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#1 |
![]() Join Date: Jun 2006
Location: Sparks, NV
Posts: 2,852
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While driving the (new to me) Z recently I noticed that the rpms seemed high for any given speed in all gears. I was informed by the seller that the differential had been rebuilt in the last two years but never asked if he changed the ratios. So I conducted an experiment. I noted the rpms at 60mph in 4th gear (1:1 trans ratio) I was running at 3300 rpm. My rear tires are 25 inches tall. Using the calculator below:
http://www.crawlpedia.com/rpm_gear_calculator.htm It appears I have 4:10 gears. ![]() Stock 3.42's should have gotten me 2750 rpm and 3.73's should be 3000 rpm all else being equal. So... unless the tach is very wrong, my first real mod is already done. Cool H ![]()
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90'ZR-1 #1461 Red/Black Ported Intake, Degreed Cams, OBX Headers & Exhaust, Fidanza FW, Secondary Delete, Custom tune, C6 GS Wheels. Sold 08 C6 Z51 Crystal Red Metallic Sold Vararam Intake, Tune, Sold 05 C6 Z51 Red/Black Sold 90'ZR-1 #1723 Black/Gray Sold but not forgotten 91' Z51 L98 White Vert. My First, you always remember your first. Sold. |
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#2 | |
![]() Join Date: Apr 2007
Location: Lake Bluff, IL
Posts: 2,065
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2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough" Last edited by WARP TEN; 06-30-2017 at 10:46 AM. |
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#3 |
![]() Join Date: Jan 2015
Location: Decatur, AL
Posts: 93
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I'm thinking of going to 4.10. Not that I ever will top the car out, but I still don't want to reduce the top end potential that got the car all that hype back in the day. Anybody have any opinions on how it impacts top end? Will it pull to redline in 6th with 4.10s where 5th is fastest gear stock?
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1990 ZR1, 1987 Mustang GT (since new), 1973 DeTomaso Pantera, 1987 928S4 Passed on: 1984 930S (gray market), 1988 Mustang Coupe Trooper car(drag) |
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#4 | |
![]() Join Date: Feb 2014
Location: AZ
Posts: 860
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#5 |
![]() Join Date: Oct 2004
Posts: 1,889
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OP - I assumed maybe the same when I first got my '90 but I had been told it was original! The '90 tachs are known to be very inaccurate and I discovered it was stock after using the ATC panel to calculate RPM and I connected a Tech1 to confirm that I actually had a 3.45 and the cluster needed attention.
When you turn the KEY TO RUN with the car "not running" if the tach needle isn't parked on 0 you have a tach error. Needs to park on 0 - not close - on 0! Use the ATC if it's a C68 car and calculate RPM using it for confirmations. |
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#6 |
![]() Join Date: Nov 2011
Location: Dunbarton NH
Posts: 7,359
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Top end in sixth gear with 4.10's is about 270 mph, so unlikely you could reach that.
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#7 |
![]() Join Date: Jan 2010
Location: Mystic CT
Posts: 2,620
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#8 |
![]() Join Date: Nov 2011
Location: Dunbarton NH
Posts: 7,359
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Doug, I'm only running 3.73's. My top end is in 5th gear.
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#9 |
![]() Join Date: Jan 2010
Location: Mystic CT
Posts: 2,620
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#10 |
![]() Join Date: Jan 2010
Location: Mystic CT
Posts: 2,620
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According to Marc's chart, with stock 3:45s
at 7500 in 6th the car would go 338! I'm assuming that's with the top on and windows rolled up? I have trouble getting over 300? Maybe I should roll up the windows? 😋 |
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