Freeway speeds, VTA, and 02Clamp - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-12-2006, 10:24 PM   #1
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Default 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 **** 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.
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Old 12-12-2006, 10:46 PM   #2
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What causing the bucking? the BOV being open while the turbo is trying to spool? Any way to fix that w/ out recirc?
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Old 12-12-2006, 11:06 PM   #3
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do the o2 clamp first then recirc. My turbo is very audible well before it's making boost.
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Old 12-12-2006, 11:26 PM   #4
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bigger turbo?????
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Old 12-12-2006, 11:27 PM   #5
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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 *****-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.
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Old 12-12-2006, 11:53 PM   #6
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I mean, are you bucking or it hesitates and feels odd before it boosts? Like a delayed switch or something...
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Old 12-13-2006, 12:11 AM   #7
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Maybe just tighten the BOV.
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Old 12-13-2006, 12:18 AM   #8
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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.
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Old 12-13-2006, 01:48 AM   #9
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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
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Old 12-13-2006, 02:10 AM   #10
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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.
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Old 12-13-2006, 05:51 AM   #11
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Thats weird, I never had that problem every with my VTA.
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Old 12-13-2006, 11:29 AM   #12
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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.
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Old 12-13-2006, 11:30 AM   #13
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Quote:
Originally Posted by getsidewaysd1 View Post
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.
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Old 12-13-2006, 11:57 AM   #14
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Quote:
Originally Posted by AndyFloyd View Post
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.
how much are the HKS SSQ I assume thats what your using?
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Old 12-13-2006, 11:58 AM   #15
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I was able to tighten my TCC ebay special knock off bov. No bucking and it sounds cool without being loud.
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Old 12-13-2006, 12:07 PM   #16
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Quote:
Originally Posted by miatamania View Post
how much are the HKS SSQ I assume thats what your using?
I paid 160 w/ free shipping. I forget the exact site I got it from.
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Old 12-13-2006, 12:13 PM   #17
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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*
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Old 12-13-2006, 12:20 PM   #18
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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.
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Old 12-13-2006, 01:12 PM   #19
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Quote:
Originally Posted by AndyFloyd View Post
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.
Except I'm running the DIY Lowes Check Valve... so I know it's not leaking under Vaccum. I'll try it both ways. First thing this weekend is to recirc. I'll take it for a spin and check the results... then throw on the 02 clamp and check the results... then the 305's... then the RX7... then dial down the MBC a little (running open for now).
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.
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Old 12-13-2006, 01:35 PM   #20
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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 ****. Or this is when it did it the most obvious.

Jay
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