higher compression or bigger blower?

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by caseyspradlin, Mar 31, 2010.

  1. caseyspradlin

    caseyspradlin Member

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    I race in T/D and run in the 6.80 range. I am finding myself at the back of the pack and would like to be in the 6.50 range.

    Combo: 540 BBC, CR 11:1, Big Chief, 871 BDS stage 4 standard blower 46% OD making 20# boost, hats and ports, bird catcher.

    Question: BDS tech said that all i needed to do was increase CR to 14:1 and reduce OD to 30% and it would haul azz.

    I was thinking I needed to pickup a used 1471 or maybe send 871 back to
    BDS and get the air lock rotors or high helix.

    I have heard someone say that higher CR reduces safety margin. Very often we start on Friday and race on Sunday and I don't like to change main during the weekend as it changes my CA ratio for dial in purposes.

    What do you guys think?
     
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  2. blown375

    blown375 New Member

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    My opinion is leave the compression alone and get a real blower !

    20 lbs @ 46% sounds WEAK !
     
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  3. nitrorelapse

    nitrorelapse Member

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    You need a lot better and bigger blower. Tim Richards told me once "motors run on fuel and air, not compression" I believe him. I would try and find a good used high helix 14:71. Their are always plenty on this board for sale.
     
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  4. jody stroud

    jody stroud ZOMBIE Top Dragster

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    Casey, a good Littlefield retro high helix 14/71 will put you deep into the low 6 sec. range.... if your chassis can handle the power. I'd say that a 6.30 something at 26% OD is real easy to do. Your problem is that BDS blower.
     
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  5. Bottlefed

    Bottlefed New to Blowers

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    I am not a fan of BDS blowers so I would also say leave the compression alone. While what they say is true that increasing the static compression and lowering the OD (mainly because the rotors are spinning way to fast for a conventional blower) would produce a lot more HP it will make your engine a touchy combo not at all well suited easy living LOL. get a good blower and pump some cool boost into it. Unless you are barely spinning the motor the standard rotors are way out of their intended RPM range at 46° over .

    Unless there is some kind of rule restiction on the blower size then a 14/71 would be the way to go, talk to Mert and I am sure he can help you. If there is a blower restriction there certainly there are 8/71s that can do a lot better than 20psi but unless rules require it the 14/71 will give you plenty of boost cheaper, cooler, and with less maintanence than a tricked out 8/71.
     
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  6. blown375

    blown375 New Member

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    Put that BDS on a street rod.
    If your looking to make some power and keep your blower maintenance to a minimum , look into a PSI there quality , tolerances, rotor and strip design and case stability are hard to beat !
    You'll make plenty of low temp boost and wont have to restrip it all the time ;)

    Most importantly... they are a sponsor of this site !
     
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  7. ibaddlizzard@aol.com

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    we ran a 2200 lb dragster a few years back 540 inch big chief 8/71 littlefield hi helix made 28 lbs at 38 over we ran 4.09 at 172 and 6.38 at 212. with a buzzard 65 sq inch of air flow we went .99 on the rear tires. i do not belive you have got enough air with a bird to run real fast. Doc
     
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  8. mike wharram

    mike wharram New Member

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    I have a 499 chevy with a littlefield 14-71 it makes about 34psi at 38 over and will run high 6.20s all day with a glide and a old TAD Uhehara chassis. I personally cant wait for our first Hemi
     
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  9. SoDak

    SoDak Active Member

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    I'd definitely get a different blower.
     
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  10. nmro2114

    nmro2114 Member

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    you are going to need a bigger injector if you chose a 14-71. Mert has great blowers for the price.
     
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  11. caseyspradlin

    caseyspradlin Member

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    thanks

    thanks guys. no blower restrictions, only wallet restrictions... only need a couple of tenths, looking to go 6.50's but i realize that I only have to spin it as hard as I want to run.

    so if i go with the 14 then is the buzzard necessary? (sorry to be so cheap)
    do the standard 14's have the open bottom or will I have to get an adaptor plate of some sort?
     
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  12. altered boy

    altered boy Outlaw Altered

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    i run a bird on a 14... either make an adapter plate or use the upper blower restraint plate as an adapter plate. i had mine made with a bird hole to fit a 14 blower. then drilled accordingly and used counter-sunk allens from below to secure the hat. never had a problem
     
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  13. thjts

    thjts New Member

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    How about try a Buzzard first, since that's the cheapest (unless you can borrow one to try) and easiest option. It's definitely a restriction for sure. If that's not enough, then go the next step; the blower...

    Friend of mine has a PSI screw. He has what we call a Top Doorslammer, I think you guys call them Promods. He had a real bad crash and the blower got flicked off during one of the car's many rolls. It went 60' in the air, landed on the grass, and it's ok. Got a bit of dust in it, but that's all. Unbelieveable! Get a screw...
     
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  14. blowntrifive

    blowntrifive Member

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    Definitly get rid of the blower and call mert at littlefields,dont waste your time on the hat with that blower. Save your money put that blower on ebay and sell it, You could get a decent blower from RBS for 3500.00 or so,or call mert and buy a new one!
     
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