Blow Off Valve vs. Diverter Valve?
#16
10-18-2009, 10:18 AM
Sorry, I don't buy it. Unless that air is directed right into the turbine inlet - which I think some rally cars may have done - the air isn't going to show any measurable benefit IMO. Someone's going to have to find a citation showing some measured difference before I'll be convinced. The volume of air moving in an intake tract to the turbo is enough that I don't see this helping - especially since one end is essentially open to atmosphere anyway out the air cleaner! If you put a gauge on that intake tract at the turbo I predict you'd see no pressure rise when the DVs pop and no measurable difference in spool vs blowing to atmo. Pressure on a good shift returns so fast it's amazing.
FWIW I'm very aware as to how fast this all occurs. My Supra blew to atmosphere and I did more datalogging on that car car than anyone I know short of a pro tuner - hundreds of hours at least under all sorts of conditions. You'd be surprised at how fast the turbo is back up to speed when you crack the throttle back open and the BOV closes. I logged turbo response specifically when folks tried to tell me I had used "too big" an intercooler on my car for the stock turbos and would see "lag". Yes, I logged it with a few other single turbos too
As is often the case this turned out to be "common sense" not being true. When you consider the volume of air it takes to pressurize a running engine it's pretty amazing to watch how fast boost recovers on a shift - big IC or not. Even if the BOV returned the piping completely to ambient pressure (I'll bet it doesn't) the turbo moves some serious air and re-pressurizes in the blink of an eye.
BTW if you've ever wondered what it's like to not run a BOV or DV at all listen to a stock or lightly modded Buick GN. When you get off the gas in one of those you get to hear all sorts of noises as the turbo chokes on the bounced airstream. THAT most certainly has to have an effect!
P.S. FWIW I'm not a big fan of whistles, chirps, and other crap done on these things - some Japanese BOV literally had whistles in them! While maybe fun for a couple of shifts it quickly becomes VERY annoying - yes I tuned a car with one of these for over a week. That said blowing to atmo reduces plumbing clutter a GREAT deal. No goofy F-hoses or badly crimped intake tracts and the valve can be placed darn near anywhere without regard to having to get the air to the backside of the MAF through some tortured path. Going blow-thru to get this simplicity is pretty tempting since I happen to be chasing a boost loss issue right now with the DV circuit being a prime suspect!
FWIW I'm very aware as to how fast this all occurs. My Supra blew to atmosphere and I did more datalogging on that car car than anyone I know short of a pro tuner - hundreds of hours at least under all sorts of conditions. You'd be surprised at how fast the turbo is back up to speed when you crack the throttle back open and the BOV closes. I logged turbo response specifically when folks tried to tell me I had used "too big" an intercooler on my car for the stock turbos and would see "lag". Yes, I logged it with a few other single turbos too
As is often the case this turned out to be "common sense" not being true. When you consider the volume of air it takes to pressurize a running engine it's pretty amazing to watch how fast boost recovers on a shift - big IC or not. Even if the BOV returned the piping completely to ambient pressure (I'll bet it doesn't) the turbo moves some serious air and re-pressurizes in the blink of an eye.BTW if you've ever wondered what it's like to not run a BOV or DV at all listen to a stock or lightly modded Buick GN. When you get off the gas in one of those you get to hear all sorts of noises as the turbo chokes on the bounced airstream. THAT most certainly has to have an effect!
P.S. FWIW I'm not a big fan of whistles, chirps, and other crap done on these things - some Japanese BOV literally had whistles in them! While maybe fun for a couple of shifts it quickly becomes VERY annoying - yes I tuned a car with one of these for over a week. That said blowing to atmo reduces plumbing clutter a GREAT deal. No goofy F-hoses or badly crimped intake tracts and the valve can be placed darn near anywhere without regard to having to get the air to the backside of the MAF through some tortured path. Going blow-thru to get this simplicity is pretty tempting since I happen to be chasing a boost loss issue right now with the DV circuit being a prime suspect!
#17
10-18-2009, 10:36 AM
Registered User
Sorry, I don't buy it. Unless that air is directed right into the turbine inlet - which I think some rally cars may have done - the air isn't going to show any measurable benefit IMO. Someone's going to have to find a citation showing some measured difference before I'll be convinced. The volume of air moving in an intake tract to the turbo is enough that I don't see this helping - especially since one end is essentially open to atmosphere anyway out the air cleaner! If you put a gauge on that intake tract at the turbo I predict you'd see no pressure rise when the DVs pop and no measurable difference in spool vs blowing to atmo. Pressure on a good shift returns so fast it's amazing.
FWIW I'm very aware as to how fast this all occurs. My Supra blew to atmosphere and I did more datalogging on that car car than anyone I know short of a pro tuner - hundreds of hours at least under all sorts of conditions. You'd be surprised at how fast the turbo is back up to speed when you crack the throttle back open and the BOV closes. I logged turbo response specifically when folks tried to tell me I had used "too big" an intercooler on my car for the stock turbos and would see "lag". Yes, I logged it with a few other single turbos too As is often the case this turned out to be "common sense" not being true. When you consider the volume of air it takes to pressurize a running engine it's pretty amazing to watch how fast boost recovers on a shift - big IC or not. Even if the BOV returned the piping completely to ambient pressure (I'll bet it doesn't) the turbo moves some serious air and re-pressurizes in the blink of an eye.
BTW if you've ever wondered what it's like to not run a BOV or DV at all listen to a stock or lightly modded Buick GN. When you get off the gas in one of those you get to hear all sorts of noises as the turbo chokes on the bounced airstream. THAT most certainly has to have an effect!
P.S. FWIW I'm not a big fan of whistles, chirps, and other crap done on these things - some Japanese BOV literally had whistles in them! While maybe fun for a couple of shifts it quickly becomes VERY annoying - yes I tuned a car with one of these for over a week. That said blowing to atmo reduces plumbing clutter a GREAT deal. No goofy F-hoses or badly crimped intake tracts and the valve can be placed darn near anywhere without regard to having to get the air to the backside of the MAF through some tortured path. Going blow-thru to get this simplicity is pretty tempting since I happen to be chasing a boost loss issue right now with the DV circuit being a prime suspect!
FWIW I'm very aware as to how fast this all occurs. My Supra blew to atmosphere and I did more datalogging on that car car than anyone I know short of a pro tuner - hundreds of hours at least under all sorts of conditions. You'd be surprised at how fast the turbo is back up to speed when you crack the throttle back open and the BOV closes. I logged turbo response specifically when folks tried to tell me I had used "too big" an intercooler on my car for the stock turbos and would see "lag". Yes, I logged it with a few other single turbos too
As is often the case this turned out to be "common sense" not being true. When you consider the volume of air it takes to pressurize a running engine it's pretty amazing to watch how fast boost recovers on a shift - big IC or not. Even if the BOV returned the piping completely to ambient pressure (I'll bet it doesn't) the turbo moves some serious air and re-pressurizes in the blink of an eye.BTW if you've ever wondered what it's like to not run a BOV or DV at all listen to a stock or lightly modded Buick GN. When you get off the gas in one of those you get to hear all sorts of noises as the turbo chokes on the bounced airstream. THAT most certainly has to have an effect!
P.S. FWIW I'm not a big fan of whistles, chirps, and other crap done on these things - some Japanese BOV literally had whistles in them! While maybe fun for a couple of shifts it quickly becomes VERY annoying - yes I tuned a car with one of these for over a week. That said blowing to atmo reduces plumbing clutter a GREAT deal. No goofy F-hoses or badly crimped intake tracts and the valve can be placed darn near anywhere without regard to having to get the air to the backside of the MAF through some tortured path. Going blow-thru to get this simplicity is pretty tempting since I happen to be chasing a boost loss issue right now with the DV circuit being a prime suspect!
I am sure my testing was not a thorough as yours, but on the Lotus TT We definately noticed a turbo lag decrease when vented to the turbo inlet. Now all that being said, those 2.5 Garrets were notorious for slow spooling to start with.
#18
10-18-2009, 12:41 PM
Your points are very well taken (and expressed). Especially regarding piping and clutter and more places to leak etc. But respectfully I will still stick with my every little bit helps principle.
I am sure my testing was not a thorough as yours, but on the Lotus TT We definately noticed a turbo lag decrease when vented to the turbo inlet. Now all that being said, those 2.5 Garrets were notorious for slow spooling to start with.
I am sure my testing was not a thorough as yours, but on the Lotus TT We definately noticed a turbo lag decrease when vented to the turbo inlet. Now all that being said, those 2.5 Garrets were notorious for slow spooling to start with.
An anecdotal story about BOV... Helped tune a turbo Ford 351+W motor in a drag car on the dyno. Owner had moved from a supercharger to a CHEAP single turbo setup with flipped headers and muffler clamps but the chassis was first class tubbed etc. Anyway, they used a water\air IC with ice in the passenger seat space and had heyuge pipes coming in. They placed the BOV in the passenger compartment pointed towards the driver.
First pass it vented FOG right into the driver's face! Smart guy draped a towel over it. 2nd pass he got a towel in the face. (lol) This thing had a sheet metal Hogan's intake that actually swelled when the turbo came on boost and it beaded water from the cool intake temps. Car made 1KRWHP on moderate boost through a powerglide, melted lots of ice. On one pass we checked a plug and someone left the wire off, car ran perfectly but pulled 100HP less and had us freaking looking for the problem. That thing really was pretty sick to work on and made a real impression on me - especially when you saw how the turbo "system" had been built!
Anyway, that intake piping carried MASSIVE amounts of volume and the BOV was as big as my fist and vented air like crazy. Put THAT much air directly into the intake of a turbo and I can see it pushing things along but 3feet away from the turbo and I think air would take the path of least resistance and not be much benefit. I'm open to being swayed and I love to learn and debate but it's going to take some data. IMO manufacturers recirculate for NVH, emissions, and to make air metering easier not for any performance benefit. <shrug>
#19
10-18-2009, 01:51 PM
Registered User
BLKMGK:
We did use a data logger but only measured sustained boost (MAP output). The Lotus has a short run between the air filter and the turbo inlets and we fed the valves back to the exit of the filter but not directly into the turbos (About 12" from the turbo inlets). It was actually easy to do as there are 2 filters one left and one right. The air comes in as it does for the intercoolers on the Porshe behind the doors, but instead of going to the intercoolers it goes into the air intakes gets filtered and then goes directly to the turbos. The Lotus V8 TT has no stock intercoolers (Stupid Really).
Honestly, it was not the best installation but it did serve a purpose, and they sounded really obnoxious if left vented to atmosphere.
Here is one of the entries to the airbox plugged for testing.
http://impconcepts.com/espritv8bov/leftairboxreturn.jpg
Here is the left Valve.
http://impconcepts.com/espritv8bov/l...rightvalve.jpg
Again, I understand where you a coming from as a lot of the Air could in fact bleed back through the filter at slower speeds.
The Tube inside the airbox was fed into the Turbo inlet pipes.
We did use a data logger but only measured sustained boost (MAP output). The Lotus has a short run between the air filter and the turbo inlets and we fed the valves back to the exit of the filter but not directly into the turbos (About 12" from the turbo inlets). It was actually easy to do as there are 2 filters one left and one right. The air comes in as it does for the intercoolers on the Porshe behind the doors, but instead of going to the intercoolers it goes into the air intakes gets filtered and then goes directly to the turbos. The Lotus V8 TT has no stock intercoolers (Stupid Really).
Honestly, it was not the best installation but it did serve a purpose, and they sounded really obnoxious if left vented to atmosphere.
Here is one of the entries to the airbox plugged for testing.
http://impconcepts.com/espritv8bov/leftairboxreturn.jpg
Here is the left Valve.
http://impconcepts.com/espritv8bov/l...rightvalve.jpg
Again, I understand where you a coming from as a lot of the Air could in fact bleed back through the filter at slower speeds.
The Tube inside the airbox was fed into the Turbo inlet pipes.
#20
10-22-2009, 07:58 PM
i currently have a Agency Power BOV and i am planning on installing it, but i want to know which hole to plug or which to put the actual BOV on. the top of the "F" or the middle?
also, if i vent it 50/50 how loud will it be, anyone have experience with the 100% vs 50/50 vent
i also want to know how the Topic Starter got the HKS SSQ on his car. is it the universal BOV or is it a 996tt kit?
also, if i vent it 50/50 how loud will it be, anyone have experience with the 100% vs 50/50 vent
i also want to know how the Topic Starter got the HKS SSQ on his car. is it the universal BOV or is it a 996tt kit?
#21
10-22-2009, 08:17 PM
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