Carb Shear plates
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Carb Shear plates

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    I'm No Expert Shaun's Avatar
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    Default Carb Shear plates

    To fork off a topic from my other thread. I just went and searched for carb shear plate on google and found a guy talking about them making 20 HP. he never gave any specs and to assume one will make 20 HP on any app is stupid but whatever. Point being, when is a shear plate needed and you guys who are running them what type of performance increase did you see?

    http://racingarticles.com/article_racing-22.html

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    Resident Ford Nut Sleeper CP's Avatar
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    Quote Originally Posted by Shaun View Post
    To fork off a topic from my other thread. I just went and searched for carb shear plate on google and found a guy talking about them making 20 HP. he never gave any specs and to assume one will make 20 HP on any app is stupid but whatever. Point being, when is a shear plate needed and you guys who are running them what type of performance increase did you see?

    http://racingarticles.com/article_racing-22.html
    " A 7 degree taper and special undercut dampens reversion pulses reaching the carburetor improving signal and increasing power."

    From Barry Grant.

    Emphisis on "dampens reversion pulses" they will help the carb signal but 20 hp is a stretch. They work like a Super sucker but their job is to kill the resversion pulse before it hit the carb. I used one on my single top T/R years ago:



    http://www.jegs.com/i/Barry-Grant/13...oductId=762336

    S CP

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    No plastic there.

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    cfm
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    A carburetor will flow air/fuel in either direction - although we'd rather have it in just one direction.

    The more the line of sight from intake runners to carb's throttle bores, the more a shear plate will help. Tunnel ram intakes have more line of sight then most single planes, so they'll help on a TR intake more. Single planes have more line of sight then dual planes, so they'll help more on the single.

    That said, intake reversion depends on other factors too, so the more intake reversion you have and the stronger this reversion is, the more the shear plate will help you. Well, help the carburetor which will help you.

    Lastly, if using a dominator carb, you should have a safety plate underneath it anyway, so why not get a shear plate. Most DOM equipped engines have generous overlap and a good amt of intake reversion anyway, so the shear plate is a good thing to get anyway.

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    I'm No Expert Shaun's Avatar
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    Is there a way to tell if your engine is creating enough reversion for a shear plate or do i need to look at cam specs, and if so what am i looking for?

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    Quote Originally Posted by Shaun View Post
    Is there a way to tell if your engine is creating enough reversion for a shear plate or do i need to look at cam specs, and if so what am i looking for?




    I think dyno tuning would be the only way to tell.

    S CP

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    Shear plates work good, BUT there is NFW is givin ya 20 hp, try maybe 4-7 at best, and if the intake is ported spot on perfect maybe 1-2 and thats well within "dyno error" lmao...but yeah they help with signal and the ones we used had o-ring instead of gaskets and that was really nice.

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    Default indications of reversion

    IF you can see dark places in the intake runners and particularly on the bottom of the carburetor, those are the easy to see marks of reversion.

    Although there are several different designs of reversion or shear plates, a few actually increase the flow of the carburetor while decreasing the reversion pulses into the carburetor.

    Some packages also provide vibration dampening by using soft gaskets that are about .090" material.

    The effects of using the shear plates can indeed be tested on a properly calibrated dyno, but simply bolting them in place is easiest but some designs require slight modification to the manifold or manifold carburetor mounting location.

    Regards,
    IG

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    We had a big block chevy engine combo on the engine dyno once that would stop using fuel at 5500rpms. Reversion was so bad that the BSFC would actually go way down after that no matter how much fuel we threw at it.

    The heads and intake were suspect because the previous owner also had a problem with them. We decided to send the sheetmetal intake to Wilson manifolds so see what was really going on along with the heads. When it came back they had done some flow work to the intake and made the air go where they wanted to. We were also told to run shear plates and anti vibration gaskets with o-rings.

    After that the combo would make power up to 8000 rpms. I always wished that I could have seen what was actually happening even though we knew what was.

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    Shear plate:



    A few spacers:



    You'll only know what they'll do by running them on the dyno.

    S CP

    "Dark Sarcasm"
    Going fast is only half the fun ... what you make go
    fast is the other half.
    " A Government big enough to give you everything you want is big enough to take away everything you have"

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