January 26, 2008 - There's a discussion of the header on the German MX-5 forum.
It's quite a long one and they bring up some good points - although I suspect it would be easier to read in German than through online translation engines! Some of the comments are ones I expected, particularly those about the welding quality. There were also questions about my choice to build such a convoluted design instead of a more traditional one with the collector down by the bellhousing, and how to prevent cracking. Since it's possible that others will be thinking along the same lines, here's what I replied to them. It provides a bit of a summation to the project so far:
I know some of the welding is ugly. I'm learning how to TIG weld on
this project. It was not easy. In some cases, I tried to hide my tack
welds (the little ones you make to hold everything in place) by
melting them down and spreading the material around. This makes the
weld look ugly, but it will look nicer when it's painted.
The tube length is chosen on musical principles. Basically, the high
pressure pulses from each cylinder will travel down the tube and
reflect back. At the right engine speed, this means you can get a low
pressure right on the exhaust valve which increases the suction and
makes more power. The tube length is determined by the cam profile and
desired engine speed. Tube diameter is a different question, although
you can cheat a bit and use a larger diameter and a slightly shorter
length for the same effect.
The Racing Beat header is surprising in a couple of ways. The tube
lengths are not all the same, which is a trick sometimes used to
spread the power band around a bit. But the short length is what's
odd. The header shouldn't work until it's up near 9000 rpm, and it
doesn't seem to improve as the engine spins faster. There may be some
secondary resonances that they're using. I did use larger diameter
tubing than the Racing Beat, but I didn't go to an extreme size. The
long tubes should give me more power in the medium to high engine
range, which is where I want it. They are almost all exactly the same
length.
The Boig headers don't fit well inside the car. They hit things, they
leak, they rattle and they bang around. I used one on my 1990 for a
short period of time. Even the Racing Beat has a dent in one of the
tubes to clear the steering column. So I decided to move my collector
high up to avoid the clearance problems. This is something that has
been used on other E Production race cars.
The english term for "glow in" is probably "heat treat" or "heat
cycle". I'll see how I can do that. I am concerned about longevity as
well.
But the biggest thing to remember is that I did this to learn. It was
ambitious, but now I'll know if it's better than the Racing Beat. I
have some room to adjust the length of the header (another advantage
of my collector location) so I can do some tuning if that helps. I've
learned a lot of about TIG welding. I don't present this as a lesson
on how to make a header, I'm giving people the chance to look over my
shoulder as I learn. I'll make mistakes. And I'll learn from them.
tags: header |
THE DIARY