<snip....snip...snip>
The best we can do is get headers that are some compromise. In the
situation of a 300-400 cu in V8 running under 7000 RPM, that length is
usually such that the collector ends up next to the transmission. If the
engine is meant to run at much lower speeds, like 1000-2000RPM, a shorter
header will be about right.
<unsnip.....>
Uhhhhh,
Nope, sorry, you have it backwards.
The longer the header pipe length, the lower the RPM's because you are
timing how long it takes for the exhaust pulse (slug) to reach the collector
to create the vacuum for the other tubes joined at the collector. If you
shorten the tube length then the pulse will reach the collector faster
(shorter length of time) and you have to have an exhaust cycle beginning in
one of the other cylinders in order to take advantage of the vacuum caused
by the pulse entering and expanding in the collector. I understand your
career and education, but I have 10 years experience in hands on, getting
major results in tuning 2 stroke exhausts. Now before anyone tries and tells
me that a 2 stroke and our Dak engines are apples and oranges, and that
there is no way of comparing them, stop and a look at the physics. You are
doing with the header on the 4 stroke, the exact same thing you are doing
with the "tuned pipe" on the 2 stroke. That is, using the exhaust pulse
created by burning the air/fuel mixture to scavenge (suck) the exhaust from
the cylinder who's exhaust valve is just opening.
What you see at the drag strip, beside a bunch of people who look around
at what everyone else is running, therefore it must be better, are header
pipes that are so long, that there is actually more than one exhaust pulse
in each header tube at any given time. When the car/truck is racing. This
only compounds the scavenging effect as not only is each cylinder helping
the others, but it is helping itself as well.
Shorties do not do this to the same extent, but they are cheaper to
produce and therefore cheaper for the consumer, are much easier to install
and on Ch**ys are usually easier to change plugs with.
I personally am torn as to which way to go. Unfortunately I do not have
a profit sharing check coming in any time soon, so I don't have the dough
for the deal. But I am also considering the Doug Thorleys as I have heard
nothing but rave comments on how they help street driving by increasing the
torque. I am concerned about the heat though as it is pretty toasty under
the hood here in Texas. But I see that the warrantee is void on Thorleys if
you wrap or coat them. Not only that, but how long would a chromed steel
header last under that kind of heat if not protected? Personally I'm not
worried about HP, but trying to get a CC 4X4 with 31X10.5 tires rolling and
on a highway can sometimes take longer than I prefer. Even with 3.92's.
Don't get me wrong, it is not a pig, but like everything else, better
acceleration is one thing I would definitely like to have.
One last question, then I'll go back into lurk more. How thick is the
coating INSIDE the headers and does it cut down on exhaust flow?
John
98 Dak 4X4 CC Sport, 5.2L, auto, 3.92LSD, T&H Package, Power Everything,
Nerf Bars, Billet Grill, Rhino Liner, Snug Lid, DDBC, home made FIPK 2
(pictures available soon)
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