"The BIG BOV thread" (Where all bov question threads get merged)

[STiBoy]

Originally posted by Blue2004WRX
It's physics. Starting temperature doesn't matter at that compression. Temperature is equivalent to air pressure. I can explain why if you want.

HOWEVER, in the low RPM band where turbo hasn't spooled, a CAI may give you better performance. Not quite sure about that.

Please do explain it...

Thanks,

TK

[Blue2004WRX]

OK quick explanation because I'm at work.

The reason air is hot is because molecules in gases are free to bounce around. The more they bounce off of each other, the more energy they release (heat). That's why colder air has a higher concentration of molecules, they don't bounce around as much. When air is compressed to a certain pressure, the distance between molecules is restricted, therefore the amount they bounce off of each other is also constant, so the amount of energy they release is also constant, and bam, you have a certain temperature, unless other factors come into play. In the case of compressed turbo air, there is no other factor until you hit the intercooler.

Feel free to correct or clarify anything I've said here. I'm not a chemist.

[dark_rex]

Originally posted by STiBoy
So you're saying that Subaru (and all the other car makers that do it), who have the technology to build an incredibly sophisticated motor, have somehow misinformed themselves and wasted time and money designing the stock CAI?

no, but for a stock factory car, higher filtration, and less noise is optimal. so resonator boxes are installed, mechanisms to keep moisture out of the bay, and ways to keep the MAF signal reliable and predictable for the ECU are employed. in a tuned car, you don't care about any of that. you're going to tune to adjust for the MOST AIR POSSIBLE.

Originally posted by STiBoy
No flames intended, but (I don't think) the theory holds. Whatever temp goes in will be heated by X%...and come out X% hotter. Unless there's an upper limit to the air temp, or that compressed air is going to be heated to Xº if at a certain pressure, regardless of its starting temp, I'd say it's a benefit. And there can be a 30-40º difference between engine bay and outside air temp. I know with my Buick GN, that my hp seems to be equivalent to at least 1º/hp. IOW, if it's 50º outside, I'll have 430 hp. If it's 80º, I'll have <400 hp. Most of this of course is attributable to the IC cooling, but it's quite obvious that air temp plays a BIG roll.

I'd think it'll help..."a little". But of course, until someone produces a viable dyno data comparison...we can argue this all day.

there are dyno comparisons all over the web. in a N/A car, you're absolutely right. that small % of air will be affected with the same heatsoak multiple, so 50 degrees will lose X%, and 70 degrees will lose X%.

but in a F/I car, you're turbo is spinning well over 200,000 rpms, and compressing ambiant air to TWICE (in our cars) atmospheric pressure. that 20 external air degrees F means squat on the hot side of the turbo. i would argue unless you are saving 40 degrees PLUS, it's not worth a CAI, and if there is a big difference, than i would further argue your IC and post compression cooling is grossly inadequate, and probably making tuning very difficult due to erratic intake charge figures. the difference in temp b/w your fender wall and just inside your fenderwall on a hot car is probably 5-10 degrees tops.

CAI's are designed to lean out an N/A car where that small diff in temp w/ make a difference. get a short ram and stop starving your turbo. you want proof of a shortram intake benefits on an STi? just ask Dan (God) he got his STi to 300 AWHP with just a shorty, BC and downpipe. .

dR

[Blue2004WRX]

Originally posted by dark_rex

i would argue unless you are saving 40 degrees PLUS, it's not worth a CAI, and if there is a big difference, than i would further argue your IC and post compression cooling is grossly inadequate

Bingo. Also, its cheaper, which is nice for poor kids like me

[STiBoy]

Originally posted by Blue2004WRX
Bingo. Also, its cheaper, which is nice for poor kids like me

I'm not trying to be argumentative, just skeptical. Firstly, the difference is roughly 30-40 degrees, engine bay vs. outside. I've got a Buick GN, which have an intake air temp sensor. I've compared the temps with and without a cold air system, and the diff is 30-40 deg. And by the looks of the set up on the STi/WRX, the intake air temp will be even higher...it's centered more in the engine bay. My guess on a warmed motor, on an 80 degree day is an intake air temp of 120 degrees...easy.

Next, I should say I have no degree in Physics, so I'm just throwing this stuff out, according to my six brain cells' reasoning. But what it sounds like, is that one is reasoning that compressed air (pressurized air), has a constant of the space between the molecules. As long as the pressure is constant, the temp will be too...which we know isn't true. If you have a can of compressed air, that tempurature can vary...obviously. This is where I get foggy...my question is, is the measurement of heat itself a direct indicator of the distance of the distance between molecules? I don't think so. As we go higher into space, and approach the outside of our atmosphere, the temp gets colder. But we all know that the air in the mountains is "thinner", but the temps still vary. These are just other examples of compressed air...altitude.

I'm confusing myself, but bottom line is that I'm still having a hard time believing that if one has an intake air charge of -30 degrees, that it's going to be 250 degrees at the other end of the turbo no matter what if it's coming out at 15 psi.

I don't know...

[Blue2004WRX]

Altitude, refrigeration... These are all adverse factors on the temperature of the COMPRESSED air. NOT the temperature of the air before that compression. Get my point?

[Shibby]

i just installed my GFB stealth FX BOV. It works excellent. However, I noticed the smell of sulfur around my car. Especially when my car idles for a while. Why is this?

[hatchy]

Are you sure something isnt burning?

[Shibby]

Originally posted by hatchy
Are you sure something isnt burning?

i dont think anything is, i sure hope nothing is

[BoostedBoxer]

how many miles on your car? maybe you smell cosmolene (stuff they put on exhaust of brand new cars) i have a gfb and i dont smell anything

[MidKnight]

I know my Forge BOV had some shiet coming out of it for the first few days and sprayed some nasty pink stuff in my engine bay that burned off and stunk to high hell. I also know that one time I parked my car over a piece of plastic that stuck to my exhaust and smelled for days while I thoguht my engine was gonna blow up.

The smell is probably no big deal... If it persists for more than a day or two it may be a problem. Check around and see if you can locate the origin....

[Web Foot STi]

The starting temperature does influence the outlet temperature of the air when it is compressed. The reason a 30 - 40 deg F delta temp doesn't make a big difference is that the calculation has to be done in degrees Rankine from absolute zero, or -460 deg F.

For a 100% efficient turbo the heat rise is T2 = T1*(P2/P1)^.283

T1 = inlet temp deg R
T2 = outlet temp deg R
P1 = inlet absolute pressure
P2 = outlet absolute pressure

At sea level here are some numbers:

70 deg F day
14.7 psi atmospheric pressure 1 bar.
14.5 psi boost

T2 = (460+70)*((14.7+14.5)/(14.7)^.283 = 643 deg R, or 183 deg F

Assuming that the turbo is 70% efficient (That's a high estimate) you have a 231 deg F inlet temperature. 231 deg F = ((643-460-70)/.70)+70

I could say that I got this out of a thermodynamics text book, but it was easier to look at page 16 of Turbochargers by Hugh MacInnes. HP books.

[CKxx]

Yes, it should blow off immediatly as you release the throttle, but no i dont know why yours does not. Refer to your instructions and see if there is some level of spring adjustability and try to lessen that.

Also, compressor surge will sound like some sort of fluttering noise.

[2003WRX]

Hmm, the smell is probably sulphur content in your gas (which is commonly added by fuel companies). I am doubting the BOV is the cause of this, although I am admittedly no expert. Is it possible you just happened to notice the smell around the same time? I noticed the same thing a few weeks back coming out of my car... nasty rotten egg smell. I switched gas brands and it went away. If you search here and NASIOC for "rotten egg smell" or something along those lines, you will find many threads. I did this myself back when I noticed the smell coming from my car. And no, your catalytic converter is likely not going bad as people will undoubtedly suggest.

[hippy78]

hey,
I thought the fluttering noise was the wastegate opening and closing so the turbo slows down?