Why no boost?

Discussion in 'PSI Superchargers Tech Questions' started by superpro453, Sep 3, 2020.

  1. superpro453

    superpro453 Member

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    Asking for a friend....

    Recently upgraded an old Mooneyham 10-71 to a new TBS Hi-Helix 10-71 on a 509ci BBC in a FED.

    Old blower peaked out at 18lbs boost. New blower gave 18lbs boost at 12.5% overdrive. Increased overdrive to 20%, and now it hits 18lbs boost at around the 60ft mark but basically flat lines thru the run (peaks at 19lbs).

    He has calibrated the boost pressure sensor and it is accurate.

    Any ideas why no more boost?

    Martyn
     
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  2. Ray Hadford

    Ray Hadford New Member

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    What happened to the performance in the ET & MPH area?

    During this lull in racing I have been watching YouTube stuff With Gale Banks. By the way that guy is a real wizard on this subject. Really fun to watch and listen to. He has worked with this stuff for 50 years. He is in his late 70s and still inventing and building very high performance vehicles and innovative instrumentation. He is very patriotic and does extensive innovation for our military.

    He and his engineering crew have developed an instrumentation system and smart gages for the high performance world. Unfortunately for us his gage system is based on the computer system used in late model vehicles that uses the information available on the OBD network that is in every vehicle today. He also adds some sensors. I would love to some how link this to my Race Pak stuff.

    His studies for supercharged and turbo applications on diesels has shown that boost is not the only thing you want to live and die by. He has also built a number of gas, diesel and methanol engines over the years for many high performance applications. He has also consulted for NASCAR, Indy and Bonneville.

    Yes ... your compressor needs to be in good condition and capable of creating boost. Various types of compressors have varied levels of efficiency. High helix roots, centrifugal, screw , and turbo. The screw , centrifugal and turbo are at the top. Roots at the bottom. When things are working properly Banks has actually measured a drop from the start boost pressure as the dyno pull progresses with an an increase in MAD and an increase in horsepower and torque output through the rpm range. Peak boost measurement is an alive or dead type test. Progressive measurement through the run or pull tells the real story. As the RPM goes up the compressor needs to keep up with the motor's air requirements and the air fuel ratio needs to match.

    Banks has instrumented a calculated MAD Mass Air Density , which is really what we are all trying to increase with our power adding devices. Boost is just a piece of that equation. Banks has illustrated this with boost and intercooling studies. Methanol increases MAD in our drag cars.

    A high helix blower's claim to fame is the ability to pump more air, while not heating the air as much and requiring less power to do it, thus increasing the MAD. It has a higher efficiency rating than a standard helix rotor set up.

    In reality a high helix blower setup should increase performance, and at the same time your boost psi may drop some , through the run , as the Mass Air Density goes up. ( this is per Gale Banks studies... watch some of his videos, which are based on his Duramax monster truck engine build testing, Bonneville and Pikes Peak testing)

    I would like to see blower dyno data comparing rpm , CFM output and air temperature between high and standard helix 8-71 blowers. It is possible that a high helix blower needs to spin faster to get to it's performance sweet spot. An overdrive % change may be necessary. I have no experience in that area. For sure jetting must be richened, possibly up to 15% . Richening will also increase the MAD to a point which will reduce the instrumented boost. I am sure this is what has caused Top fuel teams to construct Supercharger Dynos.

    I have a new Blower Shop high helix 8-71 sitting in It's shipping box, ready to go on my dragster. I will very likely experience some of the same issues that you are experiencing, as I replace my standard helix 8-71. Our motor is a 388 cu in SBC 20 pounds of boost Race Pak measured at 15 over . We turn the motor 8400 rpm. Our boost data , standard helix, is within a pound through the rpm range. We have run 6.70 and 204 with a 1700 pound car, trans brake glide. The new blower is intended to perk that up a bit. Hopefully that will happen.

    You are the second person on this forum with similar high helix issues.

    Let us know what you find.

    It would be nice to hear from a blower expert.

    Ray H.
     
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  3. Mike Canter

    Mike Canter Top Dragster
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    Make sure that when pedal to the metal the butterflies are in fact all the way open. Also what sealing method between the blower and manifold? Have you checked your manifold blower mating surface to make sure it is square so it is sealing? Are you using Prism spray in your blower before every run? Sometimes on a new tight blower it is possible that the strips get damaged on initial startup or run especially if Prism spray not used. When you tightened the blower down on the manifold did you checked that you could turn the blower blower without it binding?
     
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    Last edited: Sep 5, 2020
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  4. superpro453

    superpro453 Member

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    Mike - butterflies are pretty much all the way open (see pic1) except when this happens 59479024_601337536943090_1276599571841024000_o.jpg 66033230_1566948610107267_8272339150783381504_o.jpg .
    Manifold face is flat, and there's no sign of anything leaking from the joint. This (brand new) blower was not tight from new (so he's not bothered with Prism spray (but we will try it this weekend)). The teflon strips still look as good as new. When the blower is tightened down, it turns relatively freely.
     
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  5. Mike Canter

    Mike Canter Top Dragster
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    That’s sounds good. You need to always use the Prism spray to slow down wear of stripes. When you say the blower turns relatively free worries me. There normally should be some resistance. How many runs on the blower?
     
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  6. superpro453

    superpro453 Member

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    Blower has 4 full passes on it (and one aborted after the launch). It is tighter than my screw blower, but not as tight as I would have expected but I don't have much experience with Roots blowers. When I get the chance this weekend, I'll see if I can get a torque figure to start it moving. The owner is going to up the OD to 30% after we baseline the car tomorrow, so I should have a chance then.
     
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  7. MaineAlkyFan

    MaineAlkyFan Active Member

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    Those throttle blades look about 85-90% open.
    Nice looking digger.

    Chris Saulnier - Team Tigges
    Mechanic Falls, Maine
     
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  8. Mike Canter

    Mike Canter Top Dragster
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    Remember you need to add .3 to .35 gpm of fuel per pound of boost increase
     
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  9. superpro453

    superpro453 Member

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    Never got the chance to increase the overdrive at the weekend, as the car went from fairly predictable at the previous race, to having a miniscule tuning window to get it out of the hole ( "under power" tireshake or blowing the tires away as the convertor got to the stall speed). Owner said that there was no point trying to estimate the torque required to turn the blower as there was almost zero resistance... As he hit the rev limiter on a number of occasions, the boost did increase to 21.8 lbs at that point. The butterflies do open to as near to 100% as is possible...
     
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  10. Eric David Bru

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    Sounds to me like it needs restripped. On our standard roots blowers (not HH) it is hard to turn them over with a backdown bar.
     
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