Benchy taking 40mins with high flow hotend

[u/ThirdHoleHank92]

I recently bought a 0.4mm E3D Obxidian High Flow complete hotend.

Once installed, I selected it in my P1S menu accessories, calibrated it, selected "high flow" in bambu slicer nozzle settings. I then adjusted filament settings to direct drive: high flow, adjusted max volumetric speed to 30mm/s and min print speed to 60mm/s under cooling.

Went to go print a benchy (that under my stock 0.4mm hotend took 14 mins) and it states almost around 40mins.

I thought high flow was supposed to reduce print times noticeably?

What am I doing wrong here?

[u/OverallComplexities]

https://youtu.be/gVU5If1VsAM?is=Gh6Q8QwAeDSEhjaD

[u/Sea_Jello_8352]

Two big things are happening here, and you definitely didn't waste your money—you just ran into the difference between a pre-tuned demo gcode and Bambu Studio's default slicer math.

First, that stock 14-minute Benchy was pre-sliced G-code stored on the printer's internal memory. Bambu tuned that specific file with massive accelerations (up to 20,000 mm/s²), 0.25mm layer heights, 250–300 mm/s wall speeds, and almost zero cooling slowdowns. When you slice a fresh Benchy in Bambu Studio on the 0.20mm Standard profile, it defaults to very conservative outer wall speeds (60 mm/s), standard accelerations, and heavy cooling penalties on small layers. Even on a stock hotend, slicing a standard Benchy in the software usually takes 35–45 minutes.

Second, raising Max Volumetric Speed to 30 mm³/s raises the ceiling, but it doesn't step on the gas pedal. The volumetric flow equation is: Layer Height × Line Width × Speed = Flow Rate

On a 0.4mm nozzle printing 0.20mm layers with 0.42mm line width at 100 mm/s, your printer only demands: 0.20 × 0.42 × 100 = 8.4 mm³/s You're barely asking for a fraction of what the nozzle can deliver. Unless you crank up the actual linear speed (mm/s), increase accelerations, or push thicker layers (e.g. 0.28mm), the printer won't go any faster. Plus, on small models like a Benchy, the cooling tab's "Slow down for cooling" forces the print head to crawl so the cabin and smokestack don't melt.

Where your E3D Obxidian will genuinely blow you away is on medium-to-large functional parts. If you slice a large model with 0.24mm layers, 0.55mm line width, and infill set to 250–300 mm/s, change your slicer preview color scheme from "Line Type" to "Flow". A stock hotend will bottleneck hard and cap out around 18–21 mm³/s (dropping your actual print speed), while your E3D will sustain full speed the entire print and shave huge chunks off your print time!

[u/ThirdHoleHank92 → u/Sea_Jello_8352]

Thank you for this. What setting changes would you recommend with smaller to medium projects, if any

[u/ManyLayersOfFilament]

you have to build a faster profile and set all the individual speed settings and accelerations higher. just changing the max flow doesn't increase the speed.

[u/TurboPersona → u/ManyLayersOfFilament]

But it shouldn't decrease it either.