2.58v944/2

[turbot]

Let's see if i can stir up some view traffic 'round here.

I'm gonna document an NA 944 2.5 liter 8v engine build.

Some of it of course, will be redacted.... ;D

Subject is from an '88 auto trans donor car.

Disassembled the engine complete and evaluated all of the reusable items, sent a few off for coatings, etc.

This engine will have a duty cycle of more than 200 race hour longevity, so even though I always rely on the factory head studs, I decided to have the block decked so I set about removing the dowels and head studs.

Keep in mind, this is a 25 year old engine that had never been apart.

This is how the tale began -





Out of 10 studs, 3 of them snapped off 4 inches down to the floor of the stud bore.

T

[turbot]

Almost lost this thread...., guess I'll update it... ;D

Ok, so, many a 944 block have been tossed because of broken studs but I already had a few bucks invested in this one so I decided to work out a solution.

Ordered a special bit that fit the stud bore with zero side clearance so it would guide itself down the hole and stay centered to create a center divot for later drilling. There;s really no accurate way to center punch the broken stud because once you put a punch in the hole, you lose the ability to see what you're doing...

The studs snap jagged naturally, so even if you could make an accurate center mark with a punch, there's always the chance the first bit would walk without even be able to see what was happening. There are no two chances at this, drill off center and the block is toast. The studs have to align with the head so you can't go off center at all, and short of drilling the head for 1-3 mismatched size studs....you can't go larger either.

Anyways, after I had a perfect, smoothed, centered concave, I set the block on an immovable metal table and weighted my drill press foot to steady and immobilize it.

The 944 block has a removable lower crankcase (girdle), attached by 30 bolts and studs, so I used the nuts on the lower and adjusted them with a wrench until the block was perfectly leveled.

Using a 10.5mm bit, this removed 95% of the metal of the broken stud....then using a 12mm bottoming tap, and alternating in/out/clean over and over, I was able to restore the original threads in the block.






T

[turbot]

For those that don't know.....the Porsche 944, 944T, 968, along with the V8 series 928 cars all use an all aluminum 2 piece crankcase.

The blocks are a cast alloy, 78% aluminum saturated with silicon at 17% content....dubbed AluSil.

A special incremental honing process, polish finished with felt pads and ceramic paste, exposes silicon particles by "washing away" the aluminum at the cylinder surface which allows an aluminum piston to live in an aluminum bore without a steel sleeve.

Still, the piston must have an anti friction material on the skirts for longevity. Porsche used a "ferro" material that remains proprietary.

I have been successful using a coating dubbed "PC9" by a company called Swain Tech Coatings.

The pistons must be prepared first before they will be accepted.

Glass bead blasting cleans the piston and peens them at the same time......I wash the pistons with solvent, then acid wash them prior to shipment to insure the aluminum is free from wicked oil.

In the pic, you can see on the one that hasn't been treated yet, the scuffing of the original anti friction coating from the factory after 100k+ miles.

These are the 2nd most desirable 944 8V normally aspirated pistons, 2nd only to the Euro only version.
The 1988 944 was made to "rest of world" spec since the final year would be bumped to 2.7 liters so Porsche didn't bother with two versions (USA and Japan) so the compression is higher than 1987 and prior versions.

The piston manufacture was sublet to two German companies, Mahle and Kolbenshmidt, these are the KS pistons.



T

[turbot]

Ah gubmint jobs.....gotta love 'em.

Have 8 days off in the next two weeks, so aside of catching up some work on the engine and tub that it'll eventually power, I suspect I'll be bumping this thread up for some holiday idle time browsing...

Next up, connecting rods.

Early on in the 944 series, '82-'84-ish, the factory connecting rods were forged pieces...., either through a cost cutting measure, or just deemed unnecessary overkill for a 60 hp/ltr normally aspirated engine, the rods were downgraded to cast.

They were brought back (no additional expense for a financially struggling company at the time) for the 944 Turbo in 1986-1990 where all other engines, the NA 2.5, 944S 2.5 16V, 944S2 3.0 16V, all the way to the series pinnacle 968 3.0 16V variocam engines used the cast rods.

This is a free upgrade if you have as many spares/cores as I have laying around.....so you'll need to look at a very early NA engine or an '86+ 944T for them if you are scavenging for the most prized rods of the series.

They are identified by the part number ending in RARST raised right on the beam of the rod as seen in the pic,



In the aftermarket, there are definitely some lighter rods, 100 grams per rod is quite substantial......but they'll set you back $1000-1200.

$250-300 per rod, like everything else high performance for these engines is ridiculously overpriced by comparison of American, Japanese engines.

Yup, this is biased, but the real deal is, components for these engine from the factory can be very high quality so I guess to offer a part that is higher than factory spec, coupled with the small niche of qualifying customers, the prices are adjusted accordingly.

For example, in building up a hot rod American V8, you'd toss the factory cast crankshaft for a forged piece.....whereas ALL 944 engines already have forged, nitrided cranks from the factory.
It's the same with most, if not all Porsche engine internals.

Today, most modern "muscle" car manufacturers have stepped up to quality pieces like Mahle pistons as factory components, lightweight sodium filled exhaust valves, ceramic coated exhaust ports, etc., etc,

You can already find these pieces in 944/944T engines from 25 years ago.

There's an old saying that applies that I guess the rest of the Automotive world eventually found out,

In performance cars, you can have any two of three criteria but not all three.

Cheap, Fast, Reliable.......pick any two.

A cheap and fast car isn't going to be reliable, a cheap and reliable car isn't going to be fast, thus, a fast and reliable car isn't going to be cheap.... ;D

T

[turbot]

In the meantime, with my studs all removed, every component mounting threaded hole and remaining studs are checked and cleaned with metric tap/dies, cylinders finished and block decked,



My stud kit arrived,




While factory ones are pretty robust at 12mm, they are made of a "stretch to yield" material, I think it's called dilavar. The torque procedure is stepped in series of degrees, not a specific torque specification.....yup, a lot of you are thinking...."well, yeah, that's how all modern engines are assembled".....remember though, these are 30 year old engines.

Things is, in the past, these car/engines could have gone through some shady hands over the years, so it's wise to replace these, given that there's no way to know detailed history on a car/engine where records aren't available......some gorilla could have yanked these studs/nut to 200 ft/lbs. for all I know...

Anyway, I had pre-checked during the drilling (see tape on drill bit @ pic above) to make sure my stud depth and threads were correct.

The factory uses some obscure Loctite on the studs....part of what makes them so difficult to remove.....all I am worried about is potential for coolant to creep up the threads even though the holes are "blind" (have a bottom and are not open to passages or atmosphere). The factory concern was that the studs may spin during service but the ARP studs have a hex drive on the tip used to set the stud and/or hold it from rotating during service.

I used a GM product I have used a lot in the past, a liquid teflon sealant just as an added precaution,



Last up for today....., I set all of the studs to the factory depth and measured each accordingly.

There isn't all that much thread on the cylinder head mounting side of either the factory or aftermarket studs, so you have to be careful here that the appropriate amount of thread will be available for the head mounting nuts when final assembly is done.





T

[turbot]

Mornin' race fans....

It's T-minus one day 'til Christmas Eve.

Took a good look over my tub yesterday to remind myself what was left to do on that section of this car,

Had another thread floating around here with the body/paint work that I started many months ago but I'll bring a new pic in this one to keep everything together.

Subject is an '86 slate gray 944 Turbo shell that was destined for the track anyway that I was building up for a friend but he changed priorities to modding his road car for street/DE.
I have several other rollers but he'd already done the stripping and removal of all of the pain in the neck floor insulation and sound deadener, one of the hardest parts of prepping one of these cars.

Most of the body panels are already prepped and painted, as per the other thread, this is the car, same scheme as our others, in yellow,



So...., back to the engine.

Piston ring selection.

Here's the deal.....you can still get rings from the original manufacturer, Goetze, in the original standard bore size plus the +,5 and +1.0mm oversize sets. Problem is, the 944 Turbo uses a near identical ring set that will physically fit the NA engine but requires more loaded tension (read friction) so the boost pressure doesn't bypass the rings to the crankcase. Since the 944T rings will "work" in the NA engines but the NA rings won't work in the turbo engine, there is only one spec ring offered to cover both engines....dilemma, too much tension for my application. These are a couple of other over the counter solutions, well, at least one, but very careful here....for the same reason the pistons need special attention, you can destroy these cylinders in the first couple of hours run time if you aren't familiar with Alusil cylinders.
More than what I already covered, the piston to cylinder wall clearance is very tight since both the cylinder/block and the piston are all aluminum and expand at pretty much the same rate, not so with an aluminum piston in a steel cylinder where you leave more clearance for the piston to expand.
Alas, I worked with EBS, a well known Porsche parts supplier and came up with a ring set from Total Seal, custom for this engine using a ductile-moly top ring, cast second ring, and a chrome faced 3 piece oil control ring.

Kinda sucks, had a ton of pics of my pistons back from the coating, along with pics on balancing rods and pistons...sent 'em to my laptop from a portable tablet, looks like they are lost in cyberspace and I have since deleted them all to make memory room for an upcoming trip.

Anyways, here's one of the coated piston with a finished rod....., not a very good one but you might make some out in the background...



On the background, quickly since I don't have the pics to support the explanation, you'll want to check weights of your pistons and rods, especially if your pistons aren't assigned a specific cylinder in the honing fit process. The coating increases piston diameter by .004", so, in essence, they are slightly oversized compared to factory dimensions.....this leaves the machinist with a little to play with while honing the block....in my case, any piston can go in any hole.....if this is the case, after measuring weights of rods, pistons and pins, you can shuffle the components around to get an assembled rod/piston/pin combo as close to the same weights as possible, minimizing material taken from each rod and/or piston.

Alternatively, you can select the lightest rod and the lightest piston and make all of the other like components match the lightest ones by removing material. Pistons are straight forward, other than being careful where to remove material as to not weaken the part.
There was hardly any variance in these, again, quality parts are already that way because the tolerances in manufacturing is very close......, I only had to use a knurling wheel to remove the parts numbers from inside the skirts, maybe 1 gram at most.

Rule of thumb in performance oriented engines is +/-1 gram on pistons and rods, =/-.5 gram in highly detailed assembly.

I took mine to dead on, +/-0.00 gram discrepancy because I am a freak.... ;D

Generally, you want your bearings along for the rod on the scale for more accuracy and your pins, pin clips and rings with the piston but I weighed all of these components separately and they were already all equal.

On the rods, you need to fashion a fixture to level the rod with the scale to measure either end of the rod separately. I made a holder using an old piston pin with a stand that makes the rod perfectly level when the big end is rested on the scale for future use....my rods were so close for this build that I didn't have to bother differentiating between ends, all four were within a gram, again, this is what you get with parts that are already quality to begin with.

Anyway, to finish up on that in case rods vary....., once you measure all of the large ends of the rods, make them all as equal as possible, within a gram will do......then, once you know that either end is the same, you can just toss the entire rod on the scale and record a weight for each, any further differential with come from the opposite end that you weighed and adjusted earlier.

To all the peeps that know me and see me around the tracks...., with much more detail to come....I think you already know the answer as to why I just shrug when asked "how's your car coming".

I think I may have a borderline psychotic attention to detail that's ingrained from 25 years in the trans biz....
When you support your family with a product of your own hands without an owner or company between you and your pay, you learn to do things a certain way.

In a nutshell, a job must be finished and out the door, no second tear downs, no rechecks....basically, the way I always put it, "there is no time to fail".

Race environment is an even more brutal place, so bending and short cutting detail is out of the question...

Off to work on this last troublesome LR 1/4 panel.....

T

[turbot]

Boy, those holidays off work sure flew by....

Anyways, last checked in, I was heading back my death sentence of a quarter panel from the earlier thread.....dragging a pic from an older thread back when this panel caused to to shelve this car for a while....kinda got burned out on it and switch to working on the engine,



So, after a whole day fighting this thing, finally got it into shape, sanded the door jambs and got that primed too....you have to put the chip guard on a primed surface finished with 80 grit for it to adhere so I had to finish the left rocker anyway,



Whatever color/type primer you prefer, use a contrasting color rattle can and spray on a light misted guide coat before you finish sand for paint prep....I use cheap enamel for this...base/clear or single stage paints, usually 400 grit is fine enough for this. The guide coat allows you to see exactly what you are doing as you form curves and body lines with the few mils of thickness of your primer coat,...you can see the body line more clearly in the rear body piece that goes above the bumper.
Upper part is ready to paint, bottom still has the guide coat.

Like this,



T

[turbot]

Had a good bit of my cage tubes pre bent and had already bent and tacked all of my main hoop so I have been working on that on and off between the body and engine.



Main hoop, all welded up and ready to drop in, hoop to front floor upper halo bars.....all acid primed then finish in the factory Porsche Alpine White....will have to grind a few inches around the plates and hoop to bar joints but it's way easier to do a touch up then to try and spray a cage in the car....been there done that, got the t-shirt.. ;D





T

[turbot]

Chip guard on the rocker and lower rear quarter panel, and got the LAST white on the body. All that's left there is a black wrap around and the yellow design left and the shell will be done. Still have some floor and rear deck area left to do in white but that's gravy.

[turbot]

Back to the engine....paint still too green to be laying out a tape scheme.

From where I left off.....all my studs set,



Block finish cleaned and ready for pistons,



Checking ring side clearance,



Coated rod bearings but the mains are just highly polished,







Balance shafts and covers sealed with the factory anerobic....pistons going in, had an .002" ceramic done on the tops,



That's it for now....this is more tiring than the actual work...

T

[Admin]

Looks good T!

[turbot]

Two whole weeks since my last update....time sure flies.

I guess I'm not the type to under promise just to over deliver...

This stuff is very time consuming. It'd been 3 years since Eon's car and this was a whole other level.....conversion from turbo car, non-white tub (starting this scheme with a car that's already white is WAY easier), smashed rear 1/4 panel, etc., etc, really ate up the clock....and energy.

Since I posted up last, I had the entire 1/4, rocker and rear finished up in the factory white. The first pic with the masking paper shows the bottom of the rear 1/4 and the back license plate/tail light area and below all done in Porsche black to meet where I have left off months ago. I took care of this last weekend so it'd be dry enough to mask over for this stage.

Anyways, finally got that 1/4 panel squared away and laid out the yellow and black patches for this side,





I cut out the rear spare tire compartment on this one like my 944T project car. This takes that hump and a vertical piece of sheet metal about six inches wide spanning the entire width of the rear of the car out of the air stream under the car.

While I was at it (this is what really slows me down.. ), I vented the rear bumper to help decrease drag too....the thing just hangs out there like a big c-channel parachute...
The stock cars have these rubber pads on the bumper, so there are some mods that need to be done to shave these off.

The side benefit is, cutting out this sheet metal makes it a whole lot easier to R & R the transaxle.

I'll pop up a few pics on that later.

T

[turbot]

Back to the engine,

Got my pistons, crank, girdle all set and sealed up with the factory Loctite.

Oil pan is baffled with the aluminum trap door type baffle kit from Lindsey Racing.

These engines are basically one half of a V-8 engine from the Porsche 928, the right hand bank....so the engine is really a wedge four, and although the oil pan is a very nice finned aluminum piece, wedged on both sides like a dirt track pan.....and internally baffled with a plastic insert, the oil tends to ramp up one side of the pan in long right handers. The trap door baffle is a one way check to keep the oil pickup covered at all times. Second part of the "kit" is a stainless ring (seen in pic around pickup screen) that is welded around the pickup screen to only allow scavenging from a concave indention that's already cast into the stock pan.

These engines are inherently imbalanced, thus the two balance shafts.....what's more, it has massive rods and pistons for an engine of this displacement. Some people delete the balance shafts that creates a 1000 rpm wide harmonic buzz (did this on my 944T project) but either way, the oil pickup tube has a reputation for fatigue cracking (25 yrs old), probably due to mistimed balance belts by owners. For this reason, I am reluctant to add this ring to the pickup.
The thoughts here are that any additional weight....or any unproven changes to the harmonic load that this tube carries may accelerate failure.

We have used this on Eon's engine though and had no problems in three years of track use and I have done a few on street cars with no problems.



Oil pump, crank gear, motor mount pedestals all on.
This is almost the angle that the engine sits when mounted in the car.



T

[turbot]

Been holding off on these.....mainly the reason I shifted back to the body and covered the engine up for a while to sort this out.

I already really knew what I was going to do about it but a shortage of supply on the solution forced me to shelve the engine for a while.

While loading the pistons, checking the piston to cylinder head clearance, pistons are .024" proud of the block, about .014" more than I had planned.

I double checked using a factory unmolested block to verify this measurement even though the method seen in the pics is infallible.

I used a metal piece drilled for two of the studs to limit the upstroke flush with the top of the cylinder. Using a dial gauge and setting to -0- there, I remove the stop and turn the crank to the piston's highest reading. All four pistons read .024" past the top of the cylinder.





Toss the factory 1.1mm thick head gasket ($80) that comes with the gasket set in the dumpster because this is too little deck to cylinder head clearance for these engines.

Borderline safe/edgy clearance is .030"/.7mm.

The 1.4mm thick optional factory gasket for shaved machined cylinder heads is .055", minus the .024" my pistons are above the deck will leave me with .031" and this is not even accounting for gasket crush.

Nevertheless, the optional gasket is about as rare as hen's teeth right now and sell for $120....., I guess stock is depleted everywhere and a production run is underway but I managed to find one at 944online. (Thanks Ian).

I still have the option to use an after market cometic gasket @ 1.6mm, a multi layer steel type with less crush factor but the manufacturer only makes them in an oversize bore (+.5mm) size which would give me 1mm less clamping surface at the top of the cylinder wall thickness area.

A race engine should be mocked up and assembled multiple times anyway but I will be forced now to assemble the head, cam, belts with final cam timing several times now to double and triple check valve to piston clearance....

More on how to do that later....probably much later.

T