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08-16-2015, 03:46 PM
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#1 |
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Registered User
Join Date: Sep 2014
Location: Granite Bay, CA
Posts: 11
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RPM at freeway speed?
I have a new crate motor, 6.2L LS3, 4L65E trans. Current rear gear is 3.73. GM recommends 3.42 for this engine/trans combo. With the 3.42 and my tire size, RPM's calculate to 2201 at 70 MPH. My question is this, is 2200 rpm going to be in the right range for optimal fuel mileage. I would assume so from a GM engineering standpoint but was looking for real world scenarios. Thanks
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08-16-2015, 05:28 PM
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#2 |
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Registered User
Join Date: Dec 2002
Location: Cactus Patch So. Az
Posts: 4,749
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Re: RPM at freeway speed?
Sounds like a perfect combination to me!
I would not think you would notice that much difference in MPG , are you thinking that 2000 RPM's is the perfect number? I am thinking out loud, the difference between 20 and 21 MPG difference. You could always reduce the tire height by 1/2 inch or so.............. after you burn the first set off!!
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53 TuTone Extended Cab 350 4-Spd 3:08 (SOLD) 53 Chevy Moldy pearl green ZZ-4 4L60E 9" 3:25 55 GMC 1st Black Mll (ZZ4) ZZ6 TKO 600 5 sp 3:73 62 Solidaxle Corvette Roman Red (327 340hp 4spd 3:36) C4 & C5 suspension tube chassis LS 3 4L70E 65 Corvette Coupe 327 350hp 4spd 4:11 78 Black Silverado SWB (350/350) 5.3 & 4L60E 3:42 2000 S-Type 3.0 (wife cruiser) 2003 GMC SCSB 5.3 4L60E 3:42 |
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08-16-2015, 05:30 PM
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#3 |
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Senior Member
 
Join Date: Mar 2004
Location: Lee's Summit, MO (KC)
Posts: 742
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Re: RPM at freeway speed?
I don't know about fuel mileage because I don't care, but I'd keep those 3.73s all day long...
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-Keegan- '72 Jimmy 4x4 - 5.3/4L65E/NP205 swap http://67-72chevytrucks.com/vboard/s...d.php?t=663780 |
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08-16-2015, 07:12 PM
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#4 |
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Senior Member
Join Date: May 2009
Location: Fort Worth, TX
Posts: 6,370
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Re: RPM at freeway speed?
3.42 compared to 3.73 is not much of a ratio change to warrant changing gear sets.
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08-16-2015, 07:57 PM
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#5 | |
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Registered User
Join Date: Sep 2014
Location: Granite Bay, CA
Posts: 11
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Re: RPM at freeway speed?
Quote:
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08-16-2015, 08:46 PM
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#6 | |
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meowMEOWmeowMEOW
Join Date: Sep 2009
Location: MKE WI
Posts: 7,128
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Re: RPM at freeway speed?
Quote:
2200 is fine on the highway, and I'd say its right around where most of us sit. Your stall converter and lockup settings will also affect the seen vs calculated rpm. My 4l80e/ 373 12bolt sits about 150-200rpm higher, but the converter has a slipping problem when hot in 3rd.
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'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING  |
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08-16-2015, 09:05 PM
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#7 |
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Registered User
Join Date: Sep 2009
Location: ottawa,canada
Posts: 4,550
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Re: RPM at freeway speed?
I'm running 3:42 gears with my 6.0l/4l80, and it's right around 2200rpm @70mph....and 2200 is right about when this thing starts to pull...
 I wouldn't be able to keep tires on it at all with 3:73 gears! if you were doin a lot of freeway driving you could run 3:23 gears easily with that ls3...
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my build threads '86 C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415628 '67 C10 http://67-72chevytrucks.com/vboard/s...d.php?t=635078 '63 GMC http://67-72chevytrucks.com/vboard/s...d.php?t=674682 |
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08-16-2015, 11:48 PM
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#8 | |
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Registered User
Join Date: Dec 2002
Location: Cactus Patch So. Az
Posts: 4,749
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Re: RPM at freeway speed?
Quote:
__________________
53 TuTone Extended Cab 350 4-Spd 3:08 (SOLD) 53 Chevy Moldy pearl green ZZ-4 4L60E 9" 3:25 55 GMC 1st Black Mll (ZZ4) ZZ6 TKO 600 5 sp 3:73 62 Solidaxle Corvette Roman Red (327 340hp 4spd 3:36) C4 & C5 suspension tube chassis LS 3 4L70E 65 Corvette Coupe 327 350hp 4spd 4:11 78 Black Silverado SWB (350/350) 5.3 & 4L60E 3:42 2000 S-Type 3.0 (wife cruiser) 2003 GMC SCSB 5.3 4L60E 3:42 |
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08-24-2015, 02:07 PM
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#9 |
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Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,945
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Re: RPM at freeway speed?
6.0 4L80E with 4:10 gears and I'm cruisin at 2400RPMs @70MPH, tires are 29" tall. Truck gets about 16-17 MPG.
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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