Piston/Cylinder set differences?

[fanaudical]

Does anybody know the physical differences (and can maybe supply pictures of the piston tops) between the 911 103 928 and 911 103 949 P&C sets for a 2.7? I have run across a new set of each and trying to determine what is best for a 2.7 CIS engine I'm about to rebuild.

Thanks for the help.

[Flat6pac]

The cylinders will all be the same, nikisil by Mahle
The pistons 911 103 928 are the ones built for the RS in 1973 and continued for the Euro Carrera 2.7 application. These are used with long duration early lift cams and produced 210 horses with MFI
The other set is standard pistons with the CIS wave across the piston top made for the 2.7S, 74 to 77 USA. With CIS cams these produce 175 horse.
Both are 8.5/1 CR, your purchase depends upon application and engine configuration.
Bruce

[Steve@Rennsport]

Originally Posted by fanaudical

Does anybody know the physical differences (and can maybe supply pictures of the piston tops) between the 911 103 928 and 911 103 949 P&C sets for a 2.7? I have run across a new set of each and trying to determine what is best for a 2.7 CIS engine I'm about to rebuild.

Thanks for the help.

There are CR differences between various versions of the 911.103.949 sets as well as some are Nikasil and some are Alusil. You need the last two digits of the part number to determine what you are looking at.

[fanaudical]

Thanks for the replies.

I'm intending to build a stock motor for durable street use as a "weekend fun car". I have stock heads with CIS cams and intend to use the CIS injection setup.

Is there any advantage of putting in the RS pistons if I keep the CIS and stock cams?

[Flieger]

CIS pistons have a dome shape to help swirl the fuel/air mixture for better mixing and cleaner combustion. RS are more flat. RS will work worse than CIS if used on a CIS motor. CIS pistons might hit valves if used in an RS spec motor.

[Steve@Rennsport]

Originally Posted by fanaudical

Is there any advantage of putting in the RS pistons if I keep the CIS and stock cams?

Nossir. RS pistons in a CIS engine results in a major drop in fuel economy and sluggish low-end throttle response.

Stick with the CIS pistons as these have a swirl-inducing dome designed specifically for these applications.

[fanaudical]

Thanks for the info! That clears things up quite a bit.