Compression Ratio vs. Boost

Discussion in 'PSI Superchargers Tech Questions' started by Money Shot, Apr 14, 2009.

  1. Money Shot

    Money Shot Member

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    What is a better approach for blown alcohol? More compression and run less boost or vice versa? Also, how do you use a jet program for a higher compression engine? What compression ratios are these programs tuned from?
     
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  2. Dale Finch

    Dale Finch Member

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    To reply to your question you really need to tell us about the car, engine, blower trans etc. What class do you want to run in. This really determines how far into the zone do you want to go.
    thanks
    Dale
     
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  3. Danny Humphreys

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    more boost less compression is better
     
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  4. secondwindracing

    secondwindracing top alcohol

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    50 over with 12.1..we just change head gaskets..Dave
     
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  5. Money Shot

    Money Shot Member

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    I have a 565 BBC, Big Chiefs, 13.1 static comp. Big cam (.800+) with a 114 LC, 14/71 HH SSI. A buddy of mine sent me a EXCEL program that takes all of your variables, (Blower size, CID, over/underdrive, Fuel pump size, etc...) weather conditions, and suggest a good starting point (A/F ratio, fuel pressure)) based on your main and hat/port selection. The only thing I see wrong here is that there is no way to input compression ratio. Seems like compression ratio would affect your main jet dramatically. Example ( If you had a 13.1 engine and a 10.1 engine spinning at 15% over, what would the overall cylinder pressure difference be? Would you need to compensate for the extra compression and how much?)
     
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  6. GregM784

    GregM784 Member

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    Tamato vs Tamoto

    I like more static, less boost. Allows for cooler charge. However, less static and more boost allows to back the motor down further for golf course like starting lines.
     
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  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
    Staff Member

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    excel?

    Who makes this excel sheet? I've never heard of such for a blown alky motor.
     
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  8. JM

    JM Member

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    your 13:1 is going to give you great power - the 10:1 is going to live longer. The BBC isn't going to like the 13:1 and a 1471HH with much overdrive. If you keep the heads on it (larger studs, lifter valley head bolts, o-rings & receiver grooves), you have to keep an eye on the main caps dancing around.
    I ran a similar deal, the big compression wakes it up right now.
     
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  9. 3-D

    3-D Member

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    compression

    I have a new 540 with 12.39 compression in a conventional headed BBC. I also have that program. the answer I need is the cu in per revolution for my blower, Kobelco 8-71 HH Superman. the program works well if you will keep the Lean/rich indicators one of each.
     
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  10. GregM784

    GregM784 Member

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    Would you mind emailing me a copy of that file?

    greg@meansracing.com

    A HH 8 puts out a theoretical 500CFM per rev
     
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  11. 3-D

    3-D Member

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    you state cfm, what about cubic inches per revolution
     
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  12. TOL

    TOL Active Member

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    I tend to think it all boils down to the "dynamic compression ratio" inside the cylinder, which is a function of the static (geometric) compression and cam timing and gage boost and RPM. More or less of one or the others can get the same average results in the end, which is why there are so many different secret recipes out there. These factors all influence the dynamic trapped in-cylinder-combustion-pressures, which is what is being influenced in the end and which is what dictates when and how much power is produced at the flywheel. To each his own, and what works for one person is a good thing for them to stick to..........
     
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  13. Dale Finch

    Dale Finch Member

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    I too would like to see this program or info on it. There still needs to be a tuning adj or factor. I have made the switch from boats to funnycars. You could never run a car as lean as a boat by main jet. The car just loads the motor more. Programs are neat but they are not infallible. They have to make common sense too.

    dalefinch@shaw.ca if you want to share
     
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  14. GregM784

    GregM784 Member

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    that 500cfm is 500 cmf per revolution 'falls' out of the bottom of the blower (again, theoretically).

    My blower is a 6, and it 'seems' to only put out 405cfm per rev according to tune up data. motor is always wetter than it should be. :) I'm ok with that.
     
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  15. thjts

    thjts New Member

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    EXCEL Program

    May I get a copy too please?

    Thanks,
    Paul.

    thjts@hotmail.com
     
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  16. willy200

    willy200 Member

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    Excel program

    Would be appreciated if you could forward me a copy of the program to try.Thanks

    email pricemotorsport@xtra.co.nz
     
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  17. SoDak

    SoDak Active Member

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    PM me that file also.

    Thanks!
     
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  18. mbaker3

    mbaker3 New Member

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    It would be truly appreciated if you could share that excel sheet. We are "all" looking for a little better information or a little better way to log what is going on, so we can make better decisions.;)

    mbaker3XXXXX@tampabay.rr.com - leave out the 5 big X's.
     
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  19. Dragsterbus

    Dragsterbus Member

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    #19
  20. thjts

    thjts New Member

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    Excel Program

    I haven't had a good look at it, but if it's so popular perhaps Will could host a copy of it here for anyone to download whenever they want? And if it needs or can be updated, some way of doing that to the hosted copy?

    Paul.
     
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