Do I need a new ring gear or OD trans

[DUECE'SDAD]

Hey I have finnaly got a 1986 chevy crewcab dually and the 8 mpg is killing me. I love the truck and plan on lowering it and painting it however there has to be something some one has done to get better gas milage. It has a 454 with th 400trans and a 4:10 ring gear I think a 3:55 would be more suitable and posssibly a od trans out of a latermodel truck. My boats are both small and wiegh under 3000 lbs so i am not needing the super low gears to pull with . Has any one went thru the same things or are you guys happy with what you have since you seem to mostly have offshore rigs. Thanks for any help

[Jordy]

Changing the ring and pinion would be a permanent kind of change and dropping to a 3.55 is a pretty big drop. Something like a 3.73 would lower your RPM's while not hurting your pulling power too much. An OD tranny would be an alternative, as would running something like a Gear Vendors overdrive behind your Turbo 400.
I also had the biggest K&N filter I could find, the exhaust done and a JET 6 pack chip for it. Is your '86 TBI injection or is it still carbed?
The one thing that you have to consider, with a big block in that big of a truck you're never going to be much over the 11 mpg range. I had an '88 Chevy, same setup as you have. There is a reason most have big aux. tanks in the bed. Mine had 55 gallons or so as the right tank on the tank selector. That truck got 8 no matter what. The best I ever did in the 3 or so years I owned the truck was 11 and that was going down hill from Ely to Vegas in Nevada. I think there was a tailwind involved too. ;)

[don johnson]

Hey I have finnaly got a 1986 chevy crewcab dually and the 8 mpg is killing me. I love the truck and plan on lowering it and painting it however there has to be something some one has done to get better gas milage. It has a 454 with th 400trans and a 4:10 ring gear I think a 3:55 would be more suitable and posssibly a od trans out of a latermodel truck. My boats are both small and wiegh under 3000 lbs so i am not needing the super low gears to pull with . Has any one went thru the same things or are you guys happy with what you have since you seem to mostly have offshore rigs. Thanks for any help
For what it is worth I have done some recent modifications to my 2005 8.1l Suburban that has yielded some pretty good results... See the below;
Test- 2005 Suburban 4 x 4 8.1L
Stock= 262 HP and 386 ft lbs torque at the rear tires
Added Gibson Shorty headers and cat back= 14 HP and 27 Ft lbs of torque increase
Added Volant Cold Air Induction= 6 HP and 9 ft lbs torque increase
Added Westers tuned computer= 56 HP and 63 ft lbs of torque increase
In total picked up 76 HP and 99 Ft Lbs which maxed at 338 HP and 485 Ft lbs at the rear tires
The Westers tune was by far the biggest add on. Lyndon Westers custom programmed my computer in 4 days and the tune was set up to compliment the headers and cold air. A huge plus of the Westers is the reprogramming reduces the torque management and removes the speed limiter.
I have now made 2 trips to the river since the modifications and I am getting a 2.1 MPG improvement on average, per the on board computer. Was getting 9.2 on average. Now am getting 11.3 MPG. I am very happy with these results. I have to admit that I drive the truck harder now as it is more fun to drive so the MPG may even be better...
I do not know what kind of improvement messing with the computer on your 1986 would make.... Westers phone number is 403-377-2277
Good Luck!

[Jordy]

Don, what are you running for a tranny? At least a 4 speed???
*sorry, I'm a little slow this morning. :wink:

[don johnson]

I have the OD 4 speed. Unfortunately, the Allison is not available in the Suburban.

[Jordy]

I have the OD 4 speed. Unfortunately, the Allison is not available in the Suburban.
Actually I knew that. It's just early on Monday morning and I'm trying to do 6 things at once. :eek:

[Havasu Hangin']

Hey Don- how's the exhaust soise levels?

[Eliminator 4 Life]

Jordan if you knew anything about Chevys/Gmc you would know the first year for throttle body injection was 1987 so to answer your question no he doesnt have it in his 86... :hammerhea

[don johnson]

Hey Don- how's the exhaust soise levels?
Real moderate. I went with the Gibson single tube cat back, their quietest option. The headers and cat back did not add much interior noise at all. There is NO reverberation like the Flowmaster did in my old truck.

[Havasu Hangin']

Real moderate. I went with the Gibson single tube cat back, their quietest option. The headers and cat back did not add much interior noise at all. There is NO reverberation like the Flowmaster did in my old truck.
Thanks, Don. I wanted to go with a true dual Flowmaster. However, Flowmaster doesn't make a kit yet for the 8.1. When I called them, they told me that they are having resonance issues with the 8.1, and they don't recommend the 40 or 50 series for that reason.
They said to hang tight for 30 days, or so.
I'm on the fence about which way to go.

[DUECE'SDAD]

Get a new truck, thanks i will tell my wife im sure thats what she will wont to hear. Meanwhile i talked to a guy here at a diff. shop and he says 3:54 will do exactly what i need, but i do dig the 05 crew cab short wide half ton. I dont really need the dual it just looks tuff. Thanks for the info and your right it has a carb

[don johnson]

Thanks, Don. I wanted to go with a true dual Flowmaster. However, Flowmaster doesn't make a kit yet for the 8.1. When I called them, they told me that they are having resonance issues with the 8.1, and they don't recommend the 40 or 50 series for that reason.
They said to hang tight for 30 days, or so.
I'm on the fence about which way to go.
HH,
If you are looking for improved performance and MPG's from your 8.1l you have got to call Lyndon at Westers. The custom tune he put in my computor was nothing short of huge. It was by far the single greatest "bolt on" that I did and tested. I actually performed chassis dyno tests after each modification to document each bolt on. The headers and cat back did show improvement, but nothing like the custom tune. According to Wester's the 8.1l is extremely de-tuned by Chevy and has great potential which is obvious from the results I documented. I had him tune to 91 octane. He can also dual-tune which allows 87 and 91 to be run.
My buddies stock Dura Max used to out pull me in a drag race and now I can put the hurt on him, bad....
Lyndon's number is 403-377-2277

[Rexone]

Put a Gear Vendors overdrive in it and be done with it. They work great on T400's.
You can buy a new one for about $2500 or you can buy mine (http://www.***boat.com/forums/showthread.php?t=58336) , only thing is mine has a truck attached to it for $2900. :D

[Jordy]

Put a Gear Vendors overdrive in it and be done with it. They work great on T400's.
You can buy a new one for about $2500 or you can buy mine (http://www.***boat.com/forums/showthread.php?t=58336) , only thing is mine has a truck attached to it for $2900. :D
Very smooth Mikey. :D
The cheapest option would be a 700R4 OD tranny. Pretty simple R&R. Just have to have the driveshaft shortened or get a new driveshaft that is the right length. The Gear Vendors setup is cool too. Just a little more labor to put it in, more driveline modification as well.
Or, if you're really feeling creative and looking for a project, you could buy this complete duramax/allison combo and swap it into your rig. Double your mileage for $6500 plus shipping. http://www.***boat.com/forums/showthread.php?t=65447
The new truck is the easiest way out but also the least cost effective. :D

[Just Tool'n]

I had a 90 dually, with TBI & TH400, I put a gear vendor on it way back then.
It had 4:10 Gears in it. The best I got out of it was around 11mpg on time coming home from LA. Keeping my foot out of it with the gear vendor on it.
I dont know it I would do as Jordy say's & put a TH700r in that big of a truck.
It's kind of small for a 1 ton thruck
I think I would stick with the TH400, & maybe do as Jordy says, go with the 3.73 & put the gear vendor in it!

[Jordy]

I dont know it I would do as Jordy say's & put a TH700r in that big of a truck.
It's kind of small for a 1 ton thruck
I looked at having it done in my '88 dually. Granted it wasn't a stock 700R4. B&M made a built up bullet proof (at least at bullet proof as you can make a 700R4) tranny. Just kicking around some options of what was out there. The 700R4 would be the easiest because it wouldn't require the electronics that the later OD units do. ;)

[Just Tool'n]

I looked at having it done in my '88 dually. Granted it wasn't a stock 700R4. B&M made a built up bullet proof (at least at bullet proof as you can make a 700R4) tranny. Just kicking around some options of what was out there. The 700R4 would be the easiest because it wouldn't require the electronics that the later OD units do. ;)
Jordy this is true, they can make a stout 700R4.
Was in a little shop in the boonies yesterday, training a new dealer. This border brother was putting a 5.7L in a 53 chevy pick-up. New crate motor C/W a quadrajet carb.
He was putting behind it a 700R4. I asked him how he was going to operate the lock-up on the torque converter? Was he going to use some type of electronic's to ground out the solenoid & lock it up.
Here's what he told me, " In 84-85 they used 700R4's in carburueted trucks with no computer, that they hook up a vacuum line to the manifold to get a vacuum signal, when vacuum reached a certain point it operated some type of electrical signal for the solinoid in the converter to ground out , hence the lock-up would happen.
You familiar with this?
Or was the border brother trying to put one over on me?