troubled mpg's

[rruss86]

i have a 1987 chevy suburban 3/4 with a 454 w/TBI it has a 400 trans and 4.10 gears... mine is used for freeway use.going to shows and cruise nights.. i have 265-35-22 its a 29.3" tire... a few people say bigger tires or new gears... any ideas what i can really do to raise my mpg...

[Wrecked1982]

my 85 k35 454-th400 is a big fuel sucker i swaped the 4.10 for a 3.73 and now im waiting to put it back together to install 31 inches tires and see what it does. but im keeping my fresh rebuilt 350 ready to take the place of the 454

[mooseknuckles]

......swap the 4:10s for 3:73s!

[Goldfinger]

I second

[jhngardner367]

You can also check on an after-market,programmable chip,for your ecm.They have some I've seen on the tv show TRUCKS!,and they are proven to help.

[INSIDIOUS '86]

STAY OFF THE GAS PEDAL! Big block + 3spd + 411 gearing = no mpg ever lol
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[donut]

x2,
I was told to feel lucky if I got 10 mpg. And that would be downhill, engine off, and a strong tailwind.

Check to see what the newer big blocks are averaging, that'll give you a goal to shoot for.

What's your mileage now? A baseline will help to determine if it's a tune issue or something else, and a course of action. No point in recommending a gear change or OD if a set of plugs would help you.

[joe231]

If you spend most of your driving on the highway, you need OD.
But like donut said, make sure your engine is tuned up. I'd also check for trouble codes and a scanner with live data can be handy...
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[nekkidhillbilly]

overdrive is about your only help

[kevinr1970]

How much of a difference is this going to make?
Not arguing; my '85 3/4t Burb has 4.10's and I am thinking 3.73's.

Originally Posted by mooseknuckles

......swap the 4:10s for 3:73s!

[rruss86]

ok so i was thinking of doing the 3.42, but my brother said 3.08 to get 2200 rpm at 65.. but if i keep the 4.10 and go with a 31" tire instead of the 29" tire.. i wouldnt have to change gears.. or would i

[tkeduk8r]

From my experience to maximize your economy, you need to match your "most cruised at" RPM with the RPM point of your torque curve when it begins to flatten. With a big block that would probably be around 1700-2300RPM I would think. Then knowing that point, use one of the available online RPM calculators to experiment with tire size, transmission final drive ratio, and ring and pinion ratio. I did alot of playing around with this a few years ago on a bet with some of my students that I couldnt get my 74 c10 to 20mpg. We did it (barely) with a well tuned 305, 2004r, 3.73's and 31x10.50 hiway tread tires and 55 mph. Id bet you could get close to 15 if your set up right. My 72 c20 w/402, TH400 and 3.54 can pull 14 at 55-60 with no load and thats with points ignition and worn 120K engine. Hope that adds some insight.
--Mike

[donut]

The other thing to consider is cost vs reward.
OD, gear change, even larger tires cost $$. How much are you willing to spend to save a couple bucks at the pump?