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Thread: "Breaking up" when in boost?

  1. #11
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    There is definitely a loss of power when this occurs. Not that I keep my foot in the throttle very long. Sounds almost like http://www.youtube.com/watch?v=AEsFzeK0kB0 , just less rapid and a little louder. I have done a CASE relearn about once a week LOL. I have tried 9, 8 and 7 heat range plugs(NGK) since the rebuild. The 9's were first - I think it actually ran good on them until they became too fouled from a little street driving. 9's were recommended for my engine if running it to 20 psi. I lost the ground straps off a couple of 6's last year. The 6's are also a protruding style. I have been wondering about the plug gap as well. Although .025 is pretty well where the 7, 8 and 9's are gapped at out of the box. The 6's are around .035 out of the box.
    Last edited by DrX; August 3rd, 2011 at 01:54 PM.
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

  2. #12
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    Just went out and checked my catch can and it is full after only 3-400 miles on the rebuilt engine - who knows how long it has been full. The can is connected between the driver's side fabricated, non-baffled valve cover and common inlet box for the blowers very near the inlet to the rotors for the drivers side supercharger. The PCV tube with orifice from the LS7 valley cover is spliced into the hose. If there is any pressure in the crankcase or high vacuum at the blower inlets under boost, it would likely force oil from the can into the blower. Not sure if the DS valve cover is the best arrangement for a LSX block but there was a clearance issue so the PCV tube had to be cut off the valley cover. I never saw this much oil in the can when I was using the valley cover PCV outlet. I never was too keen on the lack of baffles in these valve covers.

    Fresh air intake side of the PCV. It is connected to the non-baffled right side valve cover and intake tube between one of the air filters and throttle bodies. Thought I would try no can on that side this time and found that there is only a light coating of oil in the intake tube. Last year I had a lot of oil blowing out that hose under boost, but half of the valve seals were crushed at that time. Still think I will put a can back on that side as well.

    This might also explain why the #7 plug appeared to have a light coating of oil on it each time I changed the plugs. Oil could sit in the lower intake, run to the back and then into #7 as my garage floor is sloped that way for drainage.


    Last edited by DrX; August 3rd, 2011 at 02:26 PM.
    2017 Camaro SS, 2014 Ram 2500 4x4 Cummins 6.7L, 2004 Chevy Avalanche Z71 4̶X̶4̶(now 2WD), 5870lb race weight, 10.93@ 124, Twin TVS1900s, Twin Throttle, 429 LSX, 4L80E, custom 14 bolt rear, V2, R̶o̶a̶d̶R̶u̶n̶n̶e̶r̶(dead), COS3......
    Gettin' the Groceries

  3. #13
    Lifetime Member swingtan's Avatar
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    Ahh, well..... Given those pics I'd say the plugs are in the right heat range

    The catch can may be the culprit and feeding oil into the engine. It's an easy test to empty the catch can and do some tests, allowing for the fact that there may be some residual oil in the tubes and manifold. Might be an idea to disconnect it entirely just for a test.

    Post some pics of the plugs if you can.

    Simon

  4. #14
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    I recently read some TBSS guys with stock or built engines have had issues with their blowers pulling oil through the catch can into the intake. Might be the case here, hope its as easy as moving the can to a different hose routing.

    BTW I was wondering what a twin blown LSX looked like, but until I read this I didnt know it was twin maggie/whipples! Figured it was a pair of turbos. Must have a big cowl hood to fit that intake system too, looks good though!
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  5. #15
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    Quote Originally Posted by DrX View Post
    Looking at the rich spikes logged on WB1 which occur both cruising(more so at MAP values below 60 kPa) and always when into boost(multiple spikes at short intervals- .1 -.3 sec), what could cause this?

    1. A bad wideband
    2. A sticky injector
    3. Intermittent loss of spark on 1 or more cylinders
    Any others?

    Now which is most likely and why would it get worse in boost?

    Injectors, plugs, coils, wires are new. Plugs are gapped at .025"
    When you figure out the extremly rich condition under boost, you will have fixed your misfire. Imo it is spark blowout. Did not look at your logs extensively but are you as rich as 9:1 - 10:1 during boost?
    1997 S10, 06 trailblazer SS LS2 swap, 4L70E trans, 76mm turbo. Factory ZQ8 suspension. 3.08, G80 w/a zexel. With a 0411 swap.

  6. #16
    Lifetime Member Mr. P.'s Avatar
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    Bad. Ass.

    How the hell do you prevent belt slip?! I can't get a single TVS1900 to reliably hold a belt, let alone two Eatons LOL.

    I had a missfire as you describe when I first installed my Paxton, could not get above 4500-rpm without mal-combustion; after helping a buddy install twin-72's on his truck we had the same thing, in both cases it was a spark plug with a cracked insulator, in fact both cases was the #7 plug because in the truck with the big-assed brake booster we got lazy with the wrenches and damaged the plugs during installation, mine actually had a visible crack on the insulator. BUT since you have switched plugs umpteen times that's probably not the issue!

    A hint taught to me by Justin Gadberry - when logging, look at the NB O2 sensors as the miss/mal-combustion is happening; if you see one NB O2 sensor switching and the other 'flatline' then that tells you which side of the engine the missfire is on! Example - if the driver's O2 sensor goes pig-rich while the passenger sensor continues switching, then the missfire is on the driver's side!

    OK I can help here, I think. Your PCV system needs a rethink, you are most likely boosting the crankcase.

    Simple physics - high pressure always flows towards low pressure. Draw a diagram and label/visualize what parts of the induction are at high (atmospheric) pressure or low (vacuum) pressure, both at WOT and idle, and add arrows to map out actual flow of air (pressure) in the PCV circuit. You will find that the PCV circuit will stall or completely reverse at WOT (depending on if boost is present in the intake or not) and depending on how the PCV system is plumbed you will have oil in the intake charge stream while you are attempting to make maximum torque, this will lower the actual octane of fuel in the cylinder from 93 premium to around 80-ish = detonation = call to a flatbed wrecker.

    This (diagram below) is the alternative I STRONGLY RECOMMEND, and the only way to completely eliminate any possible path for oil vapor to ever enter the intake manifold under power; and since a vent is present, the PCV hose from the intake manifold will not cause 'suction' in the crankcase at idle trying to suck in the gaskets, rather there will be a nice gentle breeze going from one side of the motor to the other side carrying steam & acid vapor out of the crankcase so you will still have the benefit of functioning PCV at part throttle and 4500-mile oil changes. The vent is necessary:


    Using the Ford SVO PCV valve guarantees that under boost there is no pressure buildup in the crankcase to cause weeping at the main seals, ejecting of the dipstick, and/or pushing out pan gaskets at 7000-rpm; this is possible because the SVO PCV valve truly seals the boost from the crankcase. The FoMoCo SVO valve is the ONLY one that seals totally, I personally tried every PCV valve at Oreilly's one afternoon (but I hear rumor the OE Supra PCV valve seals too). At high-RPM the vented cap allows any blowby to easily escape the crankcase rather than push your gaskets out, or force oil out the front/rear main seals. This is a diagram of the change in pressures inside a motor under boosted operation:


    My buddy and I modified my OEM oil fill cap into a vented one for 13-bucks; I bought the SVO PCV valve for 9-bucks; the 3/8" caps and longer vacuum line cost 5-bucks; we get the catch cans off scummit racing for just over 80-bucks. Proper PCV circuit for under $120 and I am sure a couple MacGyvers out there can probably do it for well under 100-bones.

    If you want to do this setup and be totally emissions-legit you can use a second catch-can instead of a vent on the passenger-side of the motor, but you need to use a large capacity catch can like the Lingenfelter unit or similar (uses 5/8" or 3/4" hoses). You HAVE TO USE A SECOND CATCH CAN, whoever thought you could tee all the crankcase plumbing into one catch can has not realized that doing so just eliminates any draft/crossflow in the crankcase i.e. doing that stops all PCV action - check it for yourself, draw a diagram and you will see what I mean. Here is an emissions-compliant catch-can install which will still keep oil out of the intake, remember the second (fresh air) catch can must be high volume to handle the high-RPM blowby:


    The diagramming portrays a centrifugal, because that is what I installed on my truck but I am sure you can follow the broad ideas here and apply to your project.

    Mr. P.
    2003 Silverado SS, with Novi-1500 "CAI mod"
    EFILive V 7.5 COS-3 (OLSD, for now!)

  7. #17
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    Interesting...Mr. P would this work just fine on a N/A truck too? Im about to buy a catch can, 23.5k without one on my TBSS and Im worried about it. Plus it makes tuning a little tricky, if Im sucking oil into the intake then my timings going to be off.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, tuned, turbo mods, etc.
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  8. #18
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    Check out RX products oil catch can pcv system. Specifically for boosted engines. It has multiple check valves. There are a few threads on the camaro5 forum. It is supposed to be the best system available. Many people are using it. There are some good pictures on that thread and diagrams. Its priced very reasonable also. They also have one for N/A engines.
    1997 S10, 06 trailblazer SS LS2 swap, 4L70E trans, 76mm turbo. Factory ZQ8 suspension. 3.08, G80 w/a zexel. With a 0411 swap.

  9. #19
    Lifetime Member Mr. P.'s Avatar
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    Quote Originally Posted by ScarabEpic22 View Post
    Interesting...Mr. P would this work just fine on a N/A truck too? Im about to buy a catch can, 23.5k without one on my TBSS and Im worried about it. Plus it makes tuning a little tricky, if Im sucking oil into the intake then my timings going to be off.
    Remember, the whole key is high pressure seeks low pressure - diagram it out:

    Diagram of OE PCV system operating at idle:


    Diagram of OE PCV system "operating" at WOT:


    Either of these two solutions will solve the PCV oiling problem on a NA motor, while still providing functioning PCV:



    Because a NA/nitrous motor has no boost, there is no benefit to swapping in the SVO PCV valve, the OEM PCV elbow (it has no guts, it's not even a valve) is still adequate.

    I have no idea what RX products sells (I have never seen their products) but yeah I would certainly check out all options.

    Mr. P.
    2003 Silverado SS, with Novi-1500 "CAI mod"
    EFILive V 7.5 COS-3 (OLSD, for now!)

  10. #20
    Lifetime Member swingtan's Avatar
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    Very good info Mr. P.

    It might be that Drx is actually "vacuuming" his crank case with the PCV system he has. The inlet for his system is inside one air filter and the outlet is right next to the blower inlet. At full song, this may cause an excessive amount of air to flow through the crank case, drawing fluid oil into the catch can and filling it quickly. It might be better to have the exhaust side of the PCV system just behind the throttle body.

    I'm not sure that this is the cause of the original problem though. The tip on using the NB O2's is an excellent one which I've used a number of times. I'm not sure if it'll help in this case though as when in boost, the commanded mixtures are very rich ( compared to stoich ) and the WB indicates a further rich spike. So the NB O2's may not show anything.

    Drx, take some video of the miss and post it up. It may be help to hear it.

    Simon.

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