My answer is "it depends"
The US stock exhaust manifold is not a particularly good flowing unit.
It's just a big blob of iron that the exhaust gasses get to fight around
in before wandering their way down the pipe, particularly the #4
cylinder. The UK stock manifold on the other hand, is essentially a
well made iron topped tri-Y header, and is very hard to beat.
Most headers are extremely poorly made, and flow accordingly. The
collector is the important part of a header, and usually the most
neglected and mangled. Crimping pipes to stuff them into an abrupt
little collector can easily result in exhaust flow that's worse then a
stock manifold. Pacesetter is an excellent example of a very badly made
header that probably does not flow any better then a stock US manifold,
and certainly worse then the stock UK manifold.
Headers are well known for blowing mounting gaskets. It's because the
mounting plate is frequently warped in the welding process, and it is
flimsy, distorting from the heat of the exhaust gasses. You can help
preclude blowing of gaskets by machining the mounting surface flat. You
can do an effective job of this with plate glass and grinding compound.
It works. Also lets you see when you finally get the surface flat. You
can also help keep the gasket from blowing by smearing coppercote on
both sides of the gasket. Do not over torque! That bends the header
mounting plate, pulling it away from the cylinder head in between the
over tightened fasteners.
>>> "Bill Gingerich" <wrgingerich@msn.com> 07/23/03 02:07AM >>>
Greetings, Fellow Listers,
Insomnia grips me as I write this. I'm not usually a 1:00 AM kind of
guy.
Anyway, I need a memory refresh: does a 4 into 1 header offer any real
advantage over the stock manifold on a basically stock 1500 street
motor? I
believe previous discussion reached the conclusion that 4-1 only helps
at
high RPM. I rarely, if ever, run above 5000. The only mods to the
engine
are Pertronix ignition and flat top pistons. Stock ZS carb and
muffler,
too. The reason I ask is that despite my best efforts, the manifold
gasket
has blown again. Rather than join the "gasket of the week" club, I'm
thinking of going back to the stock exhaust. If The Lists think the
header
offers advantages, I will try it again. Thanks!
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