2.7RS to 2.8RSR

[Mike_Moore]

Hi, this is my first post and its a big one! I am in the UK and would like to pick your USA brains to help my limited knowledge and perhaps correct some misapprehensions.

I have a 2.7 RS motor with the correct mfi, and I am considering rebuilding to twin plug 2.8RSR spec. I do not necessarily want the correct part numbers and so on, just the best way of replicating the RSR lump with the best power output and characteristics for track day and fast road use, not race!

Here are some ideas I have, could anyone offer any thoughts, or point me in the right direction. Perhaps there may have been previous posts about this?

1. I am told my 7R cases are fine
2. Best way forward is to use 2.9 pistons and barrels, better and cheaper
than 2.8.
3. Use existing heads?
4. Machining for the new plugs in the lower heads straightforward.
5. Now the tricky parts, the twin plug distributor, unobtainable but there
are conversion options?
6. Even more difficult the mfi, again unobtainable, and I gather mine will
not convert to give the higher rev limit.
7. Which butterfly stacks?
8. Am I mad to even think of this unless I am an millionaire!

I would consider having this motor built over in the states, any recommendations for these kind of specialists.

thanks Mike Moore.

[nick-moss]

There are several engine builders here in the UK that can build to that spec but expect to pay well over £10K for the parts alone. Try Bob Watson, Autofarm or JZ Machtech

[RPMClassic]

Mike -

I recently changed to another engine builder and am VERY happy with the results. My new 2.5 on 7R with Carillos, Mahles,ST heads and twin dizzy is putting out 275 HP. Send me a PM and I'd be happy to share some insights. With your proposed 2.9 liter you will be able to make great power and safely too. - Jim

[Bobby Smith]

Or just buy my 2.8 Twin Plug motor, I'll throw in the car for free.
Bobby Smith
porsche911dude@aol.com

[Bobboloo]

The 2.9 set may be cheaper but is inferior to the 2.8 set. The cylinder walls are so thin on the 2.9 that they flex and don't seal with the rings as well. This info comes from a builder who's built a lot of these motors. (2.8 + 2.9) He raves about the quality and durability of the RSR 2.8 set though.

Your RS pump should work just fine in a 2.8 configuration. It will just need to be tuned to the new motor.

You can keep the rest of the MFI system the same as well. I see no need to increase port size for your application. In fact messing with the ports could yield negative results.

Have you considered just changing pistons to raise the CR to something like 9.8:1 as oppsed to the 8.5:1. This would give you a nice performance gain without breaking the bank. The added cost of going 2.8 twin plug seems hardly worth the investment. (says the guy building one )

It is a sweet motor though.

[Paul Schooley]

Bobby Smith...how much for the engine and the free car? Inquiring minds want to know.

[Bobby Smith]

I feel the car is a $35,000 vehicle, but I'm motivated and will be starting a new project soon, so I would take $27,500. It's a hellava buy at that price.
Bobby Smith

[rst73]

Bobboloo,
You are correct about the thinner cylinder wall but, inferior? I don't think so. It has been my experiance that a properly built and maintained 2.8 or 2.9 engine will give vetually the same service life.
All the best!
Roger Grago
Porsche Motorsport of North America
R Gruppe #27
Early 911S Registry member

[kenikh]

I dig the 2.8s, but I have heard some wierdness associated w/ 2.9s. I hear that you can squeeze the 2.9 cylinders in your hands and actually bind the pistons to the point that they won't fall out of the cylinder. If I can do that with my hands at room temp, I am sketpical of my confidence in them in a motor at operating temp.

[porschefan]

Hi Bobby,

Can you post some more pics of your car?
inside and out?

where are you located?