chinoy

Whats the easyiest way to calculate optimum pipe dia.
You have flow velocity, you have pressure and you have flow volume.
I know we should try to keep the velocity under speed of sound.

Ravage70

run 2 to 2.5 and ull be fine

88b16civic

The bigger the diameter (Larger area) the lower the velocity q=VA, if you want to find the pressure drop, look up Darcy eq for turbulent flow, the pressure drop will be a function of this velocity.

All your calculate though is the bigger the pipe the lower the pressure loss so there is no "optimum". It comes down to what fits and if you go too big, its just extra volume you have to pressurize when going from vacuum to boost. If you want to calc the lag use ideal gas law divided by time.

chinoy

Thanks man just the kinda info I was looking for.
Was thinking does it make sence to design an air box just after the turbo then have a small cone leading to the rest of the pipe ?.

Need to find the time to enter it up into a CFD simulator and see what happens.

Tom-Guy

Loaded question.

Looking at gas pressure won't get you there. Yes, pressure loss (as an absolute number) due to flow friction varies
directly with the density of the gas -- but, as a percentage of total static pressure, does not change with density.

Rough, sleazy, and to be truthful a waste of time, rule of thumb is to keep charge speed below .3-.4 mach which is the point at which significant losses start to accrue. Keep in mind that mach varies with the square root of the *absolute* temperature of the gas involved, and doesn't care one whit about the density. Mach numbers are dimensionless ratios, and good for determining rules of thumb in re compressable gas flow - provided you can get the mach number right! Reynolds number (also a dimensionless ratio) is another nifty alternative, and will give as accurate a prediction of when flow separation occurs as anything.

When approaching/meeting flow speed of .3-.4 mach, you will experience a temperature drop! The energy to accelerate the charge to the flow speed comes *only* from this temperature drop. Since the kinetic energy of the charge increases with the square of the charge velocity, the temp drop becomes more and more pronounced as the speed increases. Ever hear of carburetor icing?

Frankly, the only people currently doing a single goddamn thing in re a properly constructed discharge tract are the gas turbine guys. (Joey gets half his mojo from consuming enough beer + boomers than he can pretend a combustion chamber and a combustor are the same thing) Back in the '50's typical turbojet efficiency was a pound of fuel per hour per pound of thrust, current airliner technology is .4 lbs of fuel at the same rate. Pennies from heaven and all that.

So, what do we make of this? Absolutely nothing! I typically run 1.75" to 2.25" out of the compressor to the IC, depending on the compressor exit's size and what IC I'm stuck with. From IC exit to TB inlet I run 2.5" for no other reason than it matches up groovily with a stock Honduh TB. I am inclined to run a bigger compressor exit if for design reasons I'm not able to send discharge immediately through a sharp 90 bend, as either pressure drop from pipe expansion or a sharp bend knocks the naughty out of the charge's spiral flow.

Repeat after me, "expedient"

chinoy

.3 to .4 mach
I thought it was .8 to .9 mach.
We where allways taught that keep gas flow velocity under mach.
But the funny thing. Some of our fastest Engines. Have stream velocity in the Transfers and Exhaust in Excess of Mach1 go figure.
Even the author of the software isnt able to explain why its working so well.
EVen the simulator is showing a huge boost in power. At eaxactlly the same RPMs we see in the real world.

Im honestlly not too bothered about the pipe dia for the plumbing. Its just the exhaust that has me thinking.

imadouche

Open down pipe or 3 inch piping is all I would run

chinoy

Opened up the system and measured the existing Turbo Exit.
We have a hand made flange. Waste gate opens to open air.

The exit dia at the flange is 2"
THe largest Dia pipe we can use is 2.5"
The complete exhasut system under the car is 1.4"
Id love to run a 3" open down pipe. But the cops would bust my butt for noise polution.

Tom-Guy

Supersonic flow in the head ports or upon entry to the chamber is something different entirely - Laval nozzles and suchlike. 383 strokers built with "shitty flowing" factory swirl port heads that perform far, far better than they should are a commonplace example of this. The sonic boom does wonders for fuel atomization.

Behold:




FYI, Rick Head's drag radial Camaro ran 7.72@188 last October off of "much too small" 2.5" charge piping. I think his car, also, would show discrepancies that your simulator/author could not explain.

I don't worry too much about the exhaust once past the turbine wheel. All harmonics are over with, and you just try to vent it with as little restriction as possible.