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Thread: Setup not handling high boost, finding the restriction?

  1. #1
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    Setup not handling high boost, finding the restriction?

    G'day guys, wasn't sure what to name the title but the best to describe it.

    I went for a odd setup on a RB26 rather than the typical setups people run just mainly out of curiosity.

    Standard RB26DETT R33 GTR
    BW EFR7670 IWG 0.92 A/R - for comparison similar size to a GT3076R
    Split pulse manifold, using 1 Inch runners.
    3.5" Dump, Huge Cat, exhaust etc.
    Using Internal Bypass valve on EFR Turbo
    Haltech Elite.

    This setup I wanted to tailor it not for huge power but more so response.

    The issue the dyno shop had and we couldn't quite find out exactly what is causing it, it just doesn't want to make any more power than
    around 280hp at the wheels without showing resistance. What I mean by that is, going from 8 PSI at roughly 280hp, and doubling the boost to 16 PSI, it only makes about 40HP more and I did remember
    the tuner saying timing had to be held back to stop it from wanting to ping. He also mentioned he did have issues trying to get it to hold the boost, and some time had to be spent
    tuning to get it to hold the boost. At first he mentioned it would boost up to desired pressure, run and then just want to fall off no mater if we ran direct feed to actuator, used a solenoid controlled by the haltech or used a manual tee. After they spent some time tuning the boost control they were able to get it to hold 16 PSI but it took a long time to achieve that result, but cannot get any more than 330hp, raising boost more just results in minimal gains beyond this point, where as normally on their dyno a turbo of that size would make in the 400-450hp range.

    Originally we thought there may have been wastegate creep or a intake leak - all that was checked and it doesn't appear to be the issue.
    I'm wondering if anybody can give me ideas as to what may be happening, I can try post some sheets if that can be of help.

    I don't think the turbo itself is way too small, as many people have run similar sized turbos on RB25's and RB26's without issue.
    I wouldn't think the manifold is too restrictive as a few people have run manifolds with 1" Runners on similar setups. So the issue is
    we can't pin point a reason why it's happening other than thinking the rb26 doesn't "like" this combination of parts I've put on for better words.

    I do not know if a bad batch of fuel could cause odd things like this?

    For now I will have the car at a lower power level just to drive it around a bit and when I have time I can get around to seeing what's up.

    Cheers Guys.
    Last edited by Z2TT; 04-10-17 at 01:26 AM.

  2. #2
    Arrogant wankeler Slides's Avatar
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    In terms of turbine size and compressor flow that turbo is more like a gt35R but much more responsive.

    You need to pressure test. Assuming they confirmed base timing those symptoms scream intake or exhaust blockage or intake leak causing high EMP with gates shut/nearly shut trying to maintain boost with the leak and absorbing near twice the power.

    Seal and pressurise intake, check CAT, mufflers or flex joints for collapse. All intake joiners, gaskets and intercooler core. Some leaks will only show over a certain applied pressure. Also less likely but can happen: rag in intercooler, clogged intake filter/too small filter.

    Probably oversped the turbo, I would pull the CHRA and check the turbine is still in one piece and shows no cracks.


    Edit: those runners are reasonably tight but if it revs out at lower boost and suddenly falls flat when trying to push higher I don't think that is the problem. Had a mate with similar cylinder displacement BMW Motor with manifold he made for response that revved and made big power.
    Last edited by Slides; 03-10-17 at 09:38 PM.

  3. #3
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    1" runners? you mean the inside diametre of the exhaust manifold between the head and the turbo is 1" ? Trying to shit though a straw?

    Or do you mean the intake runners are 1" inside diametre ? Either way this is not going to work....

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    inside diameter of turbo manifold tubes are 1". I had figured if there are cars running upward of 900hp with 1.25" runners, that I could step down to 1" for something that would be in the 400hp range.

    CAT is brand new and reputable brand with 5" Body, 100 CPSI.

    Pod filter is brand new and very big.

    Slides we've pressure tested the intake, no leaks
    Last edited by Z2TT; 03-10-17 at 11:15 PM.

  5. #5
    Arrogant wankeler Slides's Avatar
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    Has anyone changed the cam timing?


    I would would still be unbolting the exhaust and intake and checking it all if it was mine.
    Last edited by Slides; 03-10-17 at 11:55 PM.

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    Cam timing is at 0 both inlet and exhaust, checked it at the time I replaced the drive belts, water pump etc.

  7. #7
    Arrogant wankeler Slides's Avatar
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    Does it have a BOV?

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    Yes, inbuilt Recirc Valve on the BW EFR Turbos compressor housing. I asked them could it be a leaky/faulty bypass valve and they ruled that out during all the testing they did.

  9. #9
    Registered User JZK25's Avatar
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    Is it pinging? 1" runners are too small man, go back to the drawing board.
    David Fraser - Automotive Historian!

    Quote Originally Posted by bigmuz View Post
    You can't polish a turd but you can put 600hp in it and laugh your fucking arse off coming past someone sideways at Powercruise.

  10. #10
    あなたの母親の肛門 Shifty's Avatar
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    The correct method is to swiss-cheese everything so you can check restriction and temps throughout the system, but for those of us without unlimited budgets that's a little impractical.

    I would be double-checking cam timing and base ignition setup. Also if the manifold is not the cause, it will not be helping.

    You mentioned driving it around; don't. If it's choking you're going to melt a piston or burn a valve. RB26s aren't exactly the most reliable thing, you don't want to drive it around with extra challenges to deal with.

  11. #11
    Registered User burn is weird's Avatar
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    got any photos of manifold? how are you transitioning to a 1" Pipe out of the exhaust port on the head?

    have you got a speed sensor on the turbo?

    do you have really shit valve springs?

    can you post up a VE map? MAPvsRPM I want to see how it's breathing as you increase boost.
    Last edited by burn is weird; 12-10-17 at 01:50 PM.

    Oo___oO


  12. #12
    Arrogant wankeler Slides's Avatar
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    You think it is getting exhaust valve float with high EMP? Would explain it making reasonable power at lower boost then hitting a wall if there isn't a restriction elsewhere.

  13. #13
    Registered User burn is weird's Avatar
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    I've seen it before, but usually at higher boost. compression/valvetrain are the only things you haven't mentioned about the build, assuming there are no leaks, shitty intercooler or cat converter restrictions.

    yes your manifold is too small, but you should be able to make a lot more than what you are. 400whp would be about the max on a 2l 4cyl with 1" runners before you started seeing a restriction, so i'd expect a bit more than that on a 2.6l 6 cyl. (full race have done testing and said yank dyno 650whp on 1.25" in a 4G63 is recommended maximum, and I'm just scaling by area ratio)

    a mate of mine has a efr7670 on a 1JZ and he's making 300rwkw pretty easily.

    at only 16psi that would mean a serious serious turbine expansion ratio to get enough EMP to lift them, unless there is a large post-turbine exhaust restriction.

    if they're totally worn out then they could be lifting even at low EMPs and your VE will be going to shit. if you look at you BSFC (injected mass/power), it shouldn't be changing much if its a VE issue. if its a combustion issue it will go sky high.

    simple test, ignition cut limiter bash it for 10 seconds. if you spit some shims and start dropping cylinders then your valves aren't up to it. (don't do this)
    Last edited by burn is weird; 12-10-17 at 04:03 PM.

    Oo___oO


  14. #14
    Registered User I'm DJ!'s Avatar
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    My supra had a similar issue but we never got stuck into finding the outcome (it was at 675rwhp on the 3.4 with gt4094)

    I actually think that the cat may have been fucked, but mine would boost spike to 28psi and trail back down to 24psi. Wouldn't make more power and wouldn't take extra timing without pinging. That was adequate for what I needed anyway so never got the the bottom of it. Will once it's back from the paint shop.
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  15. #15
    BLING BLING PLAYA's Avatar
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    I made 100 rwkw in my RB26 from like 170kw to 300 rwkw just in cam timing, the rest was a little boost, I would 100% drop Ur cat at the dump and check that but I doubt it. Then move cams 1 deg at a time just to see loss or gain, start on exhaust then go to intake.
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