Jag läser i en tråd på Speedtalk om wave action versus inertia effect on VE.
Jag skulle vilja ha ett tryckmätarsystem som detta:
https://www.plex-tuning.com/products/pc ... er-logger/
Frågan är bara om jag klarar av att få ut något av det och hur känsliga komponenterna, tryckmätarna speciellt är.
De är inte direkt billiga. Och jag är mer analog än digital.
The direction can be established from the waveform if there is a dominant wave or 2 waves (description above). Since the sensor is in the port or essentially the closed end of the system then direction is easy to determine. If the sensor is anywhere else, such as the middle of the intake/exhaust, then direction is much harder to determine. However, port pressure is generally what is measured.
On the intake there are 2 main driving functions, suction from the descending piston and pressure buildup from the intake valve closing. There can also be a suction or pressure wave generated in the intake during valve overlap and the influence of waves from other cylinders getting into the runner.
Once the intake closes, pressure oscillations generated from this event continue. These oscillations may diminish only a small amount in magnitude from one oscillation to the next, or they may diminish rapidly. It all depends on the intake design. Ideally these oscillations will remain as large as possible to be of maximum benefit.
However, even in a design where the oscillations are mostly damped out before the next intake cycle, wave tuning is still important. There is still wave action happening when the intake valve is open, even just a little. Think of it like this. If you had an intake runner of the correct diameter from a velocity standpoint and just for arguments sake lets say there were no frictional losses to the airflow, such that you could make the runner any length you wanted without frictional losses (i.e. the runner would flow the same on a flow bench whether it was a foot long or a mile long).
Now suppose you ran the engine at some set rpm such as 8000 rpm, and compare what happens in the intake port between a runner 12" long and a runner 10 ft. long. Just to simplify things lets say that resonances in the intake are magically eliminated between cycles so that just before the intake valve opens there is absolutely nothing going on in the intake. For the first while after the intake valve starts to open the port pressures will look exactly the same for each scenario (12" vs. 10 ft.). However, after X number of degrees the initial suction will have reached the end of the 12" runner, reflected as a pressure wave and the port pressure will start to climb quickly. By X degrees the initial suction, in the case of the 10 ft. long runner, is only a couple feet down the runner and still has a very long ways to go to get to the end (where it is reflected as pressure) and another 10 ft. to get back to the port. This will never happen during the intake cycle and in fact probably won't happen for a few more revolutions of the crankshaft. With the 10 ft. runner there will still be a vacuum in the cylinder when the intake valve closes.
This may give the impression that it is just a simple matter of making the runner the right length for the rpm. This is a factor for sure, but you can milk more out of it than that, by adjusting cross sectional areas in the port and along the length of the runner, entry to the runner, minimizing how quickly the pressure oscillations reduce in magnitude, adjusting valve opening/closing rates, cam timing, taking advantage of what happens during overlap and the wave influence from other cylinders.
I should add that there is one place in a manifold where an additional intake sensor can come in handy and that is just out from the entry to the runner. When the suction wave comes out of the port and travels down the runner to the runner entry, it is reflected at the entry as a pressure wave and returns to the port to pressurize the cylinder. However if another cylinder is stealing air out of this entry area as the suction wave is trying to reflect, then the reflected pressure wave will be weak, port pressure will be lower and cylinder filling will suffer. On the other hand if there is a momentary positive pressure generated outside the entry when the suction wave gets there, the reflected pressure wave will be abnormally strong and cylinder filling will be better than anticipated.
One other final point to add is that inertia/wave tuning does matter for blown applications. Since the valve on any high rpm engine closes well after BDC, the pressure in the port/cylinder when the intake valve closes must be well above atmospheric pressure just to be equivalent to having atmospheric pressure in the cylinder if the piston was pulled back to BDC. If in a naturally aspirated engine for example you need 5 psi in the cylinder when the intake valve closes to be equivalent to atmospheric pressure with the piston at BDC, then the total pressure at intake valve closing is say 14.7 + 5 = 19.7 psi.
If you take the same engine and add 14.7 lbs. of boost and lets say to make things simple you cool it all down so it has the same intake A/F temperature as the NA case. If you have poor inertia/wave action, or the volume of pressurized air is insufficient to account for the cylinders using it up i.e. significant pressure fluctuations about average boost, then there may only be 14.7 +14.7 = 29.4 psi in the cylinder when the intake valve closes. If there is adequate inertia/wave action and enough volume of pressurized air then you may have 29.4 + 10 = 39.4 psi in the cylinder when the intake valve closes. Remember the intake temperature is the same for both cases and we are not accounting for any funny effects that might be generated during pressurized flow in terms of friction, swirl, tumble etc. etc. This is just a basic statement to indicate in general terms the importance of having a ram effect of a strength appropriate to the boost level, in a blown application. This is not to say that you necessarily need the nth degree of wave tuning that you might have on an NA engine, but the ram effect is still important. Average boost pressure does not tell the whole story.
Clint Gray
TFX Engine Technology Inc.
(Combustion/Intake/Exhaust Pressure Analyzers)
Han hade missförstått och det var det jag skrev om för att förtydliga.
Vi kanske ska sprida dina kunskaper över världen så tävlingsstallen kan kasta sprutet o få lite högre effekt med förgasare i stället?
Vi kanske ska sprida dina kunskaper över världen så tävlingsstallen kan kasta sprutet o få lite högre effekt med förgasare i stället?