Over there you’ll find posts of people 150% convinced shimming doesn’t do anything, then you’ll also find somebody who went through the hassle of making a FEA analysis of the block and proving that shimming in fact does work (up to a certain level, obviously). Based on that make your own conclusions.
My conclusion so far? Those who say “I shimmed my block and still cracked”, most of the time are high mileage blocks that have been beaten up (either overheated and/or ovalled cylinders, and/or ran with a aggressive tune on 87 octane), and then wonder why the block cracked after slapping an EFR7670 and cranking the boost to 28 psi. I mean……. WTF they did expect??????!!!!!!!!
Why I think most people recommend shimming RN P2R engines, even with stock tune? That’s because the engine already comes with 300hp from factory. Meaning, they already work with higher cylinder pressures than P1 RNC engines. A simple “stage 1” tune will push the engine for at least 20-30 hp more.
Why the P1 RNC engines don’t crack that often? They begin life with 80hp less than P2R. 300 hp on a RNC is only achieved once after you all do pretty much all the basic bolt-ons (Intake, intercooler, downpipe, exhaust and stage 2+ tune). And keep in mind, those “300hp” are just for a few hundreds of RPM range, because the K04 will run out of breath very quickly.
The P1 T5 engines are a compact version of the P2 engines, that had to fit inside the smaller P1 engine bay. Exterior wise they have different mounting points, revised cooling system, etc. but the most important differences between them are:
- Camshaft profiles
- Forged pistons w/8.5:1 compression ratio vs 9:1 on the P1
- Stronger connecting rods on the P2R
- Water pump (P2R spins faster than RNC, but I doubt this really makes a difference in terms of cooling.
I dount count the cylinder head as a major difference, in terms of flow because the use the same exact valves as P1. Also, some P2R guys have used P1 exhaust manifold gaskets on their cars, so ports are the same. You’ll also see that most P2R B5244T5 swaps keep the P2R head. Yes, it’s different between than regular P2 T5 heads. P2R use longer spark plugs, the same as P1.
Can you use a S60R rotating assembly on a C30 engine? yes, it has been done already from factory. Focus RS Mk2 is the example.
If you’re aiming to 400HP at the wheels, should you shim the block? I would say no, skip that and go directly to sleeves. But it’s up to you to try with a shimmed block first. You’ll have to drop the engine anyways to replace connecting rods and pistons. If engine is already out, might as well bite the bullet and do it right from the start.