Getting Frustrated , A Rant, I Guess!!!

[Already Gone]

My truck has a 396 with a TH400 and 3:73's ... I'd like to get better fuel economy on the highway and know I either have to go to 3:08 gears or change to a 700R to do that. My research tells me the ideal scenario would be a 700R with a 3:42 posi out back but that would be way expensive.. If I could put the 700r in myself I would do it in a heartbeat but it would cost me 8 to 900 to have it installed properly by a local reputable shop and I'm not counting the cost of the 700R. After doing some price checking a new 3:08
(12 bolt) with posi would also be 7-800 to purchase and then again I cant install so I'm guessing I'd be looking at another 500.00 to get it installed properly. I guess fuel economy costs !!!!
I get 12 mpg on the highway now and I'm thinking in ideal conditions doing anyone of theses changes I'd get 16/17MPG on the highway.. I probably drive 3 to 4000 miles a year and doing the math I'd save ( on our Canadian gas prices) about 400.00 a year.. I dont know if its worth the money to change anything..

I'd like to hear board members opinions on this..

[killer71]

I'm not sure what you use it for but it sound like it's highway miles. I just changed from 3.73 gears to a 3.08 and you can't imagine the difference. It has helped tremendously. The truck just seems ilike its not in a bind, quieter. I havent checked exactly but the truck indeed gets better gas milage. I simply bought the 3.08 gears and installation kit from lmc and had my mechanic install as he has all the instruments to do so. Parts/labor combined right at $500; worth every nickel.

[rophle1]

Big Block = No gas mileage!

Doing some of those changes will help some, but I don't know if you'll save those 98 gallons of gas a year. Looks like it will take a while to get your return on investment (roi). One option is to sell the gas chugging BB and get a gas sipping small block. Just an option (not a good one in my opinion because I like the BB), but an option nonetheless.

Ronnie

[piecesparts]

The change of a rear end can affect you in many ways. IF you have a TH350 or TH400, then a set of 3.08 or 3.42 gears is the answer. However if you go to the 700R4, DO NOT go to the 3.08 gears to gain more. We put a 700 in my truck and my son's truck and with his, the 70 and the 3.08 gers cost him gas mileage. We upgraded to a 3.73 gear ratio and picked up 2.5 MPG and performance to boot. There is a limit to the GM V-8 that one should not break over. Keep the RPMs around 2000 to 2500 for driving comfort and performance. I run 3.73 gears with a 700R4 and so does my son and we both get around 15 MPG. Mine is with a 383 stroker motor and his is on a 350 motor and a cam upgrade.

[70rs/ss]

Not sure why you can't bolt in a 700 r4, they are more or less a direct bolt in deal. The OD will be nice and a 3:73 is the perfect gear for a 700r4, so a tranny swap is all that is needed. A nice (read:built) 700r4 is going to be around 800-1200 depending on where you buy, but the labor if you do it yourself is free, so in a couple of years of trouble free driving the tranny will pay for itself, as well as prolonging the life of the BBC cause high RPM will be the death of all that stock heavy reciprocating mass inside there. So lowering RPM would be my concern and the extra 2-3 mpg will be the icing on the cake.

[67ChevyRedneck]

Here's my honest take on this:

I have a 350 with a 700R4 and 3.73. I've been checking my past 3 tanks of fuel (I finally got my speedo working correctly ) and I'm consistently getting 13 mpg. This is almost all city driving and my truck will only see 4th gear 20% of the time.

I haven't had a chance to this year, but I used to take the truck on the hwy a lot before the old 700r4 blew on me and my best tank was a 16.3.

I hope to get some current #'s this summer on some short roadtrips... like the Charlotte Auto Fair

Not sure if those #'s help, but just trying to give some realistic numbers.

The fuel mileage didn't pick up like I had hoped, but I LOVE the fact that the truck hums down the highway at 70 only turning 2K on the 'old tach.

The other thing to think about is the big blocks power. Unless you spend some $$$ on a beefy 700R4 it will probably poop out on you. I would think for your case the 3.08 would be the way to go and try not to worry too much about fuel mileage.

[regal8r]

12mpg huh? i get 11 on the highway with a 305 with cam, headers and same trans and gearing. not to threadjack, but what would yall recommend for city driving? 3.08s...or will a 700r4 made a difference for me as well? dont drive much on the highway...

[67ChevyRedneck]

700R4 will not be helpful with city driving. Mine hasn't been. There are very few times when I get going fast enough (around 50mph) to shift the truck into 4th. Like I posted above, I probably only use 4th gear in the "city" about 20% of the time. Not really enough to even affect fuel mileage.

BUT the great thing about the 700R4 is when I hit the highway to go to spartanburg or anderson I can cruise along at much lower rpms and a higher speed. Unfortunately, with my work commute, I don't really get to use OD.

[Already Gone]

Originally Posted by rophle1

Big Block = No gas mileage!

Doing some of those changes will help some, but I don't know if you'll save those 98 gallons of gas a year. Looks like it will take a while to get your return on investment (roi). One option is to sell the gas chugging BB and get a gas sipping small block. Just an option (not a good one in my opinion because I like the BB), but an option nonetheless.

Ronnie

I know a small block would get better mileage, but I, like you, am a big block kinda guy !!!

[Already Gone]

Originally Posted by piecesparts

The change of a rear end can affect you in many ways. IF you have a TH350 or TH400, then a set of 3.08 or 3.42 gears is the answer. However if you go to the 700R4, DO NOT go to the 3.08 gears to gain more. We put a 700 in my truck and my son's truck and with his, the 70 and the 3.08 gers cost him gas mileage. We upgraded to a 3.73 gear ratio and picked up 2.5 MPG and performance to boot. There is a limit to the GM V-8 that one should not break over. Keep the RPMs around 2000 to 2500 for driving comfort and performance. I run 3.73 gears with a 700R4 and so does my son and we both get around 15 MPG. Mine is with a 383 stroker motor and his is on a 350 motor and a cam upgrade.

I had an 87 Burb with a 350TBI , 700r and 3:08s and all I got for highway mileage was 14/15 MPG.. I ran the numbers on Bowtie Overdrives and my truck with 28/29 inch tires and 3:08's with a 700R would be turning 17/1800 RPM at 65 MPH which I think would make the 396 lug and not be fuel efficient.. I think 2200 to 2400 RPMs would be where my BB would like to be on the highway and I think with 3:08s and my TH400 that is where I'd be at 65/70MPH..

[Already Gone]

Originally Posted by killer71

I'm not sure what you use it for but it sound like it's highway miles. I just changed from 3.73 gears to a 3.08 and you can't imagine the difference. It has helped tremendously. The truck just seems ilike its not in a bind, quieter. I havent checked exactly but the truck indeed gets better gas milage. I simply bought the 3.08 gears and installation kit from lmc and had my mechanic install as he has all the instruments to do so. Parts/labor combined right at $500; worth every nickel.

My truck is a summer daily driver.. I use it to go back and forth to work and for day to day driving. I've taken her to a few shows and they are usually within a 100 miles of here. I started on this mileage thing cause last summer in August we drove 425 miles one way for a car show. At that time our gas had been bumped up to a 1.19 per litre which was the highest it had ever been in Canada. For you guys that arent familiar with the metric system I'll put 1.19 per litre in perspective for you. Allowing for the dollar exchange rate and our larger Imperial gallon it would be like you guys in the USA paying 3.85 a gallon.. Anyway it cost me 325.00 to go on 1000 mile round trip. Gas is not going to go down folks and I want to go to more shows that are hundreds of miles away so gas mileage is a factor for me.

[sleepyboy]

[QUOTE=killer71;2065616]I'm not sure what you use it for but it sound like it's highway miles. I just changed from 3.73 gears to a 3.08 and you can't imagine the difference. It has helped tremendously. concur

[Already Gone]

[QUOTE=sleepyboy;2066738]

Originally Posted by killer71

I'm not sure what you use it for but it sound like it's highway miles. I just changed from 3.73 gears to a 3.08 and you can't imagine the difference. It has helped tremendously. concur

I'm thinking that is how I'll go.. Any suggestions as to where I can get a decent price on a 3:08 and a posi for my 12 bolt ?

[paaw]

have you thought about finding a whole rearened and changing it out would be quicker, and then you could sell you whole rear, you may even can find on that is a posi

[Already Gone]

Originally Posted by paaw

have you thought about finding a whole rearened and changing it out would be quicker, and then you could sell you whole rear, you may even can find on that is a posi

I've had bad luck with used parts. I'd prefer to buy new stuff. Wreckers around here would want 400/450 for a 12 bolt used posi and it would only have a 30 day warranty. I actually bought a used Dana with 3:21 and posi for my 79 Chysler 300 from a wrecker.. I personally removed it from a 79 Chrysler Newport with 80,00 miles and had never towed anything. I put on about 4000 miles on the rearend and then it started howling and grinding.

[Blue85]

i'd go with the 3.08 if u are looking for the cheapest way out, the 700r4 can be real pricey to build strong enough to handle a big block, its too bad my truck has open diff, i'd swap ya straight up for those 3.73's lol

[Bowtie001]

There are a lot of other variables that haven't been explored here yet. Get the narrowest tires you can stand, pump them up tight. Put on a front air dam off the next gen pickup. Drive like there's an egg under your pedal - drive for momentum and not for speed. MY old 84 with 350 and TH350 got 19 mpg this way. Duct air from the cleaner to the radiator support to get colder air. Put synthetic fluid in the engine/tranny/rear end. Put in a stiffer secondary spring on the carb. make sure your air filter is clean. Drive without power steering, without AC etc...

There are other ways I am sure... but you don't have to spend lots of cash to get some real gains.
-Brian

[HeavyD]

Even with all these changes, what are you going to gain? 1-3 mpg? I too have driven these trucks many times as a daily driver, and I know it sucks to take it anywhere because of gas prices. If you plan on doing alot of highway miles I can see that a 3:08 would be a good swap, but that's all I would do. The cost of fuel is just going to eat a hole in your wallet unless you can magically make the truck get 25 mpg, and that isn't going to happen. This is why I drive a beater $1000 Honda Accord, so I can go all over the place and pay peanuts for gas. It sucks arse, but is cheap and I could never afford to drive all over the prairies and northern states otherwise. If you are planning to show your truck elsewhere, then you just gotta spend the cash and not let it ruin the trip I guess. If you are just there to look at other's eye candy, drive something else.

[cruiserman]

12MPG is excellent mileage for a big block.

[cameeks]

There is a Bolt on that no one is talking about. What about the Overdrive unit that bolts on to TH350 & TH400's. You wont have to worry about setting up the trans and the only thing that I think you would have to do is measur to get your drive shaft cut. It is like adding 3 more gears.

[67ChevyRedneck]

Your talking about a gear vendors overdrive unit. They are awesome, but very $$$$ Last I checked I think they were around $2K for one for a TH400.

EDIT: Check that.... they're up to $2,595!!!!

http://www.gearvendors.com/prices.html

[Already Gone]

Originally Posted by cruiserman

12MPG is excellent mileage for a big block.

Really, it probably is. I know my engine was redone before I bought the truck and is tight and runs very strong There is an Edelbrock carb on top ( 4bbl of course) but I've never bothered to look at which number it is and it was pretty shiny when I bought the truck so I'm figuring itwas pretty new then.

[cameeks]

Originally Posted by 67ChevyRedneck

Your talking about a gear vendors overdrive unit. They are awesome, but very $$$$ Last I checked I think they were around $2K for one for a TH400.

EDIT: Check that.... they're up to $2,595!!!!

http://www.gearvendors.com/prices.html

Ok! Never mind. I have heard about them but never priced checked them. Was thinking around $1k for them but $2.6k they can keep it.

[Already Gone]

Originally Posted by cameeks

Ok! Never mind. I have heard about them but never priced checked them. Was thinking around $1k for them but $2.6k they can keep it.

I know about Gear Vendors OD too. If they were a 1000.00 that is the way I'd go !!! Stacey David has one in Copperhead , but then Gear Vendors OD probably donated it to him for the advertising value ...

[70rs/ss]

Check the numbers on you're cab, if it is a 750 or 800 cfm, switch it to a 650 and you'll see a difference in your MPG, but performance might suffer as well. tune the carb, check the jets and rod sizing and see if you can run one or two sizes smaller (less fuel, less consumed). You are going to deal with it or drop 1500-3000 with any of the big changes, so either spend the $$$ or live with what you have? There are no magic bullets when it comes to BBC or old trucks, or in your case BOTH!