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Thread: Upgrade Path for Stock J-Spec

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    1.21 Gigawatts Club Member Wez's Avatar
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    Upgrade Path for Stock J-Spec

    Hiya Guys,

    Just wondering what would be the recommended upgrade path for a stock J-Spec, I am guessing induction and exhaust and losing one of the cats.

    What items are good and how much are they (roughly), I have also read that the stock fuel pump isn`t all that on a J-Spec aswell so i guess replacing that will need doing aswell.


  2. #2
    Subtle/Diplomatic Club Member Alex's Avatar
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    FCD
    Both cats out...(buy MY decat pipes!!)
    And free flowing catback (I have one of those for sale too!!)

    Faster spool, 1.3bar ish = big grin
    - Alex

    2012 BMW S1000RR Black
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    ex - 2008 Honda CB1000R, ex - 1998 RSP TT6 VVT-i BL-T61, ex - 1993 MSB TT6 w/ MINES ECU / BBS LM's, ex - 1995 S13 200SX Facelift
    ______________________________________

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    1.21 Gigawatts Club Member Wez's Avatar
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    Cheers Alex,

    But i thought removing both cats on a J-Spec was a bit dodgy as the waistgate is not big enough to flow the extra air therefore giving you a boost creep problem at WOT.

    Is this true?

    What is the max safe psi for a stock J-Spec, i thought it was arround 18psi.


  4. #4
    I'm addicted now! MEMBERSHIP EXPIRED
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    Fuel Cut Controller (TRL VFCC)

    De-cat both pipes (or first downpipe CAT as a minimum)

    But i thought removing both cats on a J-Spec was a bit dodgy as the waistgate is not big enough to flow the extra air therefore giving you a boost creep problem at WOT
    You may experience this. But generally it is above 11psi (stock) but below 18psi (modified), and.........

    What is the max safe psi for a stock J-Spec, i thought it was arround 18psi.
    yes 18psi is the safe maximum.

    So most people remove both CATs and get an increased minimum boost level but as this is normally below 18psi they can safely control it.

    Regards
    Pete

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    1.21 Gigawatts Club Member Wez's Avatar
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    Thanks for the info Pete...

    What is a good set of front pipes, I noticed that apexi do a downpipe set for the J-Spec, are they any good? As for the rest of the exhaust I am planning to go for the blitz nur spec.

    For induction I was looking at getting an apexi cone.

    Is the reason that 18psi is the max because of the map sensor not being able to accuratly read above 18psi?

    I was looking at your fcd device as this is the one that everyone seems to be using


    Regards
    Wez


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    Subtle/Diplomatic Club Member Alex's Avatar
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    CW decat pipes are thick solid 2.5" pipes. They allow the boost to rise above stock but keep it down to safe levels.

    300 should get you a set.
    - Alex

    2012 BMW S1000RR Black
    1996 TT Gunmetal Facelift Auto
    ex - 2008 Honda CB1000R, ex - 1998 RSP TT6 VVT-i BL-T61, ex - 1993 MSB TT6 w/ MINES ECU / BBS LM's, ex - 1995 S13 200SX Facelift
    ______________________________________

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    1.21 Gigawatts Club Member Wez's Avatar
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    Thanks for the info guys,

    So you remove the cats and replace them with restricted downpipes, or have I got it wrong?

    2.5" sounds small, i thought the apexi downpipes were larger than that, and the nur spec is deff larger than that.

    I am guessing that is because of the tiny waistgate again, has anyone bored out there waistgate to get round this problem so they can use normal bore downpipes?

    300 pounds sound like a fair price, who can supply them?



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    Me? Post? Never! MEMBERSHIP EXPIRED Adam W's Avatar
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    Well, the effect of fitting "bottlenecked" downpipes (like Chris makes) is to restrict the amount of exhaust gases coming out of the engine, and therefore the amount of exhaust gases which go through the turbo spinning it up. The result, less boost.

    If you were to enlarge your wastegate or fit an external one, this would flow more exhaust around the turbos (as opposed to spinning them up). The result, less boost.

    The downpipe method is cheaper and easier. I think Alex has a pair of Chris Wilson pipes for sale, making it cheaper still!

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    Some bloke with a Supra Club Member GavinL's Avatar
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    Originally posted by Wez


    Is the reason that 18psi is the max because of the map sensor not being able to accuratly read above 18psi?


    Regards
    Wez

    MAP we have been advised is 1.0 bar and the MAF is 1.2bar
    Gavin

    UK Silver T6

    "A good mechanic no more makes a good businessman than a good businessman makes a good mechanic"

  10. #10
    1.21 Gigawatts Club Member Wez's Avatar
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    Cheers for the info guys

    1 bar, thats only 14.5psi though, so how do people safely run 18psi on a stock car?



  11. #11
    I'm addicted now! MEMBERSHIP EXPIRED
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    The MAP sensor definitely does read up to 18psi.
    Above that and you reach the upper limit of 4.95V output from the 5V MAP device.
    So even if the sensor inside could read above 18psi the output stage is limited to a max of 4.95V

    18psi is not the max because of the MAP, that just happens to be a coincidence.
    It's the point at which safe fueling runs out. This is why you have to be aware of the dangers in hot weather with any turboed vehicle if you use more fuel as a power generator which is leaving you less fuel to cool the air charge down. Remember turbos are a big heater. As you compress a gas the molecules collide with one another in the turbo housing and collision causes energy release in the form of heat.

    The Supra normally has enough excess fuel to handle 18psi of boost and still cool the air charge enough. But on v.hot days be careful. I only run 18psi with water injection as a backup.

    As for pipes, Chris Wilson or Leon Green can supply their own versions. Chris' are 2/5" and won't cause any boost creep, Leons are 3" and you MAY find you get boost creep.
    My minimum boost level increased to around 16.5psi from 11psi stock, but as I wanted to run 18psi with a boost controller I wasn't bothered.

    Regards
    Pete

  12. #12
    1.21 Gigawatts Club Member Wez's Avatar
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    Thanks Pete,

    What downpipes are you using and is your car UK or J-Spec?

    I would also like to run upto around 18psi

    Regards
    Wez

  13. #13
    Me? Post? Never! Club Member
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    I think that you should go with the 2.5" pipes, as some j-specs have had near un-controllable boost with 3" pipes.

    Although you could of course get the 3" pipes and get a 2.5" restrictor ring fitted.

    I personally have Leon's 3" pipes, and boost is fine due to the car being UK-spec, which do not seem to 'overboost'.
    Alone in the Superunknown
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    I'm addicted now! MEMBERSHIP EXPIRED
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    I have 3" pipework
    A complete 3" Mongoose system actually

    And no excessive boost creep and mines a Jap spec.

    BUT!!!! I do have hybrid turbos and an enlarged wastegate etc.

    I had 3" downpipes with my stock back box system and NO boost creep BUT on fitting the hybrids realised there was a breathing problem and this was eventually tracked down to a collapsed back box section. Hence the replacement Mongoose system.

    (Mongoose system incidentally is 500 for the whole lot which is the same price for the fancy HKS or Blitz big bore back ends. I felt it was more ecomonical for me, plus quieter for the many motorway miles I do.)

    Pete

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    Legendary Club Member Terminator's Avatar
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    I have a 2.5' into a 3' into a Hyper. Chris had to make me a restrictor ring as my boost went to the mid 1.4'sbar. With the ring in place I get the occasional 1.2bar on WOT. I mostly use up to 1.0 - 1.1 by careful use of the throttle.

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