Do 98mm pistons and cylinders require a 3.3 crank?

[dd74]

I read a comment on another thread that said 98mm pistons & cylinders will not work with the smaller-sized 3.0L Turbo crank. One must instead use these with the 3.3 crank.

Is this true? I always believed the 98mm pistons and cylinders were a direct "bolt-in." I never heard of a need for a 3.3 crank for this modification.

Enlighten me, please...

[surflvr911sc]

According to Wayne’s rebuild book the 98mm pistons work great w/ the 3.0 SC crank for a short stroke 3.2. It’s listed in the favorite engine combo chart.

He does list a 3.2 case in there but he told me once that he could order the 98mm P&Cs that will bolt on to the 3.0 w/ CIS. Or you can get the 98mm RSR P&Cs and carb it if you really want to go nuts.

[dd74]

Hey Ryan: that's what I knew to be the case; that the 98mm p/cs work in accordance with a stock crank, and that to punch a 3.0 to a 3.4, one needs the 3.2 crank.

But with a 3.3 turbo crank in a 3.0 and 98mm pistons and cylinders, would that'd equate a 3.5?

[surflvr911sc]

Not sure. TRE just built a 3.5 for a customer. I forget what they used but I think it was a 930 (3.0 SC) case. They had to uses head spacers for the long stoke as I think you would have to do w/ the 3.3 crank but I really don’t know that much about the other cranks especially turbo (disclaimer saying that I don’t know what I’m talking about).

You have a 3.0 right? If I wasn’t doing the 3.6 thing and I didn’t have to worry about smog I would love to do the short stroke 3.2 w/ carbs. Fun Fun Fun!

[CamB]

You might have to do more research. I seem to remember reading that the early turbos were based on a 3.0 Carrera case. The 98mm P&C for an SC might be different. There are also 98mm P&C to fit a Carrera (3.2) crank (different wrist pin).

98mm P&C with a 74.4mm crank is a 3.4 not a 3.5 (which requires 100mm P&C).

[dd74]

How many mm is the 3.3 crank?

[CamB]

According to the tech info on this site, 74.4mm with 97mm P&C.

Fun with maths:

74.4 * ((97/2)^2 * pi) = 0.550 litres - you need to divide by 1,000,000

6 * 0.550 = 3.300 litres (actually, it is 3,299cc if you don't round it).

70.4 x 98mm = 3184cc

74.4 x 95mm = 3164cc

74.4 x 100mm = 3506cc

Easy.

[dd74]

Originally posted by CamB
According to the tech info on this site, 74.4mm with 97mm P&C.

Fun with maths:

74.4 * ((97/2)^2 * pi) = 0.550 litres - you need to divide by 1,000,000

6 * 0.550 = 3.300 litres (actually, it is 3,299cc if you don't round it).

70.4 x 98mm = 3184cc

74.4 x 95mm = 3164cc

74.4 x 100mm = 3506cc

Easy.

Wait, I ran out of fingers and toes...

[rick conrath]

98 mm pistons with 3.0 crank = 3.2
98 mm pistons with 3.2/3.3 crank = 3.4
100mm pistons with 3.2/3.3 crank = 3.5

That was my understanding of the combinations.
Rick
'78 930

[Bruce M.]

And 98 mm with a 3.6 crank (which is what I have in my 930) is 3.45 liters....

Closest you can get to a 3.5 in a 3.3 case without boring the spigots. Gotta chamfer the heads just a bit to fit the longer stroke.

[POVI]

Hi

I built up a neat motor a few years back .. 66mm stroke with 98 mm
3.3 turbo clys and had some J+E pistons made up
total displacement was just short of 3 liters like 2.95 liters or something like that

engine specs ..
911 carrera 3.0 case ( the ONLY 911 case that will allow early 66mm crank and 98 mm cly spacing )
2.2 s crank
906 titanium rods ( same dimen. as a 2 liter rod )
98 mm 3.3 turbo cly
98 mm custom pistons from J+E
3.3 turbo heads
906 cam grind

very quick reving engine !..not much low end, but a screamer !

- Joe -

[Wayne 962]

Hi all. Unfortunately, there's lots of mis-information in this thread:

- 1976-77 911 Turbo and European Carrera cases are the same (nearly identical). They have the smaller flywheel end (used from 1965) and the larger cylinder head stud spacing of the 3.0/3.2/3.3 cylinders from the later cars.

- The 2.7 crank and rods and the 3.0 crank crank and rods are identical in stroke. Using a 2.7 crank and rods in a Euro Carrera or early Turbo case will be nearly the same bottom end as as a 911SC engine.

- All the 3.0/3.2 CYLINDERS are the same (95mm). The 3.3 uses different cylinders (97mm, shaped differently on the exhaust fins).

- The 3.2 pistons and 3.0 pistons have the same outer bore (95mm), but do not have the same piston pin offset. As a result, you cannot use 3.2 pistons with a 3.0 crank, nor can you use 3.0 pistons with a 3.2 crank. It just won't work. The 3.2 pistons that I refer to in the Engine Book's table is a special set of pistons and cylinders that are larger bore (98mm) and specifically designed to work with the 3.0 crank ($3600 new). There is also the same set that can be used with the 3.2 to make it a 3.4. These are also 98mm, but can only be used with a 3.2 crank.

- The 3.3 and 3.2 crank are identical and can be interchanged.

- 3.0 rods must be used with 3.0 cranks. 3.2/3.3 rods must be used with 3.2/3.3 cranks. They are not interchangeable.

- If you swap your 911SC 3.0 crank and rods with ones from a 3.2, you must then switch to the 3.2 pistons and cylinders as well. At this point, you can buy the 98mm pistons and cylinders and upgrade from 3.0 -> 3.4.

- A stock 3.2 is considered a long-stroke 3.2. It is the same engine as the 911SC, but with a longer stroke (different crank,rods and pistons). The short-stroke 3.2 is a 3.0 engine (3.0 rods, crank) with a big bore kit on it (98mm).

I'm building the following engine:

- 911 Euro Carrera 3.0 Case
- 2.7 Crank and rods
- 3.2 pistons and cylinders with the offset for the 3.0 crank
- Turbo heads ported to 35/36
- Webers
- HPX Twin-plug Ignition
- Mod 'S' Cams

Displacement: 3.2, HP: est 270? Compression 10.5:1.

Hope this info helps!

-Wayne

[dd74]

It helps...but now I've forgotten my own question...