Scottie-GNZ Posted February 14, 2001 Author Share Posted February 14, 2001 To all, great dialog. Terry, thanks for the article. Great read and educational. Kevin, I use a different formula but came up with about the same numbers. I also estimated the potential on Sunday for a best ET of 11.teens but I took a less scientific route. The optimum run would have been to combine the best 1/8 with the best 2nd 1/8. The best 1/8 was 7.31 but the 60' was still off what the car normally runs, which is 1.63. My guess is that with a good (normal) launch, the 1/8 might have been 7.18 and with that added to the best 2nd 1/8 ET of 3.98 would have resulted in an ET of 11.16 with a slightly slower MPH. Woulda, coulda, shoulda. I justy need to fix the car and do it. With the upgraded injectors, I still have another 40hp I can squeeze of this stock setup. A turbo Buick is normally quicker in the first 1/8-mile primarily because Buicks are heavy barn doors. My car should be stronger than a Buick in the top-end because of better aerodynamics. E.g., my buddy's GN has the same engine/power setup and he ran 12.2 @ 109 in his 3800lb sled. My 240Z is street-driven and as I have said on several occasions, I would have no qualms about driving it any distance with no preparation. MOF, last time I made a 480-mile trip to Tallahassee, it got almost 26mpg cruising on the freeway. As I was leaving the track Sunday I looked at all the trailered cars and "street cars" sputtering and spewing black smoke in traffic, I relected on how tractable and docile mine is. Before I leave the track, I adjust the tire pressure and the Tokicos and the only thing missing from making it a "normal" street car are the sway bars. BTW, the other GNZ DRAX referred to has a bigger turbo and some head work and runs 10.50s @ 130. The GN head is downright bad and a fully ported head with larger valves is worth about 70hp!!! RickB can confirm that. ------------------ Scottie 71 240GN-Z Scottie's GNZ Quote Link to comment Share on other sites More sharing options...
pparaska Posted February 14, 2001 Share Posted February 14, 2001 O.K. call me fickle, I'm lining up with Terry more now. Yeah, the drag could be a slight effect (due to higher speeds for the last 1/8th mile), but the issue of more torque being TRANSMITTED to the wheels with the gearing, tire size, etc. taken into account as well as how much torque is available at the flywheel during that last 1/8th mile seems to clinch it. I think (I shouldn't do that). If you use the rule of thumb from the page that Terry posted about "It's better to make torque at high rpm than at low rpm because you can take advantage of gearing" seems to hold true for the L28T during the last 1/8th mile. I think, just a feeling right now, I haven't really bought into it yet . So I guess my question is, if Scottie went to a 3.9:1 diff, he'd be turning 6200 rpm at 122.5 mph. I don't know what the torque curve looks like for his setup, but I'd be surprised if it's down too much at that rpm. In other words, would it make sense to use more gear (higher numerical diff ratio) if the engine is still pulling (not down on torque) at 6200? Seems like there'd be more torque available under the time curve from 1/8th mile to 1/4 mile this way, and that's what would accelerate the car more (and offset the drag a bit ). Probably just another brain fart. ------------------ Pete Paraska - 73 540Z - Marathon Z Project pparaska@home.com Pete's V8 Datsun 240Z Pages Quote Link to comment Share on other sites More sharing options...
Drax240z Posted February 14, 2001 Share Posted February 14, 2001 Whoa. Scottie are you saying that the GN is worse aerodynamically than the Z? I didn't beleive it was possible! Do you know the Cd of the GN off hand? ------------------ Richard Lewis 1972 240z - L28TURBO transplant ongoing! Drax's 72 240Z Turbo Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted February 14, 2001 Share Posted February 14, 2001 quote: Originally posted by pparaska: So I guess my question is, if Scottie went to a 3.9:1 diff, he'd be turning 6200 rpm at 122.5 mph. I don't know what the torque curve looks like for his setup, but I'd be surprised if it's down too much at that rpm. [/b] I wasnt initially going to do this; but it looks like we're now, more-less reading from the same page. Remember the final gear ratio is not the gears in the rear but the gear attached to the wheel/rim touching the ground/surface. Adding a larger tire is comparable to increasing the diff.gears (slightly) and its easier/quicker/cheaper. Saying that; I will also agree that theory has to take into account the "Jerk" factor; in this case the "Jerk" factor being that fine line where fanasty (Theory) fades off & reality kicks in; You know Nervanna-The State of Perfect Nothingness, where we gearheads prefer to be: No limitations like gravity, cutting thru the wind/drag.., ect. Having said that-here's my numbers for Scottie's set up. I've factored in three diff.gear sets 3.5, 3.7, 3.9 with three different tire sizes 275/50/55, 275/55/15 & 275/60/15's to see what their affect on mph would be at three different RPM's: 6500, 6000 & 5500rpm's...you be the judge of the results. 1a) 3.5, 275/50/15 (25.8 tires) 6500rpm's = 142mph w/final drive ratio=3.525 6000rpm's = 131mph w/final drive ratio=3.527 5500rpm's = 120mph w/final drive ratio=3.529 1b) 3.5, 275/55/15 (26.9"tires) 6500rpm's = 148mph w/final drive ratio=3.510 6000rpm's = 137mph w/final drive ratio=3.510 5500rpm's = 125mph w/final drive ratio=3.510 1c) 3.5, 275/60/15 (27.9"tires) 6500rpm's = 154mph w/final drive ratio=3.510 6000rpm's = 142mph w/final drive ratio=3.510 5500rpm's = 130mph w/final drive ratio=3.510 2a) 3.7, 275/50/15 (25.8"tires) 6500rpm's = 134mph w/final drive ratio=3.711 6000rpm's = 124mph w/final drive ratio=3.711 5500rpm's = 114mph w/final drive ratio=3.711 2b) 3.7, 275/55/15 (26.9"tires) 6500rpm's = 140mph w/final drive ratio=3.711 6000rpm's = 129mph w/final drive ratio=3.711 5500rpm's = 119mph w/final drive ratio=3.711 2c) 3.7, 275/60/15 (27.9"tires) 6500rpm's = 145mph w/final drive ratio=3.711 6000rpm's = 134mph w/final drive ratio=3.711 5500rpm's = 123.43 w/final drive ratio=3.711 3a) 3.9, 275/50/15 (25.8"tires) 6500rpm's = 127mph w/final drive ratio=3.911 6000rpm's = 118mph w/final drive ratio=3.911 5500rpm's = 108mph w/final drive ratio=3.911 3b) 3.9, 275/55/15 (26.9tires) 6500rpm's = 133mph w/final drive ratio=3.911 6000rpm's = 123mph w/final drive ratio=3.911 5500rpm's = 112mph w/final drive ratio=3.911 3c) 3.9, 275/60/15 (27.9"tires) 6500rpm's = 138mph w/final drive ratio=3.911 6000rpm's = 127mph w/final drive ratio=3.911 5500rpm's = 117mph w/final drive ratio=3.911 After crunching all these numbers;what I found interesting is the final drive didnt change much from the diff.gears, however, its obvious the mph is drastically different in relationship to changes in tire diameter. Definately something that makes you stop & go, HMmmmmm(?) Ok, I've now added my .02c worth for the 5th time; you guys have had to put up w/a whole dimes worth (hope I'm not wearing out my welcome). Kevin, Quote Link to comment Share on other sites More sharing options...
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