LS3/LS9 Fuel Economy MPG

Discussion in 'High Tech Retrofits' started by SMCZ28, Jun 14, 2013.

  1. Aceshigh

    Aceshigh Veteran Member Lifetime Gold Member

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    1st part you stated I agreed with , but not this part.
    People said that about 500hp SBC's in Corvette's before the LS7 came out......which was true.....but times have changed.

    (Link)

    Look at what the LS7 can do. If it was rated in GROSS hp like most guys rate their SBC's to make it sound cooler, it would be in the 600hp range.
    ~600hp (Gross) and 16mpg city / 26mpg highway with a 10.99 ET on Drag Radials is something no one thought was possible.......that motor is bitchen wicked.

    Of course, several other key components in the Vette help that happen as you stated, but it's obviously feasible!!!!!! :D
     
    Last edited: Jun 15, 2013
  2. Aceshigh

    Aceshigh Veteran Member Lifetime Gold Member

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    Turbo's would be the better route if you want that better efficiency when you don't want to mash the pedal.

    Obviously bigger fuel lines, bigger injectors, and better fuel pumps still will eat more fuel, but if you keep your
    foot out of it you can get better MPG's then the SuperCharged version of the same motor I'm sure.

    That's good to know. You definitely have one of my favorite 2nd gens with your new powertrain. So jealous. :cool:
     
  3. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

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    This is the big picture here.

    I'm probably one of the most MPG-conscious 2nd gen owners on the site, MPG between two 6.2l engine combos wouldn't be a big concern to me. In general, a supercharged setup is very likely to get lower gas mileage than its N/A counterpart, simply due to the frictional/parasitic loss of the supercharger when not under boost.

    If fuel efficiency is what you are after, a twin-turbo 4.8 with small turbos that spool up super-fast is probably the way to go. This is something I've casually thought about as a cool project.
     
  4. 70 gsconvt

    70 gsconvt Veteran Member

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    Fuel economy??? Are you kidding me??? We don't get into this sport/hobby, build mega-horsepower engines and then worry if we're going to meet CAFE standards when tooling around.

    Drive it like you stole it. Just buy your wife one less set of diamond earrings and put the money towards 93 octane fuel. :)
     
  5. SMCZ28

    SMCZ28 Veteran Member

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    I figured the MPG would cause a stir. :p I was just giving myself something to think about and if you can get an advantage why not if you're going through all that trouble of building the engine. If I ever buy a 240SX I'll probably leave the FI to that instead or heck you can fit an LS in there too lol! Including if it is just going to over heat to much and slack off after a certain amount of time, but I do have to do more looking into auto x and track but it is for sure what I want to do, I've always wanted to make the car handle to shut people up that say "Oh your car is fast in a straight line but can't take a corner." We have enough muscle cars to go straight to take the crown and I like to be different. I looked at Protour73's and Mary's specs to get an idea, it seems 400-500 hp is enough for auto x and now I have an idea about track which I thought would be 500-600 hp. I guess it's my decision to choose between the LS3 block or LS9 block, it wouldn't be so much of a decision if the LS9 block didn't use a 1mm bigger bolt for the heads and the price being 1,500 more but I guess go big or go home, the features do sound nice and it's a good thing my gf is a car girl and a gamer girl. ;) I just have to buy her a video game she doesn't want jewelry.
     
    Last edited: Jun 15, 2013
  6. Aceshigh

    Aceshigh Veteran Member Lifetime Gold Member

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    I spent $10,000 for a modern drivetrain to get more power WITH better efficiency...... and I don't even drive it. :crazy:
    MY GOAL!!!!......was a Pro-Touring car I could take on adventures around several hundred miles as a daily driver amidst rising gas prices.

    Instead of filling the towel wearing arabs coffers with more money, I spent several times that on better vehicle equipment is how I rationalize it.

    Then........I did it AGAIN with my 442 getting an LSx./T56 .....LOL
    I think I just like to spend money on cool toys and then they sit.
    The real beauty tho......is everything is paid for in cash. So it can sit until I re-spark my interest if I want it to.
     
    Last edited: Jun 16, 2013
  7. mgs1971

    mgs1971 Veteran Member

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    If you have the financial wherewithal to afford a build like this why are you worried about fuel mileage or $500/yr? Build it, have fun with it and tell those of us that can't afford it how much fun it is to drive and how we can do it cheaper based on the experience and knowledge you gain while building it. Folks like me appreciate folks like you being the pioneers into the next phase of hotrodding.
     
  8. Protour-Camaro

    Protour-Camaro Veteran Member

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    You can't compare the factory engine specs....The OP is looking for best MPG with equal performing engines (~ 600hp builds). I get that a factory LS3 vs a factory LS9 the less performing LS3 will get better MPGs. If you compare equal horsepower builds, the facts will change.
     
  9. Air_Adam

    Air_Adam Veteran Member

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    Turbo LS would probably be the best route if you want lots of power and decent fuel economy when you keep your foot out of it. A friend of mine built a turbo LS engine, 402ci based on an aluminum LS2 block, and with a very small turbo (62mm iirc) it made well over 450 rwhp and 500 ft-lbs at the rear wheels, on something like 6-8psi, even before the tune was completed. I'm not sure what its at now, likely considerably higher. Thing is - if you look at the engine's mechanical specs, its a very mild motor. Very small cam, stock LS6 intake, iron exhaust manifolds, 9:1 or 9.5:1 compression (can't recall which) and T56 behind it, with a 3.23 or 3.42 geared 12-bolt.... when the car's tune is completed, he's having problems with that and other little things right now, it should get excellent mpg if he can drive it without a heavy right foot.
     
  10. SMCZ28

    SMCZ28 Veteran Member

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    Yea that's why I asked if anyone had a modified LS3 I could compare to with MPG hopefully one with close to the same power but the chart does help since I did already compare MPG to an LS3 corvette vs an LS9 one.


    I guess it does depend on the build, I hear people say they get less MPG than N/A and others that say they actually get better that or either they have their foot in it just a little more or their gear changes aren't that great. I don't want to tick anyone off that has FI but I had an instructor that said "Forced induction is only for people who can't build an engine." it made sense to me but he is REALLY old style guy and probably doesn't realize how FI can help, I've learned how they can help by looking some so my thought on it has changed mostly but I really don't know much about FI, I have grown fond of the spool noise and blow off noise. :p
     
    Last edited: Jun 16, 2013

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