mileage

[catmandoo]

i'm looking to push my 92 with 6.5 and 5spd to over 30mpg. has anyone here achieved this? i currently run 25 to 27 and was looking at adding my banks and a gearvendor overdrive. i don't pull anything of real weight maybe my lawnmower trailer once in a while. but i drive 1200 miles a week most of the time at 6o to 75.currently mmy best mileage is at about 62mph . i'm going to california next year and most of it will be at 75mph or so and if nothing else i would like to get better mileage at 70 to 75. any ideas?

[britannic]

I'd be really, really happy with 25-27mpg :D !! I was getting 11-13 with a TH400 and 4.56 diffs, but the 700R4 OD has bumped my mpg to 17-18 now.

Are you getting that mpg mainly on the freeway?

[mhagie]

CATMANDO,NEED A FEW DETAILS, ARE YOU 1500 SERIES OR 2500? DO YOU KNOW YOUR AXLE RATIO?

[catmandoo]

i have a 1500 and i'm assuming 3.42 gears the guy i bought it from was the original owner and ordered it for mileage.he also said he ordered the heavy duty trans which by the looks of it is the nv4500, gearvendor says this wasn't availible til 93?but mine was built aug of 91, go figure!

[catmandoo]

also i should note it's 2wd and around here in iowa most of it is 2 lane hi-way if i do get on the freeway at 70 or so it will drop[ to 23 to 24 it acts like my 5.7 it just seems really free at 62 thats where it wants to run so thats usually what i drive, at 55 it just seems to be laboring almost to the point of chugging.about 2 months after i bought this i put a topper on it and picked up 2 mpg. i've even had thoughts of dropping it 2 inchs, keep some of that air out from underneath. i think there is as much milage to gain from aerodynamic changes as there is from mechanical changes i just don't want to get to the point of it looking chessy. i'd try to post a pic but haven't done it here so am kinda lost. any help here?

[C & M Oilers]

I tell you what catmandoo, 25-27 is pretty daggum good, do you know what your truck weighs? I have a tough time getting my 6800 lb. sub to break 18, I don't know if Californias low sulfur fuel has less BTUs or not, I used to be able to break 20 at 55-60. I wish the 6.5 was as efficient as the B series Cummins. I ran across a device on the net that promises 10% or your money back $120.00), don't know if that applies to use little guys, it seems to be geared for the over the road guys. Your mileage sounds pretty good to me, man!

[catmandoo]

ya it's great but i want better.my goal is 30 mpg and i will get there it's just a matter of time. i wish i could take the rear end out of my 84 it's got 3.23 or there abouts that would probably be good for a couple more mpgs i would hope.but i couldn't get a speedo pickup that would work so it would be off.

[Eric Deslauriers]

I'm assuming you wish to do this from a desire to excel and not as a desire to save $$?

Gear Vendors = $2200
Diesel = $1.75/gallon (here)

$2200/1.75 ~= 1257 gallons
1257 gallons * 25mpg = 31,425 miles. That's a humdinger of a lot of miles you could go on that cash.

I say put the money in the bank. Or buy a 6 speed trans from a wrecker for less than the GV. I'm sure adapters are coming if not out already.

I'm swapping in a 4L80E for my TH400 in rather than a GV. Too much $$ for the content IMO. It's not a mpg thing, it's a noise and speed thing (I can go 75 comfortably instead of wound out). The mpg ends up being a side benefit.

Worst case, I'll have $1300 into the swap. Best case, $600. I'll keep ya'll apprised.

[catmandoo]

well i drive over 65000 miles a year so you can somewhat see my point i do wish there was an alternative to the gear vendor.whats with the 6 speeds are they geared higher in 6th ?if so this could possibly suit me.

[mhagie]

catmandoo,A couple of points here, first the 84 axle you have is probably one of three ratios in order of probability a 3:08 (1) a 3:42 (3)or a 3:73 (2).
Second I thought that the computer controled trucks with the electronic driven speedometer were programable as to axle ratios,however my experience ends with the 87 old mechanical operated trucks so I don't know for sure on the 92.
Third I wish you luck on the hopes for 30 mpg at 70/75 I do believe that you can make it at 55/60 on flat ground no headwind.
You might want to lower the truck a little especially on the nose the newer trucks like yours have a better profile on the nose which helps,my 80 silverado with that big flat front is like pushing a 4x8 sheet of plywood down the road.
Good luck I hope you make your goal.

[britannic]

With the gearing you already have, it may be worth changing the drag coefficient of your truck from a "shed on wheels" to something approaching .32 (pretty hard, but not impossible).

The underside would benefit from being smoothed out and anything else that creates an air dam or turbulence (obviously you would need to allow through the radiator).

I notice some of the long distance US semi-truck operators have applied this philosophy and in Europe it's very common.

[ 09-20-2003, 06:48 AM: Message edited by: britannic ]

[catmandoo]

thats what i've been thinkin i'd like to drop it 2 inches.but on the belltech dropped shackles it says that for ext cab that a pinion shim is required.has anybody delt with these and whats involved?

[mhagie]

Unless I have my wires crossed it is a aluminum wedge with a hole in it.
You loosen the rear spring u-bolts and install wedge on top of the spring centering bolt with the thick side either front or rear depending whether you are trying to raise or lower pinion angle.

[catmandoo]

well i had thoughts of that but figured if it was loaded to it's 1/2 ton capacity that it would set probably 1 1/2 to 2 inchs lower so whats with the shim the driveshaft would be at somewhat the same angle. whats also wierd is its just used on the ext cab and not the reg cab!if the reg cab use a 1 piece driveshaft then i could see that maybe the angle is to much on the ext cab

[britannic]

Shimming the pinion is just to ensure the driveline angles are maintained to prevent vibration and accelerated wear of the universal joints.

With a mild lift or drop, it's not always necessary. However, the angle of the drive should always be recorded before changing anything and checked afterward to see if adjustment is required.

[Dan Wilson]

Iv been getting 27 to 34 mpg with a 6.2 for 3 years now. Of corse Im not playing fair. I installed the 6.2 in a 81 gran prix that had a 5.7 in it originaly. What a grate combo. Grate milage and fun to drive. I just love this old car.
Dan

[catmandoo]

i've heard of people putting 6.2's in caprices but never a gp hows it fit did ya have to do any major mods,as some of those came with chevy motors i assume the motor mounts bolted right up .

[Dan Wilson]

The gp came with the 5.7 olds diesel originally.
had to modify the chevy motor mounts to get 6.2 low enough to close hood. They bolt in to original frame holes for chevy motor. Used 700r4 trans out of half ton pickup. Drive shaft has to be 3 inch shorter. Used air, power stearing,alternator from truck. The gp already used hydro brakes because it was a 5.7 diesel.
I love this car. Has plenty of power and gets great econamy.

[catmandoo]

doesn't it set a little low.

[Dan Wilson]

The gp came with the 5.7 olds diesel originally.
had to modify the chevy motor mounts to get 6.2 low enough to close hood. They bolt in to original frame holes for chevy motor. Used 700r4 trans out of half ton pickup. Drive shaft has to be 3 inch shorter. Used air, power stearing,alternator from truck. The gp already used hydro brakes because it was a 5.7 diesel.
I love this car. Has plenty of power and gets great milage.
I did a 82 Fleetwood Cadilac first. It also had a 5.7 diesel that I installed a 6.2 in. It gets 20 city 29 highway. A grate car. I dont use it now that I did the gp. I would sell the cad.
Dan

[Dan Wilson]

I installed 15" tires. I guess because it had a 5.7 diesel the springs are stong enough.