str33tpr3p

I know its a noob question to ask this but ive been looking around and reading lots but i cant seem to find the better answer.. What side to mount a BOV onto on my sr20det blacktop. The pros and cons between hot pipe and cold pipe, also which one is which i know its a noob question but still. Also if its better to run it recirc or atmospherically.

Thanks

tabasco122

Hot is between the turbo and inter cooler, cold is between the inter cooler and throttle body.

Edwin562

You haven’t searched hard enough; On MAF based turbo-charged recirculating the BOV is strongly recommended. Basic turbo 101, Best placement for the BOV would be 6” away from the TB on the cold pipe. A lot of Sr owners do place the bov on the hot pipe but its all in the owner’s preference.

str33tpr3p

i really appreciate it guys. Helps me out alot, well thats what i figured was on the cold side, why do many owners place on hot pipe? is there a major difference between them both?

4x4le

If they are going to recirc its closer to the turbo inelt. If its on the cold pipe the air dont have to change directions making it work better though.

Kingtal0n

The best place for the bypass is generally as close to the turbocharger as possible. Recirculated on a maf vehicle for best performance.

KiLLeR2001

Hot side for me. That way you don't have to run a long ass hose back over to the intake pipe after MAF for recirculation.

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4x4le

2 people already said hotside, close to the throttle body and gave reasons why. You decide to go against this with another one of your ignorant posts and give no explanation why.

My car ran good with it on the cold side first, not recirculated, and then i moved it to the hotside, not recirculated, and it does even better. I didnt have any problems with it dipping too low below idle when off throttle or wanting to die ever, the gain i noticed when switching sides was when i would go on and off throttle back to on the responce was much better because the air didnt change directions and the turbo didnt have to refill as much of the volume of the piping and intercooler with pressure again.

People always seem to ASSume that all maf cars are pullthrough. There is no need in recirculating a blow through setup. If you have a blow through setup its pointless unless you put the maf before the bov. Most of the time the maf is on the coldside so many people put the bov on the hotside. You may have room on the cold pipe before the maf, you could put it on the cold tank on the intercooler ect.

Saying it needs to be as close to the turbi as possible is just an uneducated answer. Break that down for me, why exactly would putting as close as possible to the turbo be best?
Dont say because thats whats making the boost, because when the throttle is shut its no longer being driven enough by the exhaust to make boost. What your trying to blow off is the pressure thats (not quite so) trapped in the pipes, without the bov the compressor would be the easiest way out and thats bad because air is reversing flow and your forcing the turbo past its surge line. Putting the bov close to the compressor only helps one of those problems, and having it real close to the compressor is actually asking for some surge when you come back on throttle because your rushing air tword the compressor and when you open the throttle your closing the bov before the turbo has a chance to become effecient again.

Kingtal0n

I didnt give a reason why because i like to keep posts short when possible. If someone happens to ask me a question, "WHY", I will HAPPILY give reasons and data to support my words. I would never supply information for which I have done no research... All of my posts and advices are given from personal experience and/or proper research.

None of the "reasons why" given so far are backed by any actual mathematical data... only speculation and assumptions. Your "reason why": speculation, no data. Did you even check the differences in visible plug characteristics over the course of varied series of driving styles?
Not everybody uses the same bypass valve as you and so experiences with this will vary- your "reason" here is a blanket statement that assumes every individual has the same exact engine/parts are you do. ex. Some bypass will hang open during vacuum situations (such as a greddy type-s that is set "loose") and the idle will dip and the car will not run right, not even at idle, as that particular bypass will hang open during idle if set loose.

I do not recommend blow-through setups for our community due to the complexity involved with turbocharged vehicles. I believe that if Nissan felt the engine would be best served with a MAF after the turbocharger- it would be there.

Ok, Excellent question, and here is a question in response to get you thinking:
What is the purpose of a bypass valve?


Answer: Protect the compressor wheel from unnecessary wear and tear.

How can we best achieve this?
Short answer: Evacuate the plumbing as fast as possible during a potential "surge" situation.

Long answer: Pressure in the plumbing above atmospheric will drive the net flow of molecules in the path of least resistance. When the engine is presenting such a path, the molecules flow into the engine and are used to drive the process of combustion. When the throttle body shuts the engine is no longer an opportunity for easy escape- instead the compressor wheel becomes the path of least resistance. Air molecules that escape past the compressor wheel cause a situation known as "Surge". The invention of the bypass valve was intended to provide a solution to this situation. When the throttle body shuts, hopefully the bypass will open, and air molecules will be presented with a better path of least resistance- one that will not potentially damage the compressor wheel.

-The speed of the evacuation depends upon what?
the size of the hole that the bypass presents, the size of the plumbing, the pressure ratio inside the plumbing above atmospheric, the kinetic energy of the molecules themselves, and more. We can speed the process by making the hole bigger, right? more molecules can fit through a larger hole at identical pressures. What else can we do? Move the hole closer to the compressor? Imagine we move the bypass farther and farther from the compressor, and make a chart of the pressure in the plumbing after the bypass opens. As you move the bypass an infinite distance from the compressor, you will find that the pressure drop occurs more and more slowly at the compressor, simply because there are more and more molecules of air that need to be evacuated on the side of the compressor that eventually will result with a drop in pressure.

Croustibat

Stop your masterbating party, any place is ok as long as you recirc it.

The op is not going to run 4 bar boost so why even bother ...

That is one of the most obvious troll on boosted engines BBS, wake up guys ...

4x4le

This still super seeds your explanation.

give me a break, air is air. Volume or pressure is fine, no need to get down to molecules, atoms, or what gasses are making up the air, your just trying to sound smart to help your case.

once again, air would have sufficed. No one would have got confused at all if you just said air. Anyways if you look at the post of mine that I quoted I bolded a statement that you pretty much just re worded to act like you are telling me something.

once again trying to use words to throw other off to make yourself sound smart. You do this every time I disagree with you on something.
Pressure ratio is a figure you get from pressure and atmosphere pressure. Saying pressure ratio above atmospheric is redundant and incorrect.

Why, you have said it yourself that it is the path of easiest evacuation of air (assuming no bov). This implies, and it also is a fact that without the exhaust driving the turbine the compressor does not have the energy inputted into it in order to compress air. The compressor is not what is in need of relief, its that air that it ALREADY compressed and sent into your pipes before you shut the throttle.

Physics owns you. Your wrong.
Lets humor your hypothetical situation of a very long distance of pipe. One the pipe being long will help cool the air and that is why the pressure drops the further it gets away. It will be just as if not more dense than the higher pressure air closer to the compressor. Lets also keep in mind the air is flowing in one direction, and that is away from the compressor. Hot dense air also wants to flow to cold less dense areas. Putting a bov at the end of your really long pipe will still out perform the bov being near the compressor. It will make the lower pressure air at the end of your really long pipe less dense and cool quick as it moves through the bov. It will be making a very easy path for the hot dense air to move to and it will continue flowing in the correct direction. The compressor is not being driven enough to overboost or go past the surge line.

Now compressor surge at closed throttle really isnt THAT big of a deal because there is such little load on the turbine or compressor, the surge that is terrible is while your on the throttle. Putting the bov close to the compressor is actually asking for this kind of surge. When you put it there your asking all of that air to change its direction of flow. During a quick shift it haults, flows backwords, then when you quickly get back on the throttle the the bov closes and that air has to change direction fast. The compressor takes back off quick too and the air actually slams into each other creating a pressure spike that is likely to put your compressor past the surge line.






Something you may not know, im not just talking about what works for me. I tune cars professionally. I have seen many examples of many different setups. I have never needed to recirculate the bov on a pull through maf car. If your able to tell the computer you dont need fuel over X rpm if the throttle is closed there isnt any more of a rich condition than you get from slamming the throttle shut on a N/A car. Where you tell the ecu you do need some fuel even with the throttle shut you tell the iacv to be ready to modulate its throttle and to not let the rpms dip. Its really that simple.

Also with your comment about blow through mafs and nissan would have done it if they thought it was needed or whatever. Fuck what nissan thinks really. If that were the mentality we wouldnt modify the cars at all.
The reason nissan didnt go blow through is for a few reasons.
The maf requires more frequent cleanings, People wouldnt want to do this.
It was cheaper for them to be made of plastic, which wont last as long holding pressure as they will just pulling in air.

Kingtal0n

I share a common interest in the love of high performance vehicles, and i seek only to improve life for everybody that would share this interest. My posts are loaded with love for safe, fun vehicles, that is my only intention.

We cannot move the plumbing of the compressor an Infinite Distance from it, that would be silly. In the real world, there is no static number of air molecules in the plumbing, the engine is still breathing, and the compressor wheel is still spinning. The situation is dramatically dynamic, such that it would take hours of accumulation of exact numerical data to perfect actual predictions of current running engine characteristics. When you are not touching the gas pedal, and the engine is decelerating, there is a much different situation inside the plumbing when compared to full throttle high boost. My example is only intended to give a snapshot of one possible situation, a most probable one as I deemed fit to describe the relationship between the distance of the bypass to the compressor- which relates to the original question: where to install the bypass?

Obviously, a real world example should be used for two situations to describe the bounding of this relationship. The first would be a real world bit of plumbing. A tire is a great example of a bit of plumbing, for it does contain AIR molecules, and they are trapped at some PRESSURE above our atmospheric, if the tire is intended to support a typical vehicle. Let us compare the SIZE of the tire to the SIZE of the plumbing- that is, bigger tires hold more air molecules at similar pressure/temperatures than smaller tires, and as compared to the NON-REAL WORLD EXAMPLE of Standard Pressure and Temperature: 22.4Liters, exactly, for an ideal gas, at Standard Temperature and Pressure.

Now put a hole in your tire. You may find through experience that a LARGER HOLE will drain the air quicker than a SMALLER HOLE. Simply, because more air molecules can fit through a larger hole during one such recorded slice of time as integrated by a function of time that describes the hole's appearance in the tire! For instance, if the hole is created slowly, then at very first instant there will only be very few air molecules escaping to our atmosphere, Followed by more as the hole gets larger and larger. And in the REAL WORLD, there is no HOLE that can just appear instantly, so it is necessary then to not only describe the size of the hole but also it's very appearance, shape, and characteristics (Is it flat or does it obstruct the exit of air molecules from the plumbing because of it's shape or design?)

Clearly, much goes into a real world example if it is to be used. So far we have agreed that the size of the hole, the shape, the way it is revealed, the temperature and resulting pressure of the gas itself, the pressure of the atmosphere into which the gas seeks to escape, even many physical underestimated and unforeseen values that play incidental roles such as the resulting deformation of the tire or plumbing due to the pressure, seemingly insignificant unrelated calculations all play important roles in the final real world result, which is why they have things like STP- real world example are often tedious to calculate with exactly accuracy. Often it is favorable to call on theoretical "perfect" examples and relate these to the real world problem in question.

In my perfect example the air pressure and molecules begin as a static time slice in which a hole appears infinitely fast, suddenly, presenting the static number of air molecules an exit the plumbing. If you merely chart the resulting decline in pressure of a tire you would find that the pressure appears to drop evenly within the tire, since gas molecules are always in constant motion at STP they are moving to take the place quickly of any escaping molecules and providing unique, constant pressure to the entire tire, even if such a pressure is in decline.

Realizing this would require a further explanation I induced the improbable situation of the bypass moving an infinite distance from the compressor. If you were to increase the size of the tire suddenly, the pressure would simply drop because no new air molecules are entering the tire. This is not the case with our real world example of the plumbing after a turbocharger: New air molecules are constantly being moved into the plumbing not only by our atmosphere (due to the demand of the engine) but also because of the compressor itself, which is probably (hopefully) spinning and applying a vector of magnitude M force to specific air molecules within it's grasp, and all of the air molecules downstream of the compressor are supposed to experience some of this force with the end result of moving more of them (QUANTITY of air molecules, which is directly related to horsepower output) into the engine.
We are once again dealing with an infinite number of calculations, some of the most "perfect" of which are assumed and given in the form of a compressor map, which you may have heard of.

The compressor map, among many thing, attempts to explain one relationship between impeller speed, temperature, and capability where regarding a situation known as "Surge" in which the compressor can no longer operate effectively do one of it's designated jobs, which happens only to be called for during certain situations. A compressor is not always applying enough force to air molecules that it will effectively compact them and create a pressure- despite the impeller speed being high enough to do so. Also, the compressor maps do not surge at exactly "XX,XXXrpm" The calculations used to derive those numbers are also "perfect examples" like the one I created because real world examples would require much more data-

So static assumptions with this "perfect" compressor assume that speeds of the impeller that would result in pressure ratios (as deemed by the engine's demand for air molecules, which is affected by the throttle body (also called air valve)) in which the compressor wheel would experience a potentially degrading/damaging situation, are achieved. What is the point of considering situations that would not damage the compressor wheel, such as idle? At the speed of the impeller during idle there is not a sufficient situation to damage the compressor wheel so operation of a bypass would not be as important- HOWEVER, that does not mean that a bypass valve could not function during idle! Nissan seems to feel, that during idle, the bypass valve should be open! Excess air molecules entering the plumbing should be allowed to bypass the compressor during their exit from the plumbing- they should return to the inlet where the pressure is atmospheric! Excess pressure there will retard the entry of atmospheric air molecules, and it will also help keep the compressor spinning. If air is forced to exit via the compressor it will apply a force to the compressor wheel opposite to that of the nature of the turbocharger's design- the EXACT situation that can potentially DAMAGE the compressor wheel when it happens during other instances.

Regardless of whether the bypass functions at idle, the main concern for most of us is preserving the life of our compressor wheel with a bypass valve the best we can. My example uses the perfect bypass, one that opens impossibly instantly, with a reasonable size hole. Reasonable of course, with respect to the situation. it would not due to have a hole the size of a peanut open up during a transition shift between 1st and 2nd gear in my car. The air in the plumbing could not expect to effectively exit quick enough due to the size of the hole.

Using a Silvia, Nissan, SR20DET Engine, OEM equipment.
Real world example "impossible" variables being considered:
Proper plumbing diameter(1.8"-2.5"), proper bypass hole diameter/position(1
-3"), proper engine displacement(1.5-3.0L), proper compressor(20lb/min +/- 50lb/min compressor), etc... with all values being subject to appropriate disagreement, for instance some of you may feel that a 100/lb/min compressor is also proper, and that would be an appropriate argument, whereas a 5lb/min compressor is simply ridiculous and would not be appropriate. So in the end even my "proper, perfect" experimental settings are subject to change, they are only set to mostly agreeable values, the same way STP is set around a general, agreeable atmospheric pressure-




Now, Returning to this point knowing all of this:
If our real world plumbing was just like a tire, then it would not matter where you put the bypass valve, since a tire experiences a force from the air molecules contained within it evenly. You could put it anywhere after the compressor and before the throttle body: hotpipe, coldpipe, doesnt make a difference.

So now I am going to add a new variable to our tire: We are Filling it, and Draining it, at the same exact time. If the same exact numbers of air molecules is entering the tire AND leaving the tire, the number of air molecules in the tire will remain constant, and the pressure will neither increase nor decrease over time. Now let us consider our situation in detail:


In order for air to be moving into the tire, there must be a greater pressure outside the tire. Likewise, in order for air to EXIT the tire, there must also be a lower pressure outside the tire. Let us position a compressor at one hole, and a atmosphere at the other hole to meet these conditions. If the pressure in the tire is to rise, the net movement of air molecules going into the tire will be greater than the number of molecules that is exiting the tire. Once the pressure on both sides of the entry is the same, the pressure in the tire stops increasing, but air molecules are still moving through the hole. That is, air molecules are still moving through the hole but an equal number of them is both exiting and entering the tire, so the pressure remains constant. Remember that the air molecules are in constant motion! The inflation of a tire is due to this very motion- the combined magnitude of the forces of all the collisions of air molecules with the insides of the tire is what maintains the shape of the tire and keeps it from collapsing!

Now, I present two situations bearing the application of this knowledge:
If the entry of the air molecules into the tire is positioned very close to the exit, then the pressure immediately near the entry point and exit point for air molecules will be higher than the pressure on the 180* opposite side of the tire.

If we did position the exit hole on that 180* opposite side, it will have the lowest pressure of the entire (symmetric circle) tire, and because of this fact, it will have fewer air molecules exiting the tire when compared to the exit that is placed directly near the entry point for air molecules. It is for this reason that I will recommend placing the bypass valve as close as possible to the entry point, the compressor wheel, for air molecules that would seek to induce a pressure in the system.

/thread

4x4le

Your right, it will function on either side. All i tried to explain is how it works better on the cold side due to the fact that air flows toward the throttle body and the compressor is done creating pressure the instant the throttle is released. It is spinning fast enough to create pressure but it does not have anything driving it. That is what causes surge, the turbine not powering the compressor enough to hold in the pressure its creating in.

Your analegy with tires dont work because they are round, the air is not super heated, and then cooled resulting in a pressure drop, which brings me to my next point, the air is dencer and at a lower pressure on the cold side. Your bov can flow more air "molecules" (thanks for even bringing that word into this, i never would have thought to use it against you) out in less time of being open.

KiLLeR2001

Whenever there are debates like this I think to myself. "How did Nissan set it up originally?"

Answer: Hot side.

I think the closer to the intercooler on the hot side the better.

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4x4le

maf vs map: everyone should run maf's
wheels: everyone should run 15x6.5's or 16x7's
no more twin disk clutches, nissan had it right with singles
vlsd vs clsd: oem is better, even if it dont work for long
Paper headgasket or mls: paper
cast pistons or forged: cast
electronic boost controller or just hook up the wastegate: just hook up the wastegate
front mount or sidemount: sidemount
cat converter and quiet muffler with crush bent pipes, or free flowing exhaust: restrictive
gauges that monitor things: dummy lights are just fine
short throw shifter: slop is better
Intercooler pipe material: everyone should use plastic
s15 front end on s14's? Nope, nissan wanted s14 front ends on them
z32/r32 brakes on s13/s14? Nope, if nissan thought we would ever need them they would have gave them to us.
Oil cooler: we would have one if we needed one
Coilovers or struts/springs: strut/spring combos, ride is better and they are cheaper


How did nissan set it up originally? In a way that was cheap to produce, easy to produce, comfortable to drive ect.

The t25 is so little there is probably little difference what side its on. The piping and intercooler is so small as well. Either side will WORK, but if you understand the physics of compressed air flow, at different temperatures you will understand the cold side makes more since.

AdamR

This thread has been lulzy. The psuedo-scientific posts killed me. It's funny how nobody on this forum ever listens to people who actually know what they are talking about.
A basic understanding of physics would tell you the cold side is better.

4x4le

Yea and I just found this on another forum. Says almost exactly what I said
I especially like that part that I bolded
Also to answer Killers question about what side did nissan put it? Depends on what car, they have done it both ways actually. Probably which ever side the coin landed on.

Walperstyle

Hilarious in here.

An intercooler will have about a 1psi pressure drop. (on average, all depends on a lot of factors). That said, a MAP sensor in the intake plenum will be able to detect this and correct accordingly what kind of pressures your intake is seeing.

that said...

I can't speak for everyone, but this is why some of us go stand-alone and MAP. Either way, its not a big deal, and you probably won't notice much difference how you plumb your BOV. Either way, cold side for me, mostly because buddies in the industry have been doing that.

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KA-T ORG-Function over Flush

KiLLeR2001

Ah yes, recirculating warmer air back to a turbo which gets over 1000F that's going to be cooled by the intercooler anyways.

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4x4le

Yes, everything makes the most minimal difference. Every argument anyone can make including myself is minor when it comes to this subject. So all we can do is weigh the pros and cons and look at how everything works and flows. Op asked for pros and cons.

"your cons dont matter" dont work, especially when the the pros for having it on the hot pipe actually dont work.

If you have the choice to put it on the cold pipe, put it on the cold pipe. If you already have it on the hot pipe dont loose sleep about it. I had one on the hot pipe for a long time. After tuning some cars with them on the cold pipe and noticing I liked how much easier it was to tune for atmospheric bov, and noticed throttle responce on and off throttle was better I changed mine to the cold side and I noticed a difference instantly. I never gave it much thought before then but it made me think out what was happening. It is best to have it on the cold side.

If you dont believe me,
molecules, kenitic energy, tires, holes, visible plug characteristics,

AdamR

This old argument. I suppose a cold air intake doesn't do any good on a turbocharged car?
But what 4x4le said is right, either side will work, but the best location is as close to the throttle body as possible.

Kingtal0n

I understand there are many points of view;
Another reasoning for the "hot side" from the point of view of maximum horsepower as opposed to protecting the compressor wheel:

The main purpose of an intercooler is to remove heat from the air, right?
Where does the heat go?

Well, it is absorbed by the aluminum material of the intercooler, first, then hopefully distributed to the atmosphere and lost.

So, if heat is absorbed by the intercooler, as air is passing through the intercooler, then more air flowing through the intercooler would make the intercooler hotter, right?

So, if you are going to discharge air from your plumbing, where will you place your blow-off valve:

A: Before the intercooler, so that the intercooler does not absorb the heat from the air that is simply being discharged.
OR
B: After the intercooler, where the heat has been absorbed by the intercooler, increasing the temperature of the intercooler.

You will find that a bypass valve on the hot-side will reduce intercooler temperatures, and therefore, reduce Cold-Side Temperature, which is the point of using an intercooler to begin with. Why cool air that is going to be discharged?

AdamR

^ Just stop.

Kingtal0n

Stop what? Stop making reasonable observations? Stop having an intelligent discussion? Stop using Zilvia.net for what it is designed?


I am only helping us see both sides of the issue. I, for one, could not care where you put YOUR bov- I know where MINE is. So far I have given several very good reasons to use the bov on the HotSide- Before the intercooler. And I have YET to see ONE good reason to install it on the COLD side.

I have ever more good reasons to use it on the hotside, but I am saving them for when my previous good reasons are shot down.
There is even math, diagrams, pictures and personal experiences to share. So bring it on, the proper discussion without personal attacks.
Use the scientific method.

AdamR

If you are not seeing one good reason, read the thread again.
You are invoking science obviously far beyond your comprehension.
When the throttle is shut, the turbo continues spinning at a speed that is creating positive pressure. IF your valve is right after the turbo, you have pressurized air rushing from two different directions (throttle plate and turbo) rushing to get out the one valve. This effect may be relatively minor, but the main reason is not.
When your pressurized air has to turn around to get out, it induces lag when applying throttle again, because it then has to reverse again.
With a throttle body mounted valve, the turbo can keep spinning, pushing air through the piping until the valve closes and it can resume building boost.

If a .1 degree difference is more significant that that, you need to rethink your core design or duct It better.

4x4le

cant argue with stupid. cant make the blind see. cant make the deaf listen

cotbu

Not True!
I heard the formula was unicorn blood and the sweat of Chuck Norris!

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LoverTechnologies "Half Broken Things!"

KiLLeR2001

Alright, I've read enough bullshit here. Time to lay down the facts.

We all can agree Garrett is the leader in turbocharged systems and they have done extensive research in the field...

You can view this document here... http://www.turbobygarrett.com/turbob...timization.pdf

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Kingtal0n

You spoil all my fun

You guys are welcome to stay and ask questions and learn about air molecules if you wish. FWIW, there is no significant "reversing" of air when the throttle body shuts... Just because the air valve is closed does not mean the engine stops breathing all together.
Even an engine at idle requires a significant quantity of... thats right: Air molecules.

AdamR

If you read that Garrett paper, it says that on a MAP system to put it close to the throttle body. Ask questions from an internet physics professor? No thanks, I have actual engineering classes to get back to.