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#1 |
Registered User
Join Date: Nov 2008
Location: Rowlett, TX
Posts: 863
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K5 with 700r4 question
hey guys, thinking of swapping in a 700r4 into my 72 K5. It is bone stock, with the original 350, TH350 trans, NP205 with 3.73 gears. Going with a 2.5 inch lift and 31.7 inch tires...235/85/16's. Can anyone give me experience or opinions on mpg and performance? Thanks in advance
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#2 |
Carpe manana
![]() ![]() Join Date: Dec 2010
Location: Eau Claire, WI
Posts: 12,376
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Re: K5 with 700r4 question
I've got trucks here with 33" tires and both 700r4 and th350 transmissions (and 4.10 and 3.73 gears respectively). IMO unless you do a lot of highway driving I'd stick with the th350. I'm building a blazer now and plan to keep the th350 even if I swap the 3.07s to 3.73s.
Not too many K5s with all original drive trains.
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1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 ![]() |
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#3 | |
Registered User
Join Date: Nov 2008
Location: Rowlett, TX
Posts: 863
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Re: K5 with 700r4 question
Quote:
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#4 |
Registered User
Join Date: Mar 2015
Location: Ontario Canada
Posts: 1,513
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Re: K5 with 700r4 question
Putting an overdrive transmission behind an old school engine wont give you the gas mileage you would expect mainly because the older engines are not designed to run efficiently at 1900 RPM. If you want fuel economy, then you will have to upgrade both the engine as well as the transmission. Your 3.73 gears are a bit low for an overdrive application especially with your tire diameter anyway, so you're looking at a big expense for everything to run nicely together.
For comparison sake, I have a 5.3 with a 4L60E and 4:10 gears turning 33" tall tires. I get a true 25 MPG (imp) which is equal to 21 MPG US. Unless you're willing to do a complete package, don't waste your time.IMHO |
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#5 |
Registered User
Join Date: Aug 2005
Location: Scottsdale, AZ
Posts: 215
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Re: K5 with 700r4 question
I have a 383/700r4
I like the combo, runs nice down the highway at 75mph. It's getting pulled for a ls2/4l70 at a later date
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1972 Dark blue, Cst, Highlander |
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#6 | |
Registered User
Join Date: Dec 2003
Location: Houston, TX
Posts: 734
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Re: K5 with 700r4 question
Quote:
Same combo here. I used to drive a lot highway miles and it worked well. Now I don't, and would like to try a 4l80 trans. On my best day, I get about 10mpg.
__________________
'72 K5, known as 'the Fox.' |
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#7 |
Registered User
Join Date: Mar 2015
Location: Ontario Canada
Posts: 1,513
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Re: K5 with 700r4 question
10 MPG ? Wow, that would kill me up here in Canada. Regular gas right now is $4.04 per US gallon and is going up in the new year.
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#8 |
Registered User
![]() Join Date: Aug 2014
Location: Arkansas
Posts: 351
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Re: K5 with 700r4 question
Hemi 43 what adaptor did you use on your trans to transfer case?
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#9 |
Registered User
Join Date: Mar 2015
Location: Ontario Canada
Posts: 1,513
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Re: K5 with 700r4 question
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#10 |
Recalculating.....
Join Date: Nov 2010
Location: New Lenox Il
Posts: 686
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Re: K5 with 700r4 question
The work involved and money spent would probably get you an extra 2 to 3 MPG. So lets say you spend 2500 for a trans (rebuilt). the motor would have to be pulled and moved (labor) drive shaft may need to be shortened or lengthened. If your not doing the work yourself add 1500-2000. If you are what is your time worth? So if you put 4k to 4.5k in your trans, how much do you have to drive it to save that much gas? I thought it out like this already. I would do a full ls drivetrain swap if I was concerned about the gas mileage. I didn't buy a K5 to save gas. LOL!
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Brian - (BBrendal) 1969 Chevy Camaro Z28 1972 Chevy Blazer CST 2004 GMC Yukon (The truck that pulls the car trailer) 1972 Chevy Blazer CST #2 (Finished and sold!) Blazer build link... http://s1213.photobucket.com/albums/...rendal/Blazer/ |
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#11 |
Registered User
![]() Join Date: Jun 2004
Location: On The Beach, S C
Posts: 613
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Re: K5 with 700r4 question
I put a crate 350 in my 2 wd with a 700R4. Pain in the backside, no advantage and cost a ton of money. Wish I'd kept the 350 trans. Cheaper - better.
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4oldcars Driving: 1971 Jimmy w/68 Chev front clip, 1953 Bel Air 2 dr hdtp, 1996 Roadmaster wagon, 2000 Eldorado The ones I let go: 1931 2 dr sedan, 1935 pick up, 1938 2 dr sedan, 1962 SS 454, 1963 409 wagon, 1970 short bed, 1972 short bed, 1972 sub, 1976 short bed, 1986 long bed, 03 short bed |
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#12 |
Registered User
![]() Join Date: Jun 2014
Location: Graham, WA
Posts: 283
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Re: K5 with 700r4 question
Its all about the smiles per gallon. No one buys a brick on wheels with a V8 for Miles per gallon
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1970 1/2 ton 4x4 4spd Suburban 1972 K10 350/700R/205/ Sniper EFI Daily Driver Sold 1971 K5 on 35s Traded 1972 K5 3/4 ton PROJECT Sold |
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#13 |
Registered User
Join Date: Nov 2008
Location: Rowlett, TX
Posts: 863
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Re: K5 with 700r4 question
agreed....too much for an occasional driver.
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#14 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: K5 with 700r4 question
No longer have my K5 but I drive it's big brother K20 Suburban.
I like the 4L60 overdrive. Lower first gear for better take off. Overdrive for less stressed engine. Small increase in fuel economy but having the engine last longer has it's benefit. Quieter in the cabin too. Moving the engine forward isn't a terrible task. Shorten the radiator hoses and lengthen the exhaust pipes.
__________________
My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#15 |
2WD Jimmy
![]() Join Date: Mar 2005
Location: Davis County, Utah
Posts: 2,564
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Re: K5 with 700r4 question
I dont like the 700r4. Its shifts like a powerglide with an over drive.
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