Carrera 3.2 P&Cs in an SC

[Brotok]

I am currently rebuilding the motor on my '79 SC and I happen to have a set of 3.2 P&Cs sitting around from an '86 Carrera, in good shape. Can I stick those into my car?

Please let me know what is involved to make this work.

Thank you

[ChrisBennet]

Originally Posted by Brotok

I am currently rebuilding the motor on my '79 SC and I happen to have a set of 3.2 P&Cs sitting around from an '86 Carrera, in good shape. Can I stick those into my car?

Please let me know what is involved to make this work.

Thank you

The piston wrist pin diameter is different so the pistons won't work. A 3.0 and a 3.2 have the same bore (95mm) so it wouldn't turn you 3.0 into 3.2 if that is what you're thinking.
-Chris

[Brotok]

Thank you for the reply.

That is what I was thinking, but I see that it doesn't make sense.

I guess I will just use the cylinders from the carrera and SC pistons.

All the best.

[ChrisBennet]

Originally Posted by Brotok

Thank you for the reply.

That is what I was thinking, but I see that it doesn't make sense.

I guess I will just use the cylinders from the carrera and SC pistons.

All the best.

Sorry to sound negative, but there are 4 different diameters for P&C so you've got a 1 in 4 chance of having matching tolerance groups. The cylinders are very durable, it's the pistons that wear out.
-Chris

[911st]

I think the Carrera cylinders can be bored out so you can be a 3.2. You would use J&E pistons and you would be able to play with the compression and valve pockets if you want to run more aggressive cams. Check with EBS in Reno if interested.

[Brotok]

Yes, a 3.2 is tempting. However, this is one of those projects that started as a clutch replacement and headed down the full engine rebuild route - can't believe the power of emotion when the engine is out . . . so irrational . . .

The carrera cylinders are 95mm, think that should work with the sc pistons right?

Many thanks

[porschenut]

Originally Posted by Brotok

The carrera cylinders are 95mm, think that should work with the sc pistons right?

Only if the Carrera cylinders are nikasil, and the SC cylinders were nikasil as well.

If the Carrera cylinders are alusil, throw them away. If they are nikasil but the SC ones were alusil, then use the Carrera cylinders with brand new JE pistons. Or buy a new set of Mahle P&C's.

[ChrisBennet]

Originally Posted by Brotok

Yes, a 3.2 is tempting. However, this is one of those projects that started as a clutch replacement and headed down the full engine rebuild route - can't believe the power of emotion when the engine is out . . . so irrational . . .

The carrera cylinders are 95mm, think that should work with the sc pistons right?

Many thanks

Like I said before, I think there is a 1 in 4 chance that the pistons will match the diameter of the cylinders. This is assuming that they are both Nicasil and that the SC and 3.2 use the same tolerance group measurements (they might not for all I know).
For example, here are the 4 cylinder tolerance (diameter) groups for a 3.2:
Group 0: 95.000 - 95.007mm
Group 1: 95.007 - 95.014mm
Group 2: 95.014 - 95.021mm
Group 3: 95.021 - 95.028mm

Group 0 cylinders are matched to Group 0 pistons. The nominal size is "95mm" but there are still different diameters.

-Chris

[YTNUKLR]

I have done this numerous times. If you do it right everything lines up perfectly.

Listen closely:

The 911SC has a 70.4mm Stroke and a 127.8mm rod length (from big hole center to small hole center).

The Carrera 3.2 has a 74.4mm Stroke and a 127mm rod length.

The TOTAL difference in stroke is 4mm (74.4-70.4=4). That means, the difference in length for one side is 2mm longer on the Carrera 3.2.

The Carrera 3.2 Piston has the pin moved down 1.2mm. To move the piston back UP to the proper height for a 911SC with the shorter stroke, you need to modify the rod.

We do some simple math:

2mm (total difference)
-1.2mm (amount pin is moved from the 911SC to the Carrera 3.2)
=0.8mm

Long story short: To utilize Carrera 3.2L Pistons and Cylinders on a 911SC 3.0L Crankshaft and Rods, you must modify the connecting rod by LENGTHENING the center-center distance on the 911SC Rod to 128.6mm from the standard 127.8mm. This is accomplished by offset-boring the small bushing by exactly 0.8mm.

IN ADDITION, the bushing must be reamed to the larger size of the 3.2 piston pin, 23mm. (911SC has 22mm).

These modifications cost a couple extra benjamins at the machine shop, but 3.2L pistons and cylinders have a superior design (no cylinder head gasket), are more readily available, are more likely Nikasil, typically are younger and have less wear than the 911SC components. After this you can use standard cylinder base gaskets and the deck height will line up around 0.040-0.060" which is right on the money.

Enjoy.

[Brotok]

Wow, this is getting deep.

I just got the SC cylinders and pistons out. The material on the inside of the SC cylinder is definitely different than on the Carrera. The carrera's are shiny, the SC's are milky, I assume that the Carrera is Nikasil.

I have another set of pistons that I would like to stick into the Carrera cylinders. I got these from someone so I do not know exactly what they are, I was told that they are 9.3 compression pistons for an SC.

So, is there any way to check if I can mix any of these pistons and cylinders? Are there any numbers on them that can be referenced to find out?

Thanks

[YTNUKLR]

It sounds more complicated than it actually is.

You take your SC rods, tell the machine shop to make them longer by 0.8mm and bore the hole to 23mm. Then you install 3.2 Pistons and Cylinders on your 911SC engine. That's it.

Why would you want to mix pistons and cylinders? And the answer to that is, you can't mix alusil pistons with Nikasil cylinders. It sounds like your 911SC is the typical Alusil and the 3.2s are the typical Nikasil.

[Brotok]

Actually, machining the rods is sounding more and more practical. Thank you by the way for the detailed write-up.

So if I do machine the rods, do I need to get a set of carrera piston bushings and tell the shop to install those in the rods?

Do the stock SC cams work fine with this conversion?

Thanks

[YTNUKLR]

I have never had to order the bushings. Whenever I have done this I send them to Ollie's (now in Arizona; used to be in Santa Ana, CA), and they sent back done, balanced, perfect rods.

The SC cams are the same as the 3.2 Carrera.

You really are not changing much about the engine. The pistons and cylinders are very similar between both engines.

[Poohsan]

YTNUKLR is right on with his technique.

He did the rebuild of my 81 SC and replaced the 3.0 pistons and cylinders with 3.2. No problems and I have a full year of daily driving on the rebuild.

:-)
- Arron