i need more speed/mileage

[spankrz]

i got a 72 lwb chevy with a 350/350. i'm not gettin the best milage, and don't have a very high top speed. i'm startin to think the 350 tranny has to go. lookin to put somethin with overdrive in. maybe even a 5 speed. automatic only, i have a low hump floor, and so on. what do you guys think?

[72BlckButy]

You can do a 700R4 swap fairly easy and IIRC can even reuse your old tranny member.

Of course you could also drop in a 250 w/ powerglide like my '69 and pull in 21 mpg.

It won't get you there the quickest but you'll have a few cents extra in your wallet.

[spankrz]

is the 700r4 4spd+overdrive? i forget

[Tx Firefighter]

A 700 is a 4 speed trans. Third is 1:1 like your current TH350 and 4th is .70 overdriven.

[spankrz]

Originally Posted by Tx Firefighter

A 700 is a 4 speed trans. Third is 1:1 like your current TH350 and 4th is .70 overdriven.

k thanks for settin me straight

[72BlckButy]

Of course you could also keep your TH350 and throw on a GearVendors OD, but you would probably be money ahead with the 700R4.

[cdowns]

how many miles per gallon do you get and about what speed are you trying to achieve?

[spankrz]

Originally Posted by cdowns

how many miles per gallon do you get and about what speed are you trying to achieve?

i don't get much right now, less than 15 for sure. as far as speed goes, maybe 110 or 120. that's not as important as being able to cruise 75 on the interstate without runnin 3grand lol. where im goin to school next year im gonna be hittin the interstate every mornin...

[spankrz]

well, sounds like 700r4 is the way to go. where should i get one? how hard will the swap be? how much is this gonna set me back?

[mark's68]

maybe try swaping some 3.07 gears.

[68C15]

Originally Posted by spankrz

well, sounds like 700r4 is the way to go. where should i get one? how hard will the swap be? how much is this gonna set me back?

I would pick up a used rebuildable one and have a local shop build it. that way if there is a problem you know where and who to talk to.
otherwise www.bowtieoverdrives.com is a good reputable shop with quality stuff and lots of valuable tech help.

[americanmusc1e]

Originally Posted by spankrz

well, sounds like 700r4 is the way to go. where should i get one? how hard will the swap be? how much is this gonna set me back?

my swap cost me $1300 for the tranny rebuild (shift kit, z-pack clutches, all the good stuff), plus probably $200 more, I used my stock crossmember and moved it back, had my driveshaft shortened $48, used my existing shift linkage, wired my own lockup and installed my own transmission

It might cost you a little more because I was given a 700r4 core to rebuild

[americanmusc1e]

Originally Posted by spankrz

i don't get much right now, less than 15 for sure. as far as speed goes, maybe 110 or 120. that's not as important as being able to cruise 75 on the interstate without runnin 3grand lol. where im goin to school next year im gonna be hittin the interstate every mornin...

what gears do you have now, i just swapped a 700r4 in my truck and I have 3.08's haven't taken my mileage except for some strait highway (18mpg at 60) but a 700r4 and 3.08's do about 1400 at 55 and thats ok If you have a big block or you have no wind, but driving with a headwind and a small block I usually have to kick it out of overdrive to keep it from bogging the motor down too much

bottom line: I would not use a 700r4 and 3.08's together, the 700r4 works better with a 3.50 to 3.73 rear end

[lowbucktruck]

Originally Posted by americanmusc1e

what gears do you have now, i just swapped a 700r4 in my truck and I have 3.08's haven't taken my mileage except for some strait highway (18mpg at 60) but a 700r4 and 3.08's do about 1400 at 55 and thats ok If you have a big block or you have no wind, but driving with a headwind and a small block I usually have to kick it out of overdrive to keep it from bogging the motor down too much

bottom line: I would not use a 700r4 and 3.08's together, the 700r4 works better with a 3.50 to 3.73 rear end

americanmuscle and longhorn all make a good point here... take a look at the gearing in your rear pumpkin BEFORE spending the money on a tranny swap. Just a suggestion. And plan on fabricating up a new tranny crossmember (or modifying your existing cross member) to fit the 700R4.
The Turbo 350 doesn't run too bad with the taller gears. My old truck was a '73 C20 with same engine/tranny (350/TH350) with 4:11 gear ratio; I looked into it and it would have been cheaper to just rebuild the TH350 and change the rear gearset than to go with a 700R4 swap. Plus dialing in the 700R4 with that TV cable gets to be real fun (insert sarcasm here).

Basically, if you are going to change something, be sure to consider how the tranny and gearing work together.

[ChevLoRay]

Custom Classic Trucks magazine had an article in the March issue about GM automatic transmissions. Until I read the article, I didn't have a high opinion about the 200R4. They say it is good for up to 800 horsepower, when built. It will also bolt to any GM engine. If it doesn't have the TV cable issues, it will get my interest piqued. There was a post a few weeks ago, and someone was talking about hooking a 200 to a Cadillac 472.

[westofb]

Originally Posted by ChevLoRay

Custom Classic Trucks magazine had an article in the March issue about GM automatic transmissions. Until I read the article, I didn't have a high opinion about the 200R4. They say it is good for up to 800 horsepower, when built. It will also bolt to any GM engine. If it doesn't have the TV cable issues, it will get my interest piqued. There was a post a few weeks ago, and someone was talking about hooking a 200 to a Cadillac 472.

The 200 r4 transmission is what I would go with. I am not sure what version of the th350 your truck has in it (my 69 has th350 with short 6" tail shaft). If yours is the same, the 200 trans is exact the same over all length and uses the same trans yoke so should be nearly a straight bolt in operation (may need to modify the crossmember). Here is a link for trans dimensions:
http://www.tciauto.com/Products/TechInfo/trans_dims.asp I will eventually go this route, but for now my newly rebuilt 350 will have to make do, I don't have to drive mine everyday so fuel mileage is not that great of concern

[Longhorn Man]

in reality, you'll be hard pressed to get more than 15 MPG... the typical MPG is 10 - 12 on these trucks.
You need to figure out what gears you have in the rear axle before you make any plans here, MPG can drop if you lower your RPMs too much.

[mrein3]

Originally Posted by Longhorn Man

in reality, you'll be hard pressed to get more than 15 MPG... the typical MPG is 10 - 12 on these trucks.
You need to figure out what gears you have in the rear axle before you make any plans here, MPG can drop if you lower your RPMs too much.

I see Longhorn Man beat me to the punch. I seriously doubt you get 15 mpg right now. My 4x4 gets 13 on a REALLY good day (all highway on a 55mph road unloaded and not stopping for any lights or stop signs). Typically I get 9-10 mpg because I rarely am not towing or hauling something.

2wd trucks get better but 15 and higher is the exception not the rule.

Once you figure out what you get for mileage you have to decide how much you want to spend to "save" money. If you need to spend $1500 on an overdrive 700r4 or similar, and it will take 10 years to pay back, you might want to reconsider.

If you run 4.11 gears, a swap to 3.07 gears will give you almost the same benefit as leaving in the 4.11 and putting in a .7 overdrive like a 700r4. And it will be a whole lot cheaper.

To make a really long post short, you need to calculate your real mileage, figure out what rear end you got, and do some math.

[70Custom10Nut]

How much longer is the 700r4 than a TH350?

[westofb]

Oh yeah I forgot, the 700 is a shade over 3 inches longer than the short tail shaft 350, 27 11/16" versus 30 3/4". See site I mentioned in other post for all kinds of trans info.

[Gleekr]

well from the LITTLE I know...more speed seldom = more mileage.

If you got the cash a gear vendors is too cool...6 speed auto. Check E-bay n they usually can be had for $1500 (+driveshaft mods).

[special-K]

It`s always the same.You can spend a bunch of money to gain a couple mpg or save your money for fuel.The other benefits of o/d make it worth it more than fuel consumption.

[speedracer]

2004r is great bolts right in, the crossmember has to be moved back a few inches but my frame already had holes for a different trans option. No drilling required, driveshaft bolted right up. got mine from a 86 monte carlo ss but many gm cars had them in the mid 80's

[spankrz]

Originally Posted by speedracer

2004r is great bolts right in, the crossmember has to be moved back a few inches but my frame already had holes for a different trans option. No drilling required, driveshaft bolted right up. got mine from a 86 monte carlo ss but many gm cars had them in the mid 80's

is that a 4 speed also? sorry, don't know my trannies very well...

[spankrz]

i'm not sure what my gears are now, but i know it was a quarry truck for the allen company new, and it was bought with the lowest gears it could be bought with. its a heavy duty truck- it's a 72 CHEVY 2wd with rear leaf springs. the only other 72's i have seen with leaves where GMC's.