Silly Question Turbo Manifolds Log vs pretty Tubes with a collector

[RobertFontaine]

I've been doing some reading. Dangerous for me.
A log manifold spools faster than a tubular manifold (shorter runner length/volume).

A log manifold in cast iron is dirt cheap and welding up one in steel is dead easy compared to the artwork I have seen for many years. I understand the desire for equal-length tubular manifolds for naturally aspirated cars... I don't understand the physics but I accept you get better power under the curve. But when you are under full boost by 3k rpm with a modern turbo are we getting anything other than aesthetics from our beautiful tubular manifolds filling the engine compartment?

The NLA steedspeed cast iron or the spa and chinesium knockoff seems to get the job done.

thanks for the edumacation.
rf

[pbonsalb]

Personally, I don’t think a snake’s nest of tubes is necessary. I also don’t think you will get full boost at 3000 rpm unless you are running a small turbo and race gas or E85. I have not kept up with the manifold options these days, but a compact twinscroll would be my first choice. I use the steedspeed twinscroll. It is good but has a poorly located wastegate port.

[NOTORIOUS VR]

The main purpose for a tubular manifold is placement options, weight (lighter than most cast manis) and sound/port/length tuning and the ability to use exotic materials (not really relevant for us but more so in motorsport with motorsport budgets).

Unfortunately most tubular manifolds don't live up to the abuse especially when many fabricators these days go for internet points instead of actual engineering and best welding practices. So the chances of a tubular breaking is a lot higher than a well cast part.

[Sio2crew]

The last minute or so of this video compares sound on different manifolds. (335) This was the first time I saw a video where I could actually hear the differences.


https://youtu.be/DArvuzDltoo?si=uypZwEr4vxf_FERw

Tubular sounds amazing even if it's a moot point. Rally road offers a rsi style manifold with stepped runners. Stepped runners can make a car sound more like a f1. My manifold looks just like the rally road one minus the stepped connections. I did not , nor would I pick a manifold based on sound. Sound, similar to looks, is secondary at best imo.

Rally road version..
Screenshot_20240803-014335.jpg

Fwiw, The t3 and t4 flange on the rsi style manifolds, it won't fit a t3 gasket or a t4. T3, leaves a lip that will catch air as it enters the turbo. T3 will also leave the metal crush seal exposed on two sides. The t4 won't fit either, it leaves a lip that faces the other way (area gets larger as it enters the t4 turbine.) I think that stepped lip is part of the rsi sound. I can tell you I was pissed when I first mocked up my new t3 and it fit terrible. Otis thought I was crazy to have a issue with the t3 gasket not sealing. His manifolds, "They are all like that" was supposed to make it ok somehow.

I ordered a t4 housing just so it would seal the metal crush gasket/ not interrupt the air flow as it enters the scroll. Basicly the opening is t3 on two sides, t4 on the other two sides so neither fits correctly. (T4 at least seals the crush gasket where the ridge is, even tho the manifold opening is smaller than a t4 opening . A t3 housing leaves the metal gasket crush ridge exposed, uncrushed on two sides. )


I wish I had twin scroll. That said, my top mount rsi manifold does sounds amazing combined with my home made exhaust. (Dynomax mufflers)

[RobertFontaine]

Honestly sound is completely irrelevant to me.
I am indifferent to top-mount turbos and what sound an exhaust manifold might make.
It is not a fashion statement and I won't be parking with my hood open for someone to look at.

My interest is in fitment, performance, and cost.

[Sio2crew]

I edited my post, to explain the issue with the t3 or t4 dual flange on rsi style. (Fitment issue)

You replied faster than my edit.

I don't have the pictures of my mock up. Here is a quick diagram with the manifold in green. A t3 gasket laid on in purple. You can see where the t3 gasket won't seal the metal ridge, and blocks air. Diagram is not perfect, but it is easier to understand.

PXL_20240803_062008443.jpg

[pbonsalb]

I’d look at this for a bottom mount twinscroll T3:
https://www.thekangaroosteam.com/sho...turbo-manifold

And this for a top mount twinscroll T3:
https://spaturbousa.com/products/bmw...turbo-manifold

No personal experience with either so I can’t comment on wastegate port location or performance, but I think either would be more than fine for the OP’s 500 rwhp goals. I would not bother with fancier stuff like tubular T4 manifolds until the power goals are closer to the 700 rwhp or beyond range.

Before buying the bottom mount, I would confirm that it locates a midsize T3 turbo high enough for a gravity drain. Simple is good and scavenge pumps add complexity, cost and potential for leaks. Also that retains the AC can be done — I am pretty certain it can with with over the subframe and just under the manifold piping or under the subframe piping. I use under subframe piping, which can be all round or transition to oval and back to round. I have helped replace melted couplers in over subframe piping and piping usually is a little smaller.

For the top mount, gravity drain is obviously no problem, but if retaining AC is required, I would confirm that it can be done without much hassle or compromise. Compromise might be a tiny puller fan or no puller fan, a custom coolant reservoir, no space for a proper air filter, etc.

[Sio2crew]

Do you have to make an adapter tube with a divider inside it for the kangaroo manifold? Is there a name for that triangle flange, and or a wastegate that fits it? If you adapt a open pipe on that flange, it will let the two scrolls mix the pulses. Making it perform similar to an open scroll design.

Screenshot_20240805-093547.jpg



That was the main deciding factor why I chose the rsi over the kangaroo top mount. Kangaroo was also sold from Australia at that time/ no reviews. (Rsi works with a.c. too)

Hindsight is 20/20 , I now know how much of a difference divided manifolds can make.

Top mount link.

https://www.thekangaroosteam.com/sho...turbo-manifold

[pbonsalb]

Ideally, I would divide the wastegate pipe. I remember Mike Radowski at Maximum Psi making a divided wastegate pipe. Probable a pain in the rear but doable. There was a thread on just welding a wastegate flange to a divided turbine housing and I said the same thing and others disagreed and thought dividing the flange stub to the wastegate was unnecessary. I am not an engineer and don’t know how much it matters.

[seagreen323i]

OK, so I have some thoughts here. I don't post here often, but I've got plenty of experience with FI builds.

Cast manifolds are going to do two things very well, not crack in 2 years, and help keep heat at bay.

Tubular manifolds have a tendency to crack, especially if the turbo isn't braced in any way, and if you brace the turbo you are going to have issues with expansion/contraction causing stress cracks on the Tubular manifold anyways.

Cast is a whole lot stronger than Tubular.

Getting down to the specific metallurgy cast is softer than stainless. Cast manifolds are less susceptible to engine harmonics, causing cracks. Tubular manifolds are made of a much harder material that can't "absorb" the frequency as much and is typically much much thinner. Less deflection + high vibration environment = cracking

Tubular headers typically have better exhaust velocity down low. Much like an intake manifold narrow + long = low rpm air velocity. However, in the end, it is a wash. Because cast manifolds typically place the turbocharger closer to the ports. You also save a good chunk of weight with tubular, depending on how complicated the tubular manifold is.

If you can't spool a turbo by 3000 rpm, you have the wrong turbo....

I'm running a 1.9 liter BP engine with a 58mm and seeing 3psi at 2200 rpm with full 21psi by 2800.....

I feather in the boost with the electronic boost controller to maintain traction and to not hammer the hell out of the rods with 21psi at such a low rpm.

Borg warner efr turbos are black magic.

Moral of the story, run cast.




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[TheJuggernaut]

Unless you're talking about ferritic stainless alloys, stainless is not harder than typical gray cast iron. Austenitic alloys like the 304 everyone uses, are in fact quite spongy which makes them such a pain to machine. The reason they crack is that they're the wrong material for the job because at the EGTs seen by turbo manifolds, 304 precipitates carbon, especially at the weld HAZ. So they're all just a matter of time. Cast iron manifolds will crack from heat cycles due to being brittle. At the temps seen by these manifolds, they should be made out of 321 with 347 filler (well... or Inconel if you have no budget cap).

[GG///M3]

I’d look at this for a bottom mount twinscroll T3:
https://www.thekangaroosteam.com/sho...turbo-manifold

And this for a top mount twinscroll T3:
https://spaturbousa.com/products/bmw...turbo-manifold

No personal experience with either so I can’t comment on wastegate port location or performance, but I think either would be more than fine for the OP’s 500 rwhp goals. I would not bother with fancier stuff like tubular T4 manifolds until the power goals are closer to the 700 rwhp or beyond range.

Before buying the bottom mount, I would confirm that it locates a midsize T3 turbo high enough for a gravity drain. Simple is good and scavenge pumps add complexity, cost and potential for leaks. Also that retains the AC can be done — I am pretty certain it can with with over the subframe and just under the manifold piping or under the subframe piping. I use under subframe piping, which can be all round or transition to oval and back to round. I have helped replace melted couplers in over subframe piping and piping usually is a little smaller.

For the top mount, gravity drain is obviously no problem, but if retaining AC is required, I would confirm that it can be done without much hassle or compromise. Compromise might be a tiny puller fan or no puller fan, a custom coolant reservoir, no space for a proper air filter, etc.

The first manifold looks like the spa s54 manifold . Good to see they made it useable for m50 based engines.


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