67-72 3/4 ton with good gas mileage - Page 2 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mitchfab · 06-16-2005, 02:13 PM

A4L80 e But its computerised like the 60 is .Is there a way to get around that?

fastwillie 696969 · 06-16-2005, 02:15 PM

i'll be glad if i get 6 miles to the gallon

mitchfab · 06-16-2005, 02:25 PM

Shoot I think it sounds good . Dont you all?

Robert1970C20rstbukt · 06-16-2005, 02:31 PM

A 350 with a 2bbl carb, 4 speed granny, spicer aux. trans, 4:10 rear, 33" tires.

When me and my dad drove the truck 80 miles to Seguin, Texas we got about 10.5MPG. Right now my Dad's been driving it back and forth to work 70 miles a day(because the 700r4 in his 85 Burb took a crap, that's a whole nother story), and it's been getting almost 13MPG! That's cool with me, but I want my truck back!

The truck has a 350/400/4:10's/33" tires, but I've worn the hell out of the 33s, gonna have to put the 31's back on.

mitchfab · 06-16-2005, 02:40 PM

Yea! I love a hard pullin big block when it pins you back in the seat and all you see is the sky. its time to hit the brakes and get in line for another pass .

FirstGen · 06-16-2005, 05:22 PM

Quote:

Originally Posted by mitchfab

Yea! I love a hard pullin big block when it pins you back in the seat and all you see is the sky. its time to hit the brakes and get in line for another pass .

On a recent trip to Austin and back, I got 19.7 mpg on the highway and I prolly make 100 horse more than that 402 makes...

SPECS:

364 CID, FI gen III small block
T56 trans
4.10 gears
29" tall drag radials

mitchfab · 06-16-2005, 05:33 PM

Quote:

Originally Posted by FirstGen

On a recent trip to Austin and back, I got 19.7 mpg on the highway and I prolly make 100 horse more than that 402 makes...

SPECS:

364 CID, FI gen III small block
T56 trans
4.10 gears
29" tall drag radials

Yea Thats what Im gettin at. You got a fI small block I think it could be done with a tbi setup and a overdrive .Anyway a gen 4 tb bb intake will fit a 402 wont it?

FirstGen · 06-16-2005, 06:10 PM

Quote:

Originally Posted by mitchfab

Yea Thats what Im gettin at. You got a fI small block I think it could be done with a tbi setup and a overdrive .Anyway a gen 4 tb bb intake will fit a 402 wont it?

Nope. They are 13 degree heads. Totally different intake runner ports. Won't work. Best bet would be an ACCEL Gen 7 fi setup.

farside847 · 06-16-2005, 02:52 PM

My 307 with a 3pd and 2bb carb gets 17, might be able to add one more if I didnt try to pass so many people

farside847 · 06-16-2005, 03:34 PM

you can try one of these... they sound like an infomercial though... bla bla bla save gas bla bla 20% increase bla bla bla helps you get girls bla bla bla

http://www.savefuel.ca/hydrogen.htm

**pjmoreland** · 06-16-2005, 03:36 PM

I would think that a manual transmission with a 3.07 gear ratio is going to be the best combination for good gas mileage. Automatic transmissions are not as efficient as manual transmissions. I had a 6 cylinder 250 with a three speed manual transmission and a .79 overdrive unit that got 21 mpg on the highway. I can get 16 mpg with my 350/700R4 if I keep it under 65 mph.

The problem is that engines are most efficient when they are near their peak torque at wide open throttle, but wind resistance becomes a really big factor at higher speeds. Little engines get better gas mileage because they can operate closer to their peak at normal highway speeds. You'd have to drive extremely fast to get a bigger engine so that it is approaching its peak efficiency, but wind resistance becomes more of a factor and more than cancels out the benefits of running the engine at peak efficiency. Big engines are really only practical if you need the power for pulling heavy loads over mountain passes. I doubt there are too many people on this board that care about being practical though, me included.

Sillyoldman · 06-16-2005, 03:57 PM

Figure out how to make it run good on four cyliders?

chevyfarmer · 06-16-2005, 04:08 PM

Retrofit a "displacement on demand" system like the new v-8's are running, the 345 hp hemi's in the new dod%e charger is suppose to be 24 mpg.

**pjmoreland** · 06-16-2005, 04:07 PM

Isn't that what Ford does with their F-350?

mitchfab · 06-16-2005, 04:27 PM

Thats a thought with the Use of Hydro-Gen!

mitchfab · 06-16-2005, 04:29 PM

Bla Bla Bla! Retrofit might work but thats some big bucks.

TP from Cntl PA · 06-16-2005, 05:16 PM

I am hoping to get around 40 with mine................But it isn't exactly a bolt in deal as you can see below

mitchfab · 06-16-2005, 06:00 PM

Quote:

Originally Posted by TP from Cntl PA

I am hoping to get around 40 with mine................But it isn't exactly a bolt in deal as you can see below

Thats sounds good.You got a pic.

TP from Cntl PA · 06-16-2005, 09:27 PM

Quote:

Originally Posted by mitchfab

Thats sounds good.You got a pic.

It isn't done yet, but I do have it up and running...............Works darn good!

Front suspension is pushed to the limit though

Others used this same engine(6AT3.4) and have averaged 30-35 mpg on the highway WITHOUT an OD................I have OD and steeper rear end gears so it should do well.

Maximum Overdrive · 06-16-2005, 05:22 PM

Quote:

Originally Posted by mitchfab

Bla Bla Bla! Retrofit might work but thats some big bucks.

If you really want 20 mpg with a 402 then no matter what you are going to be spending some big bucks to achieve it. If it was so simple the factory would have done it and so would everyone else and their mother.

mitchfab · 06-16-2005, 05:37 PM

Quote:

Originally Posted by Maximum Overdrive

If you really want 20 mpg with a 402 then no matter what you are going to be spending some big bucks to achieve it. If it was so simple the factory would have done it and so would everyone else and their mother.

You dont think a stock fi bb with overdrive will get close to 20 in a 67-72 out of a say 91 1ton gm?

FirstGen · 06-16-2005, 06:16 PM

Quote:

Originally Posted by mitchfab

You dont think a stock fi bb with overdrive will get close to 20 in a 67-72 out of a say 91 1ton gm?

Nope, no way. TBI is a poor design. Sequential FI is much more effecient. TBI is basically an electronic carb. To get the kind of milage you want you will need a very effecient head design, a great ignition system, and a good amount of overdrive. My tranny has a .50 overdrive in 6th...

72 CustomCamper · 06-16-2005, 06:56 PM

My 396 only gets about 4 mpg. The only time I got 20 mpg was when my 72 had an 84 6.2 diesel in it...

Chuck

Blazer1970 · 06-17-2005, 07:19 AM

20 mpg with any big block in one of these trucks can not be done.

68Stepbed · 06-17-2005, 07:49 AM

Comp Cams 270 or 280 cam, finely tuned Q-jet carb, HEI ignition with MSD 6A box, 3.42 rear gears with an overdrive manual tranny, Ceramic coated exhaust manifolds (not headers), Flowmaster Delta Flow Mufflers with 2.5 inch pipes. You might get 18 or 19.

For the cost to get good mileage, you could leave it like it is and come out about the same.

I had a 90 3/4 ton with a TBI 350 and a 5 spd manual and 3.42 gears and got 20 on the highway and about 18 in the city.

Just my .02

06-16-2005, 02:15 PM	#2
fastwillie 696969 ~Rest In Peace~ Join Date: May 2005 Location: CALIFORNIA NOR CAL Posts: 9,707	i'll be glad if i get 6 miles to the gallon __________________ is it fast ? it has a lighting bolt donut? B___H please, I can remove 90% of your so called "beauty" with a kleenex

06-16-2005, 02:31 PM	#4
Robert1970C20rstbukt Registered User Join Date: Jun 2004 Location: Beeville, Texas Posts: 1,943	A 350 with a 2bbl carb, 4 speed granny, spicer aux. trans, 4:10 rear, 33" tires. When me and my dad drove the truck 80 miles to Seguin, Texas we got about 10.5MPG. Right now my Dad's been driving it back and forth to work 70 miles a day(because the 700r4 in his 85 Burb took a crap, that's a whole nother story), and it's been getting almost 13MPG! That's cool with me, but I want my truck back! The truck has a 350/400/4:10's/33" tires, but I've worn the hell out of the 33s, gonna have to put the 31's back on. __________________ RJD 1984 Chevrolet C30 welding truck 454/SM465 1977 GMC C15 pickup 350/TH350 1970 Chevrolet C20 pickup 350/TH400 1970 Chevrolet K20 Suburban 454/TH350 1969 GMC 8500 478M V6/5 spd winch truck Last edited by Robert1970C20rstbukt; 06-16-2005 at 04:38 PM.

06-16-2005, 02:52 PM	#9
farside847 Registered User Join Date: Feb 2005 Location: Bay Area, California Posts: 995	My 307 with a 3pd and 2bb carb gets 17, might be able to add one more if I didnt try to pass so many people __________________ 1971 Chevy C10 Shortbed Stepside, 307v8 3-on-the-tree

06-16-2005, 03:34 PM	#10
farside847 Registered User Join Date: Feb 2005 Location: Bay Area, California Posts: 995	you can try one of these... they sound like an infomercial though... bla bla bla save gas bla bla 20% increase bla bla bla helps you get girls bla bla bla http://www.savefuel.ca/hydrogen.htm __________________ 1971 Chevy C10 Shortbed Stepside, 307v8 3-on-the-tree

06-16-2005, 03:57 PM	#12
Sillyoldman #16876 Join Date: Apr 2005 Location: Auburn WA Posts: 12,266	Figure out how to make it run good on four cyliders? __________________ Posted via Stationary Device '71 Custom Deluxe C-20 402. '67 Buick Special 455. '49 Plymouth Special Deluxe. *"I love that old car smell"* *Some people are like Slinkies... not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.*

06-16-2005, 02:13 PM	#1
mitchfab Junk Chevy C20 Big Block Join Date: Jun 2005 Location: East Texas Posts: 68	A4L80 e But its computerised like the 60 is .Is there a way to get around that?

06-16-2005, 02:25 PM	#3
mitchfab Junk Chevy C20 Big Block Join Date: Jun 2005 Location: East Texas Posts: 68	Shoot I think it sounds good . Dont you all?

06-16-2005, 02:40 PM	#5
mitchfab Junk Chevy C20 Big Block Join Date: Jun 2005 Location: East Texas Posts: 68	Yea! I love a hard pullin big block when it pins you back in the seat and all you see is the sky. its time to hit the brakes and get in line for another pass .

06-16-2005, 03:36 PM	#11
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 6,267	I would think that a manual transmission with a 3.07 gear ratio is going to be the best combination for good gas mileage. Automatic transmissions are not as efficient as manual transmissions. I had a 6 cylinder 250 with a three speed manual transmission and a .79 overdrive unit that got 21 mpg on the highway. I can get 16 mpg with my 350/700R4 if I keep it under 65 mph. The problem is that engines are most efficient when they are near their peak torque at wide open throttle, but wind resistance becomes a really big factor at higher speeds. Little engines get better gas mileage because they can operate closer to their peak at normal highway speeds. You'd have to drive extremely fast to get a bigger engine so that it is approaching its peak efficiency, but wind resistance becomes more of a factor and more than cancels out the benefits of running the engine at peak efficiency. Big engines are really only practical if you need the power for pulling heavy loads over mountain passes. I doubt there are too many people on this board that care about being practical though, me included.

06-16-2005, 04:08 PM	#13
chevyfarmer Registered User Join Date: Feb 2005 Location: Owosso, Mi Posts: 242	Retrofit a "displacement on demand" system like the new v-8's are running, the 345 hp hemi's in the new dod%e charger is suppose to be 24 mpg. __________________ 67 short wide 355ci 3 on tree 69 short wide 250ci 3 on tree 68 long wide 283 3 on tree 72 2wd Blazer project 454 5 speed

06-16-2005, 04:07 PM	#14
pjmoreland Senior Member Join Date: Jan 2005 Location: CA Posts: 6,267	Isn't that what Ford does with their F-350?

06-16-2005, 04:27 PM	#15
mitchfab Junk Chevy C20 Big Block Join Date: Jun 2005 Location: East Texas Posts: 68	Thats a thought with the Use of Hydro-Gen!

06-16-2005, 04:29 PM	#16
mitchfab Junk Chevy C20 Big Block Join Date: Jun 2005 Location: East Texas Posts: 68	Bla Bla Bla! Retrofit might work but thats some big bucks.

06-16-2005, 05:16 PM	#17
TP from Cntl PA Registered User Join Date: Apr 2003 Location: Central PA....In the Berg of Nisbet Posts: 790	I am hoping to get around 40 with mine................But it isn't exactly a bolt in deal as you can see below __________________ '72 K-20 EFI'ed 250 Inline/4spd stake body, Farm Truck '71 C-20 Cummins Diesel Powered, In storage thanks to $5.00 diesel! '69 3500 GMC 305V-6/4spd, Still under reconstruction.......... Inlines Rule! 6 soldiers standing is better than 8 laying down!!!!!!!!

06-16-2005, 06:56 PM	#23
72 CustomCamper huh ??? Join Date: Nov 2002 Location: Fredericksburg,Va. Posts: 3,368	My 396 only gets about 4 mpg. The only time I got 20 mpg was when my 72 had an 84 6.2 diesel in it... Chuck __________________ 90 Blazer Silverado 350w/ 700R4 and 32" Kelly's "I am a bomb technician. If you see me running try to keep up!"



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06-17-2005, 07:19 AM	#24
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	20 mpg with any big block in one of these trucks can not be done. __________________ Tim

06-17-2005, 07:49 AM	#25
68Stepbed Registered User Join Date: Mar 2005 Location: 10-Uh-See Posts: 5,609	Comp Cams 270 or 280 cam, finely tuned Q-jet carb, HEI ignition with MSD 6A box, 3.42 rear gears with an overdrive manual tranny, Ceramic coated exhaust manifolds (not headers), Flowmaster Delta Flow Mufflers with 2.5 inch pipes. You might get 18 or 19. For the cost to get good mileage, you could leave it like it is and come out about the same. I had a 90 3/4 ton with a TBI 350 and a 5 spd manual and 3.42 gears and got 20 on the highway and about 18 in the city. Just my .02 __________________ Matt 68 C10 stepside, LS1/700R4, TCI Engineering suspension system

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