So one of the last things I'll have do to on my build is the engine. I've got the 16V 2.5 and I am thinking that the extra displacement of the S2 or 968 engine would be a nice thing to have.

I'm planning on modding the engine for more power but don't want to go boosted - I just like N/A engines better. My goal is about 275 crank HP, which may be a bit ambitious, but then again I've seen Michael Mount build beautiful 400HP N/A motors than spin past 8000RPM. I don't intend to get that wild, and that wouldn't work well in a street car anyway.

I'm thinking cams, header and exhaust, standalone engine management, and possibly an offset grind on the crank for a little more stroke and displacement, depending on how much I can put into the budget when it finally comes time to build the motor.

I know Mr. Mount started that monster build with an S2 engine, but I'm thinking that a 968 mill would be a better starting point for me since it's already 30-some HP up on the S2, and the Variocam may help retain more streetability, which wasn't a concern for his race engine. But S2 engines tend to be easier to find and a bit cheaper to buy, so I'm also open to that path.

Can the Variocam system deal with hotter cams? Is adding ~70HP to the S2 engine much less feasible than adding ~40HP to the 968 engine?

 

I'd like to see someone do a streetable big bore using a 2.5 8v as a base for the build. Darton sleeved 106 bore with an offset ground 95 stroke would be a good 3.3 liter starting point. Webcam, bigger intake valves, some flow work on the head and intake and Tech-GT engine management and you should be approaching the stock 951 power range.

 

Stock 951 power (non-TS) is possible with a 2.5 S motor with standalone and maybe minor other mods. I think someone dynoed 200bhp with just a VEMS or something.

 

Yes, stock power but I don't think stock torque is possible with the 2.5 16v.

 

Otherwise stock S2 on VEMS made 240 crank with good tune.
I think with hotter cams (the S/S2 stuff is pretty mild) and a non-stock ECU you could get there no problem.

I would start with an S2 because I just like them better than 968s, and the engines are cheaper to start with.

 

IIRC, MM's big hp NA engine was running ITBs. Are you prepared to go that route?

The 968 makes almost all of it's extra power over the S2 with it's fancy resonant intake. I read somewhere in a book that the Variocam provides only 3-4hp.

I say get an S2 engine, convert to 968 intake, standalone, cams, and a nice exhaust, and let us know how much power that puts down.

 

here is a really good example to see what's feasible:
944 S2 280 HP with standard inlet plenum, internal changes like pistons, rods, reprofiled camshafts, 968 inlet valves with solid lifter setup, head porting and 12:1 compression ratio. --> 280 HP

https://rennlist.com/forums/944-and-...p-upgrade.html User turbotim3

 

ITBs would be cool as hell just for the bling factor, and fabbing up a setup using motorcycle TBs is probably within my ability, but tuning the intake (runner length, size, plenum size/shape, etc) would be a crapshoot, I'm no engineer. Probably best left to the experts, and I doubt my budget can stretch that far.

 

Yeah, that's the main consideration for the larger engine. It would be much cheaper to start with the 2.5, since I already own it, but it seems like hitting my power goal with it would require a race-type build. I actually want this engine to have a bit of a high-strung edge to it, but I also want to keep some streetability.

​​​​​​Another option could be to do a stroker build on my existing S mill to get to 2.7L and a bit of extra torque, I suppose.

At any rate, my plan is to have some of the supporting mods already done before I even purchase a 3.0 engine to begin building. I already have a long-tube header and a 2.5" exhaust on the S, which shares the same exhaust manifold bolt pattern with the S2 and 968, so that can swap over. Plus I plan to get it running on Megasquirt within the next year or so. Once it's working on the S motor, it'll just be a matter of adjusting the tuning to suit the larger S2 or 968 engine.

 

968 is easier to start with b/C it already has some stuff ready made, for example bigger intake valves. shouldn't be a problem to make 270hp..

 

Very nice!
I always forget to check that forum.

 

I'd do the cams aswell as they will bring most of power (othervise leaving much unused)

 

**Edited: Whoops! Missed most of the first post. Sorta want to get within the goal you set too at some point. These two definitely seem like the way to do it, at least with S2 engines. Michael Mount stuff of course.. You've probably seen it already but I'll post it anyways:

https://rennlist.com/forums/924-931-...et-engine.html

This second one would probably be more up my alley. Cams, 951 rods, stand-alone ECU, pistons, modified head, still 3.0L. Dyno reads 287 rwhp.

https://rennlist.com/forums/944-and-...big-power.html

 

The 968 head flows better so i'd start there, but the resonance intake is a big part of the entire package. Cams and a matching tune would likely get you there.

Cams are not cheap unfortunately, but can be done. I'm fairly sure RSbarn would be able to make you a chip that would run it on the stock DME, the 968 MAF is a decent size so that shouldn't hurt you. The s2/968 motor would be a fairly easy swap in an S, hell the s2 may not even need anything more than the engine harness and its DME as the S/S2 motor are very similar on the electronics front, the 968 motor would require the engine harness and some jumpers at the DME itself to make it work. Its documented (and what we did in my 68 swapped S2). You still have an easy swap since you would already be starting with a 16v car.

Now i want cams, this is your fault.

 

hot cams for 944S/S2 from Webcam are $1300/pair
they are very fast turnaround for the work too.

as arominus mentioned the 968 is sort of a "package deal" as-is. the exhaust and intake manifold are very much optimized to work with the variocam and "pulse tuning" so you need to address everything to get a gain.

an S2 is likely less sensitive to changes - you won't need to change the porting at all, the S/S2 intake port is arguably too big already (and 968 is just ridiculous )

S2 + MAF/MAP conversion + hot cams should get you way up there in power. 275? maybe not...but i could see 250+.