Freeway speeds, VTA, and 02Clamp
OK, so before I removed the cat and replaced it with a test pipe, I could manage 70-80mph on the freeway with no problem. I had a slight bucking when transitioning in and out of boost, but nothing that bothered me.
Now that the cat is gone, spool above 3k rpm's is NO SHIT INSTANT! If I'm doing 70 in 5th (about 3500rpms) and put my foot down, I'm at 7-8psi before I get the pedal to the floor. It's like the boost gauge is directly connected to the gas pedal. It makes it very difficult to just cruise on the freeway. Breathing on the pedal above 75mph puts me in boost. At those speeds, my gauge is hovering around -15vaccum and the turbo is very audible... the problem is, so is the BOV. Bottom line: Cruising at 80mph in 5th puts me in that grey area between boost and vaccum that the turbo is making pressure, but the manifold is still in vaccum, and I'm dumping air out the BOV. I can audibly hear the turbo spool and the BOV open at the same time. I'M BUCKING LIKE CRAZY!!! Time to RECIRULATE. Time to 02 clamp. The Skipper just gave us Friday off... parts on the workbench... wife working... Dyno will wait until next week. Only 200 miles on my Spec. Oh well, work in progress. No real questions from me here. I was going to do it anyways, I just didn't think the bucking would be that bad. Any input. |
What causing the bucking? the BOV being open while the turbo is trying to spool? Any way to fix that w/ out recirc?
|
do the o2 clamp first then recirc. My turbo is very audible well before it's making boost.
|
bigger turbo????? :)
|
BIGGER TURBO!!! HAHAHAHAHA, took me a minute though.
MiataMania, I know you know this, but for the uninformed: Air that is dumped by the BOV has already been measured by the ECU and fuel has been added for it. So when you VENT, all that air is released but the fuel is still added at the injector, which causes you to run mad rich for an instant... so you buck. Having the BOV teeter on the edge of VENT causes it to buck rapidly... feels like running on 3 cylinders, a broken motor mount and an out of balance tire all at the same time. The fix it to port that vented air back into the intake between the MAF and the turbo, so the air re-enters the already measured airstream and no bucking... but you don't get the all important penis-enlarging PSSSTTT/WHOOOSSH BOV sound. Brain suggests an O2 clamp, which is on the workbench... which means at those speeds, I'm probably teetering on the edge of OPEN/CLOSED loop ECU function and that's never good. |
I mean, are you bucking or it hesitates and feels odd before it boosts? Like a delayed switch or something...
|
Maybe just tighten the BOV.
|
I was having the same problem, and the O2 clamp helped tremendously. Just take the time and get the voltage that feels the best, mine was at .41V that it really felt good. I also set the pressure switch to 2psig, and that keeps it from bucking when under real slight boost.
|
Told you so. :)
I had the same issue, plumbing the BOV back to the intake fixed it 100%. An O2 clamp did nothing to help this problem for me. And I fucked around with the pressure switch and the voltage all over the place to no avail. Jay |
I wonder how much time the stock ecm is running? People don't realize that anything "below" that -15psi vacuum is boost, and you can't run full advance that far forward.
It could also be a problem if whatever ecm you're running is throwing "enrichment" off the tps, and that bov is dumping the boost...but if your running the naturally aspirated map from a stock ecm, that's incredibly unlikely. I had this problem on my old turbo vr6 when i switched to 3" exhuast. It didn't go away until we did stand alone. |
Thats weird, I never had that problem every with my VTA.
|
Is it a bosch BOV? If so then you almost have to recirculate it. That BOV opens under vacuum and thats most likely most of the cause of the bucking. I run a HKS and it stays closed unless its venting so no bucking issues for me.
|
Originally Posted by getsidewaysd1
(Post 64167)
Thats weird, I never had that problem every with my VTA.
All bov's are different...you cant put all venting bov's in one catagory. |
Originally Posted by AndyFloyd
(Post 64228)
Is it a bosch BOV? If so then you almost have to recirculate it. That BOV opens under vacuum and thats most likely most of the cause of the bucking. I run a HKS and it stays closed unless its venting so no bucking issues for me.
|
I was able to tighten my TCC ebay special knock off bov. No bucking and it sounds cool without being loud.
|
Originally Posted by miatamania
(Post 64239)
how much are the HKS SSQ I assume thats what your using?
|
w/ that one I have to have a fitting welded to the pipes, then it bolts on...or am I thinking of....*off to search*
|
The SSQV universal?
http://www.evasivemotorsports.com/me...HKS-1421-SA001 w/ the weld on thingy for it: http://www.evasivemotorsports.com/me...HKS-1410-SA001 Sorry to jack the thread Sam...it kinda has something to do with it if one is looking for a way to run VTA w/ your, my getting there setup :) Apparently this is the bov that allows for different inserts to change from the high pitched sound to the just a deep rush of air sound...kinda neat. |
Originally Posted by AndyFloyd
(Post 64228)
Is it a bosch BOV? If so then you almost have to recirculate it. That BOV opens under vacuum and thats most likely most of the cause of the bucking. I run a HKS and it stays closed unless its venting so no bucking issues for me.
Hopefully by Saturday afternoon, I'll have the bucking fixed and be able to run a consistent 10psi... put another 200miles on it and head to the dyno. |
I had a check valve on my bosch and it did the bucking thing. Under cruise it was ok, but if I tried to slowly lift while under boost it would buck like a mofo. Or this is when it did it the most obvious.
Jay |
I never had a bucking problem VTA, only an engine cutting out problem.
|
Maybe what you call cutting out and what we call bucking are the same thing?
|
Get rid of the AFM? ;)
|
Originally Posted by jayc72
(Post 64295)
Maybe what you call cutting out and what we call bucking are the same thing?
no. i mean 0rpms are hard to mistake. |
Originally Posted by braineack
(Post 64310)
no. i mean 0rpms are hard to mistake.
|
no, it's why a huge vacuum leak on a metered engine sucks.
|
...literally :gay:
|
Lol
|
O2 Clamp Installed!
Well, I just went for a nice little jaunt to test out the O2 clamp just installed. My freeway cruising jerkiness seems to be about 50% gone. At 75-80 though, I'm still in that grey area where a breath on the pedal takes me from -10vaccum to 8psi in an eyeblink. I honestly think that the turbo is spooling and making positive pressure while the manifold is still in vaccum and the boost is just going straight out VTA. I can hear the turbo wind up and can modulate the gas to keep the BOV open. I can hear both working at the same time... my record is about 6seconds, during which time, the car will jerk like crazy (but a lot less now due to the 02Clamp).
Olderguy's instructions say don't adjust the little brass screw on the clamp unless I've got a voltmeter. Can I adjust it a little bit pretty please if I mark where it was when I started just to expiriment? If so, what am I looking for in response. Is moving that little brass screw going to do something I can feel. Also, it comes set to "clamp" at .5psi... any reason I should want it to wait until more boost to clamp. What should I be trying to feel wrt driveability to "tune" the thing... or is most of it stuff to mess with on the dyno? |
You can increase the boost pressure setting by turning in the allen screw on top of the switch clockwise. I run mine about 1-1.5psi so that I don't hit clamp at high speed cruise.
Changing the voltage to the ECU during clamping should be done with a digital voltmeter. It is set to send a pretty lean signal. Counterclockwise will make the signal more rich, but it is very sensitive. |
Yeah, I can guarantee you're turbo's producing boost at freeway speeds and spitting the excess out the bypass valve. I can clearly hear my bypass valve venting on the freeway...it's built into the compressor housing (recirculating) and it makes quite a bit of noise at those speeds.
|
All times are GMT -4. The time now is 06:11 PM. |
© 2024 MH Sub I, LLC dba Internet Brands