Head Inlet Port Shape

[Mandic 0]

Porsche, Nissan, Toyota and Honda also have oval ports. Now this is probably down to smoother transition going to valve openings like jas-E says, but having oval inlet tract all up to trumpet bellmouth entry is another thing. And according to that flow research I read a bad one as it has the worst flow.

 

I know Honda tuners make manifolds which have round bellmouth entry and then go circular at head inlet.

 

Cheers

 

Ziga

Edited January 8, 2008 by Mandic

[jas-E 1]

Porsche, Nissan, Toyota and Honda also have oval ports. Now this is probably down to smoother transition going to valve openings like jas-E says, but having oval inlet tract all up to trumpet bellmouth entry is another thing.

 

That is true. Inlet manifold design is totally different to port design. And a round port will be better than an oval one. In a race engine, the cross sectional area changes from a much bigger diameter at the air entry side with the trumpet edges folding outwards,which blends into the port size at the other end.

 

The reductionin cross sectional area increases the velocity of the charge going into the engine, which becomes more apparent as the engine speed increases.

[Batfink 201]

cool! i think i'm beginning to understand this all.

 

I've drawn another diagram to explain the process - if the ports should be a perfect circle for optimum performance then it seems almost logical...

 

 

which seems to match

 

 

Rich I think the plastic "gasket" is only there to separate the hot engineblock from the induction, to maybe stop conduction of heat. I don't know if they had the carbon airboxes when these were in use.. Shape is virtually the same as the manifold

Edited January 8, 2008 by Batfink

[Sandy 191]

Yes and there has to be a transition at some point. The progression of sectional area, and the corresponding gas speed and pressure should in theory be steady, but a sharp change in shape can cause turbulence which affects the effective section of the port, a good example of this is tightly radiused inlet manifolds or trumpets. The wave propagation is also likely to be affected. Flat sections in the port increase the boundary layer relative to the sectional area, so they have to be compensated for in their size, which is probably why the section in the XU 16v head between the manifold face and split is bigger than above and below it. I would wager too that this section reduces mixing efficiency to some extent. It's obviously not severe though, because there any many heads with that transition intact that produce good results and flexibility.

[Mandic 0]

That is true. Inlet manifold design is totally different to port design. And a round port will be better than an oval one. In a race engine, the cross sectional area changes from a much bigger diameter at the air entry side with the trumpet edges folding outwards,which blends into the port size at the other end.

 

The reductionin cross sectional area increases the velocity of the charge going into the engine, which becomes more apparent as the engine speed increases.

 

True, but it shouldnt be wider than cca 12-14° ovral all, or 6-7° centerline.

 

What is also important is pressure drop or actual pressure area at the beginning of trumpet inlet, as circular cross sectional area and radiused bellmouth also contribute to good fuel atomisation if one has injector positioned right at trumpet inlet,

 

ok, back to the topic...port shape...

 

Cheers

 

Ziga

[brianthemagical 1]

my 2 cents. round port/runner will flow better than any other shape. i think i'm right in thinking that touring cars can have fettled heads, hence the increase in power and rev limit. more power equals more air, need a bigger port. more than likely machined by hand, not cast or automated as a production head. oval ports would creat less of a transition to valves if enlarged than round ports. boddies are still rounder than the manifold, so it's just extending the transition. on the idea of inlet turbulence, i doubt many pro engine, wether std or fettled would create turbulance as it would massivly effect the flow, therefore the ports are gradually radiused to eliminated any sharp edges and therefore turbulence.