Wet flow Vs dry flow results
Wet flow Vs dry flow results
(OP)
I have been reading and asking questions of people again and so far the question has remained un answered (possibly poor questions!?), hence this post. The current range of flow benches are quite advanced (and expensive) but are you able to accurately predict the effect on the wet flow (ie the flow of the intake charge) of something like flow shear at the short turn radius? given that the flow benches I have seen are all dry flow only.
I was wondering if the wet flow would react differently given the added mass of the fuel in suspension. It would seem logical that the fuel in suspension may not follow the same path as the air given the difference in mass and would this difference be more prevalent given larger droplet size in suspension?
My thinking then made me wonder if the valve shrouding that occurs due to the flow shear would then have a detrimental effect on the fuel distribution in the cylinder and then on the burn-resulting power.
I was wondering if the wet flow would react differently given the added mass of the fuel in suspension. It would seem logical that the fuel in suspension may not follow the same path as the air given the difference in mass and would this difference be more prevalent given larger droplet size in suspension?
My thinking then made me wonder if the valve shrouding that occurs due to the flow shear would then have a detrimental effect on the fuel distribution in the cylinder and then on the burn-resulting power.





RE: Wet flow Vs dry flow results
RE: Wet flow Vs dry flow results
I will be investigating new port shapes in an 8v 4cyl engine soon and will be mapping the valve shrouding due to flow shear. I will also be mapping the effect of post valve modifications on said shrouding. However I am wondering what effect on the wet flow the changes will have, given the increased mass and if that can be predicted by the dry flow results.
RE: Wet flow Vs dry flow results
RE: Wet flow Vs dry flow results
This issue is mitigated by using port fuel injection, where the last couple of inches is relatively all that matters, but many vehicles still in use, especially in performance venues, use central located carburetion systems.
When designing an intake manifold, a target RPM is selected and the manifold is optimized for that range. Wet flow systems do indeed behave differently at different airflow rates. Rich systems tend to centrifuge the fuel at short radius turns. Different tricks have been used to keep the fuel in suspension, heat, surface texture, ultrasonics, etc. Intake resonance is critical too, along with runner length, diameter, taper, radius, material, etc.
This is the leading reason for the shift from carburetors to central fuel injection, then to port fuel injection, then to sequential port fuel injection, to minimize the amount of fuel in transit. This has the effect of making all cylinders behave as if they were the same cylinder since the relative plenum length of air is not as critical since fuel is not present.
Franz
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RE: Wet flow Vs dry flow results
I believe the question Neil is asking is independent of whether the engine is carbureted or port injected. If anything it might be worse when injected, as the fuel mixture is not as homogeneous as when carbureted.
We've sprayed aerosol Dykem into a flowing port, it will give you a visible trace of where the fuel is going. Not a very exact science obviously, but the information is better than nothing. Also watch the flammables around a flow bench as the motors have brushes with lots of spark activity.
Most people evaluate the wet flow performance by reading the chambers after the dyno pulls. You want to see even coloration of the cylinder. A clean streak means raw fuel is washing the cylinder in that area.
In general a tall smooth transition short side turn will give the best wet flow results.
RE: Wet flow Vs dry flow results
This may be of interest to you.
An interesting point is made about what was once considered to be fuel wash & clean spots on the piston crowns.
www.rehermorrison.com/techTalk/40.htm
RE: Wet flow Vs dry flow results
However I am interested in investigating the port effeciency issue and reporting on my results (instead of just measuring CFM at peak lift) for a small magazine as a brief investigation in to basic theory. I was concerned that the changes in results in dry flow would not reflect the changes for wet flow and naturally this needs to be noted in the article.
The plan was to investigate 4 different port shapes in theory and test, then valve shapes in each port and then post valve modifications.
Willeng, thanks very much for the article, it was very interesting. I will follow up the author and ask a few questions.