Recirculation vs Blowoff
11-14-2002, 09:01 PM
#16
Race Director
Maybe we can come up with a new track-side accessory for mad-scientists like Rage2 & Russ. How about a BBQ attachment for the rear bumper? You can hang a chicken off the back bumper facing the exhaust pipe. Then after a full session, it's LUNCH TIME !!! 
11-14-2002, 10:17 PM
#17
Rennlist Member
I currently vent to atmosphere. Having driven both ways, here are my personal observations. Recirculation spools the turbo faster, but not significantly. Venting to atmosphere can and will lead to sucking unmetered unfiltered air into the intake, if you don't modify it. I was having a big surge when lifting throttle or with partial throttle lifts with the recirculation setup . This was very detrimental in the drivers schools, where smoothness is vital. I wanted to vent to atmosphere to improve this surge and solved the problem of any air entering the intake through the blow off valve unmetered by adding a one way sump pump check valve with a small spring on to the outlet of the blow off valve. Now, air can only go out, and not in. The car is much smoother without any significant surge on partial throttle lifts. Yes, the car is briefly rich for a split second between shifts, but I don't see a problem with this. Here is a picture of my setup.
11-14-2002, 10:32 PM
#18
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
[quote] Venting to atmosphere can and will lead to sucking unmetered unfiltered air into the intake, if you don't modify it. <hr></blockquote>
How do you know that? How do you know that at part-throttle conditions when the manifold vacumn is opening the blow-off/dump valve that air isn't LEAVING the intake tract. It's definately going somewhere (in or out) because I can hear it. If I'm cruising @ 3000 rpm down the highway my turbo is pushing maybe 6psi (boost) and the atmoshpere is 0. Which way does the air flow if the valve is open. By the way, that is a pretty slick setup with the sump valve. I hope this doesn't come off as giving you a hard time. I' m just really interested in figuring out what's going on. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
How do you know that? How do you know that at part-throttle conditions when the manifold vacumn is opening the blow-off/dump valve that air isn't LEAVING the intake tract. It's definately going somewhere (in or out) because I can hear it. If I'm cruising @ 3000 rpm down the highway my turbo is pushing maybe 6psi (boost) and the atmoshpere is 0. Which way does the air flow if the valve is open. By the way, that is a pretty slick setup with the sump valve. I hope this doesn't come off as giving you a hard time. I' m just really interested in figuring out what's going on. <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
11-14-2002, 11:09 PM
#19
Banned
[quote] Venting to atmosphere can and will lead to sucking unmetered unfiltered air into the intake, if you don't modify it. <hr></blockquote>
When in vacume blowoff valve is opened and will draw air in the reverse direction unless it is modified with a check valve.
When in vacume blowoff valve is opened and will draw air in the reverse direction unless it is modified with a check valve.
11-15-2002, 01:27 AM
#20
Three Wheelin'
Join Date: Sep 2001
Location: Calgary, Alberta, Canada
Posts: 1,596
Likes: 0
Received 0 Likes
on
0 Posts
[quote]Originally posted by Danno:
<strong>Maybe we can come up with a new track-side accessory for mad-scientists like Rage2 & Russ. How about a BBQ attachment for the rear bumper? You can hang a chicken off the back bumper facing the exhaust pipe. Then after a full session, it's LUNCH TIME !!! </strong><hr></blockquote>
LOL! Only if you don't mind the chicken tasting like fuel . Running rich with no cat... tasty!
<strong>Maybe we can come up with a new track-side accessory for mad-scientists like Rage2 & Russ. How about a BBQ attachment for the rear bumper? You can hang a chicken off the back bumper facing the exhaust pipe. Then after a full session, it's LUNCH TIME !!!
</strong><hr></blockquote>LOL! Only if you don't mind the chicken tasting like fuel
. Running rich with no cat... tasty!
11-15-2002, 07:34 AM
#21
Rennlist Member
Russ,
Very simple. I started the car with the blow off valve open to atmosphere, I put my hand against the opening, and hit the throttle. My hand was sucked against the blow off valve. From on board, initial throttle on the road causes my Air Fuel ratio to go full lean and the car stumbles. It was not possible to drive it without increasing the spring rate on the BOV to overcome the vacuum. The high spring rate made for additional surging with lift throttle situations, however, since it was not venting.
Very simple. I started the car with the blow off valve open to atmosphere, I put my hand against the opening, and hit the throttle. My hand was sucked against the blow off valve. From on board, initial throttle on the road causes my Air Fuel ratio to go full lean and the car stumbles. It was not possible to drive it without increasing the spring rate on the BOV to overcome the vacuum. The high spring rate made for additional surging with lift throttle situations, however, since it was not venting.
11-15-2002, 09:36 AM
#22
Instructor
Join Date: Jun 2001
Location: Moscow
Posts: 120
Likes: 0
Received 0 Likes
on
0 Posts
There is also one negative point with CBV against BOV:
The air that is coming back to the compressor is much more hotter than newly aspired air.
Hot air is one of the reason for detonation especially on high boost engine (air is even hotter).
As for the richness condition it is true and not , depends on the programmation of the ECU...As you have programmed fuel cut-off on deccel on the majority of electronic management...
BTW - borg Warner KKK will release an electrically assisted TurboCharger...
The air that is coming back to the compressor is much more hotter than newly aspired air.
Hot air is one of the reason for detonation especially on high boost engine (air is even hotter).
As for the richness condition it is true and not , depends on the programmation of the ECU...As you have programmed fuel cut-off on deccel on the majority of electronic management...
BTW - borg Warner KKK will release an electrically assisted TurboCharger...
11-15-2002, 10:12 AM
#23
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
David,
How was your car able to idle if it's sucking a large amount of air in through the valve? Wouldn't it be lean as you described your part throttle conditions. Blipping the throttle wouldn't simulate part throttle steady cruising conditions where the turbo is compressing the air a fair amount. Did you have to recalibrate your MAF for idle when you went to atmoshpere venting?
[quote] When in vacume blowoff valve is opened and will draw air in the reverse direction unless it is modified with a check valve. <hr></blockquote>
Thanks jimbo, but how do you know this? Did you crawl under the hood and have a buddy drive the car down the highway? If you've got -17 in/hg on the upper part of the diaphragm (3000 rpm cruising MAP,which is certainly enough vacumn to hold the valve open) you would have to have a greater vacumn than that in the intake between the throttlebody and the turbo to have air travel DOWN the pressure gradient into the intake tract. I'm pretty sure that any turbo with 3000rpm worth of exhuast flowing through the turbine isn't producing -17in/hg at the exit of the compressor side.
As for the on track barbeque, I think ribs would be a better choice to go with a nice 100 octane fuel baste.
How was your car able to idle if it's sucking a large amount of air in through the valve? Wouldn't it be lean as you described your part throttle conditions. Blipping the throttle wouldn't simulate part throttle steady cruising conditions where the turbo is compressing the air a fair amount. Did you have to recalibrate your MAF for idle when you went to atmoshpere venting?
[quote] When in vacume blowoff valve is opened and will draw air in the reverse direction unless it is modified with a check valve. <hr></blockquote>
Thanks jimbo, but how do you know this? Did you crawl under the hood and have a buddy drive the car down the highway? If you've got -17 in/hg on the upper part of the diaphragm (3000 rpm cruising MAP,which is certainly enough vacumn to hold the valve open) you would have to have a greater vacumn than that in the intake between the throttlebody and the turbo to have air travel DOWN the pressure gradient into the intake tract. I'm pretty sure that any turbo with 3000rpm worth of exhuast flowing through the turbine isn't producing -17in/hg at the exit of the compressor side.
As for the on track barbeque, I think ribs would be a better choice to go with a nice 100 octane fuel baste.
11-15-2002, 03:42 PM
#24
Banned
[quote] I'm pretty sure that any turbo with 3000rpm worth of exhuast flowing through the turbine isn't producing -17in/hg at the exit of the compressor side. <hr></blockquote>
you are if your throttlebody is opened and the blowoff is open at the same time. Witch would happen before your turbo spools and below 2500 rpms.
you are if your throttlebody is opened and the blowoff is open at the same time. Witch would happen before your turbo spools and below 2500 rpms.
11-15-2002, 08:05 PM
#26
Advanced
Join Date: Apr 2002
Location: Portland, OR
Posts: 82
Likes: 0
Received 0 Likes
on
0 Posts
I wound up just cutting a stronger spring and putting in the BOV so that it stays closed under vacuum, and only opens up when I lift throttle under boost. Seems to work pretty well.
11-15-2002, 09:04 PM
#27
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
I have a Forge dump valve with their stiffer "competition" spring and it works pretty much as you describe with opening under part throttle mostly eliminated. I just don't see a situation in which air can be sucked in through the valve other than maybe at idle.
11-17-2002, 05:49 PM
#28
Rennlist Member
Russ,
Perhaps I was unclear about part throttle situations. The BOV will have a tendency to open and suck air into the intake if you are at idle and hit the gas pedal. I confirmed this with my hand over the BOV. I was able to increase spring pressure enough on the BOV to overcome this tendency, but I was not happy with the smoothness of lift throttle situations. The BOV would also entrain air if cruising, lifting throttle to create vacuum, then applying throttle. The car would stumble and show lean on the Air fuel ratio. By the way, the O2 sensor was able to compensate at idle for the additional air on it's own, but as soon as the throttle was applied, the car stumbled.
Perhaps I was unclear about part throttle situations. The BOV will have a tendency to open and suck air into the intake if you are at idle and hit the gas pedal. I confirmed this with my hand over the BOV. I was able to increase spring pressure enough on the BOV to overcome this tendency, but I was not happy with the smoothness of lift throttle situations. The BOV would also entrain air if cruising, lifting throttle to create vacuum, then applying throttle. The car would stumble and show lean on the Air fuel ratio. By the way, the O2 sensor was able to compensate at idle for the additional air on it's own, but as soon as the throttle was applied, the car stumbled.
11-18-2002, 09:12 AM
#29
Pro
Join Date: Jan 2002
Location: N.Y.
Posts: 579
Likes: 0
Received 0 Likes
on
0 Posts
hey david i got news for you about your car problem, contact me offlist for details, i think i know why your car has positive crankcase pressure at idle and why its causing the rear main seal to leak, right? email me if you want some ideas, i went thru that too this year and solved it...
11-18-2002, 10:56 AM
#30
Drifting
Join Date: Dec 2001
Location: St. Louis
Posts: 2,058
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for the clarification David. 
I guess the range of spring rates must vary greatly in different valves. Mine is fully shut at idle and doesn't open when you blip the throttle.
Tecart,
Please share!
I'd love to know what you found, as my car has the same symptoms.
I guess the range of spring rates must vary greatly in different valves. Mine is fully shut at idle and doesn't open when you blip the throttle.Tecart,
Please share!
I'd love to know what you found, as my car has the same symptoms.