Trying to post again.

[Tony]

There is no fixed number.
Sonic velocity varies with temperature and pressure.
Match 1 is not a fixed velocity, with aircraft it varies with altitude.
In an exhaust port or rocket motor, I have absolutely no idea.

[storm]

I always thought Mach 1 was 1200 (or so) kmh

[Tony]

Yup,
The speed of sound is 343.2 metres per second (1,126 ft/s; 768 mph; 667 kn), or a kilometre in 2.914 s or a mile in 4.689 s.
https://en.wikipedia.org/wiki/Speed_of_sound

[ronm]

Faster than my Chevy! Lol

[ronm]

Faster than my Chevy! Lol

[Adrian]

Here's an excerpt from an excellent thread on the speedtalk forum by Larry of Maxracing who does the Pipemax software. a max 300 FPS seems to be a number that crops up in a few places.

>>>>>>>>>>>>>>>>>>>>
you check Velocity with 180 deg Pitot Probe
you can look at the Velocity Pressure
or you can convert the Velocity Pressure into Feet Per Second and look at FPS if you rather .

FPS = ( Pitot_Press ^ .5 ) * 66.2
350.3 FPS = ( 28 ^ .5 ) * 66.2

its possible to run 350 fps @28" or slightly higher and not see TQ/HP losses, but the overall port shape/curves have to be just about perfect
to keep mixture attached to that Shape throughout the Port

300 FPS is usually safer and will not cause a premature Choke condition in a live engine . The Curtain Area should be the Choke point .

300 FPS = 20.5" Pitot pressure when Flowtesting at 28"

240 FPS = 13.14" Pitot Press when Flow testing at 28"
is considered the "slowest" you want velocity to be,
any Velocity pressure lower or around 240 fps can start to show
TQ/HP losses at lower RPM range of the Power Curve.
This also depends on piston speed range and rod ratio,
as to how slow this can be.
At relatively low pistons speeds and larger rod ratio,
240 fps will be way too slow, and loose Torque
At higher piston speeds and/or shorter rod ratios,
240 fps will not show any Torque losses.


350 FPS on the Short Turn apex is pushing it, but i've had Cyl Heads
handle higher than 350 fps there and not loose HP/TQ, and other times had Cyl Heads that had less than 350 fps show losses.

anything around or above 400 FPS (36.5" Pitot press tested at 28")
has always shown a HP/TQ Loss in a live running Engine, depending upon overall Port Shape, around 350 fps to 400+ fps can show losses of
10 hp to 105+ hp on a V8 at approx 600 HP level.

the #041x SBC Heads that showed +105 HP Loss at 7200 RPM
had slightly over 400 fps at the pushrod area , and was much higher
than 400 fps on the Short Turn apex Floor, when Flow tested at 28"

the higher the Pitot Press is above 28" or faster than 350 fps Pitot,
and the greater that distance is away from the Valve/Curtain Area,
the more TQ/HP losses will be.

another thing that will hurt TQ/HP is to have a very hi-velocity spot or curve on one side of the port wall that is 350+ fps, then downstream velocity to be much lower in FPS velocity or if that Port wall diverges or turns too quickly with much lower velocity downstream, will cause
atleast flow separation, fuel/air separation, and Choke.

Likewise if there is too much of a pressure or velocity fps difference between an upstream point and downstream point like the Short Turn or Curtain Area, then Choke will be more severe or premature in RPM range.

the better the Short Turn shape, the better the pressure recovery in the Chamber, the straighter the overall port shape and the more constant the port cross-sectional area, the higher velocities it can handle .

Since 28" Test Pressure is the FlowBench or Flow Test Industry Standard,
you can use simple Flow conversions to scale up or down the critical Pitot Probe velocity readings.

if you flow test at 10" Test Pressure then you don't want Pitot readings higher than 10"

at any chosen Flow Test Pressure, you don't want your Pitot Probe Velocity pressure to be higher than your Flow Test Pressure

10" Test Pressure = 209.3 fps
10" Pitot Pressure = 209.3 fps

209.3 fps at 10" = 350.3 fps at 28"

60" Pitot Pressure when Flow testing at 60" Test pressure = 512.8 fps
512.8 fps at 60" = 350.3 fps at 28"

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

the thread is here:
http://speedtalk.com/forum/viewtopic.php?p=5252#p5252