K5 with 700r4 question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DBear · 10-24-2016, 09:22 PM

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

**DeadheadNM** · 10-24-2016, 09:29 PM

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.

DBear · 10-24-2016, 10:13 PM

Quote:

Originally Posted by DeadheadNM

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.

I hear that....I really don't wanna mess with this drivetrain since it's original, just thought it would be nice to have the overdrive. I plan on bringing it to NM next summer, Ruidoso area, and do some trailing.

hemi43 · 10-24-2016, 11:47 PM

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

ClassicStyle · 10-24-2016, 11:51 PM

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

mister.freeze · 10-25-2016, 09:04 AM

Quote:

Originally Posted by ClassicStyle

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

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.

hemi43 · 10-25-2016, 09:56 AM

Quote:

Originally Posted by mister.freeze

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.

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.

twp1 · 10-26-2016, 10:02 PM

Hemi 43 what adaptor did you use on your trans to transfer case?

hemi43 · 10-27-2016, 01:01 PM

Quote:

Originally Posted by twp1

Hemi 43 what adaptor did you use on your trans to transfer case?

I used the Advanced adapter. Worked great.

BBrendal · 11-12-2016, 11:28 AM

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!

4oldcars · 11-12-2016, 11:33 AM

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.

Lieferson · 11-14-2016, 12:11 PM

Its all about the smiles per gallon. No one buys a brick on wheels with a V8 for Miles per gallon

DBear · 11-14-2016, 03:12 PM

agreed....too much for an occasional driver.

Bigdav160 · 11-14-2016, 03:12 PM

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.

**Tom Vogel** · 11-15-2016, 10:13 AM

I dont like the 700r4. Its shifts like a powerglide with an over drive.

10-24-2016, 09:22 PM	#1
DBear Registered User Join Date: Nov 2008 Location: Rowlett, TX Posts: 867	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

10-24-2016, 09:29 PM	#2
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,443	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. __________________ 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 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland

10-24-2016, 11:47 PM	#4
hemi43 Registered User Join Date: Mar 2015 Location: Ontario Canada Posts: 1,526	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

10-24-2016, 11:51 PM	#5
ClassicStyle Registered User Join Date: Aug 2005 Location: Scottsdale, AZ Posts: 215	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 __________________ 1972 Dark blue, Cst, Highlander

10-26-2016, 10:02 PM	#8
twp1 Registered User Join Date: Aug 2014 Location: Arkansas Posts: 351	Re: K5 with 700r4 question Hemi 43 what adaptor did you use on your trans to transfer case?

11-12-2016, 11:28 AM	#10
BBrendal Recalculating..... Join Date: Nov 2010 Location: New Lenox Il Posts: 686	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! __________________ 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/

11-12-2016, 11:33 AM	#11
4oldcars Registered User Join Date: Jun 2004 Location: On The Beach, S C Posts: 613	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. __________________ 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

11-14-2016, 12:11 PM	#12
Lieferson Registered User Join Date: Jun 2014 Location: Graham, WA Posts: 283	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 __________________ 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

11-14-2016, 03:12 PM	#13
DBear Registered User Join Date: Nov 2008 Location: Rowlett, TX Posts: 867	Re: K5 with 700r4 question agreed....too much for an occasional driver.

11-14-2016, 03:12 PM	#14
Bigdav160 Registered User Join Date: Apr 2011 Location: Klein Texas Posts: 3,852	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

11-15-2016, 10:13 AM	#15
Tom Vogel 2WD Jimmy Join Date: Mar 2005 Location: Davis County, Utah Posts: 2,565	Re: K5 with 700r4 question I dont like the 700r4. Its shifts like a powerglide with an over drive.

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