Typical increase in MPG when swapping to OD?

[ponjohn]

Hi All-

Have not been around, sold the 85 dually a few years ago. I am looking at a 90 Burb, TBI 454, 2wd,4.10 supposed to be in real nice shape for the age.

It needs a trans, my intent will be to install either a 700r4 or 4l80e ( I have both).

Sooooo.....anybody go this route and document the increase in fuel economy?

( I put this in here because there is more traffic)

TIA-
John

[killthewabbit]

I sure am interested in hearing what you get, dude. I have never heard of anyone getting more than 18 MPG in a square body truck, no matter what (gas) engine/tranny combo they have.

I've heard some 6.2 diesel people claiming 27 MPG, but I'd like to see that one.

[Ivan D.]

Originally Posted by killthewabbit

I sure am interested in hearing what you get, dude. I have never heard of anyone getting more than 18 MPG in a square body truck, no matter what (gas) engine/tranny combo they have.

19-20mpg consistently, weekend after weekend, on 150-mile round trip, mostly freeway - 350 SBC, 4165 Holley double-pumper, non-lockup TH350, 3.08 rears, 32x10.5" mud-slingers up front, 33x12.50" all-terrains in the rear, 2wd. That's of course summer figures, we have that crappy winter-blend gasoline now, and I had to up the jet size too, so I'm down to about 15-16mpg freeway, less if there's snow on the road.

[Tom]

If you use the 700r4 you'll regret it down the road. Going from a th350 to a 200-4R in my 79 with a L31 350 and 3.07's gave me nothing around town but 5mpg on the freeway.

[chevyrestoguy]

If you use the 700r4 you'll regret it down the road

Please explain further. I can't find a real negative by having a lower first gear for around town snap and an overdrive for the highway.

[Pyrotechnic]

There's someone around here with a SWB truck with a 5.3/4L60E/3.73 combo swapped in. If I remember right he was getting really good mileage.

[PhilaTruck]

I used to get 'tween 18-22 HWY with my 305/700R4/2.73 -- DEPENDING on how I drove it. I could also make it get 12.

The 406 is a bit more thirsty and a bit less thrifty.

[Russell]

My 77 stepside actually got worse mileage with the 700r4. It had a 2.73 rear diff though, bogged like crazy till you were going way over the speed limit...

However, a big block geared to turn approx 2200 rpm on the highway would get way better mileage than a big block geared to turn 3000 rpm on the highway without overdrive.

I'd personally opt for the 4l80e. They are a far stronger transmission, but you have to buy a rather spendy controller for it..

[rfmaster]

I went from 10-11 MPG with 350/350 to about 18MPG when I switched to 700R4. I run 4.10 14B-10.5 and 33 inch tires. At 65 MPH I am turning 2050 RPM.
I word of advise - before installing 700R4 just make sure that all heavy duty upgrades are in - early stock pieces were not known for their sturdiness. Upgraded 700R4 can handle 400+ HP/FT-LB which is adequate for most stock and near stock applications. Also, most 700R4 failures can be directly attributed to mis-adjusted TV cable!

//RF

[Pyrotechnic]

TCI has a valvebody for the 700R4 now that keeps line pressure safe at all times regardless of TV cable adjustment. If I ever build a 700R4 I'd like to use this valve body.

The TV cable is the only thing that really turns me off to a 700R4 or 2004R. It just seems silly that the life of the transmission has to depend on that cable and it's adjustment when Turbo 350's and 400's are self managing and just need a kickdown cable or switch and a vacuum source.

[Thumpin455]

Originally Posted by Pyrotechnic

TCI has a valvebody for the 700R4 now that keeps line pressure safe at all times regardless of TV cable adjustment. If I ever build a 700R4 I'd like to use this valve body.

The TV cable is the only thing that really turns me off to a 700R4 or 2004R. It just seems silly that the life of the transmission has to depend on that cable and it's adjustment when Turbo 350's and 400's are self managing and just need a kickdown cable or switch and a vacuum source.

Elimination of the vacuum source, due in part to emissions and also in exercising more control over the shift points, line pressure, and shift feel were the reasons for the TV cable. At the point the change was made, electronics werent up to the task yet.

If you have ever had a stock Th350/400 and just left it in drive, how early did it shift? Most of mine were in third before the next crosswalk. The TV was a step in the right direction as its more precise than a vacuum signal.

I plan to try that valvebody in one of my 700s, possibly in the GTO. Sounds like a cool thing to have for a retrofit.

As for how much you pick up, it depends on a number of variables. If you drive mainly in town, you wont see much difference. If you are on the highway with deep gears and were previously spinning it to 3500rpm and now its turning 2200rpm, you will see a sizable gain.

454 in a Burb would do better making some more torque. The stock cam is weak, and an upgrade to something a bit better than the TBI would help. Emissions tune isnt always the best for mileage. If you are in an emissions state, dont expect to get good mileage from it. If you arent then you can make changes to help it breathe better and make more power from the same fuel at the rpm range you cruise at.

There is an 87 454 with a 700 in the 76 I have as my avatar. In the spring we will see what kind of mileage it gets, its getting a cam and intake swap, keeping the Qjet but rebuilding it, and baselined. Then I have been thinking about putting it on alky. Other projects kept me from going farther on the truck last year.

[Ivan D.]

My input on the topic - do not worry about the TV cable, Ford has been using it in the AOD tranny for years, if tis adjusted right it works awesome - with the vacuum I can never tell when my TH350 will downshift (I kinda know, but not exactly), wheres the AOD in my Lincoln I can shift as precisely as a stick-shift, it shifts exactly when I want it, no earlier and no later - total control and absolute consistency in action no matter what. Do not fear the TV cable, understand it and set it right.

Back on the GM overdrives, there's also a mod for the valvebody made by TransGo, it turns the 4L80 tranny into a stick-shift, pretty much - tis a bit expensive for a shift kit (which it essentially is), but elliminates the need of that controller, and you can now do just what you want to with the tranny, when you want to:
http://store.summitracing.com/partde...5&autoview=sku
(linky courtesy of bthomas454 from FSC, thanks man)

[Pyrotechnic]

I guess I will have to agree with you on the early shifting. By 30 MPH i'm in third gear if I'm easy on the throttle with my Turbo 350. Thats the only thing I don't like about it. With 3.08 gears, the motor tends to get loaded up around town because it never really gets to rev. Seems the only way to keep the cob webs out is to drive it like I stole it.

[Ivan D.]

What about manually shifting it? I don't like it to jump a gear up till I hit 2k, and under light throttle that's only possible with manually keeping it where I went it.

[Pyrotechnic]

Yeah manual shifting is really the only solution. When going through school zones or low speed limit roads I actually put it in 2nd gear because the truck will run away in 3rd gear. Sometimes in heavy traffic I just leave it in 2nd gear which save a shift and it gives me engine braking for stop and go traffic and when I get up to 50 or so, i'll shift into third like it's overdrive. It wouldn't be so bad with numerically higher gears because I have a feeling they would naturally keep my rev's higher.

With a 700R4 swap being so spendy, I'm debating just swapping my 3.42's in and leaving it at that. They seem to be about the best dual purpose acceleration and highway gear. It's only a few hundred RPM higher in cruise anyway and my stock 350 got great has mileage with them.

[kevinr1970]

On my '82 K5, with T350, when I bought it it would shift pretty quick. That part wasn't that objectionable.
But when I would start giving it gas it would bog in 3rd. I would really have to step on it to get it to down-shift.

There is a (down-shift?) cable that attaches to the throttle linkage. The clip that actually attaches the cable to the linkage is held on with a barrel looking thing with a screw on the end to secure it, Not OEM by any means.
The cable had quite a bit of slack in it. So I played with it a bit by taking as much slack as I could out of it until I found the sweet spot.
Now it down-shifts pretty easily, but not overly easy.

[Ivan D.]

You know Kevin, I played with my kickdown cable, could never get it to work just right and still have enough travel for the carb bracket to reach WOT position. On the other hand, the kickdown is just that, a kickdown, it controls the forced downshifts, but it does nothing for keeping the lower gears longer before upshifting - the TV cable in the OD trannies does both, at least with the AOD the tighter the cable the hinger the line pressure, which results in delayed upshifts and faster and lighter downshifts. I actually almost maxed out the TV pressure in my Lincoln's AOD, I just love how it works now, in the long long run it may kill some seals, but by then there will be a diesel waiting install so a new tranny will be in order anyways. The TH350 in my truck tho, there's that adjustable vacuum modulator that can be installed instead of teh stock unit, it supposedly allows you to tune the hifts points, but I don't really need it - the Holley carb I got have no provision for a kickdown cable to attach, so my cable is just disconnected and coiled off to the side, I downshift it manually if I need to pass someone fast or keep a lower gear longer (hooray for ratchet shifters), once I got used to it I'm pretty happy with it all.

[Pyrotechnic]

Does the vacuum modulator control part throttle upshifts and the governor controls full throttle upshifts ? This is the way I always understood it.

[Ivan D.]

AFAIK these two actually fight - the vacuum modulator tries to keep the tranny in the lower gear, the governor tries to make it upshift, the one with the higher line pressure wins: the lower the vacuum the higher the line pressure off the modulator, so the governor has to wait till the output shaft revvs high enough to build up line pressure strong enough to counteract the modulator pressure and trigger an upshift. The kickdown forces the downshift under WOT, the tranny will downshift by itself too (modulator pressure overcomes governor pressure), but that takes a while and in the mean time cluthes may slip and heat will be generated - kickdown just throws it in a lower gear right away to avoid all that mess. Or something like that...