Jetdriver69

I've done a bit of research and it seems the best bang for my buck is replacing the lump of iron exhaust manifold on my 82 5 speed with a 85/86 manifold. I have the engine out doing a valve job, so time to upgrade a bit. I have read that expensive headers aren't really that great of a value for the small HP gain. If I replace the manifold with a 85/86, how much machine work is necessary or is it a straight bolt in? I live in Texas and the car is over 25 years old with no emissions testing, so the cat is going away. Can I run a independent dual exhaust without a X or H pipe or is one mandatory with a dual exhaust? If not, is the HP gain so minimal I may as well keep the single Borla exhaust and get rid of the cat with a Y pipe from Roger. Remember, most bang for the buck and no unnecessary work for 2 or 3 HP. Thanks.

Jadz928

85-86 headers are generally bolt-up. May have to slightly open up one or two holes.

The single Borla is a really nice piece. Most likely better than what you could have your muffler shop rig up (esp duals... hard to tune up to remove droning).
Yea, lose the cat, get the Y, keep the Borla.

PS. Could you break up your thoughts/questions into separate paragraphs for easier reading, please? Thanks!

LT Texan

I did this.

You have to drill out a bolt hole at the end of each manifold.

You have to make/buy an adapter because the y-pipe does not bolt up.

I have no before/after, so I can't say the gain.

There has been work (documented here) to port the cast iron manifolds with good results.

I'd consider that, gutting the cat and Borla cat-back as maybe an alternative.

GlenL

I bolted the 85/86 to my 16V engine with zero modifications to the manifolds. Seems you'll have to give it a try.

The trick is that the manifold outlets don't end up at the same place relative to the engine. The left side is a faction of an inch further back and the right is, maybe 3, further forwards. There is no off-the-shelf Y pipe or anything that'll fit it; you'll have to get something custom done.

How much to spend? I might remove the old cats and leave it at that, after the needed extension to the right side.

Jetdriver69

I have been told that some custom exhaust work may need to be done to get the 86 manifold to fit the exhaust pipe like the extension you mentioned. Anyway, will probably give it a miss and just remove the cat with a straight pipe and o2 sensor bung welded in. Much cheaper than a Y pipe and this car is for a 16 year old anyway, no racing allowed!

IcemanG17

I would say the exhaust after the manifold is the biggest gain......sure the tubular steel 85-6 manifold should flow a bit more, but probably the biggest gain is loss of weight....

When I went from 85-6 manifolds into a single Y pipe then stock exhaust my 84 made about 194whp 233 torque....when I switched to a proper 3.5" single race exhaust it jumped to 215whp-256 torque with just a bit of fuel added....

The Forgotten On

Do any of you know who to buy the adapter from? I am going to swap on the 85 manifolds to get rid of the cast iron lumps on my 81.

Mrmerlin

Give Motorsport Utah a call IIRC they had made some of these adapters since they were also making the famous X pipes

Mrmerlin

http://www.google.com/url?sa=t&rct=j...52164340,d.aWM

Ducman82

i have a set of the S3 manifolds for sale if you guys need a set.

SMTCapeCod

THe manifolds provide nice gains in the upper reaches, where the cams start to get happy, without completely depleting the bottom end.

Deleting the cats produces an awful sound to some folks, on a street car, and also may, (IMO) reduce your torque off idle.

YMMV


It all goes back to preferences and means, of course. I am very happy with the solution on my Euro, for perfection I might think about a tuned x and aftermarket low cell count cats- but given that the cats were designed for a higher displacement engine to being with, not sure there would be much gain there- except aforementioned weight reduction.

Landseer

85/6 headers I've used require 4 seconds of mods per side. The two inner bolt holes on each pipe required slight ream out.

If you can convince an exhaust guy to wire weld in situ, then lots becomes possible.

Jetdriver69

For those who have done the 85/86 manifold sway on a 16V, exactly how much longer does the passenger side cat pipe must be lengthened for the newer manifolds to fit a 82? I may modify my current pipe or have one made out of larger diameter stock. Just need the measurement to lengthen. Thanks

Ad0911

Porting the cast iron manifold. That sounds like a good idea. Or will it never get the flow of the '86 manifold due to the design?

Landseer

Its 3 or 4 inches roughly.

Best way to do this, whack a mating flange off of an old pipe, say from one of the inlets of the 84 standard 928 cat you are replacing. Leave an inch of pipe.

Bolt that to the discharge of pass side 85/6 header pipe. Then, take a piece of std SAE exhaust tube at the exhaust shop, I forget size, 1 3/4? or 2? and MIG weld it to the inch of pipe you left on the downstream side of that flange you just bolted up.
The SAE tube we used nicely covered the 1 inch of pipe left at the flange, creating an extension. Actually used a carbon steel pipe, but its so hot there that we knew it would last for years anyway.

Then, you build from there. I mounted 87 cats. Whacked the flange from the 87 cat inlet, pass side, left an inch, bolted that whacked off flange to the 85/6 header pipe. Then, in-situ, slipped the SAE extension into the now-flangeless inlet to the pass side of 87 cat. And of course MIG welded the extension to the flange, which it nicely fit over. Voila. Pretty much.

The 87 cat had to be bolted up to the drivers side. Process wise, that was actually done first. Had to heat the drivers side pipe near the cat cherry red and bend / center the whole cat in the tunnel. Then a similar heat/bend process done to the (now flangeless) cat pass inlet to get it lined up by eyeball where the pass side is going to need to be. Simple and quick, if your exhaust guy is a doer and not a diva. This centering operation determines the length of the pass side extension.

Maybe I can get a picture sometime saturday under the avatar Euro car (Jadz old car) to show it.

You may decide on another downstream exhaust system. Even if you use the flange from the Utah Motorsports group, you will probably have some custom work to mount your downstream stuff.

Only bad thing about the 85/6 header pipes is the drivers side nearly completely blocks access to the upper A-arm mounting bolts inside the fender. I did some front suspension work this winter with the pipes installed and my final torque on that was questionable.