refresh951

211 mm worked perfectly

Bill

The Lindsey website recommends 75 ft lbs for low boost and 85 ft lbs for high boost. Mine is torqued to 85 ft lbs, running 22 psi for years now.

V2Rocket

Can anyone check their torqued down head, and tell me how many threads are exposed above the top of the nut?

My 16v head on an 86 block, not torqued yet, the stud is about even/level with the nut.

Tom M'Guinn

From memory, it's pretty close on a factory car, with the top of the stud clearly crowning above the nut with maybe one thread exposed. Where did you set the stud height? Keep in mind the head will settle down on the locating pins a bit, and a standard style gasket will crush a bit. My guess is you'll pick up enough when you torque it if its even now -- but my guessing won't buy you a new gasket if I'm wrong As long as the nut is fully engaged on fully formed threads, you should be good.

V2Rocket

studs are original to the block - haven't touched them.

would there be any concern using a thinner head washer, say 0.5mm thinner, to get more thread through?

Tom M'Guinn

Have you measured the head to see if the distance from the deck to the washer landing is the same on this head as on an 8 valve head? If so, unless you are using a thicker than normal head gasket, you should be fine. The factory washers fit into their landings with some precision, so not sure if the thinner washers you might find would fit like that, and just don't know if that would impact overall stability. If the studs are long enough, and if really needed, you might be better off getting a collet stud remover (snap-on) and backing each stud out one thread or so to make them a little taller.

67King

Anyone have a part number for the 211mm studs? Apparently from a 944S (thanks, Shawn!). But the PET does not differentiate, it specs a 944101194700, which is for the 2Vs, and only gives 2 threads of engagement.

michaelmount123

I can't help with the part no., Harry, but I have one or two sets of the 211mm studs if needed.

67King

Alright, so I keep finding out all these weird pieces of info. Turns out I don't need the 211mm studs, I only needed the regular 2.5L 2V/Turbo studs. Which is good. I have those. And they are easier to find, anyway.

Here is what goes on. The 3.0L 16V heads (S2 and 968) have a head bolt column* thickness of approximately 74mm. The 8V (turbo) and 2.5L 16V (S) heads have a thickness of approximately 55mm. So I was told a couple of pieces of wrong info by a pretty darn knowledgeable guy who I inherently trust (not MM - and I am not disparaging the guy, more making excuses for my own failings, here).

* - Column.....not sure of the nomenclature, but that is the distance from the deck face of the head to the machined pad for the fastener (washer/nut with studs, or washer bolt head w/ bolts) on the head.

Now, the blocks, too, are different. The 100mm bore blocks have MUCH deeper head stud provisions. You can see it in the castings, see attached.

So it turns out that the head stud requirements are not driven by the heads (as I'd been led to believe), but moreso by the blocks, with the S' head following the 8V head requirements, rather than the 16V head requirements.

All of this also explains why Shawn needed longer head studs. Long block + tall column. Now where those 211mm head studs came from? I have no clue. I'm just glad that I don't need 'em.

FWIW, my block is an 86 (and I did drill and tap it to accept the tensionser for the 16V belt), though the PET calls otu the same part numbers for all of the 100mm bore blocks. So I don't think it changed anywhere with the new block in 87.

It is kind of easy to see how this happened. I deal with a lot of SP3 cars. I am only familiar with one other 944S that has run SP3. All others are turbo (100mm/8V) or S2/968 (104mm/16V). So I've never run across an S head before. But at the end of the day, measure twice, cut once. And the PET is pretty darn reliable, even if the service manual may lack a piece of info (as the case with the 16V supplement). And even if you think you know everything, you probably don't.

Tom M'Guinn

Here are my old measurements for factory stud lengths, which are all +/- a few mm probably (i.e., MM's measurements might be more accurate above).

944 turbo studs: 190mm
968 studs: 165mm
89 2.7 n/a studs: 150mm

Porsche listed an installed height of 94mm for the 968 heads. To corroborate King's findings, he says the 16v heads are about 20mm +/- taller from deck to landing than the 8v heads. No surprise then that the 968 stud height is about 20mm+/- higher than the installed height for a 944 turbo.

That also supports King when he says the 100mm blocks have deeper holes. If a 968 stud is 165 end to end, and stands 94mm above the deck, then that means it sits 71mm below the deck. If a 951 stud is 190mm end to end and stands 72mm above the deck, then that means it sits 118mm below the deck, which is nearly 2 inches deeper.

Not sure where the 211mm studs fit in, but presume Porsche made some blocks with even deeper holes.

Those numbers also explain why you can't use 968 studs when putting an 8v head on an a 104mm block (like for example in an '89 2.7L motor). If the hole is 71mm deep, and the head is 55mm tall as King says, then that's only 127mm (if you add a mm for the gasket). That's why Porsche made the special 150mm studs for the 89 2.7 motor. And it explains why, if you try using a 165mm long 968 studs in a 104mm block with an 8v head, it will look like this.

V2Rocket

that's gonna need a lot of washers.

Tom M'Guinn

Very thick head gasket took care of it no problem.

refresh951

This is different than what I thought. I thought the 2.5L 16V (S) head was also 74 mm. Thus they used the 211 mm stud (long block + long head). Just an assumption however because I do not have 16V (S) stuff to measure. Sorry for the bad info Harry

If you are correct, the question remains, what were the 211 mm head studs used on?

V2Rocket

Just a thought...remember how there were early 944S heads that had cracking problems on the stud holes, and how Porsche revised the casting (without changing the PN) to fix it?

Maybe the thickness difference is in there.