lets go for mpg on a c20

[superkingd]

Okay to start we don't buy these trucks for mileage. However I want to drive mine more. I commute 50 miles a day and don't want to buy a 4 cyl for 1000 and end up buying someone else's used turd. So here we go.

1970 c20
355 th400
it had a great running 292 inline 6 and granny 4
I have a 700 r4 I could rebuild
Also has the Eaton rear axle but I have a 3:55 geared ford 9 inch.

Here are the thoughts
I could put a tbi set up (stock gm) on the 6 with a Clifford intake.
And mate that to a 700.
Or tbi on a 355 and 700r
The inline 6 would be pretty cool.
anybody tried any of this with luck
My goal which may be tough is 20 mpg.

[Ol Blue K20]

292 engines aren't known for mileage either
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[Warrens69GMC]

Test drive this, get it if is what he says....

http://indianapolis.craigslist.org/cto/3582175559.html

[jocko]

of the parts you have listed, I think the tbi 355/700R4/3.55 is the best combo, but it won't get you to 20 mpg imo. might have to go the LS route if you want to get closer, but even then, would be difficult. But, it does sound like you do a lot of highway driving if you drive 50/day (at least I HOPE it's highway driving, or your commute must suck) - so an o/d trans is priority #1. Is the 355 hot rodded or is it just an otherwise stock .030 over 350? What carb currently on it? (forget the 6, less cyls does not = better mpg in this case)

[superkingd]

355 is stock with edelbrock rpm intake and edelbrock carb, mort likely go tbi. And the one good thing about my commute is I do 45 miles highway around 55-60 miles and the rest in town. So I don't need the mpg to be there at 70. And 20 may be hard but it beats the 10 I get in my 1998 454 4x4 dually.
either engine direction I have to go with 700, so rebuild kit and converter to be ordered in the morning. I'll get some pictures up soon.

[superkingd]

Also the rear axle is a winters 9 inch in great shape, the lug pattern in that of a Monte Carlo. I'll need rims anyway so that's not a big deal. To convert the front 8 lug to 5 I'm going to get ece spindles with a 2 1\2 drop. 299 and don't have to change anything is a good deal.

[twich3136]

air dam? lose the big mirrors? lose the bumpers? cut the drag? some of that could help.

[superkingd]

I like the air dam idea. I have some aluminum I could fan it out of. Hmmm

[MARKDTN]

I have an '83 K20 and I get 17-18 city and 21-22 Highway now. It has 3.42 gears and a 700R4 trans. The stock 180HP 350 got 14 mpg. A cam lobe went down so I swapped it for a bone stock complete L98 Tuned Port from a '91 Corvette. IMHO if you want mileage and retain the ability to tow and haul, fuel injection and overdrive is the way to go. TPI units are not nearly as popular as 10-15 years ago. You can probably buy a nice one for $200-250. Either buy a $400 harness or make your own from an F-body one or a 3.1 Cavalier or Corsica. The external '88 Ford truck pump is $125 or get an S10 Blazer tank and an F-body pump. You then need a $100 or so PROM. You can get in for say $800 or less. Couple that with a 700R4 and you will get better mileage. Another option is a complete TBI or Vortec engine and trans swap from a wreck-look for vans. Also, if you are doing a lot of road miles, get road tires.

[69GWC]

I have a 06 5.3 Z71 gets 15avg, milk it on a flat road and no wind it might get 18mpg and thats with 3.42s and is getting 10 pulling a small 5x10 trailer. Getting 20 is not going to happen IMO unless your math is just way off like most peoples is, this is my 2nd 5.3L truck and the other did no better and the 6.0L 02 I had get 12/13 at best, most times it got 11, I know several other people with 6.0L that do the same 12/13 max.
Had a 94 350 Xcab that got 15avg and 18 or so on the hwy. At the same time I had a 75 with a 350/350 that got 15mpg on the hwy and about the same in town. I have yet to see a truck get 20mpg all the time unless it was a diesel and not all of them can do that.

IMO 15/16 is a better number to shoot for.
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[superkingd]

20 mpg is a goal. Maybe one not doable but worth going for. What do I have to lose. I appreciate the info. I'm going to switch to half ton suspension, do a 355 700r4, and 9 inch rear. Reason for 9 inch is I have it and I can easily swap gears cheap. It has disc so there is a weight savings and I might cut truck down to a short bed.

if I only get 18 or 17 then I'm still better off and I'm cruising something cool. I could by a 4 banger and deal with more insurance and plates and upkeep. I also don't care to have break downs with a 150,000 mile 4 banger.

Now time to order trans kit, converter, and drip spindles.
I know wiring but love my time more. I have a complete tbi with all sensors and ecm from a 1992 gm truck. What harness is best, either a plug and go or a stock that's needs slight modification.
Also the factory intake is heavy and has the heat tube broke off so ill most likely keep edelbrock intake? FYI heads are from 1992 gm truck so i "ass u me" the distributor will work. And just use an adapter for throttle body. Anyone here done this?

Thanks for help, nothing helps more than someone sharing their past mistakes.

[Longhorn 70]

Like the signature says, the big block Olds gets me 15mpg with 700R4. I have to drive like an old lady....not the one in the Beach Boys song either.

The 350 with a TH350 on the other hand got 13.....I think the differences were overdrive, age and tuning. The 350 was tired and had to work. The 425 (431 now) works less on the road thanks to overdrive.

I know it's not a fair comparison but the 68 corvette with a 350 got 18 on a cruise but my 90 with a 350 got in the HIGH 20s on the road. Differences there, overdrive, and tuning.... Heck my 450 RWHP Corvette still gets 25 on the road.

Moral of the story, Overdrive and Engine management are your fuel friends. Drive like a wuss and you may get there. Like stated earlier, the TPIs can be tuned and with overdrive they won't have to work, but will if you want.

A

[ScottG]

Just my .2. I have a '67 c20 w/350. Went from a T400 & Eaton 4.10's, to a 700r4 & Dana 60 w/3.54's. A little carb tweaking, and I've doubled my gas mileage!! Can't give you a # per gallon, because the speedo cable snapped, and I haven't changed it yet. It did get HORRIBLE gas mileage before.

[68Cummins]

Why stop at 20? 4BT cummins with NV4500 trans. That should get you over 30. Buddy had that setup in his '86 c10 (4x4 on 33" tires) and got 28mpg. 18-22 pulling gooseneck.

I'm shooting for 25mpg with mine (2wd, 6BT 5.9, 5spd)

[superkingd]

I decided to look for a half ton bolt in axle to use instead of the 9 inch. I found one on c-list. Went to buy it and small world it was 68cummins who posted above. Nice truck he's building.

ece spindles will be ordered tonight along with trans kit. Gonna have some tires, wheels, and an Eaton axle for sale.

[70blackfish]

no problem with a diesel.....

[superkingd]

I don't have a problem with a diesel other than the price, if I fell into a good deal I would go that route.

[1972RedNeck]

Originally Posted by 68Cummins

Why stop at 20? 4BT cummins with NV4500 trans. That should get you over 30. Buddy had that setup in his '86 c10 (4x4 on 33" tires) and got 28mpg. 18-22 pulling gooseneck.

I'm shooting for 25mpg with mine (2wd, 6BT 5.9, 5spd)

My 8,000 pound '93 W250 will get 24+ MPG with 3.07's, Getrag and no cruise.

[superkingd]

I'm not starting a diesel vs gas dispute. Diesels get better mpg but fuel cost more, the initial cost is more and up keep is more. I have owned, fixed, and maintained diesels.they are great engines but not what I'm going with.

[trac209]

Originally Posted by 69GWC

I have a 06 5.3 Z71 gets 15avg, milk it on a flat road and no wind it might get 18mpg and thats with 3.42s and is getting 10 pulling a small 5x10 trailer. Getting 20 is not going to happen IMO unless your math is just way off like most peoples is, this is my 2nd 5.3L truck and the other did no better and the 6.0L 02 I had get 12/13 at best, most times it got 11, I know several other people with 6.0L that do the same 12/13 max.
Had a 94 350 Xcab that got 15avg and 18 or so on the hwy. At the same time I had a 75 with a 350/350 that got 15mpg on the hwy and about the same in town. I have yet to see a truck get 20mpg all the time unless it was a diesel and not all of them can do that.

IMO 15/16 is a better number to shoot for.
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Exactly most people's math is way off. Idk how you have a 2wd Ls1 newer truck getting at best 18 mpg highway(I know plenty of guys who own these). And swap into a 67-72 gm and suddenly guys claim to get 25 plus mpg. Not gonna happen. IMHO if you want mpgs get yourself a cheap commuter and save your truck for around town pleasure drives or errands. Just my 2 cents
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[steelhorse]

Ok here we go. Go with the 350 and 700r4 combo. Unplug every other plug wire then install 2.73 to 1 gears. Remove the bed,doors,hood and fenders(to reduce weight) then put a lightweight racing seat only on the drivers side. Let me know how that works

[67ChevyRedneck]

Originally Posted by trac209

Exactly most people's math is way off. Idk how you have a 2wd Ls1 newer truck getting at best 18 mpg highway(I know plenty of guys who own these). And swap into a 67-72 gm and suddenly guys claim to get 25 plus mpg. Not gonna happen. IMHO if you want mpgs get yourself a cheap commuter and save your truck for around town pleasure drives or errands. Just my 2 cents
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I have a 2000 Z71 that averages around 14 (almost all stop n go) and will get 17.5-18 on straight highway trips.

I have a 350 700R and 3.73 in my 67 C10. I average around 12-13mpg with it (I am a little rough on it ) but I've done quite a few highway trips and seem to average 16mpg with a highway only trip. I assume most of the crazy numbers are from incorrect speedo/odometer readings from the trans swap and different tire sizes. Before I did all the swapping, the I6 and 3spd in the truck got 10-12 mpg no matter what speed I was driving, so it was an improvement.

The 700R is definitely going to help, but don't expect huge numbers.

[superkingd]

Even if I "only" get 17 avg then it beats the 10 I get in my dually. I do drive like a grandma to and from work so that helps. When my 70 was an inline 6 I got 10 probably. But I have it to drive. I racked up about 30,000 miles in 3 years. So 17 or even 15 wil be a gain.

Hopefully trans kit will be here by the weekend. The 355 is in it now with a th400. Also u bolts for my 12 bolt will be here so I can switch that out.

When my ece spindles get here, what rotors do I use. I would assume from early 90's heavy half 6 lug.?

[Z10]

Originally Posted by superkingd

Even if I "only" get 17 avg then it beats the 10 I get in my dually. I do drive like a grandma to and from work so that helps. When my 70 was an inline 6 I got 10 probably. But I have it to drive. I racked up about 30,000 miles in 3 years. So 17 or even 15 wil be a gain.

Hopefully trans kit will be here by the weekend. The 355 is in it now with a th400. Also u bolts for my 12 bolt will be here so I can switch that out.

When my ece spindles get here, what rotors do I use. I would assume from early 90's heavy half 6 lug.?

59% increase ain't bad!

[68Cummins]

Originally Posted by superkingd

When my ece spindles get here, what rotors do I use. I would assume from early 90's heavy half 6 lug.?

It has been a wile since i have looked into this but i believe you are looking for a c2500 rotor from 88-98 and maybe back to 73. These will be hub bearing centered for your spindle. c1500 6 lug should be the same part number but may be more difficult for the parts store to look up since 5 lug was most common.