turbopanda

My friend asked me if two differently sized turbos (a small one, and a big one) both boosting at 1 bar would create the same loudness & sound from the same BOV.


I gathered that it would be the same loudness, since both are running at 1 bar... but now that i think about it again.. i'm not sure - can anyone here clarify this for me?

Pritos

ack... prepare!



As for an answer, It all depends at what RPM you close the throttle. Say u shift at 2500 on a T25, u'll get a much louder sound than a td04E at 2500.

But say you're both at 1bar... I'd say the bigger turbo pushing more cfm's, though, I'd think the difference isn't obvious. If it's important to you, dunno why, then buy a decibel meter from Radio Shack and do some measurements.

shortyz

enemy territory?

good stuff!

*Boostwerks*

Different.

The loudness of the valve comes from it's actual size, geometry, and valve type.

Just compare an HKS SSQ vs a 50mm Tial. The HKS will be much louder than the Tial at a comparable boost level due to these factors.

Pritos

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bryson &raquo;</TD></TR><TR><TD CLASS="quote">Different.

The loudness of the valve comes from it's actual size, geometry, and valve type.

Just compare an HKS SSQ vs a 50mm Tial. The HKS will be much louder than the Tial at a comparable boost level due to these factors.</TD></TR></TABLE>

you are correct if they used different bov's.....

"My friend asked me if two differently sized turbos (a small one, and a big one) both boosting at 1 bar would create the same loudness & sound from the same BOV. "

*Boostwerks*

Ok wait.

Is the question more like:

If a setup used 2 seperate BOV's (the same design but different size) would make the same sound/loudness of just one similar bov?

???...

I'm confused.

Pritos

I believe he's asking if the sound would be different in either of these scenarios:

1) 2 different cars, 2 different turbos (1 on each car), and same bov's.

2) same car, 2 different turbos (1 per each comparison run), and same bov.


neway, we're both right

*Boostwerks*

OH ****! I just got off work and have been up for almost 21hrs.

I thought he was saying "different BOV's"...while it clearly states..."different turbo's"....

Sorry.

turbopanda

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Pritos &raquo;</TD></TR><TR><TD CLASS="quote">2) same car, 2 different turbos (1 per each comparison run), and same bov.</TD></TR></TABLE>

Yes, that's what I was trying to say. But also at the same boost level (small turbo at 1 bar, and larger-sized turbo at 1 bar)

So?

turbopanda

nobody knows eh?

shermanyang

iTrader: (1)

don't know but me and my dsm buddy both have the greddy type-s bov and when he turned his boost down to 9 psi when we raced, his bov still sounded louder for some reason. he's got a stock t25 and i'm running a t3/t04e. maybe piping and all that other stuff comes into play as well.

kpt4321

They will sound the same. The sound coming from a BOV is dependant on several things, such as the size of the vent hole, the pressure differential across it, the spring rate of the BOV, and more. However, since we are using the same BOV at the same pressure, these differences do not exist.

Keep in mind that, at the same pressure, most turbos will actually flow very similar rates in CFM or lb/min. And, even if the bigger turbo is flowing a tiny bit more at that boost pressure, it is a very negligible amount, and definately will not effect this.

johnisenglish

What are you talking about? Different compressors can push VASTLY different flow numbers at the same boost pressure.

However, I honestly don't know the answer Turbopanda's question, but contrary to what everyone else is saying (and certainly with good reason), I would suspect that a compressor pushing 50lbs/min is going to produce a louder, or at least beefier sound then a smaller unit pushing 30lbs/min. More air = more volume?

kpt4321

Wrongtastic.

Are you familiar with the formula for compressor efficiency? Plug some numbers into it and see what happens.

Actually, I did it for you. On a 2 liter boosting at 14.7 psi (1 bar), with a 75% compressor efficiency (very good) and a crappy intercooler with only 60% efficiency, charge temperatures will be approximately 590 R. If you lower that compressor efficiency to 65%, which is not very good, the charge temperature goes up to 601 R.

The difference in flow rates: 6 CFM, with available flows within the 360 CFM range. That's certainly is not a very big difference.

That's 1.7% more flow, with a very large difference in compressor efficiencies. That certainly is not a "vast" difference.

Now, back to the whole BOV thing. First of all, flow rate does not matter AT ALL in this scenario. Why not? Because there is no flow. When the BOV is venting, the throttle is closed, and the flow almost stops. If the flow did not stop, then there would be no need for a BOV.

A BOV is simply flow across an orifice due to a pressure differential. With basics physics knowledge, it is easy to see that this flow depends solely on the delta P, and the area of the orifice. That means boost pressure and BOV size. Those are really the only two things that determine the sound.

However, companies are starting to use silly things like horns and chambers to make BOV's sound differently (a la RFL), so two different BOV's of the same size at the same pressure can sound differently, if they have features such as these.

What can come into play is cubic feet (or whatever measurement of volume you choose). Cubic feet PER MINUTE is not considered here, but cubic feet are. However, the volume of the intake system (pipes and intercooler) determines how LONG (time) the BOV will be open, because it determines how long the pressure differential will be maintained. It does not play much of a role in the sound, just how long it lasts.

Anything else?

turbopanda

i'm trying to understand....

basically what you're trying to say is that it will create roughly the same loudness from the same type BOV.

kpt4321

With the same BOV at the same pressure, they will make the same noise.

That assumes they are on the same or similar cars with the same or similar intercooler setups and such.

turbopanda

I just talked to an old friend of mine (a mechanic) about this. He tells me that the car with the bigger turbo will make a louder sound at the same boost level than a smaller turbo - the throttle is shut, but the turbo is still spinning, and its quite logical that the bigger turbo will be pushing more air in than the smaller turbo, so I guess that it would create more pressure for the blow-off valve to release..

(i'm sorry if i'm not making sense again, but its 3am and i'm tired)

kpt4321

NO!

There are two things wrong with that statement:

First of all, if the big turbo and the small turbo are both flowing enough air to keep the intake system pressurized to 1 BAR, the flow will continue to drop off in a linear fashion once the throittle is closed. Now, like I said before, the big turbo might be flowing about 1.7% more air in terms of mass-flow, but that DOES NOT effect the sound of the BOV. It could possibly effect the duration, but only a MINISCULE amount.

Second of all, a point you guys seem to fail to grasp, is that the flow rate of the motor is inconsequential in this discussion (because it is very close to zero). It is the VOLUME of the itercooler and charge piping that makes a difference.

With a certain delta P across the BOV, which obviously has a certain area for air to pass through, it will flow air out at a set rate. This rate will always be the same for the same delta P. As the delta P drops off due to the vened air leaving the charge pipes and thus decreasing the gauge pressure there, this flow rate will decrease. That means that, the larger the volume of the thing the BOV is dumping from, the longer the sound will last. However, it will be the same sound, just over a longer period of time, with the frequency changes that occur near the end of the venting being a bit more drawn out.

BUT, we are talking aobut the same car, so the volume vented will be the same, so this really is totally irrelevant. All that matters is delta P and the area of the BOV, which are the same for both turbos.

turbopanda

ok I think i understand completely now
thank you

Daniel

Hmmm, I believe kpt4321 wins this discussion. Let me reread his posts a few more times to fully grasp the concept.

SiR Kid

I'd say the SOUND would be the same, but the kinetic energy of the larger compressor spinning would last longer, and keep the BOV open longer. That's all in theory, of course.

Cliff's Notes
Same sound, but longer blow off with a bigger turbo.

kpt4321

A: Yeah, I said that.

B: I thinkt he the kinetic energy would not make a huge difference, and you likely would not be able to tell just playing it by ear. WHile the bigger turbo does have more inertia, it also doesn't have to spin as quickly to create the same boost pressure as the smaller turbo, so its overall kinetic energy is not as high as you may think.

turbopanda

interesting

thanks for all your help anyway

ion_four

kpt4321, Thankyou for actually understanding this!

Most people do not understand basic physics/thermodynamics (pv=nrt, for example) and think that somehow a larger turbo magically flows more air. Pressure is pressure, while there will be some difference with a larger turbo, it isn't that much.

I see that you are running the stock turbo and made it into the 12's. I think it's funny how so many honda people think the T25 is too small for a 1.6/1.8 liter when DSM guys somehow manage to make good power with it on a 2.0 liter...hmm...

kpt4321

Thank you ion_four.

I'm going to college next year to be an aerospace engineering, so this is right up my alley.

I agree about the big turbos thing. There cannot be a very large change in charge temperatures with efficiency changes within the 10-15% range, especially when we consider that we have to deal with absolute temperatres here.

The gains you will see from a larger turbo are mainly from being about to turn the boost up more, and from larger turbine housings.

Also, I agree about the small turbo thing. For some reason, most of these guys seem to think that they ned a 60-1 wheel to run 10 psi. It just does not make sense.

I have a friend with a 14b on his talon, and it has done 11.85 @ 114. I also know a few other guys who have done mid 12's on the 14b.

And, A friend of mine has a 14b on his 92 Integra, with a kit we built ourselves, and it trapped at 100 mph totally untuned.