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Pitch change after getting onto straight? (KA question)

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  • Pitch change after getting onto straight? (KA question)

    I was just at VIR yesterday, and while the car did great, and really seems to want more RPM to play with on the R-Comps... But I noticed an odd sound from the motor between 5k RPM and 6k RPM after coming onto the main straights.

    It happened almost every lap after going around oak tree (leads onto back straight), and occasionally leading onto the front straight. And ONLY in 3rd gear.

    Basically, it would go from normal sounding KA @ WOT sound, to almost the high pitched sting of a Miata motor @ WOT for a few seconds, then return to normal by the time I got to redline and had to shift. Occasionally it would persist until the shift.

    I don't think its valve float as its not happening in other gears.

    Could I have been oil starving? (Yes I don't have an oil pressure gauge, and have the stock pan over filled a half a quart or so)

    Could it be something else?
    '95 240sx

  • #2
    VTEC???



    But seriously, does your car have those flapper things in the intake manifold? Tumble valves I think kids call them.

    Maybe they're not staying where they should be staying due to a weak actuator?
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


    DefSport Koni Sleeve and Spring Perch Buy!!!
    http://www.nissanroadracing.com/showthread.php?t=5902

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    • #3
      Are you talking about the PCV's that were unique to S13's?

      Assuming that's what you're talking about, I don't think so, but it could still be a possibility given how varied '95 model year cars were when it comes to emissions equipment, and the fact that I don't know what the "flapper things" in the intake manifold are.
      '95 240sx

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      • #4
        He's talking about the SCV, I think. Swirl control valve -- they're butterfly valves in the intake manifold.

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        • #5
          A 95 would not have them to the best of my knowledge.

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          • #6
            Originally posted by Colorado S14 View Post
            A 95 would not have them to the best of my knowledge.
            That's been my understanding as well. Assuming that is the case, what was I hearing?


            Boost / vac gauge didn't indicate any leaks as far as I could tell. (the gauge is a left over from a failed turbo project, its now handy when looking at in car video)


            Should I pop the valve cover and look for burn marks?
            '95 240sx

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            • #7
              oil or fuel starvation are both possible issues. I don't really notice my car sounding different when the oil pressure wiggles in the turns (never run it less than 1/2 way below the full mark on the dipstick, btw), but I do notice a different sound when it just begins to fuel starve in the corners. I don't notice any difference in power since I'm rolling onto the throttle at that point and not at full power, but I do notice the noise change.
              Originally posted by SoSideways
              I don't care what color they are as long as they are LONG AND HARD.
              '04 G35 Sedan 6MT- The DD
              '96 240SX- The Track Toy

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              • #8
                Good to know. I'll update once I've checked under the valve cover.
                '95 240sx

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                • #9
                  is there a change in the barrier at the outside of the corner at that point in the track?

                  It may be that the barrier changes and you get different levels of different frequencies bounced back, I notice this when driving through long beach pike the couple weeks prior to the LBGP each year, the concrete barriers make the car sounds more prominent, then thru the intersections everything seems more subdued....
                  I am SKULLWORKS

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                  • #10
                    True dat.. I completely forgot about that too. Even a curb on either side of the car changes how mine sounds when I'm driving through the 'hood.
                    Originally posted by SoSideways
                    I don't care what color they are as long as they are LONG AND HARD.
                    '04 G35 Sedan 6MT- The DD
                    '96 240SX- The Track Toy

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                    • #11
                      I've noticed that VTEC-kick-in sound around 5500rpm on my s14, then back to normal KA thrash over 6000. Is it like in this video (0:12)? http://www.youtube.com/watch?v=B9ADCp861T0
                      Last edited by hai1206vn; 02-23-2012, 06:33 PM.

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                      • #12
                        Originally posted by Tower240sx View Post
                        is there a change in the barrier at the outside of the corner at that point in the track?

                        It may be that the barrier changes and you get different levels of different frequencies bounced back, I notice this when driving through long beach pike the couple weeks prior to the LBGP each year, the concrete barriers make the car sounds more prominent, then thru the intersections everything seems more subdued....
                        A good point for sure. Totally skipped my mind as well.

                        It would actually make sense as it was most noticeable passing the south course pit lane.

                        Which if the blow by being sent out the motor is clogging the cat as I suspect it may be doing, there could well be enough of a leak between header and cat to cause all manner of funky exhaust sound changes.
                        '95 240sx

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