Here's some info I know (from memory)

- All the stock rods are essentially the same in length - 150 mm
- They changed the pin placement in the pistons to compensate for the longer stroke.

- They also changed the dish size or no dish to adjust compression ratio.

- The 2.7 head combustion chamber is about 57 cc +/- 1
- The S2/968 head is about 42 cc
- about 15 cc's difference
- the 968 pistons have a 28 cc dish +/-
- I assume the S2 is close to that as well

- Yes the pistons will definitely hit the head with the stock rods/pistons

A couple options that people haven't mentioned:

- Find some s2 pistons - with the 2.7 head and 3.0 crank you'll get
something like 9.2 CR - you could mill the head a little to increase the CR.
They have the correct pin placement so you should be fine there.
The CR is lower because the 2.7 head has more volume.

- Dish the 2.7 pistons - I don't know what they look like but if they
already have a dish you can usually make it somewhat bigger safely.
You still need the shorter rods - but not as short. Shorter rods aren't great
because the rod ratio is worse.

--Brian Morris
89 951

 

Another option is to use 104mm pistons for the 8V head - As rare as they are, we have a few sets. The compression ratio is 8:1 with a stock (unmilled) head, stock rod length, and a 3.0L crank. Basically you end up with a full 3L engine. Best part - The pistons were designed to be used in a turbo application, so they are built to tolerate higher cylinder pressures.

If you use a S2 or 968 piston with an 8V head, you throw away the quench area (squish area) and create a rather inefficient combustion chamber.

We have the pistons in stock - $1,300.00 for a set which includes wrist pins and rings.

Hope this helps!

 

Scott are you saying that if one had a 2.7 motor they could use a 3L crank a set of your pistons and have a 3.0L motor with an 8:1 compression ratio that could be used in 15-21 psi turbo applications?
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OH YES! - That is what I 'm saying!

These are the same pistons as used in the 968 turbo S/RS

Based on the emails I am already getting, I don't think they will be around long.

 

That's the way I read it Matt. Scott, is that the word? My dad has a 86 951 block with the cylinders scored badly. Hmm, maybe a little overbore and recoating???

 

Well, that would be more than a little overbore 100-104mm - Your dad would be better off using a S2 or 968 block and a 2.7L head, as these pistons will drop right into the bores, and the 986 and S2 blocks are significantly stronger than the 951 blocks, however, anything is possible.

Quite honestly, I have not used these pistons in a bored 2.5L block, so I cannot give you any insight on what to expect. The pistons are coated to be used with the factory alloy, and conditioned bores, so I assume this would work, I have just never done it on a 2.5L block.