What is the difference in performance between plumb back and atmospheric valves?

[Remix-]

My stock plumb back valve is no longer functional (so either way i am buying aftermarket now), what is the difference in performance between an aftermarket plumb back and an aftermarket atmospheric valve?

[dojobi]

With the atmo bov, you'll probably run rich on gear shifts and mess up your fueling the when you go on or off the throttle for a few milliseconds, but in general they're basically the same. When I tried a pure atmo one, I would often stall as I came to a stop. I wouldn't recommend one to anyone.

I run a hybrid bov now that vents to the atmosphere and also plumbs back. I don't get any exhaust "popping" or stalling issues anymore, but still have the bov sound. I probably would just get a plumbback one in the future to be honest. The sound is still good and it doesn't bother me like it does others, but it does lose its appeal after a while.

[WazR32GTSt]

can i ask how you knew your stock bov was up the shitter?

[dojobi]

Mine would let out this high pitched whistle under boost, as it wasn't staying fully closed. It almost drove me mad

[Sydneykid]

Well, the theory is by having a recirculating BOV, the hot air goes around again. Whereas an atmospherically vented BOV gets rid of the hot air and makes room for fresh (colder) air. There is also the cooling effect from the overly rich mixture that the engine runs after the atmosphere BOV has vented. Some people say that this overly rich mixture also reduces lag on gear changes as it burns in the turbo and helps spool it up.

You can overcome most of the stalling problems associated with an atmosphere BOV with tuning, it is a bit of fiddling though and I am not sure if it is worth it on a road car when you add in the legal issues. On the race cars we always have atmosphere vented BOV's.

Hope that helps

[HKS34R]

I had tried a couple of different types of BOVs on my Lancer before settling on a hybrid. In my opinion they are the best of both worlds - they vent to atmosphere and recirculate as well, which stopped my Lancer backfiring on gear shifts.

I have also sold many of these types of BOVs (GFB's Stealth FX BOVs have been popular) to friends etc and have not heard any complaints. I have yet to fit one to my Skyline, but if I had a choice, I would probably go a hybrid.

[otto]

i recon the air being plumbed back is gonna be colder, i mean the air goes through the turb is compressed and as a result increases in temp then the fmic takes some heat out then the air gets plumbed back and drops in pressure back to atmospheric so theoretically it should drop back to a temp lower than it came in cause the fmic took some heat out if you know what i mean, kinda hard to explain over the keyboard but this is exacly how the aircon works in a large aircraft (air cycle machine). Because of this i recon get the plumback What do you guys think does it make sence or have i completely lost it???

[Sydneykid]

i recon the air being plumbed back is gonna be colder, i mean the air goes through the turb is compressed and as a result increases in temp then the fmic takes some heat out then the air gets plumbed back and drops in pressure back to atmospheric so theoretically it should drop back to a temp lower than it came in cause the fmic took some heat out  if you know what i mean, kinda hard to explain over the keyboard but this is exacly how the aircon works in a large aircraft (air cycle machine). Because of this i recon get the plumback  What do you guys think does it make sence or have i completely lost it???

You have completely lost it, otto :jk:

The expansion doesn't come anywhere near close enough to removing the heat generated by the turbo (65% efficient) and only 70% removed by the intercooler (and that's a good intercooler). You can't use the aircraft comparison because the ambient air temperature is lower than the temperature that you want the air con to be. So 30% loss of I/C efficiency and 35% turbo inefficiency brings the temp up to what you want air con to be. Plus you would need to consider barometric pressure, cars don't fly, well much above ground level anyway.

Interesting theory though.

[otto]

Well actually sydney kid in an aircraft the air you breath in the cabin (on a large passanger a/c ie, 747) is bleed from the compressor section of a gass turbine engine either an apu...that noisy thing right on the ass of the plane (when its ON THE GROUND), or the engines (in flight) and enters the a/c system at close to 200 deg c from memory,

and the aircon system gets the air temp down to -4 its so effective they have to heat it at the end to get it to a comfortable temp. (I thaught this was pretty amazining)

The aircon system works by sending air from the engine or apu through a heat exchanger (the cooling air for the heat exchanger ON THE GROUND is ambient air! in flight because of ambient air being so cold and the system so effective air cooling air is either shutoff or reduced) then the comressor side of effectivly a turbo from there another heat exchanger then it goes through the turbine side of the turbo (expansion, this is where the temp really drops)

I understand that cars dont fly but do you honestly belive that aircraft only have aircon in flight! If mr boeing designed a plane with an aircon system that only worked in flight where cold air was least needed i think he would go bankrupt. anyhow sorry if its abit onesided to aeroplanes but it was the only practical example i could find that acually used the principles in my original post to lower temps. I know you will probably pick at the difference ie, the air was compressed by the engine before, theres 2 heat exchanges, the air finally goes through the turbine, The turbine section on a car is so hot But it really doesnt change the facts below.

My understanding is that on the comp side of the turbo the heat to the air was only generated by compression(honestly how much heat soak is really getting to the air at full noise when the air is traveling a million miles an hour) sometimes when i touch the cold side of my cooler it feels icy i can also remember in my days of rice (which wasnt that long ago and sometimes still is)disconecting my plumback and pulling the accelerator cable to feel the swoosh and i must admit it was pretty cold.

If compression is the cause of the heat??(I mean how else is it creating it), expansion (or returning it to the pressure it previously was) will get rid of it (return it to the temp it previously was) reguarless off how efficient the turbo is(this is a law of phisics, check out the gass laws), accept weve forgotten the cooler that you stated was 70% efficient i dont know about you but doing the math it looks to me like the final temps gonna be lower than the starting?? Does anyone get my drift yet.

OK now im gonna brace myself for your response... please be gentle

Ps. I enjoyed your explination of aircon by turbo inefficiency and intercooler efficiency did you just make that up or did you know what you were talking about?? Who has really lost it hear! (Just kidding).

[otto]

Well actually sydney kid in an aircraft the air you breath in the cabin (on a large passanger a/c ie, 747) is bleed from the compressor section of a gass turbine engine either an apu...that noisy thing right on the ass of the plane (when its ON THE GROUND), or the engines (in flight) and enters the a/c system at close to 200 deg c from memory,

and the aircon system gets the air temp down to -4 its so effective they have to heat it at the end to get it to a comfortable temp. (I thaught this was pretty amazining)

The aircon system works by sending air from the engine or apu through a heat exchanger (the cooling air for the heat exchanger ON THE GROUND is ambient air! in flight because of ambient air being so cold and the system so effective air cooling air is either shutoff or reduced) then the comressor side of effectivly a turbo from there another heat exchanger then it goes through the turbine side of the turbo (expansion, this is where the temp really drops)

I understand that cars dont fly but do you honestly belive that aircraft only have aircon in flight! If mr boeing designed a plane with an aircon system that only worked in flight where cold air was least needed i think he would go bankrupt. anyhow sorry if its abit onesided to aeroplanes but it was the only practical example i could find that acually used the principles in my original post to lower temps. I know you will probably pick at the difference ie, the air was compressed by the engine before, theres 2 heat exchanges, the air finally goes through the turbine, The turbine section on a car is so hot But it really doesnt change the facts below.

My understanding is that on the comp side of the turbo the heat to the air was only generated by compression(honestly how much heat soak is really getting to the air at full noise when the air is traveling a million miles an hour) sometimes when i touch the cold side of my cooler it feels icy i can also remember in my days of rice (which wasnt that long ago and sometimes still is)disconecting my plumback and pulling the accelerator cable to feel the swoosh and i must admit it was pretty cold.

If compression is the cause of the heat??(I mean how else is it creating it), expansion (or returning it to the pressure it previously was) will get rid of it (return it to the temp it previously was) reguarless off how efficient the turbo is(this is a law of phisics, check out the gass laws), accept weve forgotten the cooler that you stated was 70% efficient i dont know about you but doing the math it looks to me like the final temps gonna be lower than the starting?? Does anyone get my drift yet.

OK now im gonna brace myself for your response... please be gentle

Ps. I enjoyed your explination of aircon by turbo inefficiency and intercooler efficiency did you just make that up or did you know what you were talking about?? Who has really lost it hear! (Just kidding).

[Roy]

otto, what your saying may be right, but consider PV=nRT

R = 8.31 J.mol/K

P = pressure in pascals

V= volume in cubic meters

T= absolute temop in Kelvins

n= no of moles

Or put more simply for air the relationship between gas volume (V), pressure (P), and temperature (T)

PV / T = constant

What you are saying is correct, but you are talking rather large volumes of air, large changes in temperature and larger perssures, so not quite on the scale as your everyday road car.

[Sydneykid]

otto, what your saying may be right, but consider PV=nRT

R = 8.31 J.mol/K

P = pressure in pascals

V= volume in cubic meters

T= absolute temop in Kelvins

n= no of moles

Or put more simply for air the relationship between gas volume (V), pressure (P), and temperature (T)  

  PV / T =  constant

What you are saying is correct, but you are talking rather large volumes of air, large changes in temperature and larger perssures, so not quite on the scale as your everyday road car.

That's what I said :wassup:

[drifto]

My understanding is that on the comp side of the turbo the heat to the air was only generated by compression(honestly how much heat soak is really getting to the air at full noise when the air is traveling a million miles an hour)

Why then does my inlet temp gauge do this:

cruising - 10 degrees above ambient

immediatley on boost - jumps maybe another 10 degrees

sustained boost - keeps climbing gradually until after about 5 minutes of thrashing it's 50 degrees above ambient

This is not a measure of the temp of the compressed air after it's passed thru the turbo.

That air was gone long ago.

The whole system is soaking up heat from every where. Mainly, i believe from the exhaust manifold and Turbo exhaust housing.

Also consider the amount of friction the air produces went it is travelling at full velocity thru the inlet system.

[Sydneykid]

Why then does my inlet temp gauge do this:

cruising - 10 degrees above ambient

immediatley on boost - jumps maybe another 10 degrees

sustained boost - keeps climbing gradually until after about 5 minutes of thrashing it's 50 degrees above ambient

This is not a measure of the temp of the compressed air after it's passed thru the turbo.

That air was gone long ago.

The whole system is soaking up heat from every where. Mainly, i believe from the exhaust manifold and Turbo exhaust housing.

Also consider the amount of friction the air produces went it is travelling at full velocity thru the inlet system.

What you are describing is heat soak of the intercooler core. The core starts off cold and removes heat from the inlet air stream. This happens until the intercooler core itself gets hot and there is insufficient ambient air passing through it to cool the core down.

Stick a larger intercooler on and it simply takes longer to get heat soak. The idea being that, if the intercooler is large enough, you will have to back off and thus let the core cool down ready to soak up some more heat next time you need it. Plus a larger intercooler has more internal surface area to absorb heat from the inlet air and larger external surface area to pass this heat onto the ambient air.

A better way to test your theory would to measure the temperature at the turbo inlet and outlet and compare that to the ambient temperature.

Interesting thread this one

[Cubes]

I found otto's explanation interesting.

I think the difference between the two is about the size of a bee's dick.

When my car gets tuned I'll hook up a few temp sensors and find out for sure.

[neil_se]

Well, the theory is by having a recirculating BOV, the hot air goes around again. Whereas an atmospherically vented BOV gets rid of the hot air and makes room for fresh (colder) air. There is also the cooling effect from the overly rich mixture that the engine runs after the atmosphere BOV has vented. Some people say that this overly rich mixture also reduces lag on gear changes as it burns in the turbo and helps spool it up.

That is the most sense i've ever heard on the topic of atmo BOVs, thanks.

[otto]

That's what I said :wassup:

are you sure thats what you said?? if you agree with the above statement then your agreeing that your final temp will be lower.. try those formulas with whatever numbers you like and see...dont forget your 70% efficient i/c

it shouldnt matter to what scale i was talking about, cars arnt exempt from the laws of phisics......it probably wont be as huge a difference as in the aircraft aircon, but maybe just enough to kill a myth like atmo bovs get rid of the hot air.

i think the only theory on atmo bovs is that they are louder!

[otto]

joel, I would be very interested to see the results of your test.

[Sydneykid]

are you sure thats what you said?? if you agree with the above statement then your agreeing that your final temp will be lower.. try those formulas with whatever numbers you like and see...dont forget your 70% efficient i/c

it shouldnt matter to what scale i was talking about, cars arnt exempt from the laws of phisics......it probably wont be as huge a difference as in the aircraft aircon, but maybe just enough to kill a myth like atmo bovs get rid of the hot air.

i think the only theory on atmo bovs is that they are louder!

OK let's flesh this out a bit. What you are saying is if I use a plumb back BOV the air temp will be lower coming out of the BOV (and therefore going back into the inlet stream) than the ambient air temp.

So if I have a 25 degree day

The turbo heats the air up to say 80 degrees (not unusual)

The 70% efficient intercooler drops the air temp to 41 degrees (a good effort)

Then the expansion of the air as it exits the BOV drops that temp down from 41 degrees to below 25 degrees.

Have I got it right?

[Roy]

joel, I would be very interested to see  the results of your test.

otto, im guessing you are an aircraft technician or something... you will be familiar with the term negligible

The example you are using references much larger changes in temp, and much higher changes in pressure, and much larger volumes of air....i could be wrong...but if you retriculate your BOV air, im willing to bet coin it will be a higher temp then the air coming in from the air filter

If you want to get technical (and im not being a d1ck) then the benefits that you may realise with expansion will likely be lossed due to fictional losses with the velocity of air in the pipes....

Like i said i could be wrong, but looking at a few quick calcs the word negligible comes to mind