danglerb

Putting an 85/.86 tubular stainless exhaust manifold gives almost the gains of a much more awkward and expensive set of headers on a 16v, except for the pesky offset issue. Bolting up a stock exhaust leaves a 2.25" gap on the passenger side, due to I think a 1.125" offset on each side for the ports on the heads 16v vs 32v.

Normally an adapter is used or some creative bending coaxing is done to the stock head pipes down to the cat(s). I'd like to come up with something better. The driver side ends up with a flange bolt closer to the heat shield than I liked, and since I want to do both my US 83 and Euro 85 and have them ceramic coated, I feel some motivation to actually do something as long as the $$$ don't get too crazy.

First thought was to trim 2.25" off the driver side manifold, but looks like cylinder 8 pipe is too far back. Needs more looking at.

Downside of using an adapter on the passenger side to close the 2.25" gap, is that the manifold and head pipe are at close to a 45 deg angle going down and back and gap is entirely front to back. A straight back adapter puts a kink in the flow.

Option maybe on a dual cat is to put the extension near the cat entry since it is straight front to back at that point.

GlenL

Extend the right-side downpipe forwards.

The left side is almost perfect. The right side is too far forwards. An adapter added a dogleg to the flow. Not Good!

Jadz928

Extend the right-side manifold.

Landseer

I left 85 / 6 pipes as-is.

Sliced the flange off the pass side leg of the cat (actually the cats from Jadz's Perl S4).

Lenghtened the pipe, welded the flange to the end of the extension.

Then a little heating and bending of the downpipes to get it all centered in the tunnel.

But I guess you are looking for a better approach.

danglerb

Rob Edwards had good results with ceramic coating his factory manifolds, so I would like to give that a try as well, and since I am putting in some money to do that, WYAIT strikes, and I start thinking of what else to do at the same time.

Initial thought on cutting and welding the factory US 85/86 is that it might take some time to make the jigs, but thinking about it, a simple option would be two pieces of steel. Drill and tap one to bolt a couple of the head flanges of an iron manifold. Weld the second piece to the first clamped tight to the down pipe flange of the exhaust manifold, then drill and tap holes in the second piece to bolt to the flange. Remove the manifold from the jig and drill and tap two pairs of holes in the first piece offset 1.125" and 2.25", jig is ready to make either change to flange mounting. One for each side wouldn't take long, and would allow the ideal correction to stock offset on each side, one 1.125" longer, the other 1.125" shorter.

GlenL

It's all so fancy.

I cut the right side exhaust pipe ("Y") where the pipe is pointing forwards most. Then attached the section (18"?) to the downspout and used flexipipe to fill the gap. Then off to a muffler shop to have a new section welded in. Like $50 in extra cost and it all fits perfectly since it was done right on the car.

Like I said, the left side is in the right spot. It might be 1/4" too far back. Moving the pipe forwards means pulling the whole exhaust forwards. Then the hangers are misaligned and the "Y" covers the bolts of the lower bellhousing cover.

The Fixer

For me it's best to just get under the car as Glen and Landseer did and start figuring it out.

I am doing what Glen did, not going nuts with it.
(package from 928 ITNL is on it's way, great price for these beautiful manifolds)
I'll take pics of the installation. I feel my Y pipe will fit better after this because as Glen pointed out it will be on the car
when modified to fit. My Y is off a little bit.

Quick hand drawings would help to better understand your idea Mike which sounds good.
You mentioned HP gains Mike, do we have any dyno proof regarding this?
-Matt

John Speake

Pitchurs, we need pitchurs !

danglerb

I'm just a Super User, cape, but no pictures. I may put something up on Pelican.

As for the jig idea, take a piece of cardboard, set an exhaust manifold on it head side down, then fold one end up so its flat against the head pipe flange. Now imagine the cardboard was steel and mark all the holes. The key idea is that for a shortened manifold you draw a straight line through the middle of the head side bolt holes you marked, and mark for new holes whatever distance you want to change.

No way of getting around the idea though of just adapting the headpipe to fit on one side being easier. Its just not the "Porsche" way, easy way that is.

Next week I will be under a couple cars and take pictures and post someplace.

Landseer

My setup looks pretty good underneath.
Like Glen says, drivers side pipe is a tad closer to the firewall than desired.

What I don't like is inability to get to the drivers side bolts for the upper A-arm with the 85/6 tubes in place.
There was a bit more clearance with the original pipes.

The Fixer

I was excited to remove the cast iron pieces for the weight savings alone.

My only concern with installing these are the manifold studs (should one break).
If there are no problems with them, the rest is cake as far as i am concerned.
I ordered new gaskets and hardware form 928 ITNL while ordering.

The larger displacement & 4 valve per cylinder motor these tubular manifolds were designed for would suggest much better potential flow for our 16V cars than the originals could achieve (they are shaped nice though).
I think it will be a perfect match for what i have done and plan to do later to my motor.

Anyone remember a thread where a 16V car owner checked before and after installing these on a dyno. Can't find anything.

My guess is that after the manifolds will be the biggest area for gains. There is so much to consider.

https://www.google.com/url?sa=t&rct=...59026428,d.cWc

danglerb

Search for 16v headers should find discussions that include the 85/86 manifolds. Catch is few people change one thing at a time, dyno numbers really should not be used in calculation from different places or cars, so you can't say X did this and Y did that, so 14 rwhp was due to exhaust manifolds.

Hopefully a chance today to get some picts, maybe tomorrow.

SMTCapeCod

This has been done and awful lot (note Grendl, below) , and there are a bunch of threads buried here in. One of the earliest I recall was an OB named 'Nilla for some reason....a fairly comprehensive discussion, and IIRC a dyno run.

Some relics: http://www.angelfire.com/mi/lighterd...8_exhaust.html

Also note this, particularly the Ketchmi post, he provided spacers for a number of installs:
https://rennlist.com/forums/928-foru...tion-help.html

Ketchmi

We have made a lot of the adapters but we do currently have a 16v car in the shop with 85-86' headers and can make a proper crossover or "Y" pipe without an adapter. I have made over half a dozen for special requests in this exact configuration and will continue to do so while I have this car available for proper mockup. There is not enough demand to create a jig (think $$$$) so when this car rolls out of here, the availability goes with it.

Just let me or your favorite reseller of mine know and I will "git-er-done".

Kevin in Atlanta

Apropos of nothing... I have the two ends left over from when somebody cut out the cat. These are the triangular pieces that bolt to the manifolds. Maybe some enterprising soul could weld them together to make an adapter?