Ian928

I have been searching through the archives and have not found any conlusions to this. Could it be:

Cam profiles?
Valve sizes?
Ports?
Combustion chamber?
Restrictive intake manifold?
Flappy?
Ignition advance curve?
Fuel injetion system?

Maybe a combination? It sure would be nice to know!

Imo000

I'm interested in this also!

Ed Taylor

According to an official Porsche press elease dated 9/86,
"For the 1987 model 928S4, Porsche's engineers redesigned the sports car's resonant induction system to provide powerfull and continuous torque across a broad range and added two new knock sensors to the engine to allow peak performance on a wide range of unleaded fuels."
From the sales brochure,
"The first natural resonance point occurs at 2700 rpm; then at higher rpm, when torque would normally begin to fall off, a butterfly flap opens, creating another resonance at 4000 rpm, therefore extending the hightorque band."

Don '85S3

I believe this was covered on Phil Tong's 9284VR site (which unfortuntely is still down) quite well. The S4 has a slightly higher compression ratio and different intake system which accounts for the 28 extra HP.

Chris

S4 also has milder cams than the 85-86 cars, which is a -ve. right ?

Chris

Susan K Thomas

Valve sizes changed. Intake went from 35mm to 37 mm and exhaust from 32mm to 33 mm.

Susan Thomas
DEVEK

Jim bailey - 928 International

The 85-86 ignition brain used a vacuum pod to adjust ignition advance under load . The knock sensors added in 1987 allowed ignition advance to be constantly adjusted to nearly the maximum (no more need for a vacuum signal ). This is maybe part of the reason that some aftermarket chips show a much bigger gain in the 85-86 than they do for the 87 > models . Porsche was more conservative in their programing when the feed back was a vacuum signal 85-86 ; as the brain gets better information (knock sensors) 87 they could optimize the ignition advance . The 87 > also has different exhaust resonators , dual exhaust and a more " conventional " final muffler . The combustion chambers (dome of the head ) are different pistons have a different amount of dish . However , the compression ratios were basically the same at 10-1 . The intake ports are larger on the S-4 as mentioned the valves are larger BUT the S-4 camshafts are milder . The 85-86 cams are more like the GT cams . The fact that both torque 302-to 316 ft lbs and horsepower are higher 288 to 320 indicates that the engine became more efficient . Bottom line seems to be that the intake manifold improvements eliminating the T shaped sewer pipe above the throttle body made a big difference . It seems air does not like to make abrupt 90 degree turns . But one would hope that a $4,500 intake manifold (S-4) would be a pretty good design !!!

PorKen

Just curious...

I remember reading someone converting a 85 or 86 to using a S4 manifold?

Is it physically a bolt-on to the head?

Would you have to have an external rpm switch for the flapicino?

Chris

So Jim, that means the used one I picked up on ebay with throttle body and idle stabalizer was a deal at $200 ??

:-)

Chris

Shane

So by installing a 928 Developments carbon fiber intake on an 85-86 should see some significant gains.

Shane

One other thing to note that by switching to a smaller more efficient intake these cars would then have additional room for an intercooler for those interested in such items to increase RWHP!

Edit: One must also consider the price. To add this intake for the convience of installing turbos, supercharger and intercooler, would cost you at a minimum of $3700. Unless your lucky enough to find a S4 intake (like Chris) and do a conversion based on that.

Ian928

More questions for the experts here:

I have the opportunity to buy a lot of spare parts for my 928, it is in fact almost a full S4 in parts, but without a block (#2 & #6 crank oiling problems) but with extra crankshaft and complete heads from a 89S4. I do also have access to a complete '85 US S3 (32V) engine, but without the crankshaft (tip bent from a collision).

I think I remember reading that the S3 block was the same as the S4? Could I use the S3 block with S4 crankshaft and pistons?

I also think I remember reading that putting the S3 heads on a S4 block would lower the compression substantially. Is this correct? Have anyone calculated the resulting compression?

If my assumptions above is correct, I could be able to mix the parts like this:
S4 bottom end with S3 heads = low compression (good for boosting)
S4 valves in ported S3 head = S4 flowing heads with S3 cams (more aggressive cams than original S4)

Is there any reason this should not work? Is it OK to mix parts like this? I have heard about tolerance classes in the 928 engines, will that be a problem?

Don Carter

A related question about the 86.

I've always heard that the HP was 288. That's what my manual says, and I've never heard anything different. BUT while reading through my recently aquired Porsche technical specifications manual for the 86, I find that there were 3 engines in 86. A 310 HP engine for Europe, ROW, a 288 HP for AUS, and a 292 HP version for USA/Japan. It's only 4 HP more, but which is correct?

The USA motor is listed as M28.43, 5 liter, 292HP, 10:1 compression.

Jfrahm

Maybe. You'd also need to add a bunch of timing via a chip and then run quality gas all the time to make sure you didn't ping it to death.

-Joel.

2V4V

Ian,

Yes, you can "mix-n-match". Just depends on which parts...

The blocks are all essentially the same 4.7L-5L, obviously the bores are different - and the cylinder wall thickness is adjusted to suit the differing bores. The major casting really didn't evolve at all - water pump, oil fill, oil filter, oil pan, all the same. Porsch spent very little R&D time/money on our car, but it makes for easier updates - bolt it on, just like the factory generally did.

The heads can be juggled around pretty much at will. The thing you need to be aware of is valve timing/overlap/clearance when using a non-matched piston/head/cam combo. Also, you want to have a studded block ((bolting down heads is just bad) so retrofit studs to an early early 5L if it needs them.

You can run a late model intake manifold (S4) on an S3, but you do have to do a bit of work for the mount.

Avoid a crank that you know is bent. All cranks are bent somewhat - hence why machine shops offer a "straightening" service. But the kinda "bent" I'm speaking of is measured in the 10 thousandths - not in the visual range.

If that crank was in a block when it got that bent - you can only imagine what kind of forces the block saw - personally I'd probably avoid it, might be fine, might not...

Greg