adrial

Is it possible to take the head & valves n all that good stuff from a 968 and throw it on our cars? I read about someone with a 928 doing this...with 2 heads I would assume. I would assume that you would have to bore out our engines to 3.0L($$$)? Anybody do this? Maybe just adapt the Variocam system??

I'm just looking for some low end grunt to help increase driveability.

All suggestions are welcome

Tabor

PowerHaus sells a turbocharger kit for the 968 engine that leaves the variocam intact.

ribs

I believe the 8 valve engines water passages don't line up to 16 valve heads, if that is what you were trying to do. That is probably the only way you could do it (is replace the whole head) and it wouldn't work. You could get a 968 engine and heads, put lower compression pistons/rods in, and bolt on all the goodies (exhaust and intake manifolds, turbo, all piping, etc.) from your turbo motor...and then you would need to run stand alone fuel/spark management to make it work most likely, but you are looking at a 300-350 HP motor running on less than a bar, and it should be reliable if done right.

adrial

One can only dream...

But that is a lot more realistic than turboing a 968 engine that's in a 968...as I would already have all the turbo gear. Would only need the engine managment system, some dyno time & professional help and pistons.

Figure an even swap 951 engine to 968 engine (???), pay $2k for pistons (?? it's $2k for the stock 968 pistons, so I would figure low compression pistons are about there), $3k for the engine managment system and who knows how much for the professional help. $5k or so for a 3L turbo engine...not bad at all...

Would the 951 turbo be out of it's flow cycle (er whatever its technically called) in a 3.0L engine? even the K26/8?

ribs

It would be out of its efficency range (probably...I'm no expert). You would be better off getting a turbo made for an engine that size and HP figure...like a garrett T04, K29, etc...basically a big turbo. The stock turbo would be putting excessive heat into the mix, and just swapping to a more efficient (at that flow rate) turbo would probably yield 25-75 more HP at the same boost, not to mention less strain on the motor (well...detonation wise ). You would probably be best off getting a blown 968 motor (spun a rod bearing or the pistons and valves shook hands) and rebuilding it as you would have to do most of the work anyways to swap the lower compression pistons in...and you could overbore to 3.2 liters. BTW...I don't think a 952 block/head/bottom end with no accessories/plumbing is really worth much, so you might want to figure in more for your 968 motor cost, unless you find a thrashed one and do a total rebuild. Also, as with anything in life(I believe this falls under murphy's law), take your original estimate, and multiply it by 2 or 3, and you will have what it will end up costing you.

Another thought...do the reverse...Take the turbo, all of the turbo plumbing, and what ever else you need out of your car and drop it into a nice 968 with a lower compression piston set installed. Then you would have the venerible 968 turbo S, with 16 valves and variocam to boot (968 turbo S motor was pretty much a bored/stroked 8 valve 951 engine...not sure if it had a MAF or not...from this picture: it looks like the standard 951 AFM...but I don't really know).

Just a thought. Let me know where you are thinking about taking this thing.

adrial

I'm just dreaming...(thats where this is going)
Maybe in a few years I'll look into this seriously. I was thinking that if it would be easy to strap the 16 valve head & variocam onto my 8V motor I'd do it...but obviously thats not possible so I'm just thinking about possibilites for the future.
A 968 Turbo would definetely be my dream car...Maybe when I'm out of college and raking in the big bucks!

Thanks for the responses!

Ahmet

The 968 engine block will not bolt up to an 8v head...

The plumbing from an 8v will not bolt up on a 16v, and vice versa.

The best way to do things (IMO) would be to get a 2.7 liter block (89 NA), throw a 968 crank on that along with the 944 turbo heads/plumbing, and engine management. A piggy back system like an APEX-i should be able to handle the changes just fine. That'll give you 3 liters of displacement, nearly duplicating the 968 turbo.
Ahmet

Macabre

But still no variocam, which is the point of this topic

I really don't see why you're interested in doing it anyways. The nature of a single-turbocharger engine is such that adding variable cam timing technology is not going to drastically change the driving characteristics. Since you can't have any valve overlap, there's really not a whole lot of change to be made with the cam profiles, that's why you don't hear about too many 951 owners upgrading. You just optimize the cams for the RPM range where the turbo is most efficient, which Porsche has already done. Adding 500ccs of displacement, however, will make a big difference..

I think the 968 turbo used a K27 (not sure about 6 or 8 turbine), so you would probably do very well with one of those on a 3L if you weren't after big HP numbers. Good low-end below the boost threshold, very little lag, lots of reliable power..

jim968

From my limited knowledge of engine theory, I don't think that either the 16V head or Variocam will produce the big gains on a forced-induction engine that they do on a normally aspirated engine.

Remember that the issue on an na engine is getting decent cylinder filling at high rpm (really brief valve openings) with only atmospheric pressure to fill the cylinder. Extra valve area & more favorable cam timing are a huge help here.

On a turbo, the intake air is already under pretty much max pressure at high rpm. If you've got one bar of boost, you've got twice the pressure pushing air into the cylinders that an na has. So more area & better cam timing are less critical to getting max volume into the cylinder.
No doubt a 16V head & variocam would help hp numbers on a turbo, but doubt the increase would be as muc percentage-wise as it is on an na engine.

IIRC, there was an article in Excellence maybe 2-3 years ago about a guy who had a 968 turbo'd. I don't think it gave much tech detail, but if anybody wants to hear what there was, I'll probably have time Friday to dig thru my back issues.

Jim, is it coffee yet???

adrial

Well, the reason for my interest in variocam was to give the car some more low end grunt to help drivability. I'm talking 1500-2500rpm here.

Right now, the car has plenty of high end power.

ribs

Jim...16 valves on a 4 cylinder forced induction motor makes a world of difference. For example...my other car, a 1990 toyota celica all-trac. It has a 2.0L 16V I4 with a small turbo running ~9 psi. It has an 8.5:1 compression ratio, so it is pretty similar to my 951 in that respect, and its a smaller motor. It has easily 25% more low end (before the turbo kicks) grunt than my 951. It would pull on my 951 to about 20. It also has variable intake runners (like the new BMW's) called TVIS, so I am sure this helps low end torque (that is what it was designed to do). Just a thought.

adie

More valves=higher flow rate. I think I get that as the surface area of two small valves is far greater than one large one in the space allowed. However you need a decient flow, sorry make that vacum through the heads for that principle to work, not in your suggested 1500-2500 bracket. Cam profiling can help a lot here but so can primary length headers, as can ignition, you might have to sacrifice some high end bhp to gain some low down torque but I feel that this is always worth a trade off, and as previously mentioned an extre 500cc's would also do significant good things for torque figures.

Macabre

The best ways to increase low-end torque are to increase static compression or displacement. You may be satisfied with something as relatively simple as stroking to 2.8L. You can also have your head shaved to get a teensy bit more compression, but I'm not sure how much of a difference that will make.

Tabor

Jim, here is a dyno comparing just that:



It is from this article at 968.net.

Tabor

BTW, that dyno is of a non-variocam 16valve head.