Better Mileage out of LD8 Northstar
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Northstar Engines and System Technical Discussion Discussion, Better Mileage out of LD8 Northstar in Cadillac Engine Technical Discussion; Not too long ago I bought a 97 SLS off of my uncle after my previous car (99 Intrepid) died. ...
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    Country200711 is offline Cadillac Owners Member
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    Question Better Mileage out of LD8 Northstar

    Not too long ago I bought a 97 SLS off of my uncle after my previous car (99 Intrepid) died. That being said I went from a car that gets 26mpg/highway & 22 or 23 mpg/city to my large barge (which I love) that gets 23mpg/highway & 18mpg/city. So what I'm wanting to know is any useful information on how to get better fuel mileage out of an LD8 Northstar.

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Better Mileage out of LD8 Northstar

    That's the price you pay to drive a large, comfortable luxury sedan. You should be able to get 26 on straight highway driving (long road trips). Might check to see that your FPR is not leaking (see the Tech Tips section). Other than that, your mileage sounds about normal and about the only thing you can do that MIGHT improve it is to place an egg between your foot and the accelerator and try not to break it.
    94CaddyConcours likes this.

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    Country200711 is offline Cadillac Owners Member
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    Cool Re: Better Mileage out of LD8 Northstar

    Quote Originally Posted by Ranger View Post
    Other than that, your mileage sounds about normal and about the only thing you can do that MIGHT improve it is to place an egg between your foot and the accelerator and try not to break it.
    Hahaha, I'm 21 with a Northstar V8 that egg wouldn't make it for 3seconds lol.
    CadillacLuke24 likes this.

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    Ranger's Avatar
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    Re: Better Mileage out of LD8 Northstar

    I understand completely. Been there.

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    Country200711 is offline Cadillac Owners Member
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    Re: Better Mileage out of LD8 Northstar

    Funny thing is right now I'm wanting to get gas mileage any way I can, but in the end I plan on hot rodding the car.... 21yo we want it all LOL

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: Better Mileage out of LD8 Northstar

    You're gonna cry when you find out there's absolutely no "hot-rodding" to be done on a 1997 SLS. What you see is what you have.......mufflers will make it noisier, but the entire exhaust system ahead of them is the problem, and when you get under the car you'll see why. No MAFs, no throttlebodies, no injectors, no magic air filters, it already has a perfect CAI.........and so on.

    You have the highway package: a 275 hp engine coupled to a 3.11:1 final drive. No other gears available.

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    mhamilton is offline Cadillac Owners Connoisseur
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    Re: Better Mileage out of LD8 Northstar

    I'd follow Ranger's advice, I get a minimum of 26 mpg highway with my LD8. Regularly see 27-28 mpg highway, have gotten as good as 30 mpg. I don't think the roller cams in my 2000 are contributing that big a difference, but if I get silly with the gas the mpg quickly drops to the low 20s.

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    Country200711 is offline Cadillac Owners Member
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    Re: Better Mileage out of LD8 Northstar

    Yeah, I find that "Instant MPG" display to be handy, when I can do highway driving I get from 26-30mpg. But the accelerator is killer, I've watched it go from 26mpg to ooh about 14 or 15mpg... not that the drastic change has anything to do with my shoe size or age, of course. But as far as hot rodding a Northstar, I've found one company that has it down to an art, even been featured in Hot Rod Magazine. Cadillac Hot Rod Fabricators.
    They ain't cheap by any means, but they know how to modify a Cadi.

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    Re: Better Mileage out of LD8 Northstar

    .............the Northstars they modify can be used in Fiero kit cars and sand rails, NOT FWD Seville and Deville platforms.

    CHRFAB has been discussed in here for years - they do some great work, but unfortunately it doesn't help us FWD drivers.

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    Country200711 is offline Cadillac Owners Member
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    Re: Better Mileage out of LD8 Northstar

    Well there goes that idea... but if I ever get to build a dune buggy like I want to, I have a wild idea in mind. (Partly because my father knows someone who did it). Well I guess my Northstar will have "to do". However I have found out that I can get 26-28mph at 75mph, takes some feathery peddle work but it's possible. However, I don't even wanna think about the mileage the one time I had it over 100mph ........ Good thing my father isn't on this forum

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    Rocket88 is offline Cadillac Owners Member
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    Re: Better Mileage out of LD8 Northstar

    Damn, I wish I had gas mileage like you get! Add 3.71's to your engine and watch the mileage drop down to 22-23...

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    Re: Better Mileage out of LD8 Northstar

    Quote Originally Posted by Rocket88 View Post
    Damn, I wish I had gas mileage like you get!
    Add 3.71's to your engine and watch the mileage drop down to 22-23...
    Thats about what I get...21 to 23...depending on how heavy my right foot is.

    Jim

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    Re: Better Mileage out of LD8 Northstar

    The 2000-2003 STS, ETC and DTS, with the 3.71:1 final drive, will get 22.5 to 24.5 mpg highway on 87 octane. Perhaps 0.1 mpg more with 91/93.

    The same year group SLS, ELC, and Deville Base/DHS, having a 3.11:1 final drive, will get about 24.5 to 27.5 with the same gas.

    These are LONG TERM highway averages which depend on load, weather, ambient temperatures, tire inflation, and wind speeds; city driving will just about cut those figures ^^^ in half.

    Magic potions may vary those mileages by .03%, but they increase the price of a tank of gas by 25%. Do the math.

  15. #14
    Country200711 is offline Cadillac Owners Member
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    Re: Better Mileage out of LD8 Northstar

    I wind up doing a lot of city driving, but between the city and a feathery right foot (most of the time lol) I'm averaging about 21mpg overall. But if I could do mostly highway miles I could get that up to about 24-25 overall. I just use the instant MPG setting and do me best to keep the instant in the upper 20's, along with using 93octane. But with the way the motor runs, feathering that peddle take a LOT of restraint.

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    Re: Better Mileage out of LD8 Northstar

    I'm happy when I'm getting 18 long term average.

    I've seen 16 long term ave before.... I have no clue why though Damn Backroads!
    CadillacLuke24 likes this.

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