Newbie needing some help.

[Dutch Rutter]

Hey guys I'm new to the forum, but not new to the truck world. I have a 1986 3/4 ton C20 2wd. It was a 6.2l diesel when I got ahold of it. I have removed the 6.2, built a mild road performer 350sbc matched up to a rebuilt th400 that was behind the 6.2, same rear end that was with the 6.2. I have driven it like this for several years with only minor hiccups every now and then which is normal with a simi-franken-truck.

Anyway.. my problem is that I am trying to get a little better gas milage out of it. Now before I get any muy a geo metro, prius, or whatever else. I know that it wont get GOOD milage but when Iam driving it around 60mph it runs a conistant 3000rpm. I dont remember off the top of my head what the ratio in the rear is. now I guess I need to know if its my rear end or the transmission that is causing me to be running lower RPMs in the earlier gear thus causing me to run high rpm at cruising speed wouldnt be out of the norm. For a diesel I think but im not 100% on that.

So to some that up since I rambled a bit, what do I need to change out to make this run easier to where im not going to be running through gas like crazy and putting my nice sbc into the dirt?

Thanks in advanced for any advice.

 

[anubisani]

Hey guys I'm new to the forum, but not new to the truck world. I have a 1986 3/4 ton C20 2wd. It was a 6.2l diesel when I got ahold of it. I have removed the 6.2, built a mild road performer 350sbc matched up to a rebuilt th400 that was behind the 6.2, same rear end that was with the 6.2. I have driven it like this for several years with only minor hiccups every now and then which is normal with a simi-franken-truck.

Anyway.. my problem is that I am trying to get a little better gas milage out of it. Now before I get any muy a geo metro, prius, or whatever else. I know that it wont get GOOD milage but when Iam driving it around 60mph it runs a conistant 3000rpm. I dont remember off the top of my head what the ratio in the rear is. now I guess I need to know if its my rear end or the transmission that is causing me to be running lower RPMs in the earlier gear thus causing me to run high rpm at cruising speed wouldnt be out of the norm. For a diesel I think but im not 100% on that.

So to some that up since I rambled a bit, what do I need to change out to make this run easier to where im not going to be running through gas like crazy and putting my nice sbc into the dirt?

Thanks in advanced for any advice.

your rearend gears are probably 4:11s . if you don't do any towing chg them out to 3:42s 0r 3:07s and it will lower the rpm and give u better gas mileage , others may chime in

 

[Dutch Rutter]

your rearend gears are probably 4:11s . if you don't do any towing chg them out to 3:42s 0r 3:07s and it will lower the rpm and give u better gas mileage , others may chime in

Ok, I wasent sure it was going to be the rear end or if the gearing in the transmission was a factor. I do tow with the truck usually just hauling bike to the dunes and back, and helping friends move here and there. I dont totally want to strip the power away from it but just enough to lower the rpms to a reasonable level.

and I'm hoping on doing a total axel swap to save some $$$ instead of swapping the gearing and paying all kinds of $$$$$$. but it is nice to know that it is deffinately running higher then 4.10s

also I was wondering and have done some searching with no avail. can I swap my th400 for a manual transmission? and if so which would be best to run in it?

 

[Driver4r]

Heres my .02cents:
I agree on the 4.11's, my 32"s ran 3100 at 60ish.
I put 3.08's in the back and my little more radical then factory 355 can easliy break the 32"s loose with a th350.
Yes, you can go manual to bring down the Rpms, being 2wd, you have alot more options then i have, but ive been looking for a nv3500,nv4500,A833.
2wd you have ALOT more options, exspecially if you go bucket seats, You can run a car trans. T-5(GM),T-45(ford, but will bolt up with adapter), T-56(gm,lil more $$ being a 6spd), and the A833(gm).

 

[Dutch Rutter]

I'm running 32" toyos so that will probably be what I go with. If I can find a complete rear end with something close to 3.08s. Probably a dumb question but what year of rear ends can I swap under my truck with little to no modifcation?

(probably should of posted in the differential section)

I have access to a free to me, and functioning 4 speed out of a 78 (i believe) 1/2 ton but I would like to keep a rather "beefy" transmission for pulling/torque/durability. How hard would it be to make that work? cut a hole or unbolt a plate over the shifter hole thats easy enough, but what about hanging a clutch system?

 

[philjafo]

You can effectively change the final drive ratio by changing to taller tires too. It can be a cheaper less permanent way to get what your looking for. The 4 speed manual still has the same 1 to 1 fourth gear as your turbo 400 3rd gear and would only get a few hundred rpm less at cruising because of loss through the torque converter.

 

[austinado16]

If it helps with your choices, I tow with 3.42's, in the crazy steep mountains. I'm running the stock 15's and the engine twists at 1,600ish rpm at 55mph in Over Drive. About 300ish more than that in 3rd with the converter locked up, and maybe another 150-200 in 3rd w/ the converter unlocked.

I'd say build or buy a 700R4 that's built with all the trimmings and enjoy and overdrive kind of experience.

Or, throw a fresh ring and pinion at it and call it done.