2.2 to 2.5 conversion.

[71T Targa]

OK so all of this rebuild talk of Wayne’s and the 2.0 upgrade questions have gotten me thinking. What is involved with a 2.2 to 2.5 conversion? And what will it ‘really’ cost me?

I know I’ll need P/C’s, and gasket set, but what else?
Dizzy? What one?
Heads machined? What kind of $$’s for this?
Already have a ‘T’ cam.
Already have Webers, but I they would need to be re-jetted. Probably more time then money here?

Those in the know, please fill me in. To me it looks like a great project that wouldn’t break the bank. The P/C’s being the only real expense. I must be missing something…

[gator70]

How can I use 95MM pistons on a 2.4L? This is simular to the 2.5 upgrade. Except you use the longer rod.

[cegerer]

I can't be a lot of help on current prices, but I know they don't give those RS P&C sets away!!! You'll also need a Bosch S distributor. Despite BA's recommendation, I would go with an E, S, or Solex cam set. The heads and crankcase will need to be machined. This was a few hundred dollars when mine was done several years ago. If you have a 70 2.2, you'll need to install the case oil squirters.

Weber 40 IDA specs:

Emul. Tubes: F26
Venturies: 34mm
Air Correction: 180
Main Jets: 140
Idle Jets: 55

Spark Plugs: Bosch 250 P21

Timing: 34 degrees BTDC at 6000RPM

Fuel: 87 octane is like rocket fuel in this low-comp beast!!

With the Solex cams, this setup runs flawlessly for me. If you're buying new P & C's anyway, you might want to jump up to the 92mm RSR units and get 2.63L out of it!! -- Curt

[gator70]

Curt ... I like the short stroke motors. What type of power do you get from this setup?

[cegerer]

It's never been dyno'd. Stoddard (who built the motor) indicated at least 190. I extrapolated at least 190HP as well by comparing various displacement, compression and HP changes in early motors. -- Curt

[71T Targa]

So where do you source RS or RSR P&C's?
Or could you use something like these?

[jluetjen]

I've often wondered the same thing. Everyone seems stuck on using Porsches 2.7 RS pistons which already had a fairly uninspiring 8.5 to one CR. In a short stroke 2.5 the CR goes down to about 7.0:1 Why not get a set of Mahle 90mm 2.7 pistons which have a CR of 9.5 to one and would result in a CR of about ~8:1 or a set of JE forged 90mm pistons with a 10.5:1 CR resulting in 9.0:1 in the short-stroke 2.5. It would most likely help the low end torque using any kind of a radical cam. You'd most likely need to open up the intake ports to 34 or 36mm's if you wanted to use an S or GE60 Cam, but I would think that it would make a neat combination similar to a detuned 911 ST race motor.

Curt: Do you by chance know what your intake port diameters are? Were your heads ported by Stoddard? It would provide a very interesting datapoint since my data suggests that you'd be hard pressed to get over 170 HP using stock T/E heads with the 32mm ports, no matter what the engine size.

[cegerer]

I don't know if the stock 32 mm intake ports were changed. The work was done by the PO and the invoice for the engine rebuild only indicates "Rebuild Cylinder Heads & Machining of Cylinder Heads and Crankcase". I can only go by the performance of the car itself and it is very similar to 2.4S figures.

I don't know enough about the effects of port sizes to offer a real opinion. However, the stock 2.4E with 32mm intake ports is already at 165HP. I've got more displacement and a more aggressive, higher revving cam set. So are you saying that even if a turbocharger or nitrous were installed on an E motor, it's not physically possible to gain even 5-10HP with the restrictive 32mm ports?


The Stoddard catalog still lists the following:

911.103.928.01SET - 90mm 8.5:1 Nikasil 2.7 Euro Carrera P&C's

911.104.901.00SET - 92mm 10.5:1 Nikasil RSR P&C's

-- Curt

[71T Targa]

Is the bolt spacing the same for these cylinder? Or is that one of the things that you need to change?

[jluetjen]

Curt;
NO2 or Supercharging are completely different beasts since both of those are ways to force more air into the cylinders. My analysis is based on the engine being normally asperated. I've never taken a class in flow dynamics, but I have yet to find a 911 motor which pulled much more then 100 m/s at the maximum HP engine speed. The 2.4E seemed to define the limit. From what I've seen that is actually a pretty high flow number for any kind of a 2-valve engine. If you are getting more then that -- Great! How'd you get there? I suspect that there are a couple of engine configurations out there that might pull higher gas speeds, but the law of diminishing returns takes affect. The case that comes to mind is when Porsche took the 2.5 944 motor out to 2.7 - they only gained about 3% in the HP even though the engine went up 8% in size.

[BK911]

Something else to consider:

A 2.2T piston has about the same dome as a 2.4S piston. So convert your 2.2T to a 2.4S or a high compression 2.4E.

You need a 2.4 crank and rods, 2.4 dizzy, E or S cams and tweak the webers. For an S you'll also have to port the heads. I probably missed something but this should start your shopping list.

Good luck!
BK

[cegerer]

"If you are getting more then that -- Great! How'd you get there?"

Well, I doubt my engine is defying the laws of physics! So apparently, the heads must have been ported to match the performance of the Solex cams (would it even be possible to spin this thing to 7200RPM with 32mm intake ports - it pulls cleanly all the way there with no fuss??).

Also, BA actually recommends retaining the 32mm port size and the T cams for better 'seat of the pants' horsepower (low-end torque) on the street, while acknowledging a reduction in peak HP. -- Curt