Well I remember reading on here before that the difference between a cast drag or rev-hard style manifold vs. a tubular Full Race style is the manner in which they spin the turbine. The cast style using the thermal energy and the tubular using the flow of the exhaust gasses. I was thinking about it in class today and I was wondering if anyone could explain more in depth about how the cast manifolds use the thermal energy rather than flow if this is the case?
Thanks,
Craig

 

They all use the same energy, it's just that tubular are more efficient at delivering it to the turbine. Ideally in a tubular the gases flow smoother and so less pressure and heat is lost....which means more makes it to the turbine. Tubulars have their share of problems, however. For example, they're not considered as strong...

 

Ok, so if they are both using heat and flow, is there any way to explain how the heat is applied to moving the turbine...in thermodynamic terms even?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VanHonda &raquo;</TD></TR><TR><TD CLASS="quote">...in thermodynamic terms even?</TD></TR></TABLE>The turbine uses the energy of the exhaust. That includes heat & pressure & momentum. The turbine extracts energy from the exhaust as it comes out from the head. Turbo vs. non-turbo exhaust, either way the exhaust comes out of the head under pressure. In a non-turbo engine that pressure is wasted as sound & heat.

People say the turbo uses the heat of the exhaust but it's not that simple. It only sorta makes sense when you think about the non-turbo exhaust would have been hotter. But really it changes both the intake & exhaust sides of the thermodynamic cycle. It's not really an Otto cycle any more, it's a compound cycle.

Manifolds?? The air doesn't care too much how they're made. Smoother or rougher surface, that's a trade-off with flow resistance & turbulence intensity. Heat transfer to/from the manifold... trade-offs there too. Then you have to figure corrosion & durability differences between the different kinds.

 

Good reply, thanks

 

tubular manifolds especially equal lenghts smooth out the air flow of the hot expanding gasses without restrictions, obstactles (sharp *** curves and such) or anything to obstruct the flow. the hot flowing gasses build up a good amount of velocity in which the turbo harnesses as energy to move the compressor blades

Cast maniolds usually have really short tubes with all sorts obstructions..plus when casting some times they are some sharp edges left on the inside..

this is just my theory

 

I'm thinking more into the heat transfer side of things...Is it a sort of Convection force or something similar to this?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VanHonda &raquo;</TD></TR><TR><TD CLASS="quote">I'm thinking more into the heat transfer side of things...Is it a sort of Convection force or something similar to this?</TD></TR></TABLE>
to cure heat transfer with equi manis. heat wrap it. sorry to lose the bling factor, but better for heat loss and gas velocity.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VanHonda &raquo;</TD></TR><TR><TD CLASS="quote">... a sort of Convection force ...</TD></TR></TABLE>What does that mean??

Heat loss IS energy loss, so wrapping would probably make it better. But the gas residence time is pretty small, so it might not make much difference. And wrapping would raise the tube wall temperature so the manifold won't last as long?

The rough surface of a casting would have more flow resistance, but the thin wall of a tube has less material for corrosion. That's one trade-off...

How about the flow directed at the turbine? A smaller tube would trade pressure for velocity, like a nozzle. Is one type or the other made like that? If so, that's not really the same as 'cast vs. tube'.

 

Well a convection force would be the heat naturally moving to a cooler area, this could also be partially a radiant force, but since the air would be a moving fluid a convection force would apply as well. But since the cast manifold retains more heat, and is closer to the source of heat, maybe the air moving to the cooler temperature of the turbine would be a greater force relative to a tubular manifold, where the tubular manifold is more efficient in directing the flow of gasses.
Craig

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by VanHonda &raquo;</TD></TR><TR><TD CLASS="quote">I'm thinking more into the heat transfer side of things...Is it a sort of Convection force or something similar to this?</TD></TR></TABLE>

It's a pressure-enthalpy conversion across the turbine wheel. EGTs drop ~ 800 deg F across the turbine. I prefer to say that heat, which is load based, drives the turbo. It all boils down to velocity, in a manner of speaking, but without the heat to force gas expansion across the turbine, you wouldn't have the force required to spool a turbo.

While I'll agree that there is a certain power/spool gain associated with tubular manifolds, it is minimal and only noticed when you have a high power drag car, since it is mostly flow related.

While I agree that you have more velocity, it is heat I'd be mostly worried about, and with all the surface area of a tubular manifold + 20 lbs of thick walled schedule 40 (Full-Race "style" manifold) I'd say the thing operates as one big giant heat sink. Enough to offset most of the gains that increased flow would give you, right up until you're dealing with enough power (drag car) to be able to heat soak the manifold with impunity.

For a street car, run whatever's cheap and strong. There's only so much power you can put to the ground in a turbo Honda, and a regular log manifold can do that. For a nice 500+ whp drag monster, grab a Full-Race manifold. If you want to have your cake and eat it, too, you can probably find a thin-walled short runner 321 SS tubular manifold that would give you flow and not act as a heat sink. hint hint.

 

Thanks, that is what I was looking for.