Blower Overdrive for Altitude
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Blower Overdrive for Altitude

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    Default Blower Overdrive for Altitude

    Blower Overdrive for Altitude


    I am running a Littlefield 6-71 with an Enderle Birdcatcher tuned and running great at Irvine Lake on pump gas. I would like my boat to run just as hard at Lake Tahoe as it does at Irvine Lake.

    I would like to understand how much more I need to overdrive my blower to maintain the same performance.

    My question is, is there a formula or ratio for calculating overdrive for an increase in altitude?

    My current setup is:

    Pulleys: Crank 61 teeth, Blower 55 teeth, 10.9% overdriven

    Fuel Pump: 80-A
    Nozzles: 31
    Main Jet: 118

    Lynn at Littlefield Blowers suggested going to a 52 tooth blower pulley, which would put me at 17.3% OD. Jim at Enderle feels that I may need to overdrive the blower in the neighborhood of 25% and still lean it out with smaller jet and nozzle size.

    Irvine Lake is at 791 feet elevation.
    Lake Tahoe is at 6,224 feet elevation.

    Thanks in advance,

    Joe

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    Ain't Right Racin piston in the wind's Avatar
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    Quote Originally Posted by Flusher View Post
    Blower Overdrive for Altitude


    I am running a Littlefield 6-71 with an Enderle Birdcatcher tuned and running great at Irvine Lake on pump gas. I would like my boat to run just as hard at Lake Tahoe as it does at Irvine Lake.

    I would like to understand how much more I need to overdrive my blower to maintain the same performance.

    My question is, is there a formula or ratio for calculating overdrive for an increase in altitude?

    My current setup is:

    Pulleys: Crank 61 teeth, Blower 55 teeth, 10.9% overdriven

    Fuel Pump: 80-A
    Nozzles: 31
    Main Jet: 118

    Lynn at Littlefield Blowers suggested going to a 52 tooth blower pulley, which would put me at 17.3% OD. Jim at Enderle feels that I may need to overdrive the blower in the neighborhood of 25% and still lean it out with smaller jet and nozzle size.

    Irvine Lake is at 791 feet elevation.
    Lake Tahoe is at 6,224 feet elevation.

    Thanks in advance,

    Joe
    I would say 25-30 depends a lot on the blower is it stock or stripped. The higher the od the more the discharge temp raises. You shoud be ok at 30 though, Read the plugs.

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    Quote Originally Posted by Flusher View Post
    Blower Overdrive for Altitude


    I am running a Littlefield 6-71 with an Enderle Birdcatcher tuned and running great at Irvine Lake on pump gas. I would like my boat to run just as hard at Lake Tahoe as it does at Irvine Lake.

    I would like to understand how much more I need to overdrive my blower to maintain the same performance.

    My question is, is there a formula or ratio for calculating overdrive for an increase in altitude?

    My current setup is:

    Pulleys: Crank 61 teeth, Blower 55 teeth, 10.9% overdriven

    Fuel Pump: 80-A
    Nozzles: 31
    Main Jet: 118

    Lynn at Littlefield Blowers suggested going to a 52 tooth blower pulley, which would put me at 17.3% OD. Jim at Enderle feels that I may need to overdrive the blower in the neighborhood of 25% and still lean it out with smaller jet and nozzle size.

    Irvine Lake is at 791 feet elevation.
    Lake Tahoe is at 6,224 feet elevation.

    Thanks in advance,

    Joe
    You must have given them more info than you are here.
    What you are attempting to do is get back to the FINAL COMPRESSION RATIO YOU HAVE AT 791 FT. Not sure how somebody gets to that without knowing what the static compression ratio is, or what the blower is current making for boost at your current drive ratio.
    How to attempt to get back where you were, if you don't know where that is.


    Making some assumptions based on pump gas, putting your current final compression ratio somewhere around 12 to 1, I'd say Jim at Enderle is correct at 25%

    You're on your own as far a tuning the sprinkler system.



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    Last edited by gn7; 07-17-2012 at 09:59 PM.

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    Thank you piston in the wind and gn7 for the responses, I really appreciate your input.

    My primary goal is regaining the lost performance at the increased altitude. I know that it is possible to “get back to the FINAL COMPRESSION RATIO YOU HAVE AT 791 FT” by overdriving the blower, I just don't know how to calculate it or know anybody who does. I know that by simply re-jetting the current configuration for altitude, it will be a lazy dog.

    The blower is stripped, though not one of Littlefield’s “tight” race blowers. I will pull the hat off tomorrow to see which strips it has.

    Sorry for the lack of information, I was trying not to get carried away with information overload as I am still learning forum etiquette.

    I really don’t want to turn my only four days of vacation into a test and tune session, so if I may ask your opinion of what you would do in my situation; Would you try to overdrive the blower or just re-jet (and nozzles) to compensate for the altitude?

    Thanks again,

    Joe

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    Let me ask this of those of you who run blowers with mechanical injection. When you take your boat to a different lake with a substantial difference in altitude:

    1. How many pulleys do you take with you and what is the change in overdrive between each pulley? i.e., One-tooth increments? ~5%? ~7%? ~10%?

    2. How many different nozzle sizes do you take and what is the split between them?

    3. What range of jets do you take with you? Every size?

    4. Springs? Shims? Etc.?

    Thanks again,

    Joe

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    Quote Originally Posted by Flusher View Post
    Let me ask this of those of you who run blowers with mechanical injection. When you take your boat to a different lake with a substantial difference in altitude:

    1. How many pulleys do you take with you and what is the change in overdrive between each pulley? i.e., One-tooth increments? ~5%? ~7%? ~10%?

    2. How many different nozzle sizes do you take and what is the split between them?

    3. What range of jets do you take with you? Every size?

    4. Springs? Shims? Etc.?

    Thanks again,

    Joe
    The most experienced person on these boards I know of to answer this is Fiat 48.


    Remember, its not just altitude, its the altitude density.
    You can duplicate the same air at almost any physical altitude.
    Example, when we raced at Burley Idaho in June, the race days were right around 7300 Alititude density. But the physical altitude was only 4700 ft.

    I may be completely mistaken, but if you speed up the blower for to match the altitude, the jetting change will be minimal. It will be much closer as is than if you didn't speed up the blower.

    To do it right, you really need a weather station. I have never understood how anybody with mechanical fuel injection can tell what the fueling should be without one. Bad enough with carbs. With MFI, seems downright impossible.



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    Last edited by gn7; 07-18-2012 at 04:54 PM.

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    Wow.

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    Quote Originally Posted by Fiat48 View Post
    Wow.
    OK, now thats just not fair.



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    With what he understands it's a dangerous game.
    I may come up with a hypothetical but it sure won't be a suggestion. Too dangerous.

    But I did run the same nozzle and pill size.....to run 7.50 e.t with the car at Sacramento and at Fallon.
    But that is alcohol with it's wide tune band.
    12% more blower would do the job IF temperatures were typical and it was just "elevation" correction.
    Fallon is 4000 ft.

    But corrected air is the huge player here.
    Irvine at 791 foot on a 80 degree day is about 2500 ft.
    Tahoe is bad juju. 6224 ft on an 80 degree day is 9,164 ft.

    Now all you gotta do is supply the same air (somehow) and the motor kinda thinks it is at sea level....per say....but
    everything you turn takes power and you have to drive the blower faster and that is not free.
    I don't see how you can get there with "same" power.
    And pump gas? That shit?
    Rent a cruiser for the day and enjoy the waves and the traffic at Tahoe.
    Last edited by Fiat48; 07-18-2012 at 05:39 PM.

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    Default Elevation

    My Ford Lightning near sea level (LAX area) made 12 pounds of boost. On the same day at about the same temp it made 9 pounds of boost at Big Bear Lake, which is 6750 ft. It lost 25% of the boost at 6750 ft. A really low compression engine is really a dog at high elevation. Feels like they have almost zero cylinder pressure at high elevation.

    A shot of NOS really wakes things up. " Feels" like it adds more at high elevation than it does at sea level!

    On my old outboards I would add 2 degrees of timing and they seemed to run a little harder.

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    This would take care of the fuel part - Benefits of EFI - , regardless of how much boost you tune-up. Of course, if you switched completely to a Whipple setup, you could also adjust boost (bypass valve) on the fly, or have programs to run different boost at different lakes...without ever touching the motor. It depends on HOW OFTEN you want to switch lakes. If it's every year, a few times a year, you might consider at least changing to the EFI. Swapping pulleys is the easiest in the grand-scheme of your setup.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


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    Quote Originally Posted by Beer:30 View Post
    This would take care of the fuel part - Benefits of EFI - , regardless of how much boost you tune-up. Of course, if you switched completely to a Whipple setup, you could also adjust boost (bypass valve) on the fly, or have programs to run different boost at different lakes...without ever touching the motor. It depends on HOW OFTEN you want to switch lakes. If it's every year, a few times a year, you might consider at least changing to the EFI. Swapping pulleys is the easiest in the grand-scheme of your setup.




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    Quote Originally Posted by Fiat48 View Post
    With what he understands it's a dangerous game.
    I may come up with a hypothetical but it sure won't be a suggestion. Too dangerous.

    But I did run the same nozzle and pill size.....to run 7.50 e.t with the car at Sacramento and at Fallon.
    But that is alcohol with it's wide tune band.
    12% more blower would do the job IF temperatures were typical and it was just "elevation" correction.
    Fallon is 4000 ft.

    But corrected air is the huge player here.
    Irvine at 791 foot on a 80 degree day is about 2500 ft.
    Tahoe is bad juju. 6224 ft on an 80 degree day is 9,164 ft.

    Now all you gotta do is supply the same air (somehow) and the motor kinda thinks it is at sea level....per say....but
    everything you turn takes power and you have to drive the blower faster and that is not free.
    I don't see how you can get there with "same" power.
    And pump gas? That shit?
    Rent a cruiser for the day and enjoy the waves and the traffic at Tahoe.
    Thats why I said doing this without a weather station AND KNOWING HOW TO USE IT, is a crap shoot, and its the motor that will be the price tag.
    We were 4200ft(Iwas off in the previous post) at Burley and the weather stations had us at 7300+.
    You'll never EQUAL the power near sea level, specially with pump gas. The drive ratio/blower speed/power consumption and heat will stop you before you get there.



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    Well just for grins and I have so many runs sheets with info:
    Remember this is alcohol. This info is just for thinking.

    Corrected alt (Sacto) 80 degrees, 34 humidity (1851 ft corrected) ..Blower 6 under = 7.55 et 181 mph.
    Corrected alt Bakersfield (800 ft on altimeter) 85 degrees, 35 humidity (3036 ft corrected)= 7.61 et 181.67 mph. Blower 4 underdrive.

    Corrected air Fallon (4050 ft on altimeter) 75 degrees, 18 humidity (6150 ft corrected) = 7.573, 181.177 mph.
    Blower 6% overdrive.

    All this was done same pill and nozzle. 475 inches and a 6/71 blower (if that matters.)


    So....1851 foot corrected = 6 under.
    3036 ft corrected = 4 under.
    6150 ft corrected = 6 over.
    I'd have to say Irvine (smog) would be closer to Bakersfield as far as corrected air comparisons.

    So when I lost 1185 ft.....I had to drive the blower 2% faster
    and when I lost another 3114 ft I had to drive the blower 10% faster.

    Tahoe I'd lose another 10% (I bet more). 9000 ft and change.

    Hypothetical race....I'd have 25% in the blower.....and expect to be short. I'd leave fuel curve alone and
    probably only lean the barrel valve. Blowers are pretty efficient at low drives but that goes away quick as
    drive speeds go up.

    Just a hypothetical on a boring night. LOL

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