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Thread: Larger throttle bodies / intake manifods and boost

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    Larger throttle bodies / intake manifods and boost

    Just another one of those idle thoughts and google isnt bringing up anything. What are the benefits of using a larger throttle body / intake manifold on a boosted application? and , if any, what would the signs be that you need one?

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    Re: Larger throttle bodies / intake manifods and boost

    I always think of it like pouring a bucket of water down a pipe. If it doesn't go down the pipe quick enough you need a bigger pipe. I would imagine turning up the boost with lessoning affect on power would indicate a restriction. I would also imagine you need to look at the flow rates of all the pipework on the induction side as the restriction may not be the throttle etc.

    It may also be that bigger is not always better more boost more fuel and that would then need looking at ??

    experts feel free to add

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    Re: Larger throttle bodies / intake manifods and boost

    Sounds reasonable. I'm thinking a lot of people fit bigger throttle bodies etc long before the smaller ones have actually become a restriction too.

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    Re: Larger throttle bodies / intake manifods and boost

    ive been there all that happens if you use too bigger body is the throttle becomes less progressive, one of my bmw turbo motors made 320bhp full throttle, half throttle it still had 270bhp i cant remember what quarter throttle was but its was still something like 200bhp

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    Re: Larger throttle bodies / intake manifods and boost

    I wont worry about the little stock sierra efi one on my setup then, not that I was anyway. I just have these odd thoughts sometimes.

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    Re: Larger throttle bodies / intake manifods and boost

    Quote Originally Posted by theduck View Post
    I wont worry about the little stock sierra efi one on my setup then, not that I was anyway. I just have these odd thoughts sometimes.
    with forced induction even only at 1 bar boost a throttle will support at least 100% more power than in an n/a application, your sierra body isn't going to get restrictive until at least 250bhp

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    Re: Larger throttle bodies / intake manifods and boost

    Maybe I should worry then

    On the low boost map which starts at 10psi and climbs to 18 psi it is making 275bhp and 240lbft, but we had some tyre slip so think it was realistically making more power up top than that.

    On the high boost map which was targeting 20psi as early as possible it made 285lbft at 3.5k rpm and then spun the tyres.

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    Re: Larger throttle bodies / intake manifods and boost

    if you want to know how much the throttle is holding it back do two power runs one at full throttle and one slightly off full, if theres not much difference you dont need a bigger throttle.

    TBH, i think i think the plenum shape would be more of a issue than throttle body, i would suspect no1 cylinder would not get filled as well as the others.
    Last edited by Graham; 04-03-2019 at 22:35.

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    Re: Larger throttle bodies / intake manifods and boost

    Glad I made the post now. Will definitely give that a go next time I have it on a dyno, and maybe a new intake setup will be on the cards in the future.

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    Re: Larger throttle bodies / intake manifods and boost

    Good torque there!

    I use a 3" Volvo 850 GLT throttle body (similar power levels) but can't say if it is necessary or not. As you know I also have a YB style inlet manifold with a larger plenum. I am however thinking about a smaller volume plenum chamber to increase throttle response.

    Less resolution is a real risk with a bigger throttle body, ideally I'd prefer a progressive linkage/quadrant.

    Gustaf

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    Re: Larger throttle bodies / intake manifods and boost

    Gustav will that Volvo throttle body adapt to a Sierra Pinto inlet manifold easily? Thanks

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    Re: Larger throttle bodies / intake manifods and boost

    Not really, I have only used it on custom manifolds.

    My first injection engine used a Sierra EFI inlet with a slightly larger Saab TB, I used an adapter plate then. I guess you can do the same with the Volvo TB and enlarge the inlet hole, but "easily"...nah...

    Gustaf

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    Re: Larger throttle bodies / intake manifods and boost

    Thank you. Last time my car was on the dyno we checked pressure difference between the turbo outlet and inlet manifold. At 20psi boost pressure there was only 1psi difference so I doubt the Sierra throttle body is causing any significant restriction. You did only tell me that a couple of weeks ago haha. Cheers

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    Re: Larger throttle bodies / intake manifods and boost

    Good to hear from someone else running the sierra manifold and tb. Out if interest what power and torque are you making on 20psi?

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