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KA Rebuild on the cheap?

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  • #31
    Should just have displacements and restrictors.

    If I want to run my 6.0L 2800 lb car in with a whole pack of similar cars, there should be a restrictor size that makes things reasonable, rather than bumping the car to some unlimited class, when all of the chassis / suspension stuff is common boltons to more "normal" classes.

    Same with SR swapped cars.

    .... But that would make sense.

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    • #32
      The point of NASA classing is to be as inclusive as possible; most anything can be classed fairly accurately, because lap times are highly correlated with weight/power ratio. Its much cheaper and easier on everyone involved if classing rules are accurate for a broad number of cars, because it is less necessary to build a car for a specific class in a specific sanctioning body.

      Displacement restrictions end up really expensive, because you try to wring every last little bit of power out of whatever displacement motor you have.
      Flatout Racing
      #23 Z32 Chumpcar

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      • #33
        Look at SCCA GTL and GT3 for an example of what restrictors do to the classes. One car can run a 1.0l engine unrestricted at 1800 lbs or you can run the same chassis with a restricted SR20 at 2200lbs. The guys breathing through restrictors wind up running 13-14:1 compression on 100000octane fuel and spinning to 9k rpm to make the power..
        supposedly those engines are stupid reliable because cylinder pressures are low and forced are down, but I'd rather have something that breathes better with less risk of taking out the neighborhood when it goes.
        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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        • #34
          Fuel is about a third of our running cost (the other third being tires). If we had to run race fuel to compete, our costs would go up greatly. No thank you.

          No if only NASA classing erred on the side of street-tired cars, instead of race-tired cars. Then I'd sign up tomorrow...
          Flatout Racing
          #23 Z32 Chumpcar

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          • #35
            Originally posted by gbeaty View Post
            Fuel is about a third of our running cost (the other third being tires). If we had to run race fuel to compete, our costs would go up greatly. No thank you.
            probably about the same here, but i'm counting diesel to get to the track. I might use 20gal of 93 octane over a race weekend, but I'll burn 100 gallons of diesel to get there and back for a race 6hrs away.
            Entry fees for the weekend are another $450 or so, and tires themselves cost me maybe $150 for a weekend. I use BFG/Hoosier takeoffs from whoever I can pillage from, and they usually cost me under $100 a tire. Hoosiers will last 1.5-2 weekends, but a set of BFGs will last 4-5 weekends easy.

            Originally posted by gbeaty View Post
            No if only NASA classing erred on the side of street-tired cars, instead of race-tired cars. Then I'd sign up tomorrow...
            DOT-R are still considered 'street tires' in SCCA. you ain't driven nuthin' until you've driven on cantilevered bias bly slicks!
            Last edited by Matt93SE; 11-25-2013, 06:23 PM.
            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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            • #36
              Originally posted by Matt93SE View Post
              probably about the same here, but i'm counting diesel to get to the track. I might use 20gal of 93 octane over a race weekend, but I'll burn 100 gallons of diesel to get there and back for a race 6hrs away.
              Costs a lot to get that bro-dozer down the road eh?
              '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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              • #37
                Matt, we race for at least 12 hours each weekend, and test at a track only 40 minutes away. So we spend a lot more actually running the car, and fuel costs are a bigger part of our budget.

                Has anyone here tried NPR pistons? DSM and Supra guys seem to like them, and indicate NPR is the same company who makes their OE pistons. We've had ring land failure on parts-store pistons before, so I'm hoping the NPRs will be as tough as stock (if a piston can survive a DSMer's pump gas tune, it can probably survive anything). They're cheap at about $120 a set, with rings.

                Originally posted by 240sxTTC View Post
                Not sure as my project goals were 225whp and 7800rpm. Based on your pwr level, operating conditions and max rpm, you have to determine the service life.

                The half-weighted crank of the KA24DE engine beats up the bearings at higher rpm and definitely above stock redline. Oil pressure is a great indicator of bearing condition. It's obviously best to start with a fresh motor. Monitor and record oil pressure at idle and 3Krpm at full operating temp. Compare these values to the service manual min. From the recorded and service manual min values, you can establish a usable service life.
                Basically I'm wondering if we should be shifting before the stock rev limiter of 6875? Yes we do most of the time, because its not worth revving a stockish KA over 6400 or so. But in some straights we take it higher to avoid the shift to 5th. In these cases staying in 4th is only very slightly faster (less than a tenth of a second IIRC), but mostly stay in gear because we've had more transmission and shifting issues than engine issues. If it turns out this is a bad idea because of bearing wear we'd probably shift instead.

                By "beats up the bearings", do you mean just the main bearings?

                At what sort of oil pressure drop do you pull the motor and change the bearings? We've recorded oil pressure like you suggest with our Z, and have seen a slight (less than 5 psi IIRC) drop in 130 hours of racing. We also do oil analysis after every 12+ hour race and have yet to see copper spike (this is why I love tri-metal bearings). The Z of course only has a 86mm stroke, and for most of its life we were only taking it to 6500 rpm; I'm not sure if we can expect the same bearing service life out of a longer-stroke KA*.

                * Though a VG30DE without a good oil pan will blow up in short order, and I know we've been lucky not to have the multitude of other failures that engine is known for.
                Last edited by gbeaty; 11-26-2013, 11:55 PM.
                Flatout Racing
                #23 Z32 Chumpcar

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                • #38
                  I'd say fuel (for towing and the car) is at least 2/3'ds of my running costs these days. Maybe more. Instructing and maybe time trialing is by far the cheapest way to develop the car.

                  Originally posted by gbeaty View Post
                  Has anyone here tried NPR pistons? ... They're cheap at about $120 a set, with rings.
                  I've not heard of them but at that price point I'm willing to give them a shot.
                  '95 240sx

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                  • #39
                    Originally posted by gbeaty View Post
                    Basically I'm wondering if we should be shifting before the stock rev limiter of 6875?
                    Yes. The lower the revs the better the durability. Plus on a stock engine with stock cams the pwr and torque drops fast after 6Krpm anyways.

                    I haven't forgot.....still need to look and see if I have an extra 0.838 5th gear. Will let you know.

                    Originally posted by gbeaty View Post
                    By "beats up the bearings", do you mean just the main bearings?
                    Yes but I'd evaluate the condition of the rod bearings also.

                    Originally posted by gbeaty View Post
                    At what sort of oil pressure drop do you pull the motor and change the bearings?
                    Talking with the company that built my long block, a drop of 10psi is the limit. He recommends replacing main bearings somewhere between an oil pressure drop of 5-10psi. During the first rebuild, I'd evaluate the bearings and determine the condition at the recorded pressure drop. This will help determine at what pressure drop is the appropriate time to service the main bearings.
                    Last edited by 240sxTTC; 11-27-2013, 10:14 AM.
                    NASA Time Trials TT3


                    BTW I work for Garrett

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                    • #40
                      I've got a stock stroke bc fcw crank for the ka and i've been planning to get an ati damper..

                      Do I have to ask them for a custom spec one being that the one they build for the ka is meant for the half counter weight????

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                      • #41
                        I would definitely give them a call before purchasing...
                        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

                        Comment


                        • #42
                          They said that the fcw doesn't really have to do with the crank harmonics. Rather, the fcw stops what he calls the skip rope effect on the rotating assembly. The need to dampen the vibrations is still present and will be the same.

                          Does this make sense?

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                          • #43
                            Yes. Hcw cranks don't have everything symmetric when looking at reaction forces. So in a way it's kinda like a slightly out of balance wheel (very simplified)
                            '18 Chevrolet Volt - Electric fun hatch for DD duty!


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

                            Comment


                            • #44
                              The damper that ati has for my transverse setup is rated up to 900 hp. I'm no where near that. Whats the downside of over dampening? They said it's just excess material inside the damper that won't be affected.

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                              • #45
                                The damper is tuned for certain frequencies. they're capable of damping xxx force at yyyy RPM.

                                At higher power levels, the RPM doesn't change, but the forces present at those RPM are higher. thus, the power level shouldn't affect the damper.

                                BUT.. what frequencies/RPMs (yes, you can say RPMs when you're talking about multiple discrete RPM values) is the damper is designed to work at? Do those numbers change with the FCW crank? i.e. is the crank actually any stiffer or have different resonant frequencies that would change what the damper needs to be calibrated to, or does the FCW crank just have lower magnitude of the same harmonics that need damped?
                                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

                                Comment

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