I'm in the process of making a custom header. I have all the individual tubes welded up (but not attached to the header flange), and I have the stub-outs on the header flange fully welded. So all the significant heat generated by welding that would impact the flange itself should be over. Before I combine the two and have a full header, what is the general consensus on how flat the header flange should be?
For each side, the middle of the flange is the high spot. On one flange, the ends are low by about .020" and .015". On the other side, it's a bit more, .035" and .040". My cursory Googling hasn't revealed any particularly consistent opinion, but those numbers seem smaller than what most people would consider acceptable.
This is for a V8, so 4 ports / flange. Thoughts?
I don't know what constitutes "acceptable" on a blueprint, but I know that flatter is better. Why create any additional mechanical stresses on something that's going to see tons of heat and vibration? IMO it's well worth it to surface grind them after the fabrication is all done.
It will depend on what you're using for a gasket and how long a distance there is between high and low spots. You're probably fine if you can get a copper gasket for your application. However, if you have an automotive machine shop near you that has one of the monster belt sander type surfacing machines you can probably get the pair of them flat for a ten spot or so.
Please remember to anneal (possibly several times) whatever you are working on before doing any type of facing. Metal has a memory and you will not really know how straight it is until it has gone through several heat cycles. After annealing if you have more than 1MM of curvature I would spend the $ on a machine shop for facing.
How thick of a flange are you using? The thicker the flange you use the less likely it is to deform from welding. Clamping to a large piece of aluminum or copper to help wick the heat out of the flange when you are welding helps a lot.
Have you thought of doing individual flanges for each port? This is something I wish we would have done on the turbo manifold we made for my friend's 924 Turbo. It's easier to control flatness individually on 4 small plates of metal than it is on one large plate.
How long is a piece of string ?
Flat is flat.
iceracer said:
Flat is flat.
Actually...http://www.engineeringessentials.com/gdt/flatness/flatness.htm
Nothing really is flat.. it's just how much money do you want to spend making it as close to flat as possible.
use RemFlex gaskets
best thing invented since condoms
Hey,
I built a set of headers several eons ago.
Because I had several spare cylinder heads in the garage, I bolted the flanges to the spare head , (Tight, with no gaskets). and did 90% of the welding with this fixturing.
Never had a problem with leaking or cracking.
Rog
boulder_dweeb said:
Hey,
I built a set of headers several eons ago.
Because I had several spare cylinder heads in the garage, I bolted the flanges to the spare head , (Tight, with no gaskets). and did 90% of the welding with this fixturing.
Never had a problem with leaking or cracking.
Rog
tack the flange onto heavy steel box tubing or i beam works well too
I did this for a turbo manifold build. Absolutely dead flat after all said and done
Eh, my homemade headers were about as bad as you describe.
They sealed fine.
Try it. If they leak, get them ground down.
NordicSaab said:
Please remember to anneal (possibly several times) whatever you are working on before doing any type of facing. Metal has a memory and you will not really know how straight it is until it has gone through several heat cycles. After annealing if you have more than 1MM of curvature I would spend the $ on a machine shop for facing.
I have seen people suggest bolting new ones on without a gasket initially and running some heat cycles - I presume for this reason. Is that good enough? Getting them to the point of glowing, which I think you need for annealing, seems unlikely in this lifetime given my current build progress 
I forgot to measure the flanges when I bought them, but I don't remember them being perfectly flat before I started welding on them. I'm sure they moved a bit, but not much. So yeah, I'm inclined to just bolt 'em on and see what happens.
Get it flat and ditch the gasket entirely.
We've been installing manifolds and headers with no gaskets, just a bead of copper rtv, for the last four years or so and no leaks.
That comes out to at least 15-16 non-leaking installs for customers plus at least three on our own vehicles that are not leaking.
We've come to the conclusion that exhaust gaskets CAUSE leaks.
