Alright, I see.

An "S" is definitely a different block than the base,
though it looks the same from the outside.

There's just not enough metal to bore out a 2.5/2.7 into an S 3.2.
The cylinder walls would be way too thin to change the bore by 7.5mm.

So Porsche didn't just rebore the Base motor into a (relatively) big-block.
Nor did they expand the motor to accomodate increased cylinder volumes.
They kept the rest of the motor identical and just re-cast the S cylinders larger
(and maybe a mm or 2 thicker) and jammed them into the same Base block.

So there's alot less room inside the block for the water jacket.
It doesn't seem marginal either. Looks like half as much water-jacket
especially on the ends of the outer cylinders. I'm guessing heat problems.


At least that's how I read the block internals pics from Paul and BYprodriver.
Thanks guys. And thanks to boxxster who figured it out and explained it to me.

The 2.5 can be taken to 2.7, the 2.7 to 2.9, the 3.2 to 3.6. Not cheap if done right.

Mike, you bring up other Boxster motors.
There's also 3.4 and 3.8 (Jake Raby only?) that I've seen.

Is the 2.x-base 3.x-S the only semi-block (bore) change in the lineup?
The 3.2 really doesn't look like there's any room left for bore increases.
In fact it looks like the 3.2 is pretty tight on cooling already.

The 2.5 changed stroke to get to 2.7 and that's how I'm guessing they did 2.9.
Call them small-blocks.
Were 3.2 > 3.4 > 3.6 (> 3.8) similarly all the same bigger-block
with stroke-only changes between?

Was there ever an actual full-block change in the Boxster heritage,
say like when the 981 came out? (718 obviously).
Or did the one original block do the whole 20 years
with a cylinder-only recast for the S resizing?


Side questions for you all:
- Is it true that they are fitting a 6-cyl to the 718 soon?
- And if they did, would sticking the original 2.5 in, or say a new 2.2 6-cyl satisfy you?

I cited the possible displacement increases from Raby's public pages. I know he has done some custom engines. Since they cost twice what my cars were worth, I didn't pursue that route. I'm no expert on block and sleeves. Maybe look at the LN's web site since they provide the Nickies to do the blocks.

Boxx, since you are so interested in the M96 engine history, have a look at Hartech's website,
< Porsche Engine Repair and Service Specialists > and click onto "Engine guide" and then "Buyers Guide" sections. The Engine Guide takes you through the history of the water cooled engines from the 2.5 thro to the 3.8 variants.

Barry Hart is an automotive engineer and his company is the UK equivalent to Jake Raby's Flat Six in Georgia. Hartech have a enviable reputation in Europe with many years of development and competition experience.
Be prepared for a couple of hour reading though....

Bump. Good stuff here.