New shiny things

[sawood12]

Now i'm reading this post with lots of interest and it is primarily a learning thread for me as it is looking in great detail at a subject I havn't really considered much in relation to this application but I would like to raise one point/query in relation to the BOV vs. BPV disscussion. My experiance is in Civil Aero Engines where you have a dirty great compressor feeding a combustor, now one question I often get from interested semi-technically minded people is that what stops the expanding gasses in the combustion chamber going forward through the compressor as there is no physical/mechanical restriction like there is in a car engine. The answer is that the physical (considerable) mass of the airflow travelling through the compressor is balanced against the force of the expanding gas in the combustion chamber therefore the expanding gas in the combustion chamber is forced back throught the turbine. Surely it's the same situation on a BPV on a 944? I doubt that it's the case with a BPVand an AFM in the standard set up that the force of the recirculated air from the BPV pushes back on the bard door of the AFM due to the mass of the air travelling up the J pipe. Yes the air is at a higher pressure than the air in the J pipe but if you look at the difference in diameter of the J pipe and the BPV hose the pressue will be immediately dissapated as soon as the air enteres the much bigger volume of the J pipe duct, therefore the air will be diverted back with the incoming airflow in the J pipe towards the turbo. It's worth also bearing in mind that moving air has a lower pressure than static air so the air in the J pipe will be quite a low pressure (less than atmospheric) therefore meaning that the higher pressure differential of the air entering the J pipe from the BPV will mean the pressure is even more quickly be dissapated and therfore sucked the right way up the J pipe. In fact thinking about it what would probably happen is the sudden injection of volume of air into the J Pipe from the BPV will probably slow down the airflow in the J pipe therefore slightly increasing the pressure in it, which maintains the pressure on the turbo inlet.

I'm sure i've missed something fundamental but i'm struggling to understand why, in any setup, a vent-to-atmosphere BOV is a better solution and all it is doing is just wasting high pressure air, which in Aero Engine design is an extremely valuable comodity and one of the overridding design considerations.

 

[Fen]

2 things that spring to mind for me are: 1. The J-pipe has a bigger diameter than the BPV does, but it has a much smaller volume than that occupied by the pressurised air that suddenly has nowhere to go (which occupies the hard pipes and the intercooler. What effect does that have?2. How much flow is there through the J-pipe when the throttle is closed? If the compressed air with nowhere to go when the throttle closed is dumped back into the J-pipe then it has to go round the loop again. Therefore not much outside air needs to be coming in through the air filter so there is not going to be an appreciable mass to balance the pressurised air coming out of the BPV. Remeber in a car there is little or no ram air effect to the inlet unlike an aero engine. To one of Rick's points the recirculated air is relatively (compared to ambient air through the filter) very hot having been compressed once already. It also is not going to help the turbo to spin any faster as, although it has energy (in terms of pressure and heat), it never has more pressure than the other side of the turbo (as that's where it just came from) and in any case it's the hot side of the turbo that is supposed to do the driving so this air is on the driven side of the turbo. It will also heat the body of the intercooler as it passes through for 2 or more times, thereby reducing the effectiveness of the IC for a period.

 

[Indi9xx]

All very interesting.

I think that there is probably going to be a threshold where a BOV rather than BPV is going to become essential, by which point the DME will be out of the picture, or at least some additional electronics are going to be needed.

I do know from experience that once a car is developing more than a certain level of air consumption/air pressure, the pressure in the J Boot when a BPV opens defeats the standard breather system, so the pressure in the j-boot is definately rising beyond atmospheric.... or it could be that the standard JBoot design isnt a very good design in regard to the location of the BPV and breather hose, so the localised pressure increase is the problem.

In any case, a catch can (of any type) is going to reduce oil injested by the turbocharger from the breathers and so is a good thing... judging by every J-pipe I have ever seen, even standard 220 cars, is always coated in oil, which isnt a good thing.

It would be very interesting to place several pressure transducers all around the entire intake tract and data log them along with throttle position and revs.. and then on a Dyno day record the data and export that data to excell as well as the datalogged data. I know that dynodynamics rolling roads can export their data to excell, so if the dyno will allow a run where the car is accellorated through 1st, 2nd, 3rd and into 4th gear (perhaps), we could get a really good idea of whats going on throughout the intake system.

I would also be interested to see the crossover pipe pressures at the same time as well as exhaust gas tempretures.

I think this is going to be something for me to look into in september.

 

[eastendr]

You can use the sniffer pipe takeoff to fit a boost guage to the crossover pipe without too much difficulty.

I was pondering an increased size pipe out of the turbo hot housing to see what back pressure ratio would reduce to.

Also still looking for a better exhaust header design that'll fit a RHD 951 so that a better cam can come in to play.

Oh what fun [] []

 

[Indi9xx]

It is a royal pain in the bum that the turbo exit downpipe runs through such a mess off a route. I think the standard exhaust diameter is a reall problem once you pass 350 bhp or lbs yet getting some decent bends in 3 inch or greater tube and going throough the standard route isnt easy.

When I get a chance I am going to spend some time with my exhaust guy looking up under a 944 turbo at the front of the exhaust to see what can be done.

 

[944Turbo]

Tea anyone?

 

[John Sims]

ORIGINAL: 944Turbo

Tea anyone?

The content of your catch tank I presume?

 

[944Turbo]

Indeed watery stuff with an oily top, I guess the water was the remainder of the trapped stuff from the HG failure, oil going into the tank rather than the intake as planned
Tony