How fast am I really going - The 1947 - Present Chevrolet & GMC Truck Message Board Network

roughedup72 · 05-30-2006, 10:10 AM

I just installed a 3.73 posi rearend in my truck and now my speedo is off but I'm not sure by how much. I'm running 285/70/15's and the 3.73, The tranny is a th350, anybody got any Ideas, and how do I get it correct? Thanks in advance.

sdmahr · 05-30-2006, 10:24 AM

Got a GPS?

roughedup72 · 05-30-2006, 10:26 AM

No. Thats a good Idea though.

**1970 CST Short Wide** · 05-30-2006, 10:27 AM

http://www.speedworldmotorplex.com/calc.htm

Try this

cdowns · 05-30-2006, 11:27 AM

go on a highway use the mile markers and a stopwatch// with your speedo at a steady 60mph its 60seconds per mile divide the actual seconds it takes between mile markers divide by 60 take the result subtract it from 100 and that's the percentage youre off

5150 · 05-30-2006, 11:56 AM

just speed through town and a police officer will tell you quicker then any of these ideas.

Hell, probably cheaper than a GPS

Jason915 · 05-30-2006, 12:01 PM

I always figure out MPH by RPM's try http://www.4lo.com/4LoCalc.htm

lvscott · 05-30-2006, 12:49 PM

From my calculations @ 2500 RPM you're going 61.21 mph
check it out for yourself at this site http://www.1bad69.com/calc.htm

roughedup72 · 05-31-2006, 10:03 AM

Thanks for all the links guys, Really helpfull. Is there a site that I can go to and get the correct gear for the speedometer?

JAMESCHURCH13 · 05-31-2006, 10:29 AM

Quote:

Originally Posted by roughedup72

Thanks for all the links guys, Really helpfull. Is there a site that I can go to and get the correct gear for the speedometer?

Could you get it from a junk yard. Any chevy with a 350turbo that had 15 inch rims and those gears should be close. One from a truck should be golden. Peace.

70c10 · 06-01-2006, 07:54 AM

Quote:

Originally Posted by roughedup72

Thanks for all the links guys, Really helpfull. Is there a site that I can go to and get the correct gear for the speedometer?

They are on ebay all the time. The dealer should have them also.

cwilli84 · 05-31-2006, 11:05 AM

Try TCI transmissions website they have all the trans info and calculators and gears for the speedos.

roughedup72 · 05-31-2006, 09:37 PM

Thanks cwilli84, i will give it a shot.
jameschurch13,youre right it would probably be golden. I have a hard enough time finding parts for my truck without paying a arm and leg for it now.

wakeboarddrumma · 06-01-2006, 12:20 PM

I would go througha nieghborhood with the speed checker. I went to one the other day, because i am running 33 inch tires in the rear, and i was right on with my guesses. I am going 25 when it says 20

05-30-2006, 10:10 AM	#1
roughedup72 Senior Member Join Date: Oct 2005 Location: south carolina Posts: 658	How fast am I really going I just installed a 3.73 posi rearend in my truck and now my speedo is off but I'm not sure by how much. I'm running 285/70/15's and the 3.73, The tranny is a th350, anybody got any Ideas, and how do I get it correct? Thanks in advance. __________________ 1972 chevy cheyenne 10,nothing special at the moment,Its a work in progress, Working on the engine, paint and body,engine, paint and body,now its the suspenion, ahh hell I'm about tired of working on it. Maybe it will be a rat rod.

05-30-2006, 10:24 AM	#2
sdmahr Registered User Join Date: Apr 2004 Location: South Texas....the Valley Posts: 199	Re: How fast am I really going Got a GPS?

05-30-2006, 10:26 AM	#3
roughedup72 Senior Member Join Date: Oct 2005 Location: south carolina Posts: 658	Re: How fast am I really going No. Thats a good Idea though. __________________ 1972 chevy cheyenne 10,nothing special at the moment,Its a work in progress, Working on the engine, paint and body,engine, paint and body,now its the suspenion, ahh hell I'm about tired of working on it. Maybe it will be a rat rod.

05-30-2006, 10:27 AM	#4
1970 CST Short Wide Senior Moment Join Date: Mar 2002 Location: Pittsburg Ca Posts: 4,185	Re: How fast am I really going http://www.speedworldmotorplex.com/calc.htm Try this __________________ 1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565

05-30-2006, 11:27 AM	#5
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: How fast am I really going go on a highway use the mile markers and a stopwatch// with your speedo at a steady 60mph its 60seconds per mile divide the actual seconds it takes between mile markers divide by 60 take the result subtract it from 100 and that's the percentage youre off __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

05-30-2006, 11:56 AM	#6
5150 C10 Club Tennessee Join Date: Mar 2003 Location: White House, TN 37188 Posts: 8,281	Re: How fast am I really going just speed through town and a police officer will tell you quicker then any of these ideas. Hell, probably cheaper than a GPS __________________ Bryan www.gmtruckshow.com Project "Andes"-Halen's First Truck Project: Patina Burb for he is God’s servant for your good. But if you do wrong, be afraid, for he does not bear the sword in vain. For he is the servant of God, an avenger who carries out God’s wrath on the wrongdoer. Romans 13:4

05-30-2006, 12:01 PM	#7
Jason915 Registered User Join Date: Jan 2005 Location: Colorado Springs Posts: 693	Re: How fast am I really going I always figure out MPH by RPM's try http://www.4lo.com/4LoCalc.htm __________________ 1971 GMC K1500 SWB Fleetside, 4" skyjacker softride and, 14 Bolt FF, HD Dana 44 4.10's 1970 K5 TBI conversion lifted etc SOLD 1968 C20 camper truck SOLD “To ban guns because criminals use them is to tell the innocent and law-abiding that their rights and liberties depend not on their own conduct, but on the conduct of the guilty and the lawless.” Jeff Snyder

05-30-2006, 12:49 PM	#8
lvscott Registered User Join Date: Mar 2005 Location: Las Vegas, NV Posts: 84	Re: How fast am I really going From my calculations @ 2500 RPM you're going 61.21 mph check it out for yourself at this site http://www.1bad69.com/calc.htm Last edited by lvscott; 05-30-2006 at 12:50 PM.

05-31-2006, 10:03 AM	#9
roughedup72 Senior Member Join Date: Oct 2005 Location: south carolina Posts: 658	Re: How fast am I really going Thanks for all the links guys, Really helpfull. Is there a site that I can go to and get the correct gear for the speedometer? __________________ 1972 chevy cheyenne 10,nothing special at the moment,Its a work in progress, Working on the engine, paint and body,engine, paint and body,now its the suspenion, ahh hell I'm about tired of working on it. Maybe it will be a rat rod.

05-31-2006, 11:05 AM	#12
cwilli84 1FINE69 Join Date: Aug 2003 Location: Detroit, Michigan Posts: 239	Re: How fast am I really going Try TCI transmissions website they have all the trans info and calculators and gears for the speedos. __________________ Had a 69 swb fleetside 350zz3 w 400turbo trans oak lined bed with rhino coated sides red exterior. SOLD

05-31-2006, 09:37 PM	#13
roughedup72 Senior Member Join Date: Oct 2005 Location: south carolina Posts: 658	Re: How fast am I really going Thanks cwilli84, i will give it a shot. jameschurch13,youre right it would probably be golden. I have a hard enough time finding parts for my truck without paying a arm and leg for it now. __________________ 1972 chevy cheyenne 10,nothing special at the moment,Its a work in progress, Working on the engine, paint and body,engine, paint and body,now its the suspenion, ahh hell I'm about tired of working on it. Maybe it will be a rat rod.

06-01-2006, 12:20 PM	#14
wakeboarddrumma Registered User Join Date: Apr 2006 Location: North alabama Posts: 111	Re: How fast am I really going I would go througha nieghborhood with the speed checker. I went to one the other day, because i am running 33 inch tires in the rear, and i was right on with my guesses. I am going 25 when it says 20



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