firemn131

So, taking apart my early 87 (squirter block/flip up spoiler) and noticed the delta between early and later S4 intakes.
Easiest way for me to see the difference is the ridges on the center cross-over on the later ones. reading through another thread it mentioned that the fuel rails are also unique to the different intakes.
Intake part numbers are the same.
Rails look and match up. I haven't taken measurements but they look identical.

My early engine is a TBF motor. So looking to see what parts are interchangeable.

Questions;
1. Can the early intake go on the later block?
2. Do the fuel rail need to follow?
3. Any other differences that I need to consider when thinking about interchanging parts.

I understand about metal contamination with oil system components.

Overall really pleased with how clean the TBF motor is. I drove it for Two years. I did not baby it either. Chinese water pump looks OK too.

Looking to swap in from early engine;

• All timing gears and rollers
• Cam covers
• hopefully intake and rails
• injectors ?

Thoughts?

Thanks

Geza

My understanding is the intakes are interchangeable as long as you maintain your fuel rail set-up as is. Later rails mount directly to the manifold and early ones employ a spacer. Another difference I noticed is that my '87 left side cover has a tapped hole in the round boss, whereas my replacement '90 is not tapped.

Of additional interest to me is why Porsche added these ribs? Looking at your picture it appears the flappy shaft mounting boss on the later casting is taller - maybe an illusion. Did they add the ribs for aesthetics? Added stiffness during the inside machining? Perhaps the flappy valve and shaft are different in size and they used the ribs as a differentiator? Maybe all of the above? Casting tooling is just not changed for no reason. Maybe a Porsche big-wig said "I don't like the look of that". The ribs do continue on the underside, so I'm assuming it is for a functional reason, like stiffness, or to hide the look of additional material added locally. Interesting.

firemn131

Thanks for the reply,

You are correct about the difference in flappy valve heights.
I imagine that as long as I keep the rails matched with intake, I should be ok.

Later today I will try to find where the need for the spacers originated

worf928

This -^

Early ‘87 fuel rails must stay with the early ‘87 intake that uses the bonded rubber buffer stand-offs rather than the simple studs of the later intake.

Kevin in Atlanta

I don't recall the rubber buffers, but I have a handful of very thick aluminum washers that have come off early and late 87 intake manifolds. Those manifolds featured longer 6mm studs, too.

worf928

Early ‘87 intake:

Kevin in Atlanta

The three 87 squirter block cars I've owned all had aluminum spacers on long studs. Hmmm.

G.P.

My early 87 has the aluminium spacers. I suspect they were changed at some stage because the rubber ones would probably deteriorate over time and cause the injectors to come loose and then you would have a catastrophic fire.
I have not read anything about this, it is only speculation.

worf928

Yes. For whatever reason those buffers don’t last as long in that location as they do under the air box. Only 20 years or so.

They were likely replaced with metal spacers because new ones are ~$25 each and you need four of them,

No. Once properly constructed and indexed fuel rails are installed and the fuel connections tightened the rails are fixed in place by the fuel connections. Those buffers could vaporize with no ill effect; Over time the lower o-ring gets well and truly stuck in the intake manifold bore.

The stand-offs are, however, very important in locating the height of the injectors during assembly. If they are too thick or thin the lower o-rings will not seal and you’ll have false-air (aka a vacuum leak), but still no fire. Now, upper o-rings on the other hand are a different story: any upper o-ring leak is a car fire.


BTDT on the above. Got an early ‘87 on a flatbed a long time ago that wasn’t passing emissions despite all the obvious stuff and new cats. A smoke test revealed lower o-rings leaking. Disassembly revealed replacement “cheap generic” rubber buffers that were ~4mm too thick. So, original shop saved $100. Owner spent >$2k trying to pass emissions. What a saving that was...

G.P.

Thanks for your reply worf928.
Now you have encouraged me to think about it a bit more, I see your point.

SwayBar

Another data point, I have a squirter-block and flip-wing, and the fuel rail spacers are aluminum.

worf928

I've done first-intake refreshes at least 3 early-'87s and Nth refreshes on at least 2 others. All with bonded rubber buffers. I'm not implying that you can't use metal spacers and longer studs. But BRBs were original.

Kevin in Atlanta

The aluminum spacers were provided by Porsche. Where else cold they come from from?

firemn131

So,

I now have both the rubber bonded (2 years old) and the aluminum spacers.
Preference?
Does this then mean that rails and manifolds are interchangeable?

Still cant see any difference in the intakes as far as mounting heights/thickness, other than the flappy valve.

SeanR

This thread just reminded me that I had an early '87 intake and fuel rails stored together just in case I needed to do a swap. Then I took all my intakes and gave them to Roger to have him PC them for retail sale........I need to go rescue that one before it's sold and someone ends up in a scenario where they have an intake and the fuel rails don't fit. Sigh.