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05-24-2020
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#11 |
 
Join Date: Sep 2008
Location: Mullica Hill, New Jersey
Posts: 2,566
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Re: Rear end gearing calculations
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05-24-2020
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#12 |
 
Join Date: Aug 2018
Location: Tulsa
Posts: 43
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Re: Rear end gearing calculations
Paul, fantastic input and I would agree that it depends on what someone wants that determines the upgrade. I am in the Tulsa area and do some Oklahoma back roads, Arkansas "twisties" and in town driving...and I really enjoy rowing the gears.
Right now the syncro is grinding on a hard shift between 1st and 2nd so that gets fixed first. Then after enjoying the 3:45s for a bit, with the way I drive, the 4:10s are next. I am attempting to keep the budget at $2000+/- every 6 months or so. From what little I could find, I would agree the 4:30s would be more than I want. Marty - when I am ready I will check and see if you still have the "bolt and go" 4.10s |
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05-24-2020
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#13 |
Join Date: Jan 2010
Location: Mystic CT
Posts: 2,594
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Re: Rear end gearing calculations
From Marc’s chart, with 3:45s, we’d be going
338 mph in 6th at 7500 rpm!!! 🤪 Probably be a little slower when the rev limiter kicks in? What? Your ZR-1 won’t pull 7500 in 6th? |
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05-24-2020
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#14 |
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Join Date: Aug 2018
Location: Tulsa
Posts: 43
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Re: Rear end gearing calculations
Well, I hit 300 mph the other day and it scared me almost to death. I am actually getting the 410s to keep the top end under 300...😀
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05-24-2020
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#15 |
 
Join Date: Feb 2012
Location: Ledyard,CT
Posts: 7,990
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Re: Rear end gearing calculations
Well, here I am complaining about my hood pushing up above 190!
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05-26-2020
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#16 |
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Join Date: Aug 2019
Location: Maumee, OH
Posts: 19
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Re: Rear end gearing calculations
Doing the Math: Tire Size (mm) /25.4 (mm)/in X (aspect ratio x2) + Rim Dia = Tire height
So: 315/25.4 X (.35X2) + 17 = 25.68 in for tire height for a 315x35x17 tire. Tire Air pressure could factor when measuring as you did as well as being installed with the car sitting on the tires. Just sayin' |
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05-26-2020
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#17 |
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Join Date: Aug 2018
Location: Tulsa
Posts: 43
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Re: Rear end gearing calculations
Good point on using better numbers, but using the 25.68 in place of the 25.25 in my calcs doesn't get to the 3:45 ratio we came up with jacking the car up marking and spinning the tire/drive shaft per Hib's suggestion.
So good news and bad news I guess...bad news is I need to buy 4:10s, good news is I get to buy 4:10s and improve the car even more. |
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05-27-2020
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#18 | |
Join Date: Nov 2007
Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri
Posts: 6,493
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Re: Rear end gearing calculations
Quote:
__________________
Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry |
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05-27-2020
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#19 |
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Join Date: Aug 2019
Location: Maumee, OH
Posts: 19
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Re: Rear end gearing calculations
Certainly circumference (one tire revolution) is the key here [(Pi) X Diameter] => 3.14.16X25.68 in. = 80.68 in., this is probably relatively insensitve to inflation (within limits).
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05-28-2020
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#20 | |
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Join Date: Nov 2007
Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri
Posts: 6,493
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Re: Rear end gearing calculations
Quote:
__________________
Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry |
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