

Also forgot to ask. Since the head/cylinder mating has no provisions for a CE ring, what would be used for a head gasket? Nothing?

http://forums.pelicanparts.com/uploa...1416757780.jpg

For example NGK DPR7EA-9. Heat range 7 is good starting point for hot street motor.

No head gaskets are used and needed on the later 92mm RSR cylinders.

Steve why are head gaskets not needed on a 92mm?

Due to cylinder stud spacing and the 92mm bore, there was insufficient material between the CE ring groove and the bore, causing pieces of cylinder to fracture under light detonation and fall into the bores.

Mahle dispensed with the CE ring groove many years ago for improved support and thus durability, based on the success with the 95mm Carrera cylinders.

If no gasket is used then it brings up the question of the mating surfaces. I suppose it is necessary to make sure the mating surfaces are perfectly aligned with no gaps. With NOS heads and new cylinders I don't think you can assume the mating surfaces to be perfect. What procedure can be used to make sure all is well?

While I cannot speak for others, we check the heads with the milling machine to ensure everything is flat and exactly the same. New Mahle cylinders generally do not need anything right out of the box, however these can be checked in the mill or on a lathe (using a special fixture) to confirm the sealing surfaces are flat.

So I would be wise to check the heads for flatness during the valve guide replacement and grinding in the new valves.

Another question on the spark plugs. Which would be preferred, the protruding insulator or the non-protruding insulator. Seems the non-protruded insulator may be best as the protrusion into the combustion chamber would be minimized.

Iridium shown:
Protruding
http://shop.advanceautoparts.com/wcs..._alt2_detl.jpg

Non-protruding.
http://shop.advanceautoparts.com/wcs..._alt1_larg.jpg

And then iridium, platinum, or standard copper?

I always do as an integral part of our valve service & head work.


For racing, I use non protruding plugs for their colder heat ranges, however for any road work where the engine will idle, the projected-nose plugs do run cleaner and are preferred.

I prefer the Iridiums or Copper ones, current platinum ones are not good at all.

Rod bearings:

In this thread: http://forums.pelicanparts.com/911-engine-rebuilding-forum/825748-rod-bearing-controversy.html and the use of Clevite bearings over Glyco?

And what about main bearings? Are their issues with Glyco for main bearings? And the number 8 bearing, thrust bearing and intermediate shaft bearings?

BTT.

Any further comments on the use of Gylco for main bearings?

A few posts back I asked about intake valves. Any comments on preferred brand for the 2.8 10.5:1 engine.

Cheers,

Looking at the various experiences with bearings, it looks like the rod bearings are where the problems arise. The rest seem fine. In my 2.8SS case where the rod bearings had their Calico coating worn off after two sessions on a chassis dyno (total run time less than one hour), but the mains looked fine, the mains were hardly put to the test.

The 130 hour or so 2.8 I pulled apart to freshen up the bearings after the SS 2.8 blew up ended up with me regretting doing it, as rods and mains all looked like they were good for an unknown number of more hours. Those bearings were maybe six years old (but hadn't been run that many race seasons). So maybe it is a quality control thing, or a change in materials, for the rod bearings?

But it is Clevite for me from here on out.

I don't have enough experience to have valve brand favorites. However, what I'd like to know is how much larger a valve can you get in a 92mm cylindered motor? In my SS with 95mm to play with, I got 8mm stemmed 51.5s as used in the 993 RSR or something (though not sourced from Porsche - the guy who did the valve guides sourced valves and springs and retainers and I don't know from whom). But I don't know about the 92mm jobs - Porsche had to change the valve angle in the 2.8 RSR in order for the 49mm intakes to fit. Would a 48mm fit? Would you need to have the valve seat cutout in the head cut larger, and a larger OD valve seat installed? Or could you cut the stock ones larger?

Thanks Walt. What you said about bearings is what I have so far. Just verifying.

As for larger valves in the 2.8 heads, I don't think you can do it without enlarging the combustion chamber and then go with larger OD seats. But what would that do to the seating surfaces between cylinder and head? It would get smaller and more prone to blow out I would think. If you scroll down, I posted a picture of the 2.8 head and the seats are right on the edge of the combustion chamber.

I have read pros and cons on Interlake and TRW valves and then I found the SM valves from Germany. An old-school German mechanic that races his '68 2.0 believes the SM valves will be fine. I have the exhaust but need the intakes and finding the SM intakes seems to be an issue. I may have to source them from Germany. Should I get sodium filled intake valves or just go with the standard intake valves?

Ah - I had forgotten that you had real 2.8 heads. Perhaps envy did that. No need (and probably no possibility) of larger valves. You could adjust where the valves seat, though putting them where Porsche did couldn't be bad.

I was wondering about the possibilities of 2.7 and earlier heads using the 92mm jugs.