85 fuel economy and IMPROVEMENT?

[Kenneth W Larew]

Hello all,
I have an 85 1/2 ton with a 350 crate motor...pretty much stock ( I believe it has an aftermarket intake labled "summit" ) and a 4 barrel Holley carb. My son is inheriting this from my brother who rebuilt it from the ground up. The question is:
If one were only interested in improving fuel economy for a high schooler on a high school budget...mine lol, what would be thy he best way to improve fuel economy. I know power improvements and fuel economy often go together. But just to be clear in case of a subtle compromise. We are only interested in improving fuel efficiency.. if power comes as a result, so be it.
Please advise
This has been a great forum so far!

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[yevgenievich]

Driving style and carb tuning with wide band. Advance timing tuning for cruise scenario

 

[shiftpro]

Skinny tires with high air pressure.

Raising compression is one of those things that increases performance and economy. But if you need to run premium gas then it cost more and your back to pissing in the wind. And raising compression means domed pistons and proper squish zone after milling the decks down. So that's a bunch of $$ and time.
In my world the ultimate high mileage would be 11 to one compression running propane, bigger exhaust valves and bowls hogged out, symmetrical flat tappet cam with higher lift and low duration.
Proper gears of course for intended purpose.
Sorry my 2 bits aren't much help... I can't think of much more than what yevgenner just said above, other than losing any and all emissions foof.
Dual exhaust will help a hair.

 

[HotRodPC]

That Summit intake is a China made ProForm. I've heard stories of the ports not lining up with the head runners and have vac leaks. That doesn't mean they all do. But make sure there is no vac leaks at the manifold on all 4 sides. The other things have been suggested already. Well tuned QJet and properly timed and tuned all while keep your foot out of it which is hard to do. If it's hard for me, then it's hard for a teen for damn sure.

 

[fussfeld]

1) i don't think a high schooler would/should be doing that much driving, so perhaps the question is moot, IF i may be so bold to say so sir?
In other words, the money spent on improving mpg will possibly never be recouped (at least not during the course of a high-school career), since it would likely take thousands and thousands of miles to see a return.


2) What's the current mpg and rear axle ratio?

 

[1987 GMC Jimmy]

A taller rear axle ratio, a switch to Quadrajet, a compression bump from 8.5 to 9.5:1, good tire pressure, headers and no catalytic converter, and not driving it like a hellian. I wouldn’t crack into the short block. The most I would fool around with internals are heads and head gasket.

The concerns about mileage vs. investment return are valid, but I’m curious to know how much mileage the average teenager puts on a vehicle outside of commuting to school. I’m thinking quite a bit these days, but I guess there are still a number, however a dwindling one, of helicopter parents out there or ones that can’t afford to have a kid who’s out cruising the roads all day and night. My little brother runs the roads constantly in a diesel guzzling POS, and I drove a lot, too, but I lived three and a half hours from school. Almost all the mileage racked up was to get between home and school. All my friends lived in the same building as me or next door back then so that was never an issue. I drove a Volkswagen Shitta back then that got really good fuel economy (45 mean mpg) so it wasn’t unfeasible to drive 30,000 miles a year. I drive half of that now, and fuel is cheaper than it was a few years ago for the moment so my Caprice (21 mean mpg) wasn’t a big switch in terms of expenditure. Actually, in the past nine months I’ve probably spent a little less in fuel than I did when I was 16-18 because of even less driving.

 

[HotRodPC]

Not sure why everyone always thinks taller gear ratio helps fuel mileage. Nope it always doesn't. It will next to never help City mpg. It MIGHT help hwy mpg but not always and if so maybe so minimal that depending on how much you drive hwy and the low improvement, it might take 2-3 years to recover the cost of the gear change, not to mention the loss of City mpg to factor in making it even longer to recover.

I know someone who went from 4.10's to 3.21's in a 1 ton and they didn't gain ****. But they did lose the ability to tow worth a damn with the engine struggling and eating up clutches like a fat kid eating birthday cake. Why? Because now the clutch has more strain put on it.

His analagy was with the granny gear, he didn't need 4.10's, he could take off in granny gear and have 3.21's for better mpg. Didn't happen. No improvement whatsoever, just a loss to city mpg since he still doesn't use granny 1st.

 

[shiftpro]

Not sure why everyone always thinks taller gear ratio helps fuel mileage. Nope it always doesn't. It will next to never help City mpg. It MIGHT help hwy mpg but not always and if so maybe so minimal that depending on how much you drive hwy and the low improvement, it might take 2-3 years to recover the cost of the gear change, not to mention the loss of City mpg to factor in making it even longer to recover.

I know someone who went from 4.10's to 3.21's in a 1 ton and they didn't gain ****. But they did lose the ability to tow worth a damn with the engine struggling and eating up clutches like a fat kid eating birthday cake. Why? Because now the clutch has more strain put on it.

His analagy was with the granny gear, he didn't need 4.10's, he could take off in granny gear and have 3.21's for better mpg. Didn't happen. No improvement whatsoever, just a loss to city mpg since he still doesn't use granny 1st.

This ^^^^^^^

 

[HotRodPC]

I'll also add, the reason GM put taller gears in the 80's trucks, like 2.56's and 2.73's, wasn't for fuel economy. They'd hoped that happend too, but the main reason was emissions. The gubment put fleet requirements on the manufactuers. Both mpg and emissions output on average of their entire fleet for 8599 GVWR and lower. So the ones that ran a bit dirty, had to have some that ran cleaner to bring the average amount of pollutents down. They did this by running taller gears and keeping the rpms down. This is also why the Feds started the 55mph speed limit. Notice the 8600 GVWR 3/4 ton trucks didn't have to have Cats and still had the lower 3.73 and 4.10 gears ratios. I don't think the 3/4 and 1 tons got Cats until 1987. The half tons started getting Cats in the 70's sometime.

 

[fussfeld]

i know higher gear does not necessarily mean better mpg, but lower rpms generally does mean better mpg.

 

[CSFJ]

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All the fuel mileage you'll ever need.

 

[Rusty Nail]

Drive something else.
MANY squares achieve better mileage than BRAND NEW trucks...it's still a truck and it's made of steel.

Think plastic four cylinder...or a THREE.

You're wasting effort
Not ever going to match a high school student's "budget", not even with a 6.

Seriously, park it and save her for later.

 

[SquareRoot]

Park it and consider the bus or better yet, homeschooling?

 

[Kenneth W Larew]

That Summit intake is a China made ProForm. I've heard stories of the ports not lining up with the head runners and have vac leaks. That doesn't mean they all do. But make sure there is no vac leaks at the manifold on all 4 sides. The other things have been suggested already. Well tuned QJet and properly timed and tuned all while keep your foot out of it which is hard to do. If it's hard for me, then it's hard for a teen for damn sure.

Thanks to everyone for all the input this far! We did check the intake for leaks when we put a new gasket on....there were some before, not now. I'll look into a Q-jet, and I think since an intake is already in place I may as well get some headers to go with it. What has always made sense to me is by focusing on improving air flow you improve the operational efficiency and fuel efficiency of the motor. It's been a while since I've worked on older engines and carbs so I have a lot to learn. I don't know if sight moderators are reading but i think there is enough interest in topics such as this to warrant a separate "topics" section. Gas is getting pricey ...and let's face it these things guzzle gas.
For the time being, can anyone share actually calculated mpg and set ups for their 350 engines?

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[Kenneth W Larew]

Drive something else.
MANY squares achieve better mileage than BRAND NEW trucks...it's still a truck and it's made of steel.

Think plastic four cylinder...or a THREE.

You're wasting effort
Not ever going to match a high school student's "budget", not even with a 6.

Seriously, park it and save her for later.

That's all a very good point. From a pragmatic perspective you are 100 percent correct and I totally agree. There are family issues though...lol.

My Father grew up around hot rods and has a strong affinity for chevy 350s. His father owned a junk yard so he grew up wrenching...had the coolest cars in high school. Regardless, he wants his grandson to share the same experience. So he warmed my son up to the idea and helped pay for the truck. In that scenario...I don't think a cavalier and tarping the truck up for 7 or 8 years is going to go well...and having two vehicles to operate and maintain is simply out of the question. So I think I'm better off just trying to get the most out of this till college...then we will probably tarp and buy a dud.

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