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S-chassis DSP Theory

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  • S-chassis DSP Theory

    PJ, You suspension questions sound reasonable, but I have no data or experience to comment otherwise. I also haven't given DSP much thought as I'm classed DM. You've obviously given some good thought to the power:weight question, but it sounds like the Bimmer is almsot unbeatable considering you can't get the weight lower. I think it's also more work than it's worth to squeeze that much more power out of the KA. How much would all of that cost? Has anyone else successfully campaigned a DSP S-chassis? -Andy

  • #2
    S-chassis DSP Theory

    So, I did some work on my girlfriend's Sileighty yesterday, mostly repairing some damage from when her car was hit in front. I've got a smashed S14 SE that I'm about to send to the junk yard... so I'm about to spend a weekend pulling things off to swap between the two. The one thing I'm curious about is: will the S14 subframe swap into the S13? I figure, the rubber diff bushings on the S14 would give her a nicer ride for commuting, and the wider track would just plain be nicer. Anyways, what I've found out so far might actually be of interest for a possible Solo(Autocross) DSP build: For the lowered car, S13 front tension rods on the S14 (1" shorter) would be beneficial for maxing out caster. On the other hand, S14 LCA's on the S13 might help in gaining camber, but I've yet to measure the length difference in the arm mounts and their affect on caster. More caster on a MacP car = better. In the rear, I'm assuming the rear trailing arms might be shorter than the S14 ones, so like the front, you could use S13 rear trailing arms to adjust the spindle rotation, hopefully reducing bumpsteer and increasing the camber curve on the S14. Basically, you gain the ability to offset for suspension geometry in ways the current class killers (E30 & E36 bimmers) can't, so in theory you could outhandle the BMWs, while retaining a narrower car on the same tires they run (275/35/R15's or 285/30/R18's). The only problem is: we can't swap to a different diff, and 275's would end up shortening the gearing too much, and we lack power, hardcore. That makes me wonder: how far can the S13 engine go? DSP allows a small bore (I think .020?), slight decking, and minimal headwork. You can run aftermarket pistons, but you can't change the compression ratio. The big downer: you can't run aftermarket cams. So, is 180rwhp even possible? I think you'd really need 200... as the ITR is DSP legal, and will run like 220 easily. The top DSP car now runs a 328 inline 6 in a 325 E36 chassis, with probably 200rwhp and 2800lbs. A max prep 240sx would most likely be low 2700's, high 2600's, so 180rwhp is just about pushing it. So, does anyone think it's do-able? On paper, it seems as though DSP is a viable option for the 240sx.... if I had a spare frame that wasn't damaged beyond reason, I'd definitely try it :P

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    • #3
      The only place the S-chassis has had success in DSP is in Canada, where mine and Don Nimi's (Don won DSP i believe) cars are actually DSP legal, since their rules are *effed up :P

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      • #4
        the s14 LCAs work, just press-in s13 ball joint and s14 LCAs are 10mm longer. All rear suspension arms are swappable. You could use S14 vlsd in s13. Just switch out rear cover and use the front s14 bolts and bushings. S14 subframe will fit, only if you custom make some offset bushings on then that it will not swap over directly. The s14 rear suspension is about 10-15mm wider track then s13 (with respect to alignment settings changing track width, and condition of the bushings). Also J30 arms work on s13 subframe as well. They have a more box'd design, where as s13 are more open end with building the KA and staying within those rules. I think maybe 160hp is capable (is standalone available). Being that you can custom a long-tube equal length header, a custom intake manifold. If you are using a dohc. you could swap in an exhaust cam on the intake side which helps mid/top ed. I'm not sure if you can swap sohc cam onto dohc. since it has a more aggressive profile. Also how can they warrant a change in compression when Nissan released KAs that had different comp ratios and piston designs.

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        • #5
          In SP, the rear diff is unrestricted, however gearing has to remain stock. As such, I'd run a HLSD or a smooth engaging clutch diff (ATS Carbon). The S14 subframe could work, as offset bushings are allowed, and I believe you could make them using a derlin fill, as long as the amount of metal is proportional to OEM. I'm guessing the S14 is the way to go, as the front and rear overhangs are shorter, and you can get a better alignment up front using the shorter S13 rods. On the S13, you'd need custom offset bushings to pull the tension rods forward. The offset bushings for the S14 subframe in back is iffy, as offset bushings themselves aren't allowed, but you may be able to get around it under the update/backdate allowance. Otherwise, I'd wonder if S14 rear LCA's, upper arms, and toe arms, with S13 upper trailing arms would be of any benefit. For the engine, swapping cams around isn't allowed. The engine has to be swapped as a whole, so using the S13 engine with slightly lighter forged pistons, a slight bore, and slight decking might net some 150ish rwhp. Intake, exhaust, pulleys, light flywheel, and a standalone EMS (which is allowed) might bring it up to 170.... but it's pushing it to try to get 180 out of it, even with the minimal headwork/ block work allowed. In the end, the car should be around 2650 - 2700 lbs, which is still a bit lighter than the E36's, so it COULD work. You'd have to deal with the ITR's being about the same weight with more power, though....

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