Need help with gas mileage

[Dr_Snooz]

I'm driving a crew cab with a 454 and a TH400. Gas mileage is around 9 mpg and at $4/gal., that's just not working for me. Currently, the engine spins at 3k rpm at 60 mph. I'm usually in 3rd gear before I even hit 30 mph. That seems like stump pulling gearing to me, but I don't know. I'm considering the following:

1. Swap to a shorter ring gear and pinion.
2. Swap to an SM465 to get rid of torque converter slippage.

I do still want to be able to pull stuff, so I won't gear it too high. Does anyone have any suggestions for a better gear ratio? Do any other big block owners have ideas for improving mileage?

[zieg85]

A higher gear will help but in ideal conditions maybe get 15.  My 454 really drinks the gas at higher rpms and I have a 3.21 gear.  My best ever was 16.8 when I first got it.

[TexasRed]

LOL. If he gets 15 instead of 9, that's a 66% improvement in gas expenditures. I don't know anyone who would act like that was not significant. The ring and pinion would probably be your best bet in dropping those RPMs. What's in there now? A 3.23 would be right at that edge of almost too tall for a lot of towing but it may work, depending on how much towing you do. My grandpaw used to pull a popup across the hills of oklahoma with a 305 with a th350c and 2.73 gears.

[Irish_Alley]

If you don't want to go with bigger gears go with bigger tires lol. I don't think a 456 will help 3rd gear is 1:1

[slammed79]

Maybe a 4L80E? But the standalone controlers for them are kinda pricey. If you are lookin at going to a stick shift, I'd go with the NV4500, you'll get off cheaper than a 4L80 but its more labor intensive, I've seen NV4500's on CL for 1500, but then you need a clutch pedal set up, preferably from an 85+ which are getting tricky to find.

[Da67goatman]

swap in a rebuilt 700r4,  better gearing all around.  My dad's got a friend whose running 44's with a blown bigblock and a beefed up 700r4, gets 18mpg regularly.

[Stewart G Griffin]

i would say if you want to continue using a big block with 1 ton chassis, then your only hope is compression, exhaust and gearing.  Other than that running a big block today IS financial suicide.


Suggest diesel.

[1980c10]

I second the nv4500 although it will take a while to make up the cash spent.

[bake74]

     The two suggestions I would go with as previously stated are #1, rebuilt and possibly beefed up 700r4 (less labor intensive to install) or a nv 4500 ( 93 -95 will have the lower 1st gear than 96 to 03 ), but with this option as stated will be labor intensive as you have to switch over from auto to stick.

[Dr_Snooz]

Thanks for all the great suggestions. I know that the big block is going to suck down a lot of gas no matter what. Of course, a work truck is never going to get great mileage, so I'm not expecting 30 mpg or anything. Honestly, I would be ecstatic if I could get 15 mpg out of it. The NV4500 is a great suggestion and would be arguably better than the SM465. I'll have to read up more on the cost and work involved. If it's too expensive, I might just opt for the SM465 and put an even smaller diff in to achieve the same top end gearing and trust the super granny gear to help me out on the bottom end.

[Laderhosen]

I have a 700R4 with 3.08 rear end. It gets terrible mileage. I'm swapping it back to 3.42. The reason for this is because it stays in the gears FAR too long. It stays in first and I need to be doing about 20 mph before it'll change up. With such low gearing in the rearend 4th gear is useless. Even the slightest gradient it changes down to 3rd.

I'm hoping when I put the 3.42 in it'll drive a lot nicer, but I reckon it'll actually improve mileage !

[Irish_Alley]

With the 465 the gearing will be taller than the 400 final ratio for the 400 is 1:1 while the 465 is 1.1:1. Might lose some cause 1st and 2nd are also taller in the 465. It seams that you have 4.56 in the rear now. If you were to put 3.73 you would see about 2500 at 60. 4.10s will get about 2700 (this is true if you have 30" tires)

[DustyRusty]

I would vote for the 700R4 because it will be a relatively inexpensive swap.  Since this is 2wd a Gear Vendors overdrive is another option albeit more pricey that the 700R4.

I would also install a vacuum gage and modify your driving habits accordingly.  Might possibly net you 1 or 2 mpg more.

Just my $.02

Rusty

[Dr_Snooz]

I was able to gather some data from my tach, tape measure and speedo. Then I handed that data to my engineer brother and voila, figured out that my rear end is a 4.56. The 3.73 rear ends are very numerous at the junk yard and that would put my revs down at somewhere near 2400. I'll be doing that for sure.

In other news, my last two fill ups gave me mileage of over 13 mpg. I'm not sure what's going on there, but I'll cross my fingers and hope for more of that.

[bake74]

     Make sure your truck is tuned, that will help a lot.