1 fast z Posted April 12, 2009 Share Posted April 12, 2009 There are some reasons to go twins, but spool time shouldn't really be one. Sequential. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted April 13, 2009 Share Posted April 13, 2009 Sequential. I meant parallel twins.... Quote Link to comment Share on other sites More sharing options...
ShaggyZ Posted April 13, 2009 Share Posted April 13, 2009 I meant parallel twins.... Even parallel twins spool very quickly, if sized correctly like the 300ZX Twin Turbo. The purpose was drivability, which can be translated to "quick spooling," much like the tiny, stock turbochargers on the 1.8T VW/Audis and the SRT-4 Neons. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted April 13, 2009 Share Posted April 13, 2009 Even parallel twins spool very quickly, if sized correctly like the 300ZX Twin Turbo. The purpose was drivability, which can be translated to "quick spooling," much like the tiny, stock turbochargers on the 1.8T VW/Audis and the SRT-4 Neons. Yes, but the math I showed above should explain that a properly sized single will spool at the same rate or even slightly faster than equivalent twins. I would expect that packaging was a bigger concern for the 300zxTT, imagine that engine bay with more hotside piping that merged into one pipe and a slightly larger turbo(that flows an equivalent amount as the twins) stuck somewhere. It would be a nightmare. Quote Link to comment Share on other sites More sharing options...
ShaggyZ Posted April 13, 2009 Share Posted April 13, 2009 Yes, but the math I showed above should explain that a properly sized single will spool at the same rate or even slightly faster than equivalent twins. I would expect that packaging was a bigger concern for the 300zxTT, imagine that engine bay with more hotside piping that merged into one pipe and a slightly larger turbo(that flows an equivalent amount as the twins) stuck somewhere. It would be a nightmare. It already is a nightmare. Perhaps they could've figured out a way to put a slightly larger single in one place. Considering the other big three Jap cars (VR-4, Supra, RX-7) went with some variation of twins, I doubt it was merely for packaging; at the time, I don't think they were too sharp on the technology to have a larger single spooling at the same speed. I'm not necessarily disagreeing with the math, but I have no doubt that math is missing some of the "practical" variables of the time. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted April 13, 2009 Share Posted April 13, 2009 Here is some math to try and validate what I said above, any integrals could be ignored if we assume that the bigger wheel is a scaled up version of the smaller ones(they have the same basic shape). It's not optimal, but it should be close enough to compare without hours of measuring and calculation. If we assume flow is directly proportional to area, twin 40mm turbos are equivalent to a single 57mm turbo(given by sqrt(2*r1^2)=r2). Moment of inertia is given by I=(m*r^2)/2 for a thick rod about it's axis, that's not a compressor wheel but it is a scalar multiple of what the formula for a compressor wheel would be, so 40mm: I(total)=(m*800*2)/2=m*800 57mm: I = (m*1568)/2 = m*784 I would certainly bet that 2 40mm wheels would weigh more than a single 57mm wheel. Twins also have twice the bearing drag. If I've made any errors, feel free to correct me. There are some reasons to go twins, but spool time shouldn't really be one. I'm not seeing where the 800 in the 40mm equation and the 1568 in the 57mm equation are comming from. Also mass tends to go up by the cube as it's related to volume of the object. Quote Link to comment Share on other sites More sharing options...
letitsnow Posted April 13, 2009 Share Posted April 13, 2009 I must have been trying to do 3 things at once when I typed that. I divided too early. The very first equation I gave(sqrt(2*r1^2)=r2) gives 56.5 for r1=40, 56^2=3136, 3136/2=1568, then I switched to 57mm to round more properly. I multiplied by 2 twice for the 40mm equation. 40mm: (2*M*20^2)/2= M*20^2=M*400 57mm: (M*28.5^2)/2=M*812.25/2=M*406.125 Interestingly enough 56mm: (M*28^2)/2=(M*784)/2=M*392 The differences between twins and singles from an inertia standpoint are so close that if you can get a slightly higher flowing (per area, requiring a slightly smaller wheel to flow the same) single, then it would spool much faster than twins, however, if you're stuck with an old tech compressor wheel for the single or newer tech for the twins, the twins would easily win. It seems like whenever I try to do something math related on this site I mess it up somehow, probably because I'm on here way too late at night. Quote Link to comment Share on other sites More sharing options...
RUZN Posted April 13, 2009 Share Posted April 13, 2009 Hey for your "was there a system that used a smaller turbo to spin a bigger" Yes I believe so. When I was building up my 1992 Eagle Talon TSi there was an article in one of the Tuner Mags that showed umm *looks through mags* ah here it is AMS was building a 4G63 obviously hvy mod'd but it had a built Sequential turbo system that used a smaller turbo to obviously speed up the larger. Without the small turbo the engine produced just over 1000HP but it was for a build competition so they didnt have time to really get all the specs in for the smaller turbo but they have a Mounted pic of it it Modified Mag where they won the overall challenge and beat out all the Nissan Engines and Hot rodder ones. So yeah they are out there for Gasoline. This one ran 35psi on the larger turbo alone. Also! Didnt an older 280zxt used by some racer use TT on a L6 cause I see you can buy Manifolds for the TT version of a L6 still Quote Link to comment Share on other sites More sharing options...
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