Jason E

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?

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'91 Camaro RS
-Bright red, Grey leather, 305 TBI, M5, t-tops, 117k miles
-Magnaflow cat & catback, Edelbrock TES TPI Headers, Endura-Shine WP, Performer TBI Intake, Elite open element & STB, Powermaster 200 amp alt, Hypercrap Stage 2, TDS WB & SFCs, Pro 5.0 shifter, 17" TT2s with BFG KDWS's
-Xtant/Alpine/Boston System

'97 30th Anniversary Z28
-Arctic White with Hugger Orange stripes, White leather, M6, t-tops, 66k miles
-Xtant/Eclipse/Boston system, SLP bolt ons: SFCs, STB, 2OTL Exhaust, Bilsteins and CAI

'89 Camaro RS 2.8 - Sold 4/02
'89 Formula 305 TPI - Sold 7/02

NINÅ

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crytical point

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

calebzman

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.

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'85 TA, 350 TPI w/ Forged Internals, Procomp Al 190cc, Crane 212/218 .446/.459 114lsa, Holley Commander 950, LC-1, Turbo, Intercooled

my cardomain

ownor

calebzman,

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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'84 T/A HO 5speed, freshly rebuilt L69
'89 Formula, somewhat modded L03 and soon T56+3.73

do not confuse a lack of traction with an excess of torque

92 Camaro

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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Arctic White 92 RS-
Dynomax blackjack headers-> true duals with dynomax mufflers, 170 degree thermostat, Open Element Mod, 620 cfm throttle body, adjustable fuel pressure regulator, and an injector spacer.

kcb37

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.

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1989 RS Camaro 305 5 T-5, 4.56's, Powertrax Locker
2003 2500HD Chevy Silverado, Dmax, 3.73's, G80
1996 Chevy Silverado, 5.7 Vortex, 3.42's, G80
1949 F-1

Jason E

Could you email it to me? That'd be great! jasonfivestar@hotmail.com

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...

calebzman

Here ya go. It's saved as a .doc file extension, so after you save it to your harddrive, change the extension back to .xls and it will open as an excel file.

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.

Attached Files

TA RPM v MPH.doc (56.0 KB, 3 views)

ownor

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