Banks and/or Overdrive thoughts?

[88 K30]

I'm looking for opinions. I am (finally) seriously looking at upgrading my truck for a little more towing power and/or better cruising RPM's. I'd love to do both, but the cost of new parts is way more than I want to put into the truck and finding used parts is proving to be difficult.

My first dilemma is that my truck has 75,000 miles on it and, although it has been extremely well maintained and runs like a top, I don't want to make more work down the road for myself by introducing a turbo at this point in it's life, causing problems with rear main seals, head gaskets, etc... Any experiences/problems from anyone who turbo'd an engine with this type of mileage?

The other dilemma is cruising speed. The truck has 4.10 gears and a TH400, so the engine is really wound up tight at 65 mph, and I hate to cruise down the road at any more than 60, just because I hate to spin the engine that fast for extended periods. And, given what I use the truck for, if I'm trying to do 60+, it is probably going to be for an extended period of time on an interstate, although it is infrequent in the grand scheme.

With the 4.10 gears, it does pull OK when loaded, but as we all know, it would be nice to have the extra power from a turbo. I borrowed my uncle's Duramax/Allison the other day and I was REALLY jealous!!! Additionally, it would be nice to drop the RPM while cruising with a Gear Vendor or similar. Being a 4x4, I'd prefer not to go with a 4L80E swap (new front & rear driveshafts, moving the T-case, etc...). I guess those long trips on the interstate could be considered a good opportunity to borrow my uncle's Duramax... :)

It is not my daily driver, so I tend to lean toward the turbo before the overdrive, even though I don't tow for a living. I only drive the truck about 3-5K a year and I just don't think that lowering RPM mainly when I'm on the highway will gain me enough fuel mileage to justify the $2700 cost of a GV unit any time in the near future. (of course, OPEC did just cut production....:rolleyes:)

Any thoughts are appreciated.

[moondoggie]

Good Day!

"The truck has 4.10 gears and a TH400, so the engine is really wound up tight at 65 mph, and I hate to cruise down the road at any more than 60, just because I hate to spin the engine that fast for extended periods."

rpm = (mph) X (1 hour/60 minutes) x (63,360 inches/mile) / (tire dia in inches x pi) X (driveshaft rev/tire rev [axle ratio]) X (0.75 engine rev/driveshaft rev [AT OD ratio])

(The following assumes 245/75R16 tires - change the tire dia in inches for your size)

rpm @ 60 mpg = 60 x 1/60 x 63360 / (30.47 x pi) x 4.10 x 1
rpm @ 60 mph = 2714

To this you must add what you estimate your TC slippage to be, so you're probably around 2900 rpm @ 60 mph. Yep, that's getting up there.

"I just don't think that lowering RPM mainly when I'm on the highway will gain me enough fuel mileage to justify the $2700 cost of a GV unit any time in the near future." Why guess? PM me your real email address & I'll email back an Excel spreadsheet into which you input what your GV (or any proposed mod) will cost, what your present mpg is, what you guess your mpg will go to, & the price of diesel fuel. The spreadsheet then tells you how many miles it will take to pay for your GV, or ANY mod you might be considering. I will warn you though, you're not going to like the numbers. For a $2700 mod, 18 mpg now, 20 mpg after, & $2.60 for diesel, the payback is ~ 187K miles. The payback in how much quieter your truck will be (& it will be LOTS quieter) & possible longer-lasting engine, only you can say.

Blessings!

[Craig M]

With only 3000 or 4000 miles a year it will be hard to "justify" the cost of a new Gear Vendors. My dually has the TH400 and 4.10's and I am with you, she is wound up at 60/65 mph Keep an eye out for a used unit. They sometimes go for $800 to $1400. The lower rpm will give you peace of mind.

[EJohnson]

As you can see from my signature info I have the setup you are discussing. My first Sub was a '77 C20 w/454 gasser that pulled reasonably well but the mileage was 9-12mpg no matter what; fast, slow, loaded or unloaded. My second was an '82 C2500 with a NA 6.2 which pulled OK and mileage was better, 16MPG light load and 12-14MPG loaded and towing, but SLOW to the point of danger when towing as passing/merging took forever and even East Tennessee Mountains were a challenge. At 275Kmi it needed a new tranny, injection pump, valve job and rings plus the body rust had gotten pretty bad and the interior was cracking and ratty (4-5 family trips per year with 3 kids are hard on any car) so it was put out to pasture.

My current '90 R2500 Sub is as described below and pulls great with a 4500# dual axle BSA Scout equipment trailer no problem at 75+ MPH, MPG is 14-16. No trailer & light load @ 60-65mph, MPG is 18-20. The Gear Vendors 20% overdrive is a big part of that as with a 4.10 and the GV in, the engine just loafs at 70-80, and is easily managed by the factory CC. Also, I am running slightly larger diameter tires than standard and the Banks Sidewinder turbo boosts the power, torque and MPG at moderate RPMs as well. I do not have a tach installed yet so I am not sure what the actual RPMs are at 60-70 with the GV in but the engine howl level is greatly reduced with the GV. The other neat thing about the GV is gear splitting, turning my 3 speed AT into a 6 speed, great in the mountains of CO,UT,WY & MT as well as the Appalachians of the east.

However I am now starting on my third engine at 309K, an almost totally new, mil spec 6.2L, running drop in, my smoothest and most powerful yet. The original engine was a standard GM production 6.2L with the Banks Turbo installed at the factory (a standard order option in '89,90 & 91) The crank in that engine broke at 215K. A custom engine was built from rem/used parts which included all the DP discussed cooling mods, plus ceramic coated pistons, high volume oil pump w/dual bypass filters, DSG Phaser gear set and a Standyne reman injection pump. Despite all that and meticulous maintenance, the left head gasket went at 260k mi and the right at 305kmi. Both were replaced at 305k mi and then a couple of crank bearings disintegrated at 308k miles, probably from deck cleaning/burnishing trash getting in the oil passages, as the head gasket replacement was done with the engine in the Sub by a local Nashville Chevy dealer fleet truck department. My next part of this current update is to get the turbo rebuilt as the shaft seals are well worn and seeping oil into both the compressor and turbo drive side, this looks to be about a $500 job.

When I move on to my next Sub probably a '97-'99 2500 4X4 TD, it will get a GV if it doesn't have one. The GV warranty and out of warranty replacement program is great. Two years ago my 12 year old unit's hydraulic pump gave up. For a $500.00 exchange fee I had a recent production reman replacement and it was an easy swap. My plan is in 3-4 years to find a relatively low mileage Suburban with a sick or dead engine and put a Reviva / Schoolcraft / Kennedy / Pennisular 6.5 TD with low comp pistons and splayed crank bearing main caps plus the host of other cooling/durability/moderate power boost mods recommended at the DP.

Good luck with your decision but as moondoggie points out, the only way fuel economy payoff alone makes sense is with a loonnng commitment to that vehicle plus durability success which my experience doesn't come anywhere close to justifying on that economic basis alone.

[coxfmly]

My Sub had 120K when I installed the Banks kit. I was tired of being passed on hills by all of those V.W's. The turbo made an incredible difference in performance. Its a different truck to drive and I love it. It has 150+ miles now and I see no ill effects.
Unfortunately I have 4:10's and my truck scrams at 65 :( I have dreamed about a GV unit but find it hard to justify with the cost approaching the value of the truck!

Good luck.....

[88 K30]

Thanks for the replies! I like hearing other's experiences since, inevitably, I will not have been able to think of every pro and con.

While I would love a reduction in noise when cruising the highway, I guess the amount of time I spend on the highway is really too small for me to buy a GV just for the quite factor. And, although I plan on driving this truck until it won't drive anymore (then fixing it and driving it some more :) ), I just don't think I can swallow the price of a new GV unit, even with the fuel savings. I will keep my eyes out for a used unit, but they seem hard to come by for a 4x4 with an NP205. I guess some of the units are interchangeable with different adapters, though?

As for the Banks, I think I will definitely do that upgrade. If my truck makes it to 150K without any major problems, I'll be happy! At my rate of use, that would be about 15 more years!!

Thanks again!

[Craig M]

Adaptors are available from Gear Vendors, but check on the price. They want an exchange adaptor and $$$.

[moondoggie]

Good Day!

Might not hurt to check the boneyards - you might find a wrecked truck with both axles 3.73, which might be worth doing. If you turbo your truck, you'll have no trouble at all pulling these gears.

Blessings!
(signature in previous post)

[UGLYTRUK]

My 1st taste of a Sub was a rotted '86 1/2 ton 4x4 with a Banks 6.2 and reman 700R4, 155k. I could burn rubber all day long, cruise up any hill in Vermont, gaining speed all the way. After 3 months it gave a death CLANG. It's parked, waiting for a post mortem.
Luckily I found an '87 3/4 ton 4x4 6.2 with a much less rusty body. But the 4.10's are reedikulous! I'm reluctant to put the Turbo on it w 180k, but might put the 700R4 in place of the TH400. My fuel mileage is under 15 unloaded. The 1/2 ton got close to 20, even under boost. Gotta' be the 3 speed...

[Craig M]

Hey Uglytruck.

Your 1/2 ton probably has 3.73 gears. That and the 700R4 keeps the rpms down real nice. Our 1/2 ton suburban with 3.73 and 700R4 gets 20 mpg on the freeway all day long. A 3/4 ton with 4.10 gears and TH400 is a bit different. Nice for pulling but unhappy at 65 mph (high rpms). Swapping the 700R4 and getting bigger diameter tires will help get your 3/4 ton close to 20 mpg.

[britannic]

My military truck has 4.56 ratio diffs. So I fitted a custom turbo, injector pump and 6.5L injectors to my rig, along with 33" tires and an HD 700R4. It made for great cruising and good fuel economy when I could restrain myself from enjoying the power! Search my old posts for more details.

[UGLYTRUK]

Or buy a rust free straight axle, or maybe upgrade to an IFS. Tell me about your 6.5. I'd just like to stick with the older style to keep it simple, and the 6 5's are way more money... Got one 4 sale? Nothing too fancy... Andrew