Base vs S - weight

[Boxx]

Boring is usually something you do when you go to a bigger block.
And the 7.5mm bore increase seems like alot of aluminum to cut away.
I thought that was roughly how thick cylinder walls were in total.
Cutting half the cylinder wall away seems like bad mojo.
-- A 7.5mm bore increase seems like a different block.

On the other hand if an "S" has a bigger block, I would think
it would be more than 80 lbs heavier, especially considering
all the other heavier pieces like rotors and pistons adding weight.
80 lbs heavier total car doesn't seem like a heavier block.
Also, Paul said they were all the same exterior dimension.
-- Same dimensions and not much heavier seems like same block.

So which is it afficianodos?
- Is the "S" a different block, larger and heavier than the Base?
- Or does the "S" block have thinner cylinder walls than the Base.

It's got to be one of those two with a bore change.

[Paul]

Check this out:

3rd assembly page - Page 3

[Boxx]

Wow, that is really good. I'm about 2/3 thru and I'm saving the rest for later.

I don't really get the crankshaft 'stroking process' that takes it from 2.5 to 2.9
by going from 72 to 78.4 on assembly page 1 (especially when going from 72 to 78
gets you from 2.5 to 2.7)? You don't just adjust a crankshaft, like with a screwdriver.

I'm going to guess that the 'stroking process' is a euphemism for 'buy and install
a new crankshaft'.

[BoxsterSteve]

Originally Posted by Boxx

Boring is usually something you do when you go to a bigger block.
And the 7.5mm bore increase seems like alot of aluminum to cut away.
I thought that was roughly how thick cylinder walls were in total.
Cutting half the cylinder wall away seems like bad mojo.
-- A 7.5mm bore increase seems like a different block.

On the other hand if an "S" has a bigger block, I would think
it would be more than 80 lbs heavier, especially considering
all the other heavier pieces like rotors and pistons adding weight.
80 lbs heavier total car doesn't seem like a heavier block.
Also, Paul said they were all the same exterior dimension.
-- Same dimensions and not much heavier seems like same block.

So which is it afficianodos?
- Is the "S" a different block, larger and heavier than the Base?
- Or does the "S" block have thinner cylinder walls than the Base.

It's got to be one of those two with a bore change.

You're getting hung up in old-school bore concepts.
The cylinder bores on these engines are varied size sleeves that are cast into the block when it's formed. The factory just substitutes different liners for different engine displacements.

[Paul]

He was getting there....

[Boxx]

I don't really think I am getting hung up on concepts.

I assumed a liner when I got that the engine was aluminum.
The XK Jaguars of roughly the same timeframe used 'Nicasil' liners.
Nickel is a real hard metal.
(They had problems with this alloy but I can't remember exactly what.
Something to do with leaded gas maybe.)

Liners are fairly thin. You don't just shave 4mm off of a liner (8mm bore increase).
You don't start out with a 10mm thick liner. At least I don't think.
What you do is increase the aluminum cylinder size (bore)
and put a similar-thickness liner inside of that.

If you had a liner. But - that is not how Porsche does it.

They have some coating placed on the inside cylinder walls.
I forget the name, but it acts just like a liner.
I distinctly remember reading that is why you can't just rebore
a cylinder in a Boxster.

Cylinder liners are not for changing bore sizes.
And in a Boxster they are not for changing period.

Unless you can show me how, my question stands:
- Bigger block or thinner walls?

(And keep in mind, that is even if the Boxster had cylinder liners instead of cylinder lining.)

[boxxster]

I'm not an engine expert, but it seems to me you could maintain the same cylinder wall thickness and block dimensions at the expense of smaller (narrower) cooling jackets?

Someone can probably correct me on this.

[Boxx]

Maybe, but that would be a different block.

And if it was a different block, they probably wouldn't choose
to narrow the cooling jackets to increase bore size.

[Paul]

From wikipedia:

All 986 and 987 Boxsters use the M96, a water-cooled, horizontally opposed ("flat"), six-cylinder engine. It was Porsche's first water-cooled non-front engine. In the Boxster, it is placed mid-engine, while in the 911, rear-engine. The flat, mid-engine layout provides a low center of gravity, near-perfect weight distribution, and neutral handling. The engines had a number of failures, resulting in cracked or slipped cylinder liners, which were resolved by a minor redesign and better control of the casting process in late 1999. A failure for these early engines was a spate of porous engine blocks, as the manufacturer had difficulty in the casting process. In addition to causing problems with coolant and oil systems mingling fluids, it also resulted in Porsche's decision to repair faulty engines by boring out the cast sleeves on the cylinders where defects were noted in production and inserting new sleeves rather than scrapping the engine block. Normally, the cylinder walls are cast at the same time as the rest of the engine, this being the reason for adopting the casting technolog

[j.fro]

Here's a little chart I've put together regarding M96/M97 engines. They all have a very similar block, except for the 996 GT3:



Be careful comparing factory weight specs. Options can throw things off. Just a guess, but I'd bet that a fully loaded base 00-04 986 manual would weigh about the same as a really low option manual S model.
FWIW, somewhere I read that the 6sp is about 100 lbs heavier than the 5sp.
I don't know the weight of the tiptronic, but it wouldn't surprise me if it weighed the same or more than the 6sp.

[Paul]

The 996 GT-3 and 996 Turbo do not have M96/97 motors.