Better gas Mileage

[ab positive bulldogs]

OK GURUS...I have a 67 GMC with a 351E in it...because of my financial situation she will be my daily driver for a while. So far I have added power steering, Holley 500 carb, rebuilt my heads, and rebuilt the tranny. Now I have heard i can change to 3:54 gears I believe for better gas mileage or get a new tranny....what do you recommend is cheaper and or better? Which tranny do you guys recommend i swap to for better gas mileage and better freeway cruising speeds? Thanks in advanced!

[BarryGMC]

Gear swap is the cheapest, and has the fastest payback.And Its the first thing that I do. As money permits then maybe a gear vendors OD on top of the gear swap. This is cheaper to do and more flex able than a 480le swap. Some will say the 460le or its earlier kin. Well thats fine until you hook up a heavy trailer.

[Rick]

A rear end gear swap is a possibility, however this will cost around/about $500. This will work if you are sure that you will be getting what you are looking for. You might also consider some sort of overdrive transmission. You will have to investigate all possibilities with this. My 62, has 3:07 rear axel plus a .78% overdrive. This gives me 1750 RPM at 65 mph. Do the math before spending money.

[tommyduncan]

You just got two conflicting answers. Welcome to the forum!

Since you just rebuilt your transmission I doubt you would want to replace it?

The easiest overdrive swap is a t5 manual... if you can find the correct version and it isn't already trashed. It is also a fairly light duty trans so if you still want to use your truck for a truck it might not last. Some people have great luck with them on here but no one I know has. I destroyed a brand new one in a 4 cylinder S-10 when I was young and dumb(now I'm just dumb).

A swap to an o/d auto would require finding an adapter(not cheap or easy to find), probably shortening/modifying your driveshaft, building or buying a cross member, cutting a hole in the floor for a shifter, buying a shifter, trans cooler, cooler lines, possible trans tunnel clearance issues... and a TV cable depending on trans.

Do you know what your rear ratio is now? Most of these trucks are geared pretty low. There are gear ratio calculators online that help you figure what is best for your needs.

[raycow]

Ok, here is a third conflicting answer.

You didn't say what kind of transmission you have in there now.

If you have a 3 on the tree, a 3 speed + overdrive will be almost a bolt-in. These were a factory option on Chevy cars and trucks from 1955 until about 1969 and are still fairly easy to find. They will bolt to your stock bellhousing.

If you have a 4 speed, the easiest swap will be a T-5 from an S-10. That's what I installed on my truck about a dozen years ago and I have been happy with it ever since. This will also bolt to your stock bellhousing. If you use the truck seriously hard, you might want a stronger 5 speed like an NV4500. This one will NOT bolt to your bellhousing without an adapter like this:
http://www.advanceadapters.com/produ...ter-plate-kit/

If you have an automatic, you probably have an adapter on the engine now that will let you use a Chevy pattern transmission. The most durable of these (in stock form) is the 4L80E, but that one requires an electronic controller. Non-electronic transmissions which will work are 700-R4 and 200-4R. These are not as strong in stock form as the 4L80, but can be modified to survive severe usage.

Ray

[tommyduncan]

I had a 3 on the tree with od in a 61 Brookwood wagon with a power pack 283. Loved that car!

[GMCv6inND]

oh boy, using as a daily driver! hey, I love driving my 67 around and i put a 351c in last year and installed the holley 2-barrell. My pickup came with the 3:08 rear-end and 3 on the tree. it starts, runs and cruises nicely - turns around 2000 at 65-70 mph. I only checked my mileage once and it was just a 90 mile trip in decent wx. I got 11 mpg. but i still love it. anyway, I think your best bet may be the highway gears AND an overdrive trans if thats possible. I would love to find an original 3-speed overdrive to install but would HAVE to be careful with the torque. good luck and have some fun!

[ab positive bulldogs]

OK so I passed by Hoopers Rear Ends today and i now now that I have a Dayna 60 rear end so the gears are 4:10's...guy said he can go as high as 3:54's BUT now I am wondering if that would be too much...and loose too much low end? I really need to do something since i am red lining at 50 mph right now...

[BlockHead]

I put a 3:54 on 3 days ago on my 64 with a 305 and it is a substantial difference but still need an overdrive if you ask me since the torque will handle the high gears on the Nevada flats. Wouldn't that be cool to be lugging or chugging along at 80 with no problem? My friend is a tranny/driveline guy and says that Volvo had an overdrive that might work. If not it needs a Brownie or Gear vendor. Going to put a Holley 500 on this week since the old carb I rebuilt was good for a few days and won't idle now. Not messing with it. R and R with Holley sounds good to me.

[tommyduncan]

Originally Posted by ab positive bulldogs

OK so I passed by Hoopers Rear Ends today and i now now that I have a Dayna 60 rear end so the gears are 4:10's...guy said he can go as high as 3:54's BUT now I am wondering if that would be too much...and loose too much low end? I really need to do something since i am red lining at 50 mph right now...

Most of the recommendations I see are 3:54s. The formula to figure out what rpm at what mph isn't hard to figure out.