Heat Stress Stainless

Apart from the material spec, which I am not qualified to comment on, part of the secret with tubular exhaust manifolds for turbo charged engines is supporting the turbo, and waste gate, if a remote `gate is used. If you care to have a look on my ftp server at ftp://ftp.chriswilson.tv/F1_turbo you can see how Renault did it in the F1 turbo era. All the other engine manufacturers did it a similar way, and when I have run turbos on tubular manifolds I have always supported them by a means that allow expansion and contraction in as many plains as possible, yet kept the weight of the turbo and `gate off the red hot tubing. Consider slip joints rather than a fully welded assembly, done right these will virtually seal gas tight when up to temp, yet allow free expansion and contraction. You can also include commercially made stainless bellows in the pipes to do the same thing.

I tend to go the quick and dirty fix these days and run cast iron manifolds on road car turbo installations as they are a lot less hassle, and the weight and slight flow penalties are trivial, given a totally maintenance and trouble free installation ftp://ftp.chriswilson.tv/hks_manifold

Hope this helps a bit. If the budget allows I think Inconel is the best material for tubular turbo headers.

Here are some scans on heat treating

Is it going to look anything like this?

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

The other thing to watch our for is the difference in coefficient of expansion between stainless steel and the cast iron or aluminum the head is made from. Aluminum is about 13, cast iron 6.6, and stainless steel

9.6 microinches per inch per deg F. If your header flange is 24 inches long and stainless steel on a cast iron head then starting both at 70 F room temperature, if the head gets to 450 F and the header flange to 1000 F, then the head will grow 24*(450-70)*6.6 uinch=60192 uinch=0.060" while the header flange grows 24*(1000-70)*9.6 uinch=214272 uinch=0.214". That means the header grows .214-.060" more, or 0.154". If the center is fixed then each end will grow half that, or 0.077". That could be enough to cause sealing failure over time, and could be enough to jam or shear the header bolts. I bought a set of 304 stainless steel headers for my turbo Regal, and when the exhaust flanges started to rust I was pretty upset. Then I learned that on cast iron heads a steel flange (6.3 uinch/inch/deg F) was actually a pretty good idea overall :-). The match is better with aluminum heads, which at 450 F have grown 0.119", twice as much as the cast iron would, and only 0.095" less than the stainless steel flange. I don't really think the head is going to get up to 450 F, since that is enough to start cooking the motor oil. I have seen the tubes an inch from the flange glow red-orange many times on a high hp turbo motor so the flange is going to be pretty hot, but maybe not 1000 F since it is in contact with the head. Plug in your own temperature estimates and you may get less growth, but the point is that you at least think about it.

-- Regards, Carl Ijames carl.ijames at verizon.net

Beautiful work.

321 would be my first choice, 304L second.

my motor may only push about 250hp with turbo.

as for expansion, dont holes also increase in diameter when heated? although a diff between AL and 321, the diff has to account for the mounting holes getting larger.

i figure i will drill header bolt hole 1/32-2/32" larger than stud size.

...and also the stud bolt material. i forgot that piece. many studs are chromoly, so i'll need to see how those expand when heated.

Here is some glow. Turn up the sound real loud for this one

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

But the studs/bolts/holes are so small that they grow only a tiny amount. For example, a steel 5/16" bolt going from 70 F to 450 F will only grow .3125*6.3*(450-70) = 748 uinch = 0.00075" in diameter. Corky Bell's book on turbocharging has a good discussion of this.

-- Regards, Carl Ijames carl.ijames at verizon.net

i have the book, will need to check. thanks