Header
I want to weld a exhaust manifold myself. What about the length and
diameters of the tubes? Is there a common knowledge of the best
solution? What about the cam shaft and the rpm of max power or
torque, do they influence the manifold design?
Thanks for everything answered, Rüdiger.
There are numerous factors which influence the design of a "header"
or tubular exhaust manifold.
I would recommend 1.5" (38mm) tubing for a 1.9 or 2.0 engine used
for the street. The length of the tubes depends mostly on the rpm's
and camshaft, but definitely no shorter than 32" (813mm) and as long
as 38" for high torque (965mm). I usually choose 34" (864mm) for a
fast street car or ITB racecar (Nearly stock race class here in the
US).
Of course, for a larger engine such as a 2.2 or 2.4 litre, 1.625"
(41.27mm) tubing would be a better choice. And very high rpm engines
with modified heads and camshafts might need even larger tubes. I use
1.75" (44.45mm) tubes on engines which rev over 9000 rpm's.
If you have specific information about your engine I can maybe help
out more.
Bob Legere
Thanks for your very fast answer!
My engine is a big bored 2.0 CIH. Now it has 2.4 litre with a Schrick
302° camshaft, 45mm/41mm valves, and distributor limited revs to
6,300 rpms, modified ports, I have no information about rods and
pistons. So it has 174 hp. I bought 90 degree bends and straight
tubes of 40 mm x 1.5 mm. That means 40 mm outer diameter with a
thickness of 1.5 mm results in an inner diameter of 37 mm. Your value
of 32 to 38" is the length of each single tube before they are
connected? So I had to join them under or behind the engine but not
where they are connected now with the stock sprint manifold? So I
need much more space for 4 tubes running down the engine. I had
dreamed of a service friendly solution. And then all four tubes
should be connected at the same position? Not first cylinder 1 with 4
and 2 with 3?
I don't particularly like 4-2-1 type exhaust headers. I prefer
the power band of a 4 into 1 design. They are more flexible in power
output if designed well. This is one reason why there are very few
proper manifolds designed this way. They are admittedly more
difficult to package under the car. More space is needed, and
installation is more difficult. The 4-2-1 designs are easier
(cheaper) to build as a result, and this is one reason most
manufacturers build them this way. I've tested various 4-2-1 designs,
and didn't like the power band. They were a little better at
mid-range, but never made the peak power or even the low-end power of
a proper 4-1 header. And the sound...yuck. A 4-1 sounds much better,
at least to my ears. All four tubes will be the same length. This can
sometimes be difficult I admit, I always make #1 tube as straight as
possible to make it go as far to the back of the car as I can. This
way #4 tube is not as twisted under the hood. They will be all joined
together at one point.
And with what tube shall I then go to the
catalyst muffler combination?
I would use a 2.75" (about 70 mm ) collector that was 10" long (254
mm) and then out to a 2.5" (63.5 mm) exhaust for that sized
engine.
I want to only use one muffler with catalyst in
front of it to have a light and aerodynamic exhaust system. No tubing
over the rear axle, just a one tube end to the passenger side in
front of the rearwheel. I have bought a Trush CVX muffler and will
weld a longer duplicate of it out of non rusting steel. Comments? I
want to make it a bit longer to eliminate higher frequencies and
reduce more noise. At now the sound is very good but a bit too loud
and at speeds over 88 mph the exhaust is no longer hearable. Maybe
the other noise sources are louder ore the muffler is then full
working.
I have found that a street Opel needs two mufflers to be quiet, but
maybe the catalyst will do a lot of that for you. A longer exhaust is
better for torque as well. I would point the exhaust tip down towards
the ground, as this also makes the car a few decibals quieter. I know
in Europe sound is a great concern, as it is becoming over here
lately. We have to pass 86 db I believe now.
What do you think of the advantage of such a
header. Can you give an amount of hps or percents?
I think you will see about 7 or 8 hp over a cast iron manifold, but
the main improvement is throughout the ranges with better overall
torque. Two hp at 6000 rpm's means nothing compared to 4 or 5 hp at
all other rpms. This will improve the acceleration. You will probably
notice better fuel usage though, and the spark plugs should have
better color compared to the 4-2-1 design.
Bob Legere