Cast exhaust manifold vs. fabricated.

[Risk10k]

I've been informed that cast iron manifolds are nasty and too be avoided, but I'd like a little more information on why?


Cheers.

[Alt_F4]

Nothing wrong with cast iron manifolds, but some factory ones have rubbish flow, while others flow well ie RB26 ex. manifolds.

On the other hand, you often hear of stainless manifolds cracking, especially cheap china spec ones.

[magic1]

http://www.relationship-economy.com/wp-content/uploads/2009/01/thriving_on_vague_objectives_cover.jpg

[Lonewolf]

cast iron is about the best material you can use for an exhaust manifold, as its resistant to cracking and keeps heat in well.
As mentioned, flow can be lacking a bit with some factory designs though.

[kurbn]

A Stove pipe manifold is the way to go. Majority of Cast Iron manifolds crack.

In the past I have found cheap chinese stainless dump pipes and manifolds tend to flex at the flange and can cause exhaust leaks, you end up having to tension them up all the time

[Fukushima]

the new hks sr20 highmount cast manifold is baller

[AGIT8D]

what about that steam pipe shit? :)

[Marti]

cast manifolds are geneally the best but as said above only manufactured cars have them as they are quite hard to make as a one off, they are strong and resist heat quite well, but having said that if you get something like steam pipe(being easy use, my little brother just made his own steam pipe manifold and it looks awsome ) you can create a manifold that not only looks good and can be ceramic coated to reduce heat, it will also flow very well. a good example would be the 6 boost manifolds

[mitchy]

A Stove pipe manifold is the way to go. Majority of Cast Iron manifolds crack.

In the past I have found cheap chinese stainless dump pipes and manifolds tend to flex at the flange and can cause exhaust leaks, you end up having to tension them up all the time

none of the three ~12-15 year old cast iron RB25 manifold's i've had have cracked? :confused:

[AGIT8D]

none of the three ~12-15 year old cast iron RB25 manifold's i've had have cracked? :confused:

Have you just been interchanging them on your 31? It might be because the car hasn't been driven :D

[Marti]

my s13 copped a beating for 2 years when it had a standard manifold and never cracked

[mitchy]

Have you just been interchanging them on your 31? It might be because the car hasn't been driven :D

lol cockhead. 3 different cars... the other 2 got daily driven. :p
snapped exhaust studs cause of the cast iron manifold expanding along the length of the head, but never an actual manifold issue.

[duste]

My turbo's exhaust housing cracked incredibly bad whilst my stocko cast manifold has no cracks whatsoever, but that's not to say I haven't heard of them cracking...

Personally, I'd prefer steam-pipe, but thick-wall staino gives just as good result with a good finish (ceramic coated steam-pipe has just as good of a finish mind you). The problem with staino is that the market is plagued with thin-walled Chinese rip-offs that frequently crack and this gives everyone the perspective that all stainless steel manifolds will do the same.

[kurbn]

none of the three ~12-15 year old cast iron RB25 manifold's i've had have cracked? :confused:

thats why I said Majority :P None of my 20 manifolds have cracked either

Must be a Nissan thing

[Lump]

+1 to infamoust & lonewolf's replies.
ive never heard of cast iron manifolds cracking but i did break one clean off when an engine mount broke :P

[kurbn]

Falcon 6's crack, Comodore 6's crack, few suzuki's crack, corolla manifolds crack, jeep cherokee manifolds crack, thats just from what I have seen a few times, im sure there are more out there that have this problem

all these are cast.. I blame the heat shrouds they put on them but what else are you going to do to keep the heat in.. loose loose situation

[Lump]

ive never owned any of those but when/if my territory manifold cracks i might agree with you :)

[Mad_Aussie]

My turbo's exhaust housing cracked incredibly bad whilst my stocko cast manifold has no cracks whatsoever, but that's not to say I haven't heard of them cracking...

I cracked a manifold on my old B6T, and also cracked the stock cast dump (due in part to dropping it)... But it does depend on how the thing has been treated, I think the manifold may have been over tightened due to the cracks forming from and around the drilled holes. CA20 pintara also had a cracked manifold.

Have seen a few HKS cast manifolds, would probably choose one over a stainless "octopus with a leg"

[Tocchi]

falcon exhaust manifolds dont crack, that ive seen.
its the turbo exhaust housing - due to inferior quality rear housings used in the rest of the garrett rear housings, only revised in FGs (have higher nickel content to reduce cracking)

[duste]

I cracked a manifold on my old B6T, and also cracked the stock cast dump (due in part to dropping it)... But it does depend on how the thing has been treated, I think the manifold may have been over tightened due to the cracks forming from and around the drilled holes. CA20 pintara also had a cracked manifold.

Have seen a few HKS cast manifolds, would probably choose one over a stainless "octopus with a leg"

Yup it's mainly the B6T manifolds that I've heard of cracking actually.

[adzmerc]

my factory cast iron manifold cracked on my not so old sr20det blacktop

[Lump]

anyhoo cast iron manis cope much better with thermal stress than steel fabricated - in general.

[lysdexia]

in the case of rb20/25/30, the factory manfolds are actually twin scroll too (although the original turbos are open collectors still)

[schnoods]

Repaired a few cast manifolds before /csb.


Most often than not, the heat is a part player but not the cause, generally vibration from an insecure exhaust. Another is lack of any play in expansion joints/points and a nasty vibration or jolt can cause a crack. Or going over a speed hump and exhaust scrapes which pulls dump pipe, turbo and manifold will cause a crack and breakage too.

Doesnt take much to fix them too, anyone with access to a $100 dollar stick welder, an oven and some decent welding rods suited for the job can take a hour to do. Cast iron rods are needed but are dear ($200 a kg ~ $7 a rod), but can be done with a hardfacing rod (cobalarc austex is the best) or a 304/316 stainless rod will do the job well too.

Need to preheat manifold in oven between 70-100 degrees, grind crack out so you can get decent penetration (but not too much so you blow a hole), use 2-3 runs to seal crack, peen the weld after each run (to prevent more cracking from extra heat and cooling from weld). After job is done, put back into hot oven and switch off so it slow cools.