Topic: Small bov placement writeup: Hotside (Read 6502 times)

TTC · « **on:** December 30, 2009, 11:50:17 AM »

What you guys make of this. I'm moving my bov to the hot side since i dont want fucking 10feet of bov return piping. While googling i found this. What you make of it. I figure in all honestly, sure it should be near throttle plate, but as long as it stops compressor surge its doing its job.

Blow Off Valve Placement
Blow off valve placement is not the most important thing to think about when building a turbo kit, however is does make a difference. It's the small differences that separate an event winner from the rest of the field.

The vast majority of people will tell you that you are supposed to place your blow off valve within a couple feet of your throttle body. I am here to tell you that this is not the best location for your blow off valve.

The best location for your blow off valve is going to be in between your turbo and intercooler, on the hot side.

Think about it. If you put the blow off valve on the cold side (after the intercooler), you are pushing hot air through your intercooler for nothing. This increases the speed at which your intercooler and motor become heat soaked.

By putting the blow off valve before, or even on the intercooler itself - you allow all of the hot compressed air to escape to atmosphere prior to passing through the intercooler. A blow off valve does the same thing no matter where you place it on the charge piping. Knowing this - it's only logical to put it in a place where it relieves hot air rather than cold air.

turbob16hatch · « **Reply #1 on:** December 30, 2009, 05:03:27 PM »

I agree with that, and would do that if i could on my own car. i'm placing it on the cold side for ease of rerouting to intake.

WPPF · « **Reply #2 on:** December 30, 2009, 05:08:26 PM »

This is factual. Also blow off valves are made to stop compressor surge, not throttle body surge.

danz · « **Reply #3 on:** December 30, 2009, 06:20:36 PM »

take a look at my car.

hint; bov is right off the turbo compressor.

not only does it help the turbo avoid extra stress (pushing air through the intercooler isnt as easy as NOT pushing air through the intercooler) it will also allow the compressor to keep spinning faster longer keeping you in boost better between shifts.

Whitey · « **Reply #4 on:** December 30, 2009, 09:21:22 PM »

Thats all fine and good in theory but in real life it really doesn't fucking matter, put it where its most convienient to you.

Quote from: WPPF on December 30, 2009, 05:08:26 PM

This is factual.

So your saying there's datalogs showing that BOV placement decreases IAT? $:-\$

Quote from: danz on December 30, 2009, 06:20:36 PM

take a look at my car.

not only does it help the turbo avoid extra stress (pushing air through the intercooler isnt as easy as NOT pushing air through the intercooler) it will also allow the compressor to keep spinning faster longer keeping you in boost better between shifts.

If your throttle plate is closing and the BOV is opening when your racing, than you need to learn to drive. Keeping your foot on the gas keeps a turbo spinning, not a BOV.

bigdaddyvtec · « **Reply #5 on:** December 30, 2009, 10:24:11 PM »

Being that my compressor is coupled directly to the Intercooler via hump coupler..... It couldt be any closer...

WPPF · « **Reply #6 on:** December 31, 2009, 02:43:41 AM »

Quote from: Whitey on December 30, 2009, 09:21:22 PM

Thats all fine and good in theory but in real life it really doesn't fucking matter, put it where its most convienient to you.

Quote from: WPPF on December 30, 2009, 05:08:26 PM
This is factual.

So your saying there's datalogs showing that BOV placement decreases IAT? $:-\$
No. I'm just agreeing that it's a better placement in an "ideal" set up. Also this is intentionally misquoted because my phone won't let me scroll down.

Quote from: danz on December 30, 2009, 06:20:36 PM
take a look at my car.

not only does it help the turbo avoid extra stress (pushing air through the intercooler isnt as easy as NOT pushing air through the intercooler) it will also allow the compressor to keep spinning faster longer keeping you in boost better between shifts.

If your throttle plate is closing and the BOV is opening when your racing, than you need to learn to drive. Keeping your foot on the gas keeps a turbo spinning, not a BOV.

danz · « **Reply #7 on:** December 31, 2009, 02:33:54 PM »

im all for going fast, but i like my transmission to last more than a few passes. 60+ 10-11 second passes on the same tranny, no issues. ill leave FTS'n to the rich people who can afford to replace synchros.

anyways you dont need to FTS to keep in boost between shifts.

HiProfile · « **Reply #8 on:** January 01, 2010, 04:04:42 PM »

Think about THIS: when your throttle plate closes, your exahaust is pushing a fraction of the energy into the turbine. That alone will "despool" the turbo to nothingness, so while it drops to zero psi it also drops to zero cfm's and doesn't flow the fraction of air through the intercooler. To add insult to that idea's injury, as it's dropping pressure & flow, it's also dropping down to a far more efficient "island" for the majority of that wasted flow, so it's not +200F like it was 1 second previous when you were on the throttle.

The fact is you want to capture any wave of backwards air that bounces off the t-body towards the turbo - more so than keep an extra 2-3% turbine shaft speed or reducing your fmic temps 1-2F. The placement near the turbo on most stock cars is because it makes recirc'ing it far cheaper & easier. The secondary reason is because in a restrictive setup, there's a pressure drop of 2+ psi in many cases. That alone is a good reason to put the bov near the compressor.

I've never actually seen anyone prove or disprove a BOV location with hard data, just experience and heresay. It would be notoriously hard to calculate any data due to the specific head loss of each elbow, coupler, and intercooler for the entire flow curve a turbo goes through as it "blows off".

SloS13 · « **Reply #9 on:** January 02, 2010, 06:55:06 PM »

On my miata, the BOV is right off of the turbo. Much easier return

Robb · « **Reply #10 on:** January 03, 2010, 11:33:25 PM »

Who cares. Either way works. I seriously doubt anyone on this site is making enough power to worry about this.

TTC · « **Reply #11 on:** January 04, 2010, 02:00:31 AM »

I'm putting it at the compressor, gonna recirculate it, im sick of hearing a bov all day long.

turbohf · « **Reply #12 on:** January 04, 2010, 03:21:41 AM »

mine is on the cold side... cuz it looks baller and i want it to be seen, by noone cuz i dont show my shit off lol.

but also, its really in the best spot room wise. short vacuum line. and its speed density so no reroute needed.

Conceptz-X · « **Reply #13 on:** January 04, 2010, 08:49:33 AM »

Quote from: Robb on January 03, 2010, 11:33:25 PM

Who cares. Either way works. I seriously doubt anyone on this site is making enough power to worry about this.

exactly

kgx · « **Reply #14 on:** January 16, 2010, 09:09:55 PM »

Quote from: TTC on December 30, 2009, 11:50:17 AM

however is does make a difference. It's the small differences that separate an event winner from the rest of the field.

the event winner is likely the guy who's not using a BOV. in road racing, running without a bov is worth seconds per lap.

the only thing i've ever found that was better for speed than no BOV at all was this:

that's a throttle on the inlet of the turbo. when the main throttles closed in that engine, the secondary would close allowing the turbo to spin an a relative vacuum (read: no drag on the compressor wheel) which maintained impeller speed and prevented surge. the main throttles would also open a split second before the secondary, pulling slight vacuum across the compressor helping it spool up as well- at least that's what the patent documents say.

for reference, that is a BMW/megatron M12 formula one engine from the mid 80's. 1400-1500hp, 1.5L, 12,000rpm, 5.5bar of boost in qualifying. only difference between qualy and race engines was that the race engines had wastegates on the turbos.

BMW F1 Turbo / www.unoturbo.com.br

edit for a couple more pics:

Porsche 956 - Old Le Mans (On Board) *Good Sound*
hear the compressor surge.. wait til he gets on the mulsanne straight, it's like the car just launches into warp speed and the world blurs away..

dvst8r · « **Reply #15 on:** January 16, 2010, 09:18:42 PM »

Carbon fiber compressor cover. Bad ass.

kgx · « **Reply #16 on:** January 18, 2010, 01:20:10 PM »

there really wasn't much about those cars that wasn't bad ass. how many cars can spin 6th gear at 190mph rolling on 18" wide gumballs?

Robb · « **Reply #17 on:** January 18, 2010, 04:25:04 PM »

Quote from: kgx on January 18, 2010, 01:20:10 PM

there really wasn't much about those cars that wasn't bad ass. how many cars can spin 6th gear at 190mph rolling on 18" wide gumballs?

917/30.
They had a hard time finding drivers because the fucking thing was so damn scary to drive. 1000whp and see the horizon disappear in the rear view on a 190mph straight. Fuck that shit.

kgx · « **Reply #18 on:** January 18, 2010, 04:27:30 PM »

were those the ones with the aluminum space frame and the nitrogen gauge on the dash? the frame was pressurized and when the gauge went to zero, it meant the frame was fatigued/cracked somewhere and had to be junked..

dive_miguel · « **Reply #19 on:** February 04, 2010, 08:50:15 PM »

Some of the old turbo dodges had the throttle on the compressor intake. It had a real interesting snarley sound.

cool video

Eggylshatch · « **Reply #20 on:** February 05, 2010, 12:40:59 AM »

That secondary turbo-throttlebody wouldn't be too hard to rig up. Quick, someone with a turbo car go do it. ARGH I'll be turbo again some day.

HiProfile · « **Reply #21 on:** February 06, 2010, 02:52:16 PM »

Actually I don't think it was a secondary - it was the only TB. With the wind resistance from the big wings and huve ports/cams, 28" Hg isn't much different from 8" Hg of vacuum on decel. It practically won't surge because the boost literally gets sucked up by the motor instead of pushing out the turbo.

It might be interesting to try that on a beater some day. Lengthen the iacv and tps wires, use a GSR tb/cable, and go to town...

rsmith2786 · « **Reply #22 on:** February 06, 2010, 04:09:50 PM »

I'd agree with the argument if you are venting to air. But if you are recirculating then I'd rather have the air go through the IC before it has to go through the compressor again.

kgx · « **Reply #23 on:** February 06, 2010, 09:11:13 PM »

Quote from: HiProfile on February 06, 2010, 02:52:16 PM

Actually I don't think it was a secondary - it was the only TB.

on the dodges, maybe.

on the BMW M12 i posted, that is a secondary throttle. the engine has individual throttle bodies under the plenum. there's a vid of it somewhere the sole purpose of the secondary throttle is to keep the turbo spooled in vacuum while the main throttle is closed. as i posted too, the patent documents suggested that there was some benefit in spool from the engine sucking air across the compressor as the throttle cracked open. they weren't more clear on it than that, so i don't know if it's bullshit or not.

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Author Topic: Small bov placement writeup: Hotside (Read 6502 times)

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