Water Atomization & Smooth Manifold Walls

[NAnderson]

This question kind of relates back to the days when carburetors and "wet flow" intake manifolds (fuel and air mixture flowed through the manifold, not just air) were the norm. So, all you "old timers" chime in. :wink:

I'm thinking of having an intake manifold Extrude Honed and am concerned about the atomized water falling out of suspension as it travels through the manifold. Most race shops that deal solely with carburetors highly recommend NOT Extrude Honing the intake manifold as the roughness of the casting causes a desirable disruption in the airflow and prevents the fuel from puddling on the runner walls. Should I be concerned at all about this with water/methanol injection and smooth runner walls in the intake manifold?

BTW, this is in a port-injection setup with each nozzle ~5" (12.7 cm) away from the cylinder head. My one saving grace may be that this is a three-piece manifold and I could have the two pieces of it that flow only air Extrude Honed, and leave the final piece that the nozzles are in rough, as-cast.

Comments or thoughts?

[Richard L]

This is getting very technical.

As far as water injection is concern, it rarely actives at low boost or no boost. Under boost, I believe the air flow is sufficiently ample to dry-off any water droplet clinging onto the internal wall.

[NAnderson]

Originally Posted by Richard L

As far as water injection is concern, it rarely actives at low boost or no boost. Under boost, I believe the air flow is sufficiently ample to dry-off any water droplet clinging onto the internal wall.

Good point. Hadn't really thought of that. ops:

Airflow through the manifold while under boost should be more than adequate to keep the water/methanol from puddling on the runner walls and falling out of suspension. Also, being that it's a port-injection setup with the nozzles relatively close to the cylinder head ports this shouldn't really be a problem.

[hotrod]

The other thing you can do is get the manifold extrude honed then take an abrasive roll (about 50 grit) and just lightly rough up the last few inches of the runner after the water injection point. That is where the water wetting would be an issue and this sort of surface roughning is frequently used by professional porters to solve that problem.

Larry

[NAnderson]

Great idea, hadn't thought of that! Looks like I'll have to break out the Dremel once the manifold is back from Extrude Hone.

[ride5000]

i wonder if a tighter-patterned nozzle, directed right at the throat of the head port, would be beneficial to keep media off the walls? a la your typical fuel injector spray pattern with a low-degree cone.

although things are very fast and furious in this area with very high charge speeds, so i really doubt there's going to be much opportunity for wall adhesion.