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Thread: Roots blowers and engine stress

  1. #1
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    Roots blowers and engine stress

    I've been running my m112/v6 since July. I've put over 8k miles on it to date as my daily driver. In the summer I was getting max boost of between 5-6psi with my pulley config. Lately I'm getting 7psi with the cooler/drier air. All has been fine at this level. But I'm wondering, how strong is the crank snout on these 3.8s? Right now I calculated at 6k rpms, under full boost, my eaton's demanding ~45hp. One of my concerns is at such time I crank the boost up, am I going to twist the end of the crank off. SC cranks are forged. But then my option of going to 4.2 liters may not be wise. Positive displacement blowers are less forgiving on an engine's rotating assembly because of the little to no lag time that max boost can occure. What are the options of getting a stronger crank?

    Tom

  2. #2
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    As far as I know there isn't any options for a crank unless you pay out the nose for a custom crank.

    If you are running a M112 at 6 PSI with a SC crank. Don't worry. There are guys running a M90 at 25 psi and spinning the crXp out of it and the crank is holding up.

    Worry about your harmonic balancer and I've read that the front crank bearing wears a little more than the rest.

    XR7 Dave had almost 200K on his and the last time he dyno'd around 440 HP and 440 TQ.

  3. #3
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    Quote Originally Posted by 90blkbrd View Post
    As far as I know there isn't any options for a crank unless you pay out the nose for a custom crank.

    If you are running a M112 at 6 PSI with a SC crank. Don't worry. There are guys running a M90 at 25 psi and spinning the crXp out of it and the crank is holding up.

    Worry about your harmonic balancer and I've read that the front crank bearing wears a little more than the rest.

    XR7 Dave had almost 200K on his and the last time he dyno'd around 440 HP and 440 TQ.
    The Eaton is on my stock splitport 02 Mustang 3.8. Hmmm, I never concidered the harmonic balancer. What effects would happen there? Are the main/rod bearings in the Ford GT made of a stronger material that can handle the extra stress? I read the new Shelby engine is using the same bearings.

  4. #4
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    Well then you aren't running a SC crank. They are different than the N/A cranks.

  5. #5
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    Stang man,

    Are you using a SC short block?

  6. #6
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    Quote Originally Posted by Toms-SC View Post
    Stang man,

    Are you using a SC short block?
    No. The engine is a stock 2002 splitport 3.8 v6. The only thing that's not stock, besides the Cobra blower setup, is the GT exhaust and a 25% UDP.
    More info here: http://www.cardomain.com/ride/2452794/3

  7. #7
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    Get a SC lower motor and up the boost..Any type of IC?
    They don't call me "SLOWPOKE" for nothin!
    http://www.sccoa.com/forums/garage_v...vehicle&id=110
    Quote Originally Posted by ricardoa1 View Post
    I love the filter. Its pimp. paper element and 10Mircron filtration, 12" long cause size matters.

  8. #8
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    I don't see any reason why that motor wouldn't hold up.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  9. #9
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    Quote Originally Posted by DamonSlowpokeBaumann View Post
    Get a SC lower motor and up the boost..Any type of IC?
    No innercooling system on it yet. This winter I'll be working on that.

    I've read there maybe problems with breaking harmonic balancers. At what boost output are these situations happening? Has anyone used a billit crank?

  10. #10
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    Are you reading about SC balancers or balancers related to your engine? On our cars it isn't power related it's age related. (for the most part)

    I believe there has only been a couple of cranks made for us. No one that I know of has broke a crank due to that engines power levels. David N just ran a mid 10 on a stock crank with a 100 shot of NOS and he pulled 425 on a dyno without NOS.

  11. #11
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    The problem that I have run into with cast or nodular iron cranks with roots type superchargers is that the belt drive puts alot of unsupported weight and extra stress from that weight on the crank snout. You not only get that extra unsupported weight but its also further from the main bearing. If you are running a one belt system that isnt as much of an issue however the drive system running off the crank pulley is either way. I think it be well worth it to look into a SC lower in the future. As has been said the balancer issue is age related.

    I have cracked twisted and bent non steel cranks with roots type blowers
    They don't call me "SLOWPOKE" for nothin!
    http://www.sccoa.com/forums/garage_v...vehicle&id=110
    Quote Originally Posted by ricardoa1 View Post
    I love the filter. Its pimp. paper element and 10Mircron filtration, 12" long cause size matters.

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