Stock Turbos - Preventing Manifold Cracks
 

My car has a relatively new engine (12k) and original turbos (62k). These turbos are cracked and leaking past the gaskets in a few spots. So I'm in the process of getting a used set with only 19k on them and no known cracks.

In order to 'Say no to Crack' I intend to continue driving the car with a good easy warmup and cooldown, keep the heat shields in place, and maybe get the housings cryo treated. (If I do the cryo, I'll try to get it hardness tested before/after to see if there is a difference)

So my questions are this:
- Can I safely disassemble/reassemble the turbos to remove the housings, or just have the whole thing cryo treated? Has anyone done this?

- What's the longest you've seen a manifold last without cracking?

Dave

I've heard from a turbo shop that they've seen manifolds crack after just one warmup/cooldown cycle.

The big thing to remember is exhaust doesn't care what the inside of the manifold *looks* like. If the cracks are big enough to compromise the wastegate flap sealing or has cracked under a gasket sealing surface and the gasket blows out, that's the only time to worry about it. Most of the cracks are cosmetic, and you just simply don't seem 'em with the turbos in the car :).

Cryo treating will likely help out the manifolds, but it's hard to say how much time that buys you on the manifolds.

Taking the turbine housings off the turbo cartridge is relatively straightforward, and you can do it no problem.

Dale

Hey.. I'm planning on getting an FD soon when my finances are in order (steady paycheck from new job...) and I came across this thread and it got my attention. Then, I realized I've fixed basically everything on the current beater/dragslut camaro I have with J.B.Weld.

Could you do that to the stock turbo manifold?

Due to the amount of heat there; not likely.

Possibly ceramic coating the inside of the manifold could help. As for cryo treating I am pretty sure there has been no real data that proves it actually helps anything.

Nothing will ever cure the stock manifold cracks. Ever.

The reason the stock manifold cracks is not because it gets really hot, it's because the thickness of the casting changes wildly throughout the part. When the part gets hot the metal expands but since the thickness varies so greatly some areas expand more than others. The metal then contracts when it cools. This creates stresses throughout the casting and they appear as cracks.

The only way to prevent the cracks is to keep the manifold from getting hot, which is impossible if you ever run the engine. The manifold is fundamentally susceptible to cracks because of its design.

Heating alone does not create internal stresses. It's the local differences in heating which causes changes in part thicknesses to get thermal cracking - the center of the thick spots always heats/cools slower than the thin metal. This is why the design rule is to keep part walls of similar thickness in areas of high heating and cooling. If the whole manifold is cooled and heated slowly and evenly, there are no thermal stresses. This is why I mentioned the heat shields and warmup/cooldown habits. One thing that has me mildly concerned is how rich the car runs on a cold-start warmup - I think it causes afterburn in the manifold area.

Just for the practice, I'm going to model the manifold when I get mine torn down and do a thermal FEA analysis to see what kind of internal stresses it suggests. Not that an analysis will help with anything, I need the practice with FEA :)

But I look at the subject of brake rotor cracking for reference - and reading the results of racers suggest that these cast iron parts have seen improvements wrt thermal cracking. Cast iron apparently precipitates carbide formations during cryo, and relieves internal casting stresses from the quench. Those variances in part thickness could actually mean that every new stock manifold has internal stresses because Mazda didn't quench or post-heat-treat them in the best way. Given the extreme heating and cooling cycles seen there, it holds promise for cyro + manifolds.

Dave

I thought that's what I said above ;)


It would be a valient effort but impossible to achieve. EGT's themselves change wildly from idle to hard on the gas and back off the gas etc. You cannot control the heat fluctuations in the manifold no matter how many heat sheilds or attempts to warmup or cool slowly. What does the damage to the manifold is throttling the engine. If you constantly change power settings the manifold will constantly be exposed to wild temperature extremes and will thus be prone to crack.

changing the mix of the "trace metals" in the mix of the metals probably is your best bet of avoiding cracking.

1g mitsubishi turbos/manifolds...crack...errode...ect...bad...

2g with same dimmensions...but just a different mix of metals...I believe i've heard more chromium...no cracking and little to zero errosion.

this is WILDLY circumstantial evidence ;) but looking at my used 1g parts laying around...that are cracked...and looking at my used 2g parts laying aroun...uncracked...and looking at the used FD3s turbine housings (low miles with a small amount of cracking)...based on the color/depth of the surface rust on the 3 types of pieces...there is clearly a difference in the metals. The FD3s is very similar in color, texture, and depth of surface rust to the 1g parts.

John

Replace with single turbo.

I you wanna buy me an ECU, intercooler, manifold, turbo kit, boost controller, and pay for tuning, I won't get pissed that you would make such an asinine comment.

Dave

dgeesaman: it was tongue in cheek... but unfortunately.. the ultimate manifest destiny when it comes to the ancient twins in the stock setup. :-/

Ok then - the 'go single' posts that some people write are actually in earnest and very insulting IMO... :bigthumb: It's sad to see how many people dump thousands$$ because of a popped hose or dead solenoid...

Dave

The shop that recently did a run of 3g housings may actually be an improvement on the stock parts. Reference: https://www.rx7club.com/showthread.p...ghlight=%24900 I wonder what material they used.

I wonder if the 99 spec turbos have improved durability in this regard - Mazda did improve many other little things.

Nope. My mechanic just pulled a low mileage (under 10k miles) set of 99s off a car and they already have the hairline cracking. No fix there....

I think one problem too is the INSANE amount of heat that's in the stock manifold and turbine housing. There's a reason Mazda used *Inconel* turbine wheels.

I know Carlos tried every known ceramic coating on his turbine housings and manifolds - none held up.

I think it may be something you just have to accept. Fortunately it seems to take a VERY long time for the cracking to get bad enough where you'll have a problem with gasket sealing and such.

Dale

150K and multiple track days on the stock turbos... no cracks that I know of... or at least no cracks severe enough to cause a noticable problem.

Drill thru the crack tips to stop them from growing.

Dave

Ok, one more angle: I wonder if overtorquing the studs could contribute to cracks?

<ducks and runs>

Dave

Is there an aftermarket manifold that is more crack resistant? Do other turbo charged cars have this kind of problem?

Any idea what kind of EGTs are there?

(I am aware that on the outlet side of the turbine, the flow temp is reduced due to the drop in pressure - and the cracking is taking place on the hotter high pressure side).

Salamander - I haven't heard of anything beyond what was mentioned in this thread. I have an email in with turbochargers.com to get more info.

Dave

John, I guarantee you have bad cracks. If you put on a brand new set, I bet you'd be surprised by the quicker spool and smoother transition. Still, 150k miles is pretty damn impressive.

Here's mine at 85k:

http://img.photobucket.com/albums/v2...neHousing2.jpg

My manifolds had cracking even when pulled off the car at ~3,000-3,500 miles. They all crack eventually, to greater or lesser extents.

No one has mentioned (at least that I saw) that cracks typically form at hard edges. Radiusing the edges would reduce the chance of stress risers forming and cut down on cracking. The same theory that applies to cross-drilled cast iron brake rotors applies here. Radius the edges of the holes and they won't be as prone to cracking. After that's done, ceramic coat the parts.

Ceramic coat the inside, or outside? Like Dale said, doesn't it peel off?

Dave

I just got a response from the turbocharger.com guys:

http://www.turbochargers.com/Turbos/...es/MazdaS2.htm

They made no comment about if it was an improved material, except to say it's a cast iron.

Regarding the resistance to cracking:
"there are just some smooth rounded places were there use to be edges that would make it hotter or (hot spots)" and "the factory wouldnt reproduce the housings so we did it ourselves
we just modified the hot spots as they are called and made them stonger so they wouldnt crack as easily"

Dave