2.7 crank...2.8 Mahle pistons...CR?

Tspringer · 04-03-2005, 01:17 PM

Im looking at a car and wondering about the engine specs based on what the owner is saying.

The car is a '74 Euro RS Carrera. Stock it had the 2.7RS engine with MFI. The engine has been rebuilt by a place called Sugarcreek Motorsports in Ohio that is no longer in business.

The owner says the stock 2.7 was rebuilt using the stock case, crank and rods but with "factory 2.8L Mahle" pistons and cylinders. He says the MFI pump was rebuilt with a 2.8RSR space cam. IT has high butterfly MFI stacks and he says it has 11:1 compression ratio. It is twin plugged and running dual MSD units. I believe its using a 964 modified distributor.

My understanding was the factory 2.8 pistons and cylinders were extremely rare. The owner has no receipts for parts (this is a huge worry of mine.... but thats being factored into the price). The car is also using stock rods which he says were shot peened and balanced and then ARP hardware used.

If a stock 2.7 crank and rods were used with 2.8 pistons and cylinders.... what CR would result?

Is there any way to tell what the CR is by a test? If it is in fact 11:1 I would think the twin plugging would be mandatory and you would need race gas?

He says it dyno'd at 278hp but does not know if that was at the crank or rear wheels.

Eagledriver · 04-03-2005, 02:41 PM

If I recall correctly the information in Bruce Anderson's book this modification will result in about 11:1 compression ratio or more. This is why it's not done very often. With the twin plug you might be ok with 92 octane on the street and mix in some race gas for the track. The use of stock 2.7RS crankcase and crankshaft and rods is fine. They should work reliably up to 7000 RPM. If the case is shuffle pinned then the engine will last for awhile. Keep in mind that these engines were stressed to the limit and so you may find the case leaks and won't last as long as other 911 engines. I wouldn't buy this car if it's got alot of miles or alot of track time on it.

-Andy

BURN-BROS · 04-03-2005, 02:49 PM

You will definitely need race gas no matter what. If the guy doesn't have reciepts I would break down the cost of what I can see to come up with a value.

Steve@Rennsport · 04-04-2005, 12:49 AM

Hi Terry:

Sounds like a trick engine, if everything was done right. That 278 HP is likely flywheel HP.

92mm P/C's are now quite rare (out of production) and these have a 11.2:1 to 11.6:1 CR using 2.7 heads. The 2.8 RSR had VERY unique heads with larger chambers that gave 10.3:1 to 10.5:1.

Its almost impossible to accurately assess compression ratios by reading compression test figures, but if you have documentation about the 92mm P/C's and you know it has 2.4-2.7 heads, that 11:1 is pretty close. Actual CR will vary with the year that the heads were made, how many times they were resurfaced, deck height, and how the valves were setup on the seats. Chamber volumes varied from 62cc to 67cc on these '72'-77 heads.

11:1 with twin-ignition is not compatible with any pump gas,....this setup is a race-gas engine only.

Wayne 962 · Wayne 962's Garage

Actually Steve, I think Mahle's been making some of the 2.8 sets on and off again. Last year I was offered a special on some kits from one of my suppliers...

-Wayne

Wayne 962 · Wayne 962's Garage

Quote:

Originally posted by Steve@Rennsport
11:1 with twin-ignition is not compatible with any pump gas,....this setup is a race-gas engine only.

Agreed - for the early cars. I might add, however, that the 3.6 engines were close to 11:1, but they had twin-plugs, knock sensors, and adjustable timing to compensate for poor gas quality...

-Wayne

Tspringer · 04-04-2005, 05:26 AM

The heads were supposedly built by Dawe. Ported, bigger valves, titanium retainers...

Thanks for the info. The car is in columbus Ohio so I am going to see if I can find anyone who could go check it out for me.

Steve@Rennsport · 04-06-2005, 12:16 AM

Quote:

Originally posted by Wayne at Pelican Parts
Actually Steve, I think Mahle's been making some of the 2.8 sets on and off again. Last year I was offered a special on some kits from one of my suppliers...

-Wayne

Hi Wayne:

Mahle had not made any for 4 years and then made a small batch to fill some OLD back orders. I've been waiting,......

LOL,..I bought 4 sets and my partner bought 3 of them. Mahle tells me there will be no more. Based on my 30+yr history with these folks, it will be a LONG time before they make them again, if at all.

These are really THE item for those who build these smaller engines with all the appropriate caveats.