Is it a 2.4 or a 2.2?

[edmayo]

Rod length has more to with leverage on the crank arm and slowing the piston speed to allow more cylinder filling, also longer rods lessen the piston thrust against the cylinder wall. Smokey Yunick was a big proponent of longer rods.

[jac1976]

Jim,
Thanks for the clarification. Makes better sense now using actual numbers.

[SIMI BOB]

Just remember that the difference between a 66mm crank and a 70.4mm crank is 4.4mm of stroke, but the rod journal on the crank only moves 2.2mm out from the center line. Also, a 70.4mm crank has 2.2mm shorter rods, so you can put a 70.4mm crank in a 2.0 or 2.2 and you would be good to go, as long as you use the shorter rods.

Also a lot of talk here about longer rods giving more compression. The bottom line is you can't just put longer rods in a motor and magically have more compression, because the piston will hit the head or the valves. You have to deal with deck height and piston to valve clearance. And you can't just put more shims under the barrels, because then you screw up the geometry of the chains and tensioners. Normally you would buy a custom piston with the wrist pin moved towards the crown to accommodate a longer rod.

Now here is my take on the 2.2S pistons making more power in a 2.4 motor. I have been told that all the 2.2 and 2.4 heads have the same combustion chamber, the difference being port and valve size for the T, E and S.
2.2 motors:
T= 8.6:1 compression
E= 9.1:1 compression
S= 9.8:1 compression
2.4 motors
T= 7.5:1 compression
E= 8.0:1 compression
S= 8.5:1 compression
So if all the combustion chambers were the same, that would mean that the 2.2 T, E and S motors had a larger dome on the piston to achieve the higher compression ratio than the 2.4 motors. Also the S piston had a slightly larger dome than the E, and the E had a larger dome than the T on both motors. So putting either T, E or S 2.2 pistons in a 2.4 motor would give a compression boost in that motor due to the larger domes of the 2.2 pistons.

So the OP went from 7.5:1 compression of the 2.4 T to 9.8:1 compression of the 2.2 S motor.

2.0 motor = 1990.5cc
2.2 motor = 2194.5cc
2.4 motor = 2340.8cc (Porsche cheated a little here)

I am sure that there are people on this forum that know more than me about this, so feel free to correct me if I an wrong.
Bob B

[goodtogo]

Ok, here's a question from another perspective.

I have a 1965 bare 2.0 sandcast case and also a 2.2 T complete engine with allegedly 'breathed on' internals, but of unknown specification, but which runs fine.

Question:

Regarding the 2.2, with unknown internals, would I be able to just transfer all the internals (incl crank p&c's & cylinder heads etc) straight over to the bare 2.0 sandcast case (and it would run fine again)?

[Richy]

This is a crazy thread . Jim's math is goofy , and I don't believe the O P has 2.2 S pistons in a 2.4 T engine , the compression would be too high for T cams .
(365+x)/x =9.1

[BOYER73S]

I have had the 2.2S into a 2.4S upgrade done before makes a sweet motor.

Will the same relative affect happen (increase in compression) if I switch 2.2E pistons into a 2.4E with all other 2.4 E STD operating bits?

[Jon B]

Regarding the 2.2, with unknown internals, would I be able to just transfer all the internals (incl crank p&c's & cylinder heads etc) straight over to the bare 2.0 sandcast case (and it would run fine again)?

A 2.2 intermediate shaft and gear will not work in a 2.0 sandcast case.
There's also an issue with the chain housing attachments, but the early case can be modified for that.

Jon B.
Vista, CA

[NeunElf]

I have had the 2.2S into a 2.4S upgrade done before makes a sweet motor.

Will the same relative affect happen (increase in compression) if I switch 2.2E pistons into a 2.4E with all other 2.4 E STD operating bits?

2.2E pistons are the same as 2.4E pistons so that change in itself shouldn't affect the compression ratio.

To go from 2.2 liters to 2.4 liters Porsche increased the stroke with a new crankshaft. Both the 2.2 and 2.4 liter 911E engines used the same part # 911.103.916.01 84 mm pistons and cylinders (I just looked at PET). Any change in compression ratio would be from different shims, any machine work on the heads, and possibly length differences between two sets of cylinders.

It's possible to calculate cylinder head volume from bore, stroke, and compression ratio but only if nothing else changes.

[Jon B]

2.2E pistons are the same as 2.4E pistons so that change in itself shouldn't affect the compression ratio.

Jim, 2.2E pistons are not the same as 2.4E pistons. The 2.4 pistons have lower domes for reduced compression.

Jon B.
Vista, CA

[NeunElf]

Jim, 2.2E pistons are not the same as 2.4E pistons. The 2.4 pistons have lower domes for reduced compression.

Jon B.
Vista, CA

Well, I share some of the blame with PET.