Gears for tow / haul

[Roper]

Shortbox

I dont see how its possible to get better fuel mileage with 308 gears if your hauling a load. Like I said my truck originally had 308 gears, then I swaped in one ton axles that have 4.10s and my mileage definately got better. But mostly when I use my truck im hauling something.
Maybe the people who got better mileage with the 308 gears who dont haul tend to cruise down the highway 80mph? See im mostly on gravel roads and im never really in a hurry to go anywhere these days.

Greg
Thats just it, about a new diesel truck. You would have to be hauling a trailer a lot of miles to ever justify the cost of one.

[shrtbx]

I didnt say you could get better gas mileage by having 3:08s and hauling a load. I actually stated 4:10s would be the way to go.

[Thumpin455]

With a 350 pulling you will be working that little thing to death no matter what gear you run. When you are towing, especially on grades, you want your cruise rpm to be just over your torque peak, that way you have some power left a bit lower for hills. If you are only working with 250ftlbs at the flywheel it wont matter what gears you run, it will be a pooch with any of them.

If you are serious about a pulling rig based on your old truck you need to change more than just the gears. More torque with less throttle angle will pull better and not burn fuel at a kill more dinosaurs rate. How do you get more torque? Make your engine more efficient for one, make it bigger for another. The 80s engines are weak suck in stock form for the most part, but upgrades are available and you can retain smog legality to an extent.

Using your 350 as a base I would suggest a few changes in addition to a set of 3.73 gears with 33" tires. First freshen the bottom end, bore it .030, use quality rings and gaskets, dont go gapless with the rings. Have it balanced because that will help with longevity and they also seem to run much better when balanced.

You can pick up a new set of Vortec heads for the small block for around $400-$500 ready to bolt on. You can get them drilled for your 87 intake, that way you can use the TBI and keep it looking smog legal. No Holley for you in California. They are the best factory head you can find regarding flow, combustion chamber, and availability. its tough finding a set in a junkyard that isnt cracked, so just pony up for a new set. The stock springs are good for around .450 lift, but that works since you dont want a huge cam in there.

Speaking of the cam, a Comp XE262 will give you plenty of power and it wont lope at idle. Alternatively you can run an inexpensive Summit Racing cam with 224/228 degrees duration at .050 lift. It might be a bit difficult to get that to pass smog though, and those are the biggest cams you will want to run anyway. More duration will move the power band up in RPM and you will lose torque under 3000 rpm with a 350.

If you can find some smog legal headers that fit your truck, then that would be advisable too. Otherwise run the stock stuff, it wont hurt the bottom end at all. You wont be spinning it to 5000-6500 rpm anyway.

Next up is the trans, the Th350 will work for a while, but a Th400 would be better. A 700R4 would still work, although you shouldnt tow in OD with one. The 700 will cost more than a TH350/400 to build and install, but the OD when you arent towing will be nice. I can get you a list of upgrades to use in a 700 if you like. Stay away from the cheap tiny coolers and get one that has some surface area. A quality converter is a must, a stock stall speed and a tight coupling will limit heat generated by slippage. You could use an L88 Corvette style converter, they stall around 1900-2200, are full size converters, and can be picked up at any trans shop. They are tight for the stall speed and use a full size 13" case. Otherwise just use a stock stall speed. Th350s and Th400s use the same converter, the 700 is different and will not work. There was a Th350C that had a lock up converter but they were problematic and you really dont want one.

The high dollar alternative is a 4L80E, for about $3k you can have a bulletproof trans that will take any abuse you throw at it, with an overdrive. Its computer controlled so it needs a controller to use one. There have been threads about them here if you are interested. The 4L80E is a descendant of the TH400 but with an overdrive and electronic valvebody.

A lock up converter simply has a clutch plate inside it that connects the input shaft to the engine with no slippage when its applied. This cuts down the heat generated by the fluid shearing inside the converter, it also picks up some mileage in addition to reducing heat. All OD auto transmissions since the 80s are lock up converters from the factory.

Now if you move up to a 454 with a mild cam like the XE262 or even the XE274 it will make enough torque to pull almost anything. its relatively easy to make 500ftlbs with a rat or any large displacement engine (455 Buick, Olds, Pontiac), the problem with the alternative engines is smog, not cost. No matter what anyone tells you, a rat is pricey to build and actually if done right the BOP 455 can be built for much less and make the same or more power. You just cant stuff one in there and stay legal. You will also need to move up to a TH400 at the very least, yes a manual is nice but a clutch can burn up as easily as an auto.

If you want a really nice but expensive upgrade to your drivetrain, a Duramax swap from a newer truck would be perfect. It wont be cheap but that engine and trans will pull anything and get decent mileage doing it. We pull 34ft boats, and two car trailers with 3/4 and 1 ton 4x4 Duramax trucks, no matter what we put behind them we rarely see under 18mpg and usually its around 22mpg. Pulling a loaded 8000lb car trailer through the hills around Atlanta the 3/4 ton 4x4 didnt have to kick down very often. The new 6 speed 07 is even nicer to pull with. That is going to be expensive to swap in though, at least $5k if you can find the parts cheap enough and do all the work yourself.

The basics are more torque on the bottom, easier towing and better mileage all the time.

[Thumpin455]

Almost forgot, you could also swap in an L92/LQ9 6.0L, actually that wouldnt be terrible expensive considering what you get. I have read about some junkyards selling those engines for around $1000-$1500, you will need a computer for it but you can get aftermarket stand alone systems. HOTROD did an article on them a while back, they got 500hp/tq really easy from one, just a mild cam and a set of headers. Now that would end your towing problems right quick.

[Roper]

I would like to swap in a 4L80e. Read on here one time that the stand alone computer is over $1000? Anyway what about the bolt patterns? Im guessing it would bolt right up to my 350 engine but what about my 208 transfer case? Im guessing you would have to make a cross member, new driveshafts, etc? Sounds expensive.
Wouldnt a TH400 with a gear venders overdrive be cheaper, easier? I just recently replaced my th 350 with another th350. Wanted to upgrade to a TH400 but I couldnt find a 4x4 version. I see now though there are outfits like Bowler who sell them. If my new th350 calves again im definately going to upgrade it to something bigger.
One thing I dont like about duramax or cummins besides the price is they are just so heavy. To heavy for a 4x4. My friends all have new quad cab dually diesels and they suck off road. Part of the problem is they are to heavy and also the way the weight is distributed.
I know a guy up in Calgary who put a Cummins in his 86 GM 4x4. Huge, expensive swap!
GM is coming out with a new 4.5L diesel though that will sapposedly bolt up anywhere a 350 will. This might be something to think about?
What about the old 6.5 diesel? Does anybody offer a crate 6.5L? When I replaced my motor I was thinking about putting in a 6.5 but I couldnt find a good one locally. Gas was only half of what it is right now so I stuck with a 350 gas motor. With current gas prices the 6.5 looks better than ever. Would also be a simple straight forward swap to wouldnt it?
Wondering about smog regulations with swapping from a gas to a diesel?
Maybe with smog regulations or future smog regulation concerns a 6L swap would make the most sense? I dont know much about the new engines though. I do know a friend of mine has a 96 GM with a 6L and it doesnt hhave anymore power than whaty my 350 does. I guess the newer vortec versions of the 6L has more power?
What about all these BB GM crate motors like the 502/ 572? Guess none of these will pass a smog test?

[74 stepside]

Originally Posted by 454HO

I think the TH400 will be your limiting factor. Yes it's a strong tranny, but it is only a 3-speed and the ratios aren't that great for towing. And since it is a non-lockup, it will be extremely inefficient. The TC slippage will generate lots of heat, and longevity will be poor. Not to mention the horrible fuel milage and increased wear on the engine from revving so high. You really should consider swapping to a manual transmission.

Personally, I would go with 4.88 gears and then look for either an aftermarket T56 6-speed or a TKO-600 5-speed. That would give about 14:1 starting line ratio and yet still be able to cruise around 2200rpm in top gear at 70mph.

Incidentally, you can check various rear gear and transmission combo ratios here -
http://www.5speedtransmissions.com/gear_calculator.html

!st time I have ever heard this. 73-91 duallys that had BBC all had 400 transmissions except for the optional manual stick. Im pretty sure they are just fine for towing.

[Gregs71]

Wow 74, you brought back an old thread!!! FYI, I ended up going with 4.10's and it has done great for the last 4 years. The 350 is old and tired, but it continues to get the job done.