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Old 05-09-2011, 09:28 AM
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1988 Gmc 454

Alright Guys,

Gotta brag a little bit. I have been wanting a 454 in ANYTHING since I was 17 and finally got it (now 28). Shes not pretty but is reliable, and has SO much power. Of course everyone complains about the gas mileage, but so far I have only averaged about 7MPG. I guess my real question is how do I get it in the 10-13MPG area. I don't raw dog it, I am not pulling a trailer with it, just picking the kids up from school and doing errands. Do K&N air filters and Lucas gas treatment actually help or are they useless? If y'all need the specs on the tranny and rear end I can pull them. I know a tune up wouldn't hurt, just seeing if anyone has some helpful hints, like putting the max air pressure in the tires(my brother swears by this trick in his 2004 Silverado) but i have no clue if he is just delusional or if it actually helps. Thoughts??

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Old 05-09-2011, 11:39 AM
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It all helps to a certain degree. re-work the distributor, a different carb and manifold, freshen the motor to make sure it is operating at full capacity, overdrive transmission, you should get at least 12 mpg....
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Old 05-09-2011, 01:04 PM
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Quote:
Originally Posted by jimbobhog
Alright Guys,

Gotta brag a little bit. I have been wanting a 454 in ANYTHING since I was 17 and finally got it (now 28). Shes not pretty but is reliable, and has SO much power. Of course everyone complains about the gas mileage, but so far I have only averaged about 7MPG. I guess my real question is how do I get it in the 10-13MPG area. I don't raw dog it, I am not pulling a trailer with it, just picking the kids up from school and doing errands. Do K&N air filters and Lucas gas treatment actually help or are they useless? If y'all need the specs on the tranny and rear end I can pull them. I know a tune up wouldn't hurt, just seeing if anyone has some helpful hints, like putting the max air pressure in the tires(my brother swears by this trick in his 2004 Silverado) but i have no clue if he is just delusional or if it actually helps. Thoughts??
Is the engine controlled by the computer, and do you have smog inspections in your area?

In any event, you can open up the exhaust system, add a cold air intake set up of some sort so the engine isn't breathing hot underhood air, a chip will help if it's computer controlled, there are cams and intakes that are smog legal- but it depends on what kind of legal restrictions you may have to deal with.

Do a search for "hypermiling" for ways to save gasoline.
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Old 05-09-2011, 02:46 PM
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no emmisions testing down here in LaGrange Ga. This thing still has the original Cat on it with dual exhaust breaking out past the cat.
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Old 05-09-2011, 03:10 PM
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Tune up would be a good place to start. I Seafoam my engine to remove deposits on the valves. 88? Carburated right? Adjusting the tire pressure does help. I run 35psi min. in my minivan. Overdrive trans. should help. That 454 is only rated at something like 190hp if i remember correctly.
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Old 05-09-2011, 03:19 PM
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Keep in mind some things may help mileage a little but can make your truck dangerous in some situations. Over inflating the tires is just one of those, it may help mileage some but get it in the wet and see how it steers and or brakes. Some hyper-milling tips are not only dangerous, they can be illegal.
Your excitement for getting a 454 will quickly be diminished by $4.00 gal gas. Some of the engine breathing changes can help but they usually lead to you running it harder negating any fuel savings. It is a brick on wheels.
Find something smaller to install the engine in.
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Old 05-10-2011, 12:39 AM
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I know theres a ton of people that dont believe it but I just removed my flex fan and converted to a 16" 2500 cfm electric fan for my 454 and it gave me 2-3mpg increase plus adjusting the timing helped also.
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Old 05-10-2011, 02:35 PM
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Originally Posted by chevyrestore
I know theres a ton of people that dont believe it but I just removed my flex fan and converted to a 16" 2500 cfm electric fan for my 454 and it gave me 2-3mpg increase plus adjusting the timing helped also.
If the changes were made at the same time, I would strongly suspect the timing change was the difference. Even an electric fan has to cause the alternator to work harder- no free lunches there, and in fact a properly working thermostatically controlled clutch fan has been shown time and again to be among the thriftiest ways of cooling the engine.
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Old 05-10-2011, 05:00 PM
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Originally Posted by cobalt327
If the changes were made at the same time, I would strongly suspect the timing change was the difference. Even an electric fan has to cause the alternator to work harder- no free lunches there, and in fact a properly working thermostatically controlled clutch fan has been shown time and again to be among the thriftiest ways of cooling the engine.

An electric fan does not operate enough to be a major strain. If you maintain a highway (25mph+) speed the fan never even thinks to cycle until it has sat for some time. Some of the more advanced 2 stage fans will draw current even when driving but I don't know many people who use them. I have seen electric fans net pretty high HP gains on other cars.
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Old 05-10-2011, 10:21 PM
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I'm planning on going the electric fan route on my 454 also. Mine gets horrible mileage, but its not the mileage thats causing me to switch to the electric fan - its the dead fan clutch and the fact that i've had too many people tell me that replacement fan clutches dont last very long.

I bet 7-8mpg is about all I get. 454 w/qjet, stock qjet manifold, stock HEI, TH400 trans, 14 bolt rear with 4.10 gears. GAS HOG let me tell you.

An 88 454 should be fuel injected but probably still has a TH400 trans. I dont think the 4l80e was used until 89 or 90.

I think I need to work on my distributor a little, and tune the carb. 10-12 mpg would be nice. I already have headers and 2.5" magnaflow mufflers, no cats and only 36" of exhaust on each side. Exhaust pressure shouldnt be a problem.

A free flowing exhaust should help you and maybe change the oxygen sensor.
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