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#1 |
Registered User
Join Date: Jan 2009
Location: Calgary, AB
Posts: 1,181
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th350 + highway speed
Having to do a bit of highway travel this weekend I noticed with my truck it seems to be really screaming about 110km/h (70mph).
Now I have no idea what my rear gears are and will soon be finding this out nor what my rpms are (no tach yet) but I was told I had 3.73 gears. Does this seem about right? |
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#2 |
Living la vida broka
![]() Join Date: Jan 2003
Location: P'ville California
Posts: 221
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Re: th350 + highway speed
28 inch tall tires with 3.73s should give you 3200 rpm give or take at 70 mph
http://www.csgnetwork.com/multirpmcalc.html
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1976 C10 Longbed lowered 5/7, hot 355/TH350. ~ SOLD 1974 C10 Shortbed Stepside 350/Saginaw ~ SOLD 1984 C10 Longbed 6.2l diesel 700r4. ~SOLD 1985 GMC C20 350 700r4, ~under the knife Last edited by Trick76; 02-15-2009 at 04:59 PM. Reason: linky |
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#3 | |
Registered User
Join Date: Jan 2009
Location: Calgary, AB
Posts: 1,181
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Re: th350 + highway speed
Quote:
Hmm guess that could explain heavy gas usage on highway! haha I can see now why people prefer the TH700r for highway driving. Last edited by enaberif; 02-15-2009 at 05:09 PM. |
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#4 |
Registered User
Join Date: Jan 2009
Location: greensboro, nc
Posts: 174
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Re: th350 + highway speed
I feel your pain, mine has 4.10's - 29" tires and definitely needs OD bad!
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#5 |
Slugish
![]() Join Date: Jan 2005
Location: Earlysville, Va.
Posts: 1,024
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Rather than go thtu all the expense & time of an overdrive tranny , just get you a 3.42 ring & pinion for under 200.00 . With a 3 speed this is aboutthe best of both worlds . with a 3.73 or 4.10 you need overdrive if you do any freeway cruising at all . You must be screaming at 50 mph with a 4.10 - 3 speed .
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#6 | |
Registered User
Join Date: Jan 2009
Location: Calgary, AB
Posts: 1,181
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Re: th350 + highway speed
Quote:
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#7 |
Registered User
Join Date: Jan 2009
Location: Calgary, AB
Posts: 1,181
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Re: th350 + highway speed
I've been doing some reading and can someone tell me if there is any truth to this.
Some people say that based upon tire height it can actually make your gear ratio seem lower. For example say you have 28" high tires and you have a 3.73 gear ratio, with the 28" tires the 3.73 may seem more like 4.10 gears? Any truth? I currently run 28" tall tires. Last edited by enaberif; 02-16-2009 at 01:00 AM. |
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#8 |
Another Day, Another Dollar
Join Date: Nov 2008
Location: North Vancouver, BC
Posts: 1,316
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Re: th350 + highway speed
the bigger the tires, the higher the speed, and the lower the revs
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-78 K20 Cheyenne 454 long box, 4" lift, 35" MT's, '84 cab, '80 box "its hip to be square" ![]() |
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#9 |
Registered User
Join Date: Feb 2009
Location: NorCal Humboldt County
Posts: 14
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Re: th350 + highway speed
My 77 gmc 4 speed 4.11? screams in 4th @ 50mph 15" tires
__________________
1977 GMC C2500 5.7L V8 Long Bed 4-Speed Stick 12/08 ~12/08 Sanded/Primed/Rhino Lined inside bed 1988 Chevy C3500 5.7L 1-Ton w/utility bed10/08 ~1/09 Tie Rods, Ball joints, spindles, wheel bearings, steering gearbox ~11/08 distributor, cap, rotor, wires, plugs, thermostat 180' & chrome water inlet, radiator flush, hoses, Trans filter & pcv, air & oil. ~11/08 Sanded & painted blue. new brake booster & master cylinder w/flush & adjust. ~Bought 285/70/16 orig. chevy rims w/tires on C/L$100 |
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#10 |
Registered User
Join Date: Mar 2005
Location: North Coast
Posts: 1,012
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Re: th350 + highway speed
This question would be easier to answer if more truck info was offered. I've run 3.73's with T350 trannies for 30+ years in several GM trucks with no problem at highway speeds. I do run 33/12.50-tires though,(no lift required on squarebodies). This is a good tire size for those gears and transmission. No problem running 70/75.
Last edited by Dooley; 02-16-2009 at 02:29 AM. |
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#11 | |
Registered User
Join Date: Jan 2009
Location: Calgary, AB
Posts: 1,181
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Re: th350 + highway speed
Quote:
I can't guarantee I'm running 3.73 so next few days I'll get the rear diff oil changed and find out. |
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#12 |
1962 C-10
Join Date: Apr 2005
Location: Las Vegas, New Mexico
Posts: 4,978
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Re: th350 + highway speed
Sounds to me like you have 3.73's. The best gear ratio for a th350 and lower profile tires to me is 3.08's. I ran 3.08's on my '62 for a while with no o/d. It did 75 on the freeway with no problems. If you plan on running overdrive, I'd go with 3.42's or 3.73's. When I put a gearvendor overdrive in my truck with the 3.08's, it tended to be a little doggie on the hills.
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Joseph Chavez ![]() "See the USA in a Chevrolet!!" ......................_____ .........________//__{\_____ ,,,,,,,/__(O)___//___/__(O)_/ 1962 C10 Shortbed Fleetside 327/th350 GV overdrive 1974 C10 Longbed Fleetside 350/th350 "The Trash Truck" 1999 Chevy 2500 OBS, Longbed 5.7/4L80E 4x4 2015 GMC Sierra SLE 1500 4x4 |
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#13 |
Registered User
Join Date: Sep 2005
Location: Sun City West, Az
Posts: 3,822
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Re: th350 + highway speed
my th 350 with 3.08's turns 2500 rpm at about 75 mph on the freeway.that's with 29.8 inch tire's.it does good on gas too.it lack's a little off the line.but,i didn't build it for the quarter mile.i like the lower rpm's to freeway cruise.
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