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Jeff9727

S30 RB25DET T4 Twin Scroll Turbo Manifold Design

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13 minutes ago, Neverdone said:

Usually you put the expansion joints just aft of the exhaust header to help mitigate vibration through the really long pipe that it's connected to.

 

Where would you put them?

Would you please give me a link to a typical arrangement?

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The euro L28et manifold has them.

 

im no expert by any means, but isolsating the left 3 cylinder and the right (splitting flange in 2), and then putting something like the burns stainless double slip joint in the lowest portion of the big “U” for each side of the manifold.

 

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I could understand using these in certain situations where the material isn't rated for such high temperature intermittent duty cycles (cast high carbon steels). Is the purpose to reduce fatigue on the welds due to thermal growth? If so, I lean towards the bellows being on the down pipe, some flex piece on the turbo air outlet flange, and reducing vibration on the engine itself through dampening. Thoughts?

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Take my opinion with a grain of salt. I’d take Tim’s advice seriously though. From my internet research most people including Tim who have used an aftermarket tubular header, experience cracking. This isn’t seen much in 4 cylinder applications, but the straight 6 is does.  I don’t know Tim, but he is one of the few who have gone down the unknown path of high horsepower L series engines and I’m sure has a wealth of experience from failure.

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Hmm I've heard of the stock cast manifold bowing so maybe there is some merit, although my current cast stainless one seems to be holding up fine.

 

I thought the concern was with thin wall manifolds? I guess it depends how thick OP went with his manifold if it would be a concern, then it may need bellows and support stays from the flange. The newer manifold styles seem to have similar dip down then come up design on the turbo honda's and they seem to get by without any bellows on thick wall tube.

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FYI, I did a test fit because I was worried about the steering column. As it turns out, I'm clearing it just fine but I'm getting close to the engine mounts (Whitehead performance). I had a small set back (unexpected expenses) and will not be able to have these fabricated for another month. But I will keep everyone posted as progress is made. 

 

Jeff

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Posted (edited)

8.png

 

A recurring problem with exhaust manifolds for this head is that as they heat up they grow longitudinally.  Since they're held captive on the head, this eventually results in warpage and/or cracked primaries.  As HuD 91gt pointed out, this is why the Euro manifolds have them (expected extended high speeds on the Autobahn).  For the manifold in this thread, a slip/expansion joint on each of the two runners running longitudinally after the 3-1 collectors and before the wastegate/turbo would help alleviate that.  I post about this pretty much every time one of these designs comes up and nobody ever listens 😜

Edited by TimZ

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I have very little exposure to RB heads so ^ his advice would be more sound.

 

I've seen even nice mazworks manifolds crack which I imagine quality would not be the culprit which points towards an expansion issue being the culprit. Adding some supports off the head flange to the turbo flange and adding some bellows or those fancy 3 way slip joints would be snazzy and show quite a bit of intelligent design.

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