928 and 944 motor design and construction

It's a beautiful, bulletproof, and expensive design. There are no bearing caps like you see in an American V8. The bearings, and crankshaft, are held in place by a full length girdle, which bolts to the main section of the block. Cast aluminum oil pan is heavily finned to dissapate heat, and that sump is much larger than an equivalent 4.7 litre V8 from another manufacturer.



Cylinder bores are aluminum. The aluminum, however, has such a high silicon content, that once the bores are finished and honed, the actual wearing surface of the cylinder bore is "glass". These engines hardly ever need attention to the cylinder bore, they are just about wear-proof.


2-valve (16-valve) SOHC 928 motor, initially offered in 4.5 litre, and then 4.7, eventually in 5.0 litre form.


The heads on the early 928 are almost identical to the 944, which was designed after the 928 and which eventually used what was basically 1/2 of the 928 motor. The 944 is a higher compression rig, and the valves can come in contact with pistons if the timing belt breaks. The early model 928, up until the 4-valve motors, is not an interference engine. The 4-valve versions are interference engines, and true to form, when the 928 went to the 4-valve design, so did the 944.

All said and done, the 2-valve engines sound better, pull well in the lower gears, but the 4-valve jobs continue to "pull like a freigt train" all the way to redline.





This "spider intake" system brings cold fresh air in over top of the radiator, into the large oversized filter box, down under the filter box, over to a plenum, up into the plenum, and then finally out through those 8 spiders and into the cylinder head. At the point where air enters the cylinder head, fuel is injected into the air stream.

The spider intake design is lengthened to promote torque. The Euro design is similar, but the runners are not as long, but the power is up by 70. Even without the additional 70-hp, the 1983 928 was the fastest car sold in North America, beating out all turbocharged cars, all Ferrari, Jaguar, Lamborghini, Lotus, Aston Martin, etc.


Here's another view of the spider intake, this one is polished and looks a lot better than mine, but it doesn't run any better! You'll note those spiders are moved to one side or another, so a long handled socket can be used to pull spark plugs. It works, there's just enough space to get the job done.







By comparison, here is a photo of my 1984 944. Note how it looks like 1/2 of the 928 motor, because that's what it is. Due to inherent balance problems with doing this, especially with a large 4-cylinder motor of 2.5 litres (eventually bumped up to 3.0 litre) Porsche used two balance shafts to compensate for internal vibration. I actually ran the car for a while with the balance shafts disconnected, it had full power, and a hint of harmonics at certain rpms, but nothing serious. With the shafts spinning, the motor is turbine smooth.



This is a thing of beauty. It's the bottom end of the 928 V8 motor, and you can see how the full length girdle holds all the bearings and the crankshaft in place. When people wonder what makes a Porsche cost more money, it's machine and casting work, and the labor to get pieces to fit up within tolerances, like this. The 928 was not a cheap mass-produced motor, and neither is the 944. The 928 bottom end remained the same, for all engines produced from 1977 to 1995, ranging from 219-hp to 350+, and it is adequate for race prepared engines producing 400 and 500+ horsepower.


Here is another view of the girdle concept used on the 928 and it's 944 variants. This is a race prepared 944, and you can see some superb workmanship on those "knife edge" crankshaft counterweights. Photo below is the same motor. Pretty awesome piece of work, even in dead stock form. The 944 block has been able to withstand 600-hp in full race turbocharged form, from houses like Kelly Moss.





Here is the 4-cylinder version of the girdle, as used on the 944. Even though the 944 was considered an "entry level" Porsche, you can see Porsche spared no expense when it came to their engine designs. This is a case where engineering dictated to the marketing department what to say, and not vice versa.






In 4-valve trim, the main cam drive cogs remained in the same place they had been in the 2-valve motor, but that second cam is driven by a chain connecting the first and second cams together. This drive chain needs attention on high milage 4-valve engines, but it's a good solution and it works fine.



Here is a magnificient view of a full race 928 4-valve motor, compliments of the Kelly Moss Racing Team. Believe it or not, this motor was destined for a custom built full race 944. Note, it is the same general design as 1/2 of the 4-valve 944. My S2 is a 3.0 litre version of this motor, putting out 208 normally aspirated horsepower (see image below).



ABOVE: View of the 3.0 litre 4-valve 4-cylinder DOHC hemi used in the S2 944.




Here is a pic of M21Sniper's dressed motor, in his 1983 16-valve 4.7 liter 928S. This motor runs VERY STRONG, so if you're in the Philladelphia area, >>>>>>> BEWARE <<<<<<<<


Here's a photo of Heather's 1983 928, hmmm, is it possible the "Snipe" has put his hands on this motor too? I think I see some similarities, and since they're both in Philly, I'm starting to wonder.

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I'm reserving this spot for Rui Costa's photo of his GTS motor!






And now a couple photos of the 16-v heads otherwise known as the 4-valve head. These are essentially the same as on the 944 4-valve or the 928 4-valve. I have a 944 S2 with this head, and they have about the same general amount of torque and pull as tha 2-valve head down low, but the difference is, the 4-valve heads pull like a freight train right up to redline. I suspect the 4-cylinder and V8 cars have the same general characteristics. Where the 2-valve motor is a beautiful thing, the 4-valve is just an improvement in design, power and torque.