T-5/3.08 guys...what's your RPM at 75?
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2011 Norwood Gathering
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From: Sarasota FL
Car: 99 WS6 / 00 SS / 11 CTS-V / 13 300
Engine: LS1 / LS1 / LSA / 5.7 Hemi
Transmission: 4L60E / T-56 / 6L80E / W5A80
Axle/Gears: 3.23 / 3.42 Auburn / 3.23 / 2.62
T-5/3.08 guys...what's your RPM at 75?
My tach claims 2,400 RPMs at 75...is that true? Seems kinda high to me for 3.08 gears...I highly doubt my rear end has different gears in it. I have a 3/90 Motor Trend road test of a '91 RS, that showed 60 MPH at 1600 in the spec chart...mine shows 2k at 60.
Any help is appreciated...I assume my tach is off?
Any help is appreciated...I assume my tach is off?
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Joined: Jan 2006
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From: Mooresville NC
Car: LOWERED ♦ CRIMSON METALFLAKE
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Transmission: 765R4
Axle/Gears: EATON POSI 4.56
.
.
We ran the math in our pit laptop and it matches Motor Trends’ numbers.
If parameters =
3.08
.7 OD
27” tires
1610 RPM
Speed = 60
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If People Drove Any Slower They’d Be Going BackwardsHow bout those dorks too scared to drive without headlights in the daytime!
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Joined: Feb 2008
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From: Sanford, FL
Car: 92 RS Camaro
Engine: 305 TBI
Transmission: T5
Axle/Gears: 3.08
Re: T-5/3.08 guys...what's your RPM at 75?
Im about 2200-2400 to but my car just cruises fine at that speed but im also on stock 16 rims with 50 profile tires
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From: Charleston, SC
Car: '85 TA
Engine: 350 turbo
Transmission: T56
Axle/Gears: 3.70 posi 9bolt
Re: T-5/3.08 guys...what's your RPM at 75?
Your tach is off. So is mine, so I made a spreadsheet of my rpm vs speed. Here is yours and I guessed on your tire size. I can email the spreadsheet if you want it.
Last edited by calebzman; Feb 27, 2009 at 08:33 AM.
Joined: Sep 2006
Posts: 952
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From: Austria
Car: 84 TA / 89 Formula
Engine: LS1 / L03
Transmission: T56 / 700R4
Axle/Gears: 3.73 / 3.27
Re: T-5/3.08 guys...what's your RPM at 75?
calebzman,
can you upload this spreadsheet as a picture by changing its extension to jpg?
could be helpful for a couple of us. thanks
can you upload this spreadsheet as a picture by changing its extension to jpg?
could be helpful for a couple of us. thanks
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From: Palm Coast, Fl.
Car: 1992 Camaro RS, 66 Mustang, 78 t/a
Engine: 5.0 TBI, 289, 400
Transmission: 700R4, C4, th350
Re: T-5/3.08 guys...what's your RPM at 75?
I don't know if that chart applied to autos too, but I cruise at 70 mph doing about 1550 rpm.
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Re: T-5/3.08 guys...what's your RPM at 75?
My tach says 2750 at 75. That's how I judged my speed on the interstate, cause my speedo dosen't work.
I don't know how accurate my tach is though either. That's also with my GPS at 75 MPH.
I don't know how accurate my tach is though either. That's also with my GPS at 75 MPH.
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Thread Starter
2011 Norwood Gathering
ThirdGen Firebird Rep
ThirdGen Firebird Rep
Joined: Jun 2000
Posts: 3,435
Likes: 4
From: Sarasota FL
Car: 99 WS6 / 00 SS / 11 CTS-V / 13 300
Engine: LS1 / LS1 / LSA / 5.7 Hemi
Transmission: 4L60E / T-56 / 6L80E / W5A80
Axle/Gears: 3.23 / 3.42 Auburn / 3.23 / 2.62
Re: T-5/3.08 guys...what's your RPM at 75?
I'm using 245/45/17 BFGs at the moment...could that have something to do with it? Based on having other cars clock me on the highway, I know the speedo is accurate. I figured the tach was off...it seems like it gets to 3k in first gear a little on the quick side
Is there any way to re-calibrate a stock tach? Thanks... Senior Member
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Joined: Oct 2004
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From: Charleston, SC
Car: '85 TA
Engine: 350 turbo
Transmission: T56
Axle/Gears: 3.70 posi 9bolt
Re: T-5/3.08 guys...what's your RPM at 75?
After that you can modify the tire size, rear gear, and transmission parameters to match your current combo. It's also helpful to see how a different tire size or rear gears will effect speed.
Last edited by calebzman; Mar 2, 2009 at 12:20 PM.
Joined: Sep 2006
Posts: 952
Likes: 2
From: Austria
Car: 84 TA / 89 Formula
Engine: LS1 / L03
Transmission: T56 / 700R4
Axle/Gears: 3.73 / 3.27
Re: T-5/3.08 guys...what's your RPM at 75?
thanks a lot for the spreadsheet!
if you are changing tires, you will need this site to determine how much off your speedo will be compared to the stock tires
http://www.miata.net/garage/tirecalc.html
based on this, you could change the speedo gears in your trans to correct it
OR
you can use another link to check for tire alternatives and find out which ones you can use without having to correct your speedo:
http://www.dsm.org/tools/tiresize.htm
if you are changing tires, you will need this site to determine how much off your speedo will be compared to the stock tires
http://www.miata.net/garage/tirecalc.html
based on this, you could change the speedo gears in your trans to correct it
OR
you can use another link to check for tire alternatives and find out which ones you can use without having to correct your speedo:
http://www.dsm.org/tools/tiresize.htm
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