So I hear that the exhaust manifolds for all of our engines are prone to cracking, which is why everybody sells the three- and two- piece manifolds.

If the problem with the manifolds is the rapidly changing temperatures, which I would assume is the case, has anybody ever tried to weld heat sinks on it or cool it somehow?

Just curious...

 

ive never heard of any problems with the manifolds cracking. only when a set of twins is hanging off them unnsupprted.

 

The manifolds are prone to cracking even when stuff is stock. I have no clue why though.

 

They crack because the head is a large chunk of cast iron. it expands at a certain rate based on temperature. The exhaust is also cast iron and expands just like the head BUT it has alot less mass to shed the heat and because of that it expands/contracts at a higher rate than the head. So while heating up the exhaust manifold is trying to pull the head apart and tries to compress the head while cooling down. The head is stronger so it will always be the manifold that dies due to thermal cycling

 

Adding a heat sink fins to the manifold would rob energy from the turbine. Usually there is more than enough heat for it which makes wastegates necessary but in the case of twin turbos you're trying to extract as much energy from the exhaust as possible so cooling it with fins would be counter productive.

I doubt that making the manifold from heavier cast iron would help but making it from more malliable and tougher steel would allow it to absorb the heat cycling better without cracking.

Does anyone make a tubular steel "header" type replacement for our trucks that would both flow better and resist cracking and look cool (hot?) also?

Edwin

 

I haven't seen any in person, but I know Woodruff diesel has built a set. I've thought about doing this on my truck since I have access to a CNC plasma table. I'd just use black iron weld-elbows like we do for the twins fabrication. Then I'd have a T6 turbo flange.

brandon.

 

There was a picture of a header style exhaust manifold for a 5.9 cummins kicking around here a few months ago , but i seem to recall it was rather expensive , like over 500$.

 

Another reason that they manifolds crack is just by virtue of being a cast piece. There's little to no stress relieving done on the part, and over time, it will actually shrink.

I saw a pic on TDR once of a head that was cracked because the manifold had shrunk so much that the front bolt had leverage on it that split the #1 cyl portion like a log splitter.

In general, it has to do with the physical properties of cast iron, and the fact that nothinbg is done to address them in the manufacturing process.

You could make the exact same piece out of billet 4340 (for many $$) and never ever have a crack, even with twins hanging off it unsupported.

jh

 

most larger inline diesels do use a multi-piece unit.

 

and up till they started going overhead cam's, they also had 2, 3, and 6 piece cylinder heads on the I6 engines..

 

What most of them said above, and also because of the long stretch of that part. You seldom see V-8 manifolds that crack, but 6 cylinder manifolds, all the time. The Ford 300-6 cyl., I have seen many of those crack. Ask mechanics that have experience with a straight 6 gas engine.
When I went to install the twins on my truck we pulled the manilfold to flip it and found the stocker already cracked, at about 81K. It was welded to get me by until I could get an ATS, but the weld was a temporary thing since cast iron is difficult to weld and make it last.

Chris

 

So where do the cracks usually form? Between two of the cylinder ports, or lateral down the side of the manifold?

Nobody's ever tried to proactively weld reinforcement onto the stocker manifold or something along those lines?

Probably could make a custom header out of an old piece of engine block and a drill press...

 

There are 3 "collectors" on the stocker. It usually cracks in the middle one towards the rear a tad on the side towards the engine and the crack migrates around to the top and side where you can see it. If you have a loud cluncking or pinging after you shut down as the engine cools you have a cracked manifold. The crack is usually so tight there is not much gas excaping, but I'm sure there is some. I did notice a 1 PSI increase in boost, but that could be due to a better manifold. I also noticed a 200 degree drop in EGT's.

It is caused by heating and cooling. Expanding the manifold and shrinking it in a way that will cause cracks. The best solution is the 3 piece. Don't replace it with a stock one. Fairly easy install, but a pain getting at the bolts underneath.

 

The 24 valves crack where Geico said and are more prone to cracking than earlier 1st gen and 12 valves.
The 12s usually crack where the hold down bolts pass though at cylinders #1 or #6, sometimes cracking the head instead.
Easy to tell if your manifold has shrunk and may be getting ready to crack, just look at the bolts at #1 and see if they're bent.

 

My cracked stocker.

The ATS manifold was originally developed mainly to prevent cracking. One of ATS's (of Utah, now owned by ATS from Denver) 12v trucks was going through stock manifolds every 4 to 6 months, prompting the development of their manifold.

Work them long enough, and hot enough, and the exhaust manifold will crack. 12vs manifolds will also shrink to the point of breaking off mounting studs. I've personally seen a 3rd gen CR manifold, used on a local towing rig, crack on down through an ATS manifold, and through the turbo, itself. It had previously cracked out the stock manifold. ATS replaced the manifold, and the dealer repalced the turbo.

The added benefit of using an ATS on the 3rd gen is getting rid of the bigtime restriction on the #5 cylinder port in the stock manifold.