Whatever floats your boat as long as the lower injector o-ring is properly seated in the manifold bore upon assembly. No part of the o-ring should be 'proud' of the surface (maybe a millimeter.) And, obviously not too deep.

The early '87 fuel rails are different from the later fuel rails. Their construction assumes the extra thickness of the buffers mounted to the intake while the later rails won't mount if you use a buffer/spacer. You *might* be able to mix and match by using spacers/buffers to use early '87 rails on a later intake or use late rails on an early manifold with buffers replaced by studs. I've never tried or thought about it as it's never come up. As long a) as the lower o-rings are seated correctly, b) you've got the injector clips properly securing the injectors to the rails and c) you've done a fuel pressure/leak check then I can't see why it wouldn't work just fine. On the other hand, it may also be that there are boss height differences that you can't "see" but might be able to measure.

 

To me this is a clear case of either a design error by Porsche (in their design layout) or a manufacturing error by their supplier(s). Could be a myriad of things that went wrong, but the problem needed to be solved. They're building their first engines of a new type, and things are not going together right - there's a problem with the fuel rail mounting. Luckily, the addition of a spacer will solve the problem - if the error went in the other direction, they would have a real problem. Challenge is, adding a spacer does not leave enough thread on the studs that are there (for the nut), so they pulled the studs and replaced them with a COTS (commercial off the shelf) studded vibration isolator that makes up the space. Now they have a reasonable solution that will allow the first 50, or 100 or whatever number part sets they have in stock to work without scraping them. Going forward, they make the design change to eliminate the "fix", and reconfigure the fuel rails. Another day in the work life of an engineer.

 

To close this loop.
If time permits today, I will provide side by side measurements for data points.

Intake and rails

1. rail mounting bases
   1. A
   2. B
2. intake mounting bases
   1. A
   2. B

 

Looks like another casting change was on the 2 inner inlet tubes - they do not have the rounded trumpet ends like later manifolds.

 

Photos used in last post are stock photos pulled from google.
Not representative of the intakes / rails that I will measure.

 

So I can’t find any differences in measurement between the two intakes and the mounting locations for the fuel rails. It appears that the only differences are the use of spacers or bonded rubber studs.

I am also unable to find any measurable differences between the two different sets of fuel rails.

This will lead me to believe that fuel rails and intakes are interchangeable. As far as fuel rails and mounting hardware.
The main factor is to ensure the bottom injector o ring is not proud above the intake recess.

I will be going back with the original set up I believe, older intake with bonded rubber studs and original rails.


If I am off the track please let me know what I am missing. Thanks


Earlier intake with bonded studs

Later intake with stud/ spacer configuration

 

If there are *no* differences in the fuel rails then one set is “mismatched” with the intake. The later rails have a “taller” mounting base such that they mount to the intake without a spacer/buffer.

Given your measurements, it looks like you can interchange early and later rails provided that you either use or don’t use a spacer depending upon which rails you use. If you had different rails that is. Since both your rail sets are the same, you’ll have no choice. You’ll either need the spacers/buffers or you won’t be able to use them.

 

Having the choice of using the aluminum spacer vs. rubber spacer, I'd go with the hard mount aluminum, which more closely matches Porsche's final design: Fuel rails bolted directly to the manifold casting.

 

Thanks Gents,

Will use the best set of rails and solid spacers.

Now I want to see the later rails to understand the difference.

 

Your wish is granted...

 

Thanks Kevin

 

Rubber was bad idea. I would not use it simply to be sure rails stay in.

IIRR very early S4's had rails which have upright metal to cover rails from heat. So there are many different variations.

 

Those were S3/4 fuel rails for sure. I've never seen them on an S4.

 

Possibly modified S3.

 

If you can’t find an original squirter block to replace your block, John Kuhn is finishing a tool kit that can be used to turn any S4 block into a squirter block. With stock rotating assembly and normal aspiration the squirters aren’t functionally necessary, I was just thinking in case you want to keep it a squirter block engine for sentimental etc. reasons.