flowbench
flowbench
(OP)
why is the industry standard 28in/hg?
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RE: flowbench
RE: flowbench
Reidh
RE: flowbench
RE: flowbench
RE: flowbench
RE: flowbench
RE: flowbench
RE: flowbench
Reidh
RE: flowbench
RE: flowbench
RE: flowbench
Most experts seem to agree that Mach .55-.61 (~700 fps)is the maximum velocity you can achieve before a "choke" condition occurs in the port and hp losses begin to occur.
With proper inertia wave tuning, you can achieve ~125-127% volumetric efficiency under the 28" H2O condition. Many people feel that ~130% VE is the max. possible with a naturally aspirated engine.
If you wanted to perform a "real world" test of your NASCAR vechile would you test at a track speed of 7" H2O (~120 mph) or 28" H2O (~250 mph)?
28" H2O more closely simulates the real world conditions of a race engine (intake port only). In addition to just getting the "flow numbers", head porters us a pitot tube to create a map the port velocities and search for excessive high and low velocities and make corrections as necessary.
Some head porters us 36" H2O to try and identify marginal areas (usually the short turn radius) and make corrections based on 36" H2O, but correct the flow numbers back to 28" H2O to communicate with peers.
RE: flowbench
What has track speed got to do with airspeed in the port
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RE: flowbench
If you set up your race car to turn corners at 120 mph it might not perform the same during the race when it has to turn the corner at 250 mph. So, flow the head in as close to real world conditions as possible.
On the exhaust side, when the valve begins to open, the differential pressure is ~500 psi (~10000" H2O, supersonic). It's hard to find a flow bench to duplicate those conditions. Flowing at 28" H2O can fool you into thinking things are OK, so flow the exhaust port at the max. pressure differential (especially at low lifts) then convert the flow to 28" H2O.
RE: flowbench
Ford Dearborn USA measure to 3 different pressure drops.
10 inches of water, 20 inches of water and 5 inches of Mercury or about 68 inches of water.
I've worked with/for a few OEMs and none I know work with 28 inches of water. It must be the after market.
The 68 inches of water is deemed to be in the ball park of the conditions of the exhaust port during blow down.
"With proper inertia wave tuning, you can achieve ~125-127% volumetric efficiency under the 28" H2O condition. Many people feel that ~130% VE is the max. possible with a naturally aspirated engine."
I'm not sure where these VE numbers are coming from.
Are you referencing ambient or pressure/temp conditions in the inlet manifold? I always reference ambient as referencing inlet manifold (EVEN for Boosted engines) means you cant do performance development work on anything upstream of the inlet manifold.
A Honda S2000 makes about 120% VE, an BMW M3 S54 may reach just under 110% VE. Racing engines may achieve 120 to 130% reference plenum/outside the trumpet/ambient.
There isn't an easy way to relate the 28 inches of water to the inlet conditions of a running engine as the flow is highly transient and pulsating. The only real way to relate pulsing transient flow to a steady state flow bench device is through flow theory such as Annand , Navier Stokes, Mass ,Momentum, energy as covered in modern 1 D cycle simulation codes such as Ricardo Wave, GT Power etc etc.
RE: flowbench
It seems that flow bench's have become more of a marketing tool then a performance tool.
I have always felt the the dynamics in a reversion wave and the impact of a moving piston should be reflected in any viable flow numbers..
I am looking forward to something like a Spin-tron to add flow data to their parameters...
Cheers
I don't know anything but the people that do.