P1000 Auxiliary Electrical System Build

[Eric450X]

Fluid dynamics is not one of those things I've been schooled in, but then, not much else is either. However, I do know that it isn't always straightforward and that small things, like intentionally turbulating the flow etc. can have a dramatic and sometimes unexpected effect (think dimples on a golf ball). That said, you have to give the engineers at Honda credit, even if they haven't always been right. If a 2" intake tube would work just fine and be more than adequate, why did they use 3" (or 75mm)? And when putting in a snorkel, why not drop it down to 2" for the whole run and make it that much easier to route and a "cleaner" install? Folks make changes, I'm one of them, but it's good to know that changes move things in the right direction towards better performance, utility, and or reliability. Going from 3" to 2" on the intake doesn't seem all that logical.

Fluid dynamics is also not my expertise. I can, however, explain your question about why not make it all 2". The longer the run the more the diameter affects the flow. If you make the whole system out of 2" that 2900CFM on a 1' run turns into 900CFM on a 10' run at engine operating pressures. The 3" insures adequate flow volume to the engine over the length of the intake tube run. The approximate 1' of my system should not have a negative impact on performance (flow) according to basic calculations. With that being said, we all know the real world does not always match the theoretical. That is why I plan to test and make changes if changes need to be made.

 

[Admin]

 

[Robobrainiac]

Fluid dynamics is not one of those things I've been schooled in, but then, not much else is either. However, I do know that it isn't always straightforward and that small things, like intentionally turbulating the flow etc. can have a dramatic and sometimes unexpected effect (think dimples on a golf ball). That said, you have to give the engineers at Honda credit, even if they haven't always been right. If a 2" intake tube would work just fine and be more than adequate, why did they use 3" (or 75mm)? And when putting in a snorkel, why not drop it down to 2" for the whole run and make it that much easier to route and a "cleaner" install? Folks make changes, I'm one of them, but it's good to know that changes move things in the right direction towards better performance, utility, and or reliability. Going from 3" to 2" on the intake doesn't seem all that logical.

I don't know alot either but the nitty gritty stuff is always neat. It's like why run a trans cooler thru a "hot" radiator? If you ever get board Banks put alot of cool stuff on YouTube that is informative.

 

[bumperm]

Zactly! When I was installing my "4" under seat bilge blower" I measured flow velocity with an anemometer at 35 mph. Since I was not using any ducting, with the blower pointing directly at the headers, I figured I'd remove the intake "bell" which decreases duct connections to 4" (the body of the blower being larger). I figured removing that unneeded intake restriction, and "moving" the intake away from obstructions, would improve flow, so tested again to find out how much gain. With my mod, flow velocity at the output actually dropped to 30 mph. So much for my logic.

The install post my mod.

 

[Eric450X]

Zactly! When I was installing my "4" under seat bilge blower" I measured flow velocity with an anemometer at 35 mph. Since I was not using any ducting, with the blower pointing directly at the headers, I figured I'd remove the intake "bell" which decreases duct connections to 4" (the body of the blower being larger). I figured removing that unneeded intake restriction, and "moving" the intake away from obstructions, would improve flow, so tested again to find out how much gain. With my mod, flow velocity at the output actually dropped to 30 mph. So much for my logic.

The install post my mod.
View attachment 331742

Your findings with your bilge fan may seem counter-intuitive but they match physics fluid dynamics. A reduction in cross-sectional area (diameter) of a pipe will increase flow velocity while an increase in area (diameter) will slow flow velocity. I am a Physics teacher by trade and I tell my students being wrong (having an incorrect hypothesis) is sometimes the best way to actual learn. Thanks for sharing your learning!

 

[bumperm]

Your findings with your bilge fan may seem counter-intuitive but they match physics fluid dynamics. A reduction in cross-sectional area (diameter) of a pipe will increase flow velocity while an increase in area (diameter) will slow flow velocity. I am a Physics teacher by trade and I tell my students being wrong (having an incorrect hypothesis) is sometimes the best way to actual learn. Thanks for sharing your learning!

Yes, I agree. However, I did not change the exhaust side, only the inlet side. So IF the fan was pulling in more air via the less restricted inlet, which I reasoned would be less disturbed air as well, then when it hit the reducer and 4" exit, it would speed up - - and of course it did. The fan is a ducted design with blades curved to be efficient in only one direction - all of that was left stock. Still, flow was reduced.

 

[PJon]

Yes, I agree. However, I did not change the exhaust side, only the inlet side. So IF the fan was pulling in more air via the less restricted inlet, which I reasoned would be less disturbed air as well, then when it hit the reducer and 4" exit, it would speed up - - and of course it did. The fan is a ducted design with blades curved to be efficient in only one direction - all of that was left stock. Still, flow was reduced.

Just a note of caution on mounting the bilge fans. I used to have a 4” mounted directly under the rectangular frame tube that goes across at the back of the seat. Only ran the fan when the heat started building up and the plastic deformed from the heat and stalled out the fan and blew the fuse.

 

[bumperm]

Just a note of caution on mounting the bilge fans. I used to have a 4” mounted directly under the rectangular frame tube that goes across at the back of the seat. Only ran the fan when the heat started building up and the plastic deformed from the heat and stalled out the fan and blew the fuse.

ABS plastic has a "use range" topping at 173* F, it'll begin to deform at 212*F, and a melting temperature of 392* F. You are spot on, especially with the radiant heat from those headers, with the fan off and thus not able to "protect itself", keeping distance from the heat source is important.

 

[Scoop]

Brutal honesty:

In most circles, folks often tell me I'm one of the most intelligent people they know. However, trying to follow along in this thread (the fluid dynamics bit) makes me feel like a complete idiot. 🤪

🤣🤣

 

[ODAMO]

Simple logical deduction says k and n makes it bigger so that obviously always means better .... Right



I think you are spot on and true independent calculations are always awesome! Great job.

If I remember correctly the only other "variable" would be a "quick" intake vacuum surge like from idle to wide open throttle. It can sometimes require a little "extra" oomph if that makes sense. I am not sure of the technological terms used but it's why you may often see a large "box" like structure on some filter housing or intake tubes. It may not apply to these smaller engines tho.

The bulbous box you refer to is a helmholz resonator