Geneqco

Well, the time has come for me to seriously consider a 16v head (for my 951).

I have already done a bit of research on this but all I really have are some pretty vague figures. What’s really appealing about the 16v to me is the more efficient chamber design. From what I understand, because of this, you don’t need to run as much timing advance (all else being equal) so there is less opportunity for knock – ie, you can run higher boost and/or use a higher CR to start with. The stronger 3.0l block would also help here.

As for flow and costs… I’m pretty clear on the 8v… around 180 cfm stock and around 250 cfm for Stage 3 and I know the costs. I also have an idea of what 16v heads go for but don’t know their stock flow rate or the cost of working on them or solid lifter conversion costs etc. I’ve heard that they can flow well over 300 cfm with work but I’m not sure what’s involved to get them to that point. I’ve also heard that a stock 16v will flow much like a heavily worked 8v but not sure whether that’s true.

The only other thing I’ve heard about the 16v is that there may be some reliability issues with the chain guides and tensioners and that the variocam system in the 968 setup can also be the source of problems and catastrophic failures which sounds a bit scary.

Any info available on the 16v setups to help me fill in some gaps would be greatly appreciated.

V2Rocket

I'm no expert on the 16v head, but if you wanted a cheap swap for higher flow consider an NA head.

Without the ceramic exhaust ports temps will rise, but the 8v head naturally aspirated will flow about 230-240 cfm out of the box.

StyleLab

When I was looking into this, I was going to use 2 exhaust cams to completely eliminate the tensioner. Do a search, I think Chris White has some pictures up of the setup.

jtsporsche

StyleLab- what kind of spoiler is that?

can you just do a swap of an n/a 16v head onto an n/a block that originally had an 8v head?

V2Rocket

yup. as long as the block and head are both off 2.5L engines.

any idea on duration/lift of both stock intake and exhaust cams? does the exhaust have higher numbers?

FRporscheman

The point of using two exhaust cams is that the exhaust cam actually pokes out of the valve cover and you can put a sprocket on it. Therefore you can drive both cams with the timing belt, and you don't need a chain.

You can put a 944S 16v head on any 2.5L block: 944 1983-1988 or 951 1986-1991.
You can put a 944S2 or 968 head on any big bore block: 1989 944, 944S2, 968.

The chain tensioners are reliable, as long as you don't neglect them. The 944S head had a weak mounting point for the tensioner so they sometimes get ripped off and everything gets munched. The 944S2 was better and as long as the tensioner and pads are not old, they will function fine. The 968 variocam will be bad for turbo applications because when the DME activates it, it creates valve overlap which kills boost. It is extremely robust though, better than the S2 design. You can either leave it unplugged (to disable variocam and just use it as a tensioner) or you can get a standalone EMS which can operate the variocam off-boost and just leave it alone on-boost.

StyleLab

yup my tensioner mounting point got ripped off...

my spoiler is 968 TRS with carbon fibre center section...

slawek

If you are looking for S2 head, I have a spere one which I wouldn't mind to part with. It is freashly rebuild to factory specs. Please pm if you are interested.

cambria

You can not put a 16v head on a n/a motor. The head will fit but the intake valves will strike the piston. You need to change the pistons.

V2Rocket

mmm this is true.

Geneqco

PM sent

FRporscheman

Did this happen to a 944S head or a S2 head?

Thank you - and I changed the word "motor" to "block".

eman930

I thought the 16v head had different oil passages thus making it hard to install on a 8v block

Raceboy

Any 2.5 liter head fits to any 2.5 liter block. Any 3.0 liter head fit's to any 3.0 or 2.7 (1989 NA) block. PERIOD.

And regarding VarioCam, it's GOOD for turbocharging as Markus951 had it working and it flattened torque curve considerably.

Please state ONLY the facts that you know out of 1st hand experience, not those that you only heard of or think of.

FRporscheman

Variocam is only good for turbo if it is controlled by a programmable EMS, otherwise the stock computer will actuate it from 1500 to 5500 rpm. This is what I already said. And since typically boost will come on at about 3000rpm, you get that whole range from 3000 to 5500 where you have boost and variocam, and the variocam is creating valve overlap, you need to figure out how to tune the variocam to make good use of the boost and the valve timing. Markus951 used a standalone EMS and had the variocam work from 1500 to 4500.