Michael Eisenhut

I've got an '85 US 928 and after doing some of the standard service in my spare time (timing belt, water pump, top end refresh, other bits and pieces) I've gotten really tired of the intake manifold design. It's bulky and the rubber boots that attach the left and right plenums to the runners and central riser are kind of pain to work with. My question is whether or not intake manifolds from later 5.0 liter cars are compatible with the 1985 engine. I'm not concerned about keeping the car original and I'm not looking for any performance upgrades, it's simply that I'd like a more compact intake manifold to make working around it easier without having to remove it every time I need to check spark plugs/leads etc... I've googled just about everything I can think of to no answer one way or another. Does anybody here have experience with this topic? Thanks!

Rob Edwards

The shape of the intake runners on the 85-86 heads are markedly different from those on the base of the 87+ intake. Wouldn't work.

Michael Eisenhut

Rob, thanks for the reply. When you are referring to the shape of the intake runners are you referring to the 3D shape of the runners within the space above the engine and the intake ports or the geometry of the flange that mounts to the ports themselves (or both)? I'd imagine if the flange of the later intake manifold is the same profile as the old one you'd be able to (maybe with some fabrication) mount the newer intake on the older cylinder head. Any thoughts? Have you directly compared the profile of the flange of an 85-86 with an 87+? If so, are they completely different? I'm aware that the size and shape of the runners is different in the 87+ (more compact) which is what I'm looking for but I'm not sure if the flange that interfaces with the intake ports is a different geometry.

-Michael

monkez

Interesting idea and I agree: The side plenums on the '85 are a real pain. Off of the top of my head, I could think of a few challenges:

1. Would need the throttle body that would also attach 87 intake manifold
2. Would need to get the throttle cable set-up as that is also different in an 87
3. Would probably need an 87 computer to deal with the difference in air/fuel mixture (different plenums, different ratios needed?), which would then require a knock sensor.
4. the MAF would likely work, wouldn't it?

I'm sure I'm missing loads and others with much more knowledge would be able to chime in.

GregBBRD

I've seen this done. Quite a bit of grinding required to get the ports to match up. The bosses that hold the lower intake elbow on the '85/'86 block need to be chopped off the block.

In the end, it pretty much ruins all the pieces.....and for the time spent, you could take the '85/'86 intake on and off abut 20 times.

If you want an S4, sell the S3 and buy one.

Michael Eisenhut

Woof, you got me at block modifications. I would gladly sacrifice an intake from eBay and do some mods to the throttle and computer but I don't want to get into irreversibly modifying the block in the manner you suggest. You're right, compared to the work it would likely require I'll just deal with the plenums. Thanks for the 2¢.

-Michael

RSMartin

Bigfoot928

Fixed it for ya.