Random header thoughts

[Michael Gough]

The tube designs are MUCH nicer than the log designs. Logs are great if
you're making a manifold for a naturally aspirated car. It's easy, and the
gains from going from N/A to turbo are so huge that nobody cares if the log
design isn't the best. However, on a car that already has a turbo, and a
somewhat decent (well it's better than some) manifold, going to a log
shouldn't be an option. In "Turbochargers" by Hugh MacInnes (great book
BTW), he mentions that on a highly tuned BMW turbo motor, switching from a
log to tubular manifold increased power output by over 100hp. So please go
the tubular route.
Another idea. I've been looking over the stock EM pretty well (comparing it
with the AAN manifold too) and I'm noticing 2 major issues with the stock MC
manifold. The first is that the wastegate doesn't vent gas from all
cylinders, only the back 2 or 3. The second thing, is the collector. The
collector vents cylinder 1 by itself out of one of the large outlets. The
cylinders 2 and 5 come out of the smallest, top outlet, and cylinders 3 and
4 come out of the other large outlet. I always thought the small outlet was
the single one, but upon closer examination, this is not the case.
And I have no idea where I'm going with this now...Just don't do a log
design :) I haven't started on my collector yet, but it's going to be very
similar to a 4-1 collector. Since I'm (probably) using a KKK turbo, I am
going to start with a piece of 2" pipe, tube, whatever, and then cut the
sides out of 5 pieces of tube, and in the end, I hope to end up with
something that looks a bit like a 4-1 collector, but with the tube for
cylinder #3 in the middle of the other 4 tubes. I don't know how well space
will permit this, but I'll try!. Also I've decided to go with schedule 10 1"
pipe with an ID of 1.1" The idea size would be 1.3" but the only thing with
this ID is 1.5" tubing with a .095 wall (still can't find any of this) The
reason I'm going with the 1.1" schedule 10 pipe instead of 1.25" schedule 10
pipe with an ID of 1.4", is that the smaller tube should help keep up
velocity at low RPM, and I figure that it'll be a large improvement over the
stock manifold (with the restrictive collector) that it should give good
results. I haven't completely made my mind up on this, but I'm probably
going to go with schedule 10 1" pipe.
Another idea for someone with too much time on their hands and no money, You
could try cutting off the collector on the stock manifold and making a new
one...There's nothing inherently wrong with the runners, they're fairly big,
the major problem I see is the collector. So get out the metal cutting band
saw and make a new collector!
Mike


> Ok, so I've been surfing like crazy, checking out all
> the different header designs out there.  I like the
> tube design over the log, but making a 5 tube
> collector seems rather difficult.  What if one was to
> join two of the runners together, near the collector,
> so you would only have a 4 tube collector?  It should
> work if you put two cylinders together that are close
> to being on opposite strokes (I've heard 270 degree's
> is optimal), so when one fires, the other is
> scavenging?  Who knows, just looking for ways to save
> money if I decide to do this some day.  Thoughts?