Exhaust Manifold cracks...is this a thing?
 

Hi All,

Without mentioning names, someone once told me that the exhaust manifolds in 944s are prone to cracking. He went so far as to say "If yours aren't cracked now, they will be soon."

Now this person is without a doubt very knowledgeable about the 944 but I got to thinking and I don't recall ever reading about this on this forum or anywhere else for that matter.

To be fair, the person that told me this wasn't trying to sell me anything so I believe the advice was given in good faith but...

So, has anyone else ever heard of a common problem being cracks or pinhole leaks in the factory exhaust manifolds?

Thanks in advance,

GHEN

Most definitely a thing! Old and brittle cast iron, heat-cycled thousands of times, is prone to cracking. Doesn't matter if it's on a Porsche, Toyota, or Chevy.

Definitely a thing... more than half of the tubular manifolds I salvaged from 944s leaked.

Hmm, my factory cast headers look very beefy (and I had them ceramic coated).

High mileage, and no sign of cracking. Missing exhaust hangars and leaks might contribute to these failures.

My understanding is that the cast headers are fairly durable but the later welded tubing version are rather fragile, at least at this point in their 30+ year old lives. My 87 924S came with a seized, toasted engine and the tubular design; they’re nice looking things but mine were cracked in a couple of places. The replacement motor I bought had cast manifolds (reminded me of 4-cyl Alfa items), and that’s what I’m sticking with.

John

Thanks to both of you.

I wonder if the ceramic coating helps avoid cracking? I’m certain it helps with heat management.

GHEN

Hi John,

How might one tell the difference? Can I assume the cast headers have no seam?

GHEN

GHEN,

tubular, later model, said to be worth 5BHP (gurus: true?), nice looking but fragile:


... and earlier style, somewhat less sexy but more reliable:


John

These are the original exhaust manifolds from my car ('87 NA coupe).
I THINK they are cast.

http://forums.pelicanparts.com/uploa...1617996007.JPG

These are what I have in the car now, leading into an aftermarket cat, then a factory muffler.

http://forums.pelicanparts.com/uploa...1617996007.JPG

I need opinions here. Do I stick with what I have, or is there any advantage to sending the originals off to Jet Hot to have them coated, then put them back on the car?

This is a street car, nothing more.

Thanks,

GHEN

GHEN

Stay with the cast iron manifolds. My first 944 (83 with cast iron manifolds), had over 120K track miles on it with cast iron and they were as good as new the day I sold it after 30 years (long story due to divorce.)

Unless you drop them off a cliff or hit them with a jack hammer, they will survive intact.

And the cast pieces look dead sexy with black ceramic.

I believe this was covered in an old post.
From my experience, the tubular 1-4 pipe is the issue. The older ones had no expansion bellows on them. ( Like the one on my 86 944). They all, or most, seem to crack at the Y joint from thermal expansion of the aluminum engine block. The 1-4 seems to fail a lot more often than the 2-3 pipe. I would guess because of the length. I searched high and low for a replacement, but as was mentioned, most are cracked and leaking. You can try welding it, but that would involve removing the reinforcing piece that is covering the joint and welding it back on again. From experience, it will fail again. I haven't had any experience with the cast iron units, but from what I see, they don't seem to fail as often, BUT, try to find a set......
I finally bit the bullet and sprung for a set of Billy Boat headers.
They fit perfect. Bolts up to existing exhaust without any mods.
Nice thing is, the 1-4 Comes in 2 pieces with a sexy slip joint to deal with the expansion.
The 2 piece pipe also makes installation a breeze without jacking the engine or dismantling everything. I've had them on for 2 years without an issue.
Sorry if I sound like an ad for Billy Boat. I just have had good luck so far.
They don't come cheap though.
Just my 2 cents.

Oh yea,
I left mine raw stainless, no coating.
They have developed a pleasant "Bluing" over time

The cast manifold seems like a pretty decent design to me. Does a header really make that much difference?

Would anyone kindly confirm from the photo I posted that my headers are indeed cast?

Yes, definitely cast iron.

Yup...those are indeed cast iron.
(edit - apologies George, you posted just before me)

Have heard that they don't breathe quite as well as the tubulars...but from what I understand any differences are very minor.

Had my cracked tubulars welded...then ran them for 5K miles prior to dropping the engine - have now re-installed them but am thinking about switching out with cast iron units (a friend is holding some for me) prior to re-installing engine.

This is the later 944 Turbo headers. They have a built-in bellows to allow for the expansion but they still end up leaking.

https://www.dragtimes.com/parts/Porsche-944-Turbo-Headers-Exhaust-Manifold-Pipes_164305870426.html

I have an S2... tubular manifold, 3 bolt flanges and incompatible with the other 944 models (cant switch to cast).

My 1-4 pipe is cracked at the #1 cylinder right at the head flange (the existing weld is cracked). I bought another 1-4 pipe on ebay, also cracked in exact same spot (but not as bad). Seems almost all used 1-4 S and S2 manifolds are cracked in this same spot.

Welding requires rare 347 stainless filler rod and need to be tig welded - many welders dont carry 347 filler. I am considering buying a welder and fixing it myself (will need lots of practice first)...

Anyone else with an S or S2 had to deal with cracked manifolds and what solution did you ultimately come up with (besides the $900 sfr header)?

Tuned headers make a big difference, they add the power, sound great. Only 1 down side, the cylinder head flange bolts need constant attention. There are some locking header bolts out there, but you have to match em up, hot rod shops sell em.