Braymond

I see lots of threads about building 2.8+ liter turbo engines, but I can't find too much info about NA builds. Has anyone here had any recent experience with building a NA stroker with the S2/968 crank?

Seems like a pretty straight forward build - 3.0L crank (knife-edged), rods, and pistons. I may end up doing this soon anyway as part of an engine refresh.

MAGK944

IMO it's better and cheaper going down the hybrid stroker route using the 2.5 crank stroked to 86mm. 3.0 cranks are not cheap and you will also need to clearance the block. There's some details on this website: refresh951.com

Edit: just noticed 16v in your title, probably be cheaper to buy a 3.0 engine complete than build a 16v 2.8 stroker.

V2Rocket

^^what he said
no reason you "cant" do it but if you want a 16v head and a 3.0 crank...you just need a 3.0 block to go with it lol

SloMo228

I haven't been down that road, but I did spend a lot of time reading the map. IMO, it's not really worth it to build up a 2.5L 16V unless you're really going to go all out and make it an 8,000+ RPM screamer, and even then I'm not sure. You can do basically the same work to a 2.5 as a 3.0 but you just get better returns on the larger motor, with the added benefit of the 3.0 block being stronger.

The 2.5L 16V is a nice drop-in upgrade for an 8V, but building it up doesn't really make a whole lot of financial sense. At most, I'd do a standalone EMS, reground stroker crank, and a set of mild cams. That would probably get you to around 210HP at the flywheel without costing too much money.

Braymond

Yes, I see the dilemma.

I'm not totally opposed to just swapping out my engine with a 3.0L, but unless I get crazy lucky, I will need to rebuild the new engine anyway and I like the idea of trying something new.

How about a 3.0L block bored and stroked to 3.5L?

I see the 104mm should be able to take a bore out to 108mm without going crazy. The crank can be stroked to 95mm. That totals up to about 3.48L.

Just maintaining the current efficiency (about 75hp per liter) this should be good for about 260HP at the crank in NA form. With some big headers, a competition valve job, and EMS for tuning, should be able squeeze out a bit more.

It would be a great candidate for a supercharger at a later date too.

Before anyone asks, LS swap is not an option

V2Rocket

108 bore is really only feasible with wet sleeves at which point it doesn't matter which block you use to start with (2.5 or 3.0)
106 in a dry sleeve might be doable in a 3.0 block but it's getting sketchy.
Reynolds aluminum who came up with the alloy our blocks (and the 928) are made of suggests minimum alusil barrel thickness of 6mm or about 1/4" but i believe that is if unsupported by steel liner.

Braymond

Okay, so 106mm with dry sleeves and some block filler and a 95mm stroke gets me to 3.35L and about 250HP at the crank. Still a nice upgrade from 187HP (which at 130k miles is very optimistic).

MAGK944

I'd love to see a well sorted na big bore but I'm guessing maybe 210hp if you are lucky without extensive head and intake flow work, higher compression, lifted cam, bigger intake valves and a well tuned standalone.

jhowell371

The empty 3 liter block and crank in my garage keeps calling to me......... 106 = 3106.

V2Rocket

based on a lot of info over on the 928 side of the world (which uses nearly identical heads to the 944 S /S2) there's no need to port the 4v head or even fit larger valves - they are HUGE to the point of being oversized as-stock for the intended airflow.

compression sure to go with hot big duration cams but the 4v heads are very limited in the amount of lift you can get - stock S/S2 intake does 11mm and you *might* be able to squeeze 12mm out but it might be necessary to clearance the heads next to the lifter bores. but the heads flow so much that really lift isn't needed (remember there isn't a whole lot of flow to be had once the valve lift exceeds the valve head diameter divided by 4 due to curtain flow area being equal to valve diameter at that lift point) so duration is really key...stock cams are super mild.

Raceboy got 240hp on a fully stock S2 engine solely by converting to MAP based (VEMS) ECU and adjusting the tune for like 93 octane gas.