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  1. #21
    Quote Originally Posted by LT1GMC View Post
    Thought I might add that a wastegate is on a turbo and relieves exhaust pressure to keep the boost under control by slowing the turbo. Superchargers use a blow off valve (BOV) or a bypass valve which recirculates boost back to in front of throttle body.
    That is the basics to both a wastegate and blow off valve. Advanced is when a boost controllers and venting into atmosphere come into play. Blowoff valves are open/close only and controlled by vacuum source. a wastegate opens and closes by pressure against a diaphragm and will open to keep boost at a preset value(based on spring) when you add a boost controller it meters the pressure going to the against the wastegate spring to give you more boost than the spring is set to open at. A wastegate on a Supercharged motor will only allow the boost level you want into the motor and bleed off excess into atmosphere.

    Im going to a 18/20 impeller and will see how much low to mid range I loose. If I don’t like the loss in midrange, I will probably change the supercharger wheel and limit my RPM as a way of controlling what I want.

    Again, I don’t profess to be a know it all but every internal combustion engine I’ve worked with, it’s always better to make more power at a lower rpm than revving it to the moon.

  2. #22
    Just installed my Mini Tach, hopefully the rain holds off and I will test tomorrow.

    Im going to check rpm/top speed with 13/18 and compare with rpm/top speed with the 13/20. Im also curious to see differences in Safe Mode.

  3. #23
    1_Fast_SHO's Avatar
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    Why would you go to a 18/20 impeller ? That does not even make sense. I am not sure what you are trying to accomplish but i promise you that impeller is going to get you no where.

  4. #24
    Saum700p's Avatar
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    Quote Originally Posted by 1_Fast_SHO View Post
    Why would you go to a 18/20 impeller ? That does not even make sense. I am not sure what you are trying to accomplish but i promise you that impeller is going to get you no where.
    What experience do you have on a 13/20? What setup are you running?

  5. #25
    95.4mph FZR FZeeR's Avatar
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    If you’re going slow on 13/18 you’ll go even slower on a 13/20. You should go down to a 13/17 or 13/16.

  6. #26
    Quote Originally Posted by FZeeR View Post
    If you’re going slow on 13/18 you’ll go even slower on a 13/20. You should go down to a 13/17 or 13/16.
    I’m trying to go same speed at a lower rpm, with current setup I rarely go balls out and usually stay at about 7500-7800(Stock Tach) and run 72-74. Max speed on the 13/18 was 82ish but don’t have a tach so don’t know RPM. All speeds are GPS and I have a Riva 1 Plus (Rapid Throttle Response) with supporting mods. Water temps are 68 degrees, air temps 70-85 @ 600-800 ASL.

    Whats the Mustang in Sig run ?

  7. #27
    95.4mph FZR FZeeR's Avatar
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    In my experience if you’re running under 8500ish rpm you’re not in peak power on stock wheel or any wheel for that matter and a steeper pitch will slow you down while decreasing your rpm for sure. I think you really need to be in that 8800 to 9k area to have a steeper prop decrease rpm and push you to same or higher mph. But hey give it a shot. I think peak boost level on these wheels and the ET wheels is on the 8500 to 9k area. Any lower and you not making peak power/boost thus going slower. It’s a pretty direct relationship between rpm and boost/power on the things. I’ve run a boost gauge and seen it myself where my boost basically didn’t change on a 20 to 25 lb wheel from 9k up to 9500rpm. 25lb ET wheel was making 25 psi almost the whole way past 8500ish rpm.


  8. #28
    FZeeR has had like almost every aftermarket wheel you can think of he is 100% correct. OP it seems like you don't have a clear goal. Its hard to measure mid range increase unless you have a vbox or some sort of tool to measure improvements. You're tuning blind and your goal is not a normal one. I think the 13/20 will be better cause of your limiter being so low. There is not much else you can do besides NA cams, FX/VX TB or bigger wheel.

  9. #29
    Quote Originally Posted by FZeeR View Post
    In my experience if you’re running under 8500ish rpm you’re not in peak power on stock wheel or any wheel for that matter and a steeper pitch will slow you down while decreasing your rpm for sure. I think you really need to be in that 8800 to 9k area to have a steeper prop decrease rpm and push you to same or higher mph. But hey give it a shot. I think peak boost level on these wheels and the ET wheels is on the 8500 to 9k area. Any lower and you not making peak power/boost thus going slower. It’s a pretty direct relationship between rpm and boost/power on the things. I’ve run a boost gauge and seen it myself where my boost basically didn’t change on a 20 to 25 lb wheel from 9k up to 9500rpm. 25lb ET wheel was making 25 psi almost the whole way past 8500ish rpm.

    Hey bud, I really appreciate this feedback and information. Very informative, the other member I was going to trade impellers with had shipped so I’m going to hold off on this idea for now.


    Quote Originally Posted by d00m View Post
    FZeeR has had like almost every aftermarket wheel you can think of he is 100% correct. OP it seems like you don't have a clear goal. Its hard to measure mid range increase unless you have a vbox or some sort of tool to measure improvements. You're tuning blind and your goal is not a normal one. I think the 13/20 will be better cause of your limiter being so low. There is not much else you can do besides NA cams, FX/VX TB or bigger wheel.
    D00m, thanks for the info in this post. My goal is to not blow this thing up, I was happy with stock midrange but want more top speed. I was happy with stock low end and midrange and could live with that, the low end mid range power with Tune and 13/18 is great but I would also be happy with a 80mph ski sacrificing mid range, keeping top speed of the 13/18 but lowering the RPM. In the calmest waters I find myself cruising around at about 75mph under 8000 RPM. I will give it short bursts and run at WOT for less than 1 minute 5-10 times on a day(tank of fuel) I’m not scared of the speed, I’m just concerned with preserving my machine and it sounds like a raped ape at WOT. You are probably correct, my goal is not a normal one.

    I’m assuming you are recommending NA cams because they have a Duration/lobe separation for more midrange ?

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