Fabio421

I was just measuring this the other day and I found that the "on center" exhaust stud spacing is different on the 16v vs 32v 85/86. If memory serves me correctly there was a 2mm difference. I'll go back out and measure again later today to verify this.

tilac999

But why does the 32V stock '85 downpipe/cat bolt right up to my engine with my stock 16V manifolds? It's designed for the '85 32V.

Jadz928

I don't know. Are you sure it does?

DR

It does, and the answer to this riddle is in the design differences of 16v (2 valve) vs the 32v (4 valve) engines......

Jadz928

OK, I'll bite DR...

So, the 16V heads are interchangeable left to right, with the left exh. port forward, the right exh. port aft (similar reason the intake runners are interchangeable l-to-r).
The 32V heads have a a left and right head (are not interch.), and are port-matched side-to-side.

If this is all true, then I see no way 32V downpipe would fit on a 16V, without modification.

In this case, the 32V left-side downpipe would need be cut (or the right side extended).

The inverse applies when mounting 32V exhaust manifolds to a 16V.

Am I missing something? Wouldn't be the first time, won't be the last.

SMTCapeCod

Are 85 16V manifolds really the old style we usually think of when talking about 16V? Normally on the 32V manifold install its a retrofit S3->S2. In your case its same model year- I've never been under an '85 Euro but would make sense to manufacture 16V and 32V to both mate up to a similar system manifolds back?

danglerb

All of the 16v are the same iron thing AFAIK, hence the nice power bump with the better flowing US 85/86 32v manifolds.

Podguy

I agree with DR. I do not see the confusion. If you were Porsche what would you do in designing the car. Make different cats and exhaust systems or make up the difference in the headers. It makes a lot of sense from a manufactruing standpoint to keep as many things as possible the same. Sub contractors do not get as confused. Otherwise you end up with a Boeing Dreamliner there nothing fits together.

I tried putting S4 headers on a 16 valve engine and everything is off. My thinking since there are many extra S4 headers around it would be possible to adapt them to the 16 valve engine. It could probably be done but you would have to weld on new flanges.

As far as Euro S engines I see no difference between an US 4.7 block and a Euro Block. The differences are in the pistons, heads and cams.

tilac999

The '85 32V cat downpipe assy also fit Brian's '84 Euro perfectly.

SMTCapeCod

85 manifolds to my 83 Euro required a bit of slotting/clearancing on a couple of the bolt holes.

Affixing S4/GT cats to that 85 manifolds on my 83 Euro required spacer.

IIRC I had a S4/GT downpipe/crossover bolted directly to the factory 83 Euro manifolds with no spacer.

John Speake

Can anyone clarify if US 85/86 LHD manifolds would fit a RHD EUro S2 ? i.e clearance around steering components etc.

Jadz928

So, what's the scoop. DR?

I still don't get it. Did it fit and also bolt up properly to the rear exhaust sections?

Landseer

The 32V stock exhaust downpipes (85/86 is my dataset) almost exactly bolt up to the 16V stock cast iron manifolds.
I've done this multiple times.
A couple times I had the exhaust shop heat and slightly bend the downpipes relative to each other to make the fit easier.
The air pipe linking early 32V cat to 16V air pipe on the USA cars aligns and fits exactly.

The early 32V SS headers fit-up to the 16V engines pretty well. But you have to take a drill bit slightly larger than the diameter of the existing holes in header to ream-out the mounts associated with cyls 2,3,6,7. When you enlarge those holes in the headers they fit perfect. Let me qualify this. The car was 84 Euro with SS studs. Carbon steel studs 25 years old might degrade in diameter enough to fit, who knows. I highly recommend the SS studs.


I last installed 85 SS header pipes on 16V Euro (Jadz car) and coupled them to 87 stock downpipes and Cats (from Jadz' perl car)

The drivers side SS pipe comes out a little longer than stock, getting it close to the heat shield on the body.

If you bolt the 87 downpipe onto the drivers side, then the pass side is both short and offset.
And, the Cat is not centered in the 16V's body tunnel space. NOTE--the 85 SS header pipes have flutes for expansion and they can get bent and change the configuration a bit.

So, you heat the down pipes red hot at key locations (one place at a time) and bend the drivers sideso that the Cat is centered.

Then, you cut off the passenger side downpipe a bit back from the flange. Bolt the flange onto the passenger side header flange. Then, heat the passenger downpipe red hot near the cat and bend it to get rid of offset to the flanges, while using a prybar to keep the cats centered. Then, cut and weld-in a short piece of pipe as an adapter pipe. You can choose a US diameter that works. I think it slid over the downpipe and just over the remaining pipe protruding from the flange.

Cheburator

John,

They fit like a glove. Joel's car has a S2 engine running the US 86.5 manifolds and last time I drove it, the steering wheel was fully functional When he first had them fitted, GT One in Chertsey had to make up a small spacer as the driver's side manifold is slightly shorter, but that was the only "problem" encountered during the swap. At present he is running a custom Y-pipe and a 3" single pipe all the way back with custom mufflers. As far as I remember he made 321bhp at the crank during the last dyno. S2 engine with S K-Jet. It seems that this particular mod makes the S2 engine even happier to rev at the top end.

Alex

John Speake

Thanks Alex !