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SM 240sx thought experiment

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  • SM 240sx thought experiment

    I currently have an s14 I drive in DSP, it's fun but not competitive there. Considering that there's often not even someone to lose to in DSP, and that the 240 can clearly get it done in SM, it seems like a better idea to go there.**

    The formula for a car in SM seems to be, get it as light as you can, and then use that as the target to pick an engine with a displacement that gives you that minimum weight. The weight formula for RWD is 1800lbs+200lbs/liter. +1.4 liters (280lbs) for forced induction, and -200 lbs if running 275s or narrower.

    PJ and Jason are both having good success with the KA-T and massive tires, which gives them a minimum weight of 2560 lbs. I think PJ is around 500 hp, not sure where Jason's at. That gives PJ a HP/weight ratio of 5.12. I'm curious if similar success could be had with something lighter and lower power.

    A SR16VET with 275/35/17s would have a minimum weight of 2200 lbs. First, is this even possible in SM? Keeping the same HP/W, I'd need 430hp. With the lower power, I could stick with some of the lighter and lighter duty stock parts vs the Z32 trans and diff PJ is running, for example. I'd also love to run a supercharger instead of turbo. I don't know if it would be any lighter, probably a wash, but I think the different power delivery of a supercharger would be better for autocross and could allow for a lower power goal, which would help since I think the limits of the stock SR trans and diff is more like 350-400 hp.

    Less power [to weight] and less tire seems like a recipe for not winning. But it sounds like fun at least. Is there anything I'm missing that makes this not a terrible idea?

    **This is a thought experiment because I'll never go to SM. I don't have the time to build or tune, in addition to the $$, and the fact that a competitive SM car is basically no longer streetable. I don't have the money or space for a tow vehicle and trailer either. If I make any changes, it'll be to a different car in a lower class. **

  • #2
    An SR20VE+T would be well worth the extra 80 lbs, and would yield a still very difficult 2280 lbs to get to in SM trim. Honestly, I don't think you can get an S chassis there within the rules as I understand them, so maybe a 90 mm sleeved engine for ~2.2L might make sense, which would still give a hard to hit 2320. But an SR20VE with wide tires at 2480 lbs might ultimately be faster...

    Then you could run an aggressive rear gear and rev it to 9k RPM, which should hold together for autox usage/duty cycle. Something like a 7163 would provide plenty of juice, and should hold power out to 9k RPM ok.

    The KA would out torque it, but the SR would have a broader powerband with a VE head IMO, and the shorter rear gear and still likely higher top speed when zinging it out would likely give you equal thrust as a KA, maybe even higher because the volumetric eff. of the VE head is insane under boost.

    The SR is about 40-50 lbs lighter than the KA, so that's weight loss where it counts the most.


    No way you're doing that much power on an SR16VE with a SC - you'd be giving up 100 HP+ to drive the SC alone. SR16VE in general doesn't make sense given it's only 80 lbs to go to a 2L that will make much more torques.
    '18 Chevrolet Volt - Electric fun hatch for DD duty!


    DefSport Koni Sleeve and Spring Perch Buy!!!
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    • #3
      The 80 lb increase was something I was thinking would be beneficial too, I just wanted to stick with the most extreme example to avoid writing out a book of options. If you can't even get to 2200 lbs, then the lack of displacement is wasted. I guess the main question is, how light can you get a 240 within the rules? There's really not that much you can do in SM for direct weight reduction. Of course some rules allow you to replace parts and you might as well replace them with something lighter (like the suspension).

      I think the conclusion Jason came to is the mega wide tires are worth the 200 lb hit, so maybe we should be looking at this at 2400 lbs vs 2480 vs 2520.

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      • #4
        Yea, I think you'd really really struggle to get an SM S13 down below 2300 lbs with an SR. Maybe 2400 lbs is doable with a lot of work and some custom panels, since I think you still have to keep the front interior in.

        Can you do composite doors/hatch? And lexan on the hatch and rear quarters? Need to keep in side windows?


        I still think the SR with a VE head makes a superior engine to the KA, but there is obviously more cost there.
        '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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        • #5
          Read the rules really close when it comes to what you can replace or remove to lose weight. I've got an S14 shell I'm working on for SM and I don't think you can legally get an S13 or S14 light enough to take advantage of the 275 tire weight break, and that takes away the advantage of a smaller displacement engine.
          Don Johnson (really!)
          Just so you know.

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          • #6
            Originally posted by djsilver View Post
            Read the rules really close when it comes to what you can replace or remove to lose weight. I've got an S14 shell I'm working on for SM and I don't think you can legally get an S13 or S14 light enough to take advantage of the 275 tire weight break, and that takes away the advantage of a smaller displacement engine.
            I'm assuming you could run a VE head on an SR since it just has to be any Nissan engine right?

            I'd honestly see that having at least a comparable power output, and not down much on midrange torque due to the excellent head vs. a KA24DE. Plus the engine will be about 40-50 lbs lighter, which being that it's over the front axle, that's a pretty huge weight reduction when your options for legally reducing the weight are limited.

            The other advantage of the VE head is it can zing to the moon for brief periods of time without much issue. So 9000 RPM in 2nd gear would be great for those few faster sections while still having strong pull around 3-4k RPM.
            '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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            • #7
              Don and logr managed to get to 2300ish lb in their s13 coupes, maybe a touch heavier (it's posted on here but I'm on my phone so it's harder to search.

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              • #8
                Originally posted by e1_griego View Post
                Don and logr managed to get to 2300ish lb in their s13 coupes, maybe a touch heavier (it's posted on here but I'm on my phone so it's harder to search.
                Don went as far as using titanium fasteners. I doubt Logr did that, so I'll see what I have left after putting the interior in and the suspension on.
                Don Johnson (really!)
                Just so you know.

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                • #9
                  Here's the most pertinent thread I found on SM legal weights. I found another post by LOGR in 2010 at 2420lbs, but he still had the stock hood and lights. There are lighter cars around but you can't cut sheetmetal, strip the wiring harness, or remove the bumper supports in SM. This is also without a rollbar or cage, so not a good example if you also want to do track days. 240sxTT listed his at 2550# with a full cage, which is reasonable.

                  This thread lists LOGR at ~2300# and Don at 2340#, both running SR20DET's

                  http://www.nissanroadracing.com/show...ghlight=weight
                  Don Johnson (really!)
                  Just so you know.

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                  • #10
                    Can you make new bumper supports? Or 100% stock?

                    I figured mid 2300 lbs was the practical limit, so it seems some have pushed it lower.

                    The VE head gives a power bump all by itself, -'d can enable another 10% revs for short bursts. Seems like a good thing for autox.
                    '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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                    • #11
                      Originally posted by Def View Post
                      Can you make new bumper supports? Or 100% stock?

                      I figured mid 2300 lbs was the practical limit, so it seems some have pushed it lower.

                      The VE head gives a power bump all by itself, -'d can enable another 10% revs for short bursts. Seems like a good thing for autox.
                      In SM you can't cut the bumper supports or replace them with other market models or custom supports. An SR20VET is a monster by all accounts, but done properly it's $$$. 500whp is pretty standard in SM these days. Robert Thorne won SSM this year in an S2K that's probably heavier than what you can get a 240sx to, but he was pushing 635rwhp and a real anti-lag setup, with a separate combuster can connected to the exhaust manifold. He was running 335 A7's on the rear and roasting them.
                      Don Johnson (really!)
                      Just so you know.

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                      • #12
                        SR20VE with an EFR8374 sounds like it'd be an interesting experiment, but it might make more power than it can really put down. Maybe 7670?
                        '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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                        • #13
                          Even though I know nothing about SM or anything AutoX, I do have a fairly gutted S13, but with a robust cage, as a data point for sharing.

                          2420lbs weighed on LongAcre scales
                          -Full 1.75"OD x 0.095" wall tubing roll cage; driver & pass side NASCAR style door bars
                          -stock KA24DE
                          -2/3-3/4 tank gas
                          -No side and 1/4 windows
                          -No headlights and motors
                          -No rear hatch window
                          -Gutted stock hood
                          -Gutted doors (could've gutted even more here)
                          -Completely gutted interior, all sound deadening removed
                          -Stock wiring harness ziptied everywhere
                          -Front "drift" style bumper bash bar instead of OE bumper beam
                          -Stock rear bumper structure
                          -Odyssey PC680 battery
                          -Z32 brakes all around (No ebrake equipment)
                          -16" Z32 NA wheels
                          -5 lug hubs, stock knuckles/spindles
                          -OE suspension links
                          -Momo Daytona XL Halo seat
                          Core4 Motorsports
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                          S14 VQ AER Endurance Racing Team

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                          • #14
                            Originally posted by djsilver View Post
                            Read the rules really close when it comes to what you can replace or remove to lose weight. I've got an S14 shell I'm working on for SM and I don't think you can legally get an S13 or S14 light enough to take advantage of the 275 tire weight break, and that takes away the advantage of a smaller displacement engine.
                            So the consensus seems to be pretty much the same as what's out there minus 50 lbs from an SR. I'm sure it's cool, but not going to happen in my garage then. Thanks for the discussion. Feel free to continue if you like.

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                            • #15
                              I know that the turbo KA is pretty heavy......what about stripping as much weight from the chassis as allowed and running a supercharged vh41 or vh45....are they that much heavier than a turbo KA. ...also although I don't think it was an issue on Panda but wasn't JM having some understeer probs? That extra big v8 lump up front might help with front wheel traction....

                              Ch

                              sent from knee deep in snow

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