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#1
11-12-2007, 05:57 PM
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rear end ratios
i am swapping a t-56 into a 3rd gen camaro and have a few questions.
are there any rear end ratios between 3.73 and 4.11? 3.73 will give me 1200-ish rpms at 70 mph in 6th gear. 4.11 will give me 1880-ish rpms at 70 mph in 6th gear. i fear that 1200 is a bit low and 1880 is a bit high. is there anything inbetween, like 3.90? if not, which would you suggest? i hear that TPI engines do not do well at low rpms. where exactly does low start? the engine in question is a 350 .040 over. it has around 400 crank hp and 430 crank lb-ft. i am thinking that i might go with 3.73 and plan to drive 75, but that poses some problems with the law  essentially, it comes down to this, cause there will be hardly any difference in acceleration with either gear as it will be able to do second gear burnouts, and have no shortage of power in third. if anyone was wondering, the final ratios are 3.73: first - 9.9218 sixth - 1.865 4.11: first - 10.933 sixth - 2.055 
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#2
11-12-2007, 08:07 PM
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Re: rear end ratios
Something isn't right about your calculations. A 3.73 should be about 8 percent slower (RPM-wise) than a 4.11 - theoretically if a car is doing 1000 RPM at a given speed (in direct drive) with the 3.73, it should hit perhaps 1100 RPM with the 4.11.
__________________
1988 9C1 - Modified LM1 @ 275HP/350TQ - TH700R4 - 3.08 8.5" Disc Rear - see it at http://www.silicon212.org/9c1! 2005 Crown Vic P71 - former AZ DPS - 4.6 liters of pure creamy slothness! 1967 El Camino L79/M20 old school asphalt raper Remember - a government that is strong enough to give you everything you need, is also strong enough to take everything you have.
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#3
11-12-2007, 10:06 PM
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Re: rear end ratios
well i am using a .5:1 6th gear.
rear ends are either 3.73 or 4.11 multiply 3.73 and .5 and you get 1.865 final multiply 4.11 and .5 and you get 2.055 final 70 mph = 31.3 meters/second. radius of tire is 12.822 inches = 0.326 meters (31.3 m/s) / (0.326 meters) = 96.108 rad/sec (96.108 rad/sec) / (2*pi) = 15.296 rev/sec 15.295 rev/sec = 917.76 rpm 917 rpm is how fast the wheel is turning at 70 mph. now, i can multiply this by the final drive ratio to find the engine rpms. 917 * 2.055 = 1884 rpms 917 * 1.865 = 1710 rpms. well it looks like i must have made a math error. lol ok, so i guess i found what i need now. 3.55 rear end ratio sounds about right i used 2.73 by accident in the first calculation. stupid fat fingers... (yall get a math lesson for free now lol... use it to figure out your ideal rear end ratios)
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