another pick a impellar question ?
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another pick a impellar question ?

  1. #1
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    Default another pick a impellar question ?

    Dyno sheet reads 797hp @ 7200 rpm on motor. Boat turns 6400 on the motor & 7300 on the bottle. I want to leave quicker & lose a few rpm on top . Running a b-c now. What do ya'll suggest ? Boats a lite weight cp tunnel.
    Last edited by cpjet; 07-27-2010 at 08:12 PM.

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    B1 Racing cs19's Avatar
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    Id like to see the dyno sheet.

    There sometimes has to be a sacrifice when your trying to get it to run good both on and off the bottle, especially if your running alot of nitrous. I'm thinking you may need something a little bigger if you run it on the bottle all the time, thats if the power goes somewhat flat before peak power which it likely does?

    In the end I'd look at keeping it below peak power on the bottle if at all possible. Your peak power RPM number shouldnt change on the bottle vs. NA, lots of people miss that and rev them up to high and your going backwards at that point usually. Right now your only 100 over thats not too big of deal but like I said earlier if the power is real flat upstairs, like within 10 HP at 300 Rpm below peak, a bigger impeller is going to help you most likely.

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    Headed to work on geaveyard shift.....see what I can do about posting dyno sheets tomorrow......Thanks Chris

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    Quote Originally Posted by cs19 View Post
    Id like to see the dyno sheet.

    There sometimes has to be a sacrifice when your trying to get it to run good both on and off the bottle, especially if your running alot of nitrous. I'm thinking you may need something a little bigger if you run it on the bottle all the time, thats if the power goes somewhat flat before peak power which it likely does?

    In the end I'd look at keeping it below peak power on the bottle if at all possible. Your peak power RPM number shouldnt change on the bottle vs. NA, lots of people miss that and rev them up to high and your going backwards at that point usually. Right now your only 100 over thats not too big of deal but like I said earlier if the power is real flat upstairs, like within 10 HP at 300 Rpm below peak, a bigger impeller is going to help you most likely.
    Yeah, what he said.

    S CP

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    Quote Originally Posted by Sleeper CP View Post
    Yeah, what he said.

    S CP
    Yeah what he said!!!!
    No matter how good she looks , someone is tired of her shit!

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    Chris , here it is......if I understand correctly then I'm within 15HP at 300rpm under peak , so you think I would benifit from a bigger impeller ?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	dyno 048.jpg 
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    Last edited by cpjet; 07-28-2010 at 07:58 PM.

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    Assuming your set-up is close to this extended chart maybe an "A/B"
    depends on where you think you stack up. How big of a shot are you running ?

    " I'd look at keeping it below peak power rpm on the bottle if at all possible "
    From what Chris wrote earlier. Nos engines (most anyway) typically make max peak Nos horsepower 100-300 below the N/A peak. I've seen many many at 200 rpm below. I'd use an A/B cut to start out with and see what it does. I've always set-up ours (since '91) to run just a tad under peak N/A hp rpm when on the Nos. Some people use the over rev theory, I've never liked that approach.

    S CP
    Last edited by Sleeper CP; 07-28-2010 at 02:57 PM.

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    Quote Originally Posted by Sleeper CP View Post


    Assuming your set-up is close to this extended chart maybe an "A/B"
    depends on where you think you stack up. How big of a shot are you running ?

    " I'd look at keeping it below peak power rpm on the bottle if at all possible "
    From what Chris wrote earlier. Nos engines (most anyway) typically make max peak Nos horsepower 100-300 below the N/A peak. I've seen many many at 200 rpm below. I'd use an A/B cut to start out with and see what it does. I've always set-up ours (since '91) to run just a tad under peak N/A hp rpm when on the Nos. Some people use the over rev theory, I've never liked that approach.

    S CP
    interesting choice, based on this chart,why wouldn't you pick
    the closest cut based on the intersecting lines of HP and RPM?

    ie 7200 rpm and 800HP looks like a C cut to me.
    Not trying to be a smart a$$ , just curious??

    as an example, Jack recommended an A cut for my application of 800HP
    and 6200 RPM, granted a little on the small side but he said he can
    adjust it once I run it and see what it actually spins.

    EDIT BTW thanks for the extended chart
    Last edited by Outlaw; 07-28-2010 at 03:19 PM.
    #55

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    Quote Originally Posted by Outlaw View Post
    interesting choice, based on this chart,why wouldn't you pick
    the closest cut based on the intersecting lines of HP and RPM?


    ie 7200 rpm and 800HP looks like a C cut to me.
    Not trying to be a smart a$$ , just curious??

    as an example, Jack recommended an A cut for my application of 800HP
    and 6200 RPM, granted a little on the small side but he said he can
    adjust it once I run it and see what it actually spins.

    EDIT BTW thanks for the extended chart

    Why wouldn't you read the 1st post? :

    " I want to leave quicker & lose a few rpm on top . Running a b-c now. What do ya'll suggest ? "

    Assuming it's more important for him to lose a few rpm on the top if he runs a straight C cut what do you think will happen when he hits the button?

    He needs to do an overlay with his observed HP and the corrected, plot them on the chart and see where they are. Something like this:


    S CP
    Last edited by Sleeper CP; 07-28-2010 at 04:34 PM.

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    21 Daytona Outlaw's Avatar
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    Quote Originally Posted by Sleeper CP View Post
    Why wouldn't you read the 1st post? :

    " I want to leave quicker & lose a few rpm on top . Running a b-c now. What do ya'll suggest ? "

    S CP
    sorry just got caught up in the chart
    #55

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    Quote Originally Posted by Outlaw View Post
    sorry just got caught up in the chart


    I can assure you I've never done such a thing

    S CP

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
    fast is the other half.
    " A Government big enough to give you everything you want is big enough to take away everything you have"

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    Running a 250 shot

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    here's one of uncorrected data , you may have to click it to enlarge...
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    Quote Originally Posted by cpjet View Post
    here's one of uncorrected data , you may have to click it to enlarge...
    Did you notice the chart at 650hp at 6,400 is a B/C ?

    So just follow the chart for what rpm you want one the Nos.

    I need to go back and compair the A/B cut to your uncorrected numbers.

    S CP

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
    fast is the other half.
    " A Government big enough to give you everything you want is big enough to take away everything you have"

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