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Thread: Underdriving supercharger

  1. #1
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    Underdriving supercharger

    I'm going to have to use my Supercoupe as a daily driver for a while and I was wondering if they make pulleys to underdrive the supercharger so I could get better gas mileage and less wear. I've considered pulling the blower belt off completely, but it sure would be nice if I could meet in the middle and get around 8 psi. I plan on upgrading to an s-trim blower by the way (if I can find one).

  2. #2
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    Quote Originally Posted by kenshi
    I'm going to have to use my Supercoupe as a daily driver for a while and I was wondering if they make pulleys to underdrive the supercharger so I could get better gas mileage and less wear. I've considered pulling the blower belt off completely, but it sure would be nice if I could meet in the middle and get around 8 psi. I plan on upgrading to an s-trim blower by the way (if I can find one).
    If you still have the stock 89-93 pulley on your car find a 94/5 pulley. There a little larger circumference wise and will underdrive your blower some.
    SCCoA Member # 490 since 1997
    1995 SC (five speed) [email protected]
    Best 60' 1.7489

    1994 SC (automatic) [email protected]
    Best 60' 1.8539 On a stock long block with bolt on's
    http://www.sccoa.com/forums/garage.p...ge_view&id=638

  3. #3
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    But like I said, I'm switching to an s-trim (94-95) blower, so it'll already have that pulley and still produce full boost. At least the newer blower will produce less drag for that reason and probably better gas mileage, but I would like to step it down another notch for daily driving.

  4. #4
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    Quote Originally Posted by kenshi
    But like I said, I'm switching to an s-trim (94-95) blower, so it'll already have that pulley and still produce full boost. At least the newer blower will produce less drag for that reason and probably better gas mileage, but I would like to step it down another notch for daily driving.

    Well, if you drive it reasonalbly, as in shift around 2500 RPM and accelerate modestly (not dog slow) you will only develop about 8 lbs of boost anyway, At least thats what my 94 does. I guess I might have better control because of the 5-speed, but shouldn't it be even easier on automatics?

    I wouldn't take the SC belt off. It's much slower than a NA 3.8 due to the blower being in the airpath. I was completely disappointed with the performance of mine when I replaced the belt and had to go to the store without one on because they gave me the wrong one first....

  5. #5
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    Let me get this right....your going buy an S port blower because it's more efficent, and then underdrive it because you don't want to use too much gas ?

    Sorry but that makes no sense, it's only more efficent under boost. Save your money and keep the blower you have and get a good dyno tune instead. If your really concerned about the gas consumption, remove the supercharger belt and wire the bypass valve open. Then you can run the cheaper 87 octane fuel. If you want to make the car into an even slower lump of steel...pull the octane plug.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat.............10.597 @ 135.78

    My Garage

  6. #6
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    Yea, what David said. The newer blower should give you '20 HP', to make more power you need more fuel. But you want to lower the boost to save fuel?!

  7. #7
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    Quote Originally Posted by RustyUL
    Well, if you drive it reasonalbly, as in shift around 2500 RPM and accelerate modestly (not dog slow) you will only develop about 8 lbs of boost anyway, At least thats what my 94 does. I guess I might have better control because of the 5-speed, but shouldn't it be even easier on automatics?
    I have a 5-speed as well.

    I wouldn't take the SC belt off. It's much slower than a NA 3.8 due to the blower being in the airpath. I was completely disappointed with the performance of mine when I replaced the belt and had to go to the store without one on because they gave me the wrong one first....
    Oh I've already driven it around without the blower belt since my coupler is shot. (That's why I'm replacing the blower in the first place. I could fix it, but it's a good excuse to upgrade.) It actually feels close in acceleration to my LX. That's still pretty freakin slow though.

  8. #8
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    Quote Originally Posted by David Neibert
    Let me get this right....your going buy an S port blower because it's more efficent, and then underdrive it because you don't want to use too much gas ?

    Sorry but that makes no sense, it's only more efficent under boost. Save your money and keep the blower you have and get a good dyno tune instead. If your really concerned about the gas consumption, remove the supercharger belt and wire the bypass valve open. Then you can run the cheaper 87 octane fuel. If you want to make the car into an even slower lump of steel...pull the octane plug.

    David
    Like I said, I've considered running it without the belt and have already done it some, but it's slow as hell. With the blower, I can at least pass people on the highway reasonably. Twelve psi is extreme for casual driving though. Yes, I can go light on the throttle (well... I can try), but the blower is still spinning faster than it needs to, causing more load on the engine and wearing itself out faster. I was just looking for a solution where I could meet in the middle when I'm going to work or whatever and easily change back to full boost for the weekends. I know I'm not the first to employ more moderate settings for casual street use than spirited driving or racing. Hell, the thing that gave me this idea was a V8 guy saying he was adding a blower to his setup and running 6 psi on the streets and 9 psi at the track.

    Anyway, I doubt they make any aftermarket underdrive pulleys since I'm apparently the only Supercouper to consider using one (and I wouldn't spend much on it anyway), but I figured perhaps one of the other M90 applications (one of the GM cars maybe) came with a larger pulley that could be bolted on. Hell, if I can spend $20 to $30 on Ebay for a pulley that will give me maybe 1 more mpg and a few thousand more miles on the life of my blower bearings, then I'll be damned if it isn't worth it. If there's not one, I'll just leave the belt off, deal with the sluggishness, and put it on when I'm in the mood, or leave it on and try to lighten my foot. I hope I've explained my reasons well so I can get an answer to my question.

  9. #9
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    Cant juice a turnip.

    I would just save the hassle and lighten your foot. the SC's 8:1 compression is really nice for boost, but makes the efficiency you seek impossible (in my opinion).


    Tyler (Tickler)
    1990 SC

  10. #10
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    Unless you push the throttle hard enough to drop the vacuum and close the bypass valve, the supercharger isn't under any load and it only consumes about 1 HP.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat.............10.597 @ 135.78

    My Garage

  11. #11
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    It's not hard at all to dive without going into boost with a 5 speed. I usually don't go into boost at all unless i want to pass some one quickly. Just lighten your foot and shift right. I usually shift @ just over 2000 rpm for fist then with less rpm as i get going. You can tool around in fifth at around 1000 rpm without lugging the engine. If you want to save on gas learn to drive a standard and don't push the gas so much! Take off slowly and keep your speed down.

  12. #12
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    Quote Originally Posted by ipeefreely
    It's not hard at all to dive without going into boost with a 5 speed. I usually don't go into boost at all unless i want to pass some one quickly. Just lighten your foot and shift right. I usually shift @ just over 2000 rpm for fist then with less rpm as i get going. You can tool around in fifth at around 1000 rpm without lugging the engine. If you want to save on gas learn to drive a standard and don't push the gas so much! Take off slowly and keep your speed down.
    That's kind of what I was thinking..........I drive my 5 speed around everywhere and hardly ever get into boost. It's actually fairly easy. But then again.......I may be considered an old fart now a days........lol

    Can anyone show me where this octane plug is..........I want to make sure mine is even on my car.

  13. #13
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    Quote Originally Posted by LIL QIK
    Can anyone show me where this octane plug is..........I want to make sure mine is even on my car.

    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat.............10.597 @ 135.78

    My Garage

  14. #14
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    If you remove the blower belt, you don't have to pull the octane plug to run regular unleaded, do you?

  15. #15
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    Quote Originally Posted by kenshi
    If you remove the blower belt, you don't have to pull the octane plug to run regular unleaded, do you?
    No you don't need to remove the plug if the SC belt is off or if the bypass valve is held to the open position.

    David
    1991 SC AOD 4.2..2.3 Whipple..........10.910 @ 125.61
    2016 SRT Challenger Hellcat.............10.597 @ 135.78

    My Garage

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