Re: Putting 4000 quattro manifold on '85 Coupe GT?

[Huw Powell <human@nh.ultranet.com>]

> OK, I've heard that for some reason, the 4000 quattro manifold is superior
> to the stock Coupe manifold, and swapping one in my car will yeild
> performance gains.  Anyone care to comment on this

Well, the stock manifold is a crummy little casting that crams all five
cylinders gases into one outlet about 1-1/2" around a few inches from
the head.  The 4kq manifold is a tubular header which doesn't reduce the
area the gases have.  It first goes down to three holes, two big and one
smaller, then the downpipe brings them together into one 2-1/4" or so
outlet.  

> Am I correct in thinking that the manifold will drop right in, but using
> both the manifold AND downpipe from a 4000 would require me to modify my
> stock exhaust on my Coupe?

No, you must use both.  You'll need (5) new exhaust manifold/head
gaskets and a new manifold/downpipe gasket.  While you're at it, if you
have any time at all, send the new stuff out to be jet-hot coated or
some such.  Use nice new stainless steel hardware for future ease in
dismantling.  You will need to at least get a custom downpipe to cat
pipe made, I'd recommend planning on upping the whole system to 2-1/4"
with one muffler at some point.  The early 5kt cat is the right diameter
or you can get a new one.  You need to install the OXS in the pre-cat
connector pipe also, since the stock one is in the manifold.  Use a
heated OXS since it's a lot further from the heat of the head.

On my (82) coupe there was a boss on the transimission which did
nothing, that touched the downpipe.  Caused no harm but Mr Sawzall
eliminated any potential damage/noise.

This may sound like a lot of trouble, but I spent less than $400 to get
a manifold and downpipe, all new hardware, re-use a 5kt muffler (ok that
was free) and have the rest of the stuff bent up out of aluminized pipe
at Meineke.  Price a stock system lately?

BTW, it now sounds like a 5l Rustnag when idling, isn't irritating on
the highway, and anecdotal though it may be, certainly *seems* to have
more "Get-Up-And-Go".  Verified semi-scientifically by my favorite
"let's see what my maximum exit speed is" ess curve.  Can't try it any
more it scares me, I have to back off a bit.  Wimp.

-- 
Huw Powell

Astronomer:
      (n) 1. Someone who is happy to get the order of magnitude correct
in the exponent.