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Thread: cosworth yb boost pipe size/exhaust size

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    cosworth yb boost pipe size/exhaust size

    evening people

    carrying out a yb conversion on my capri which is going to run stage 3. I'm starting to measure up for intake pipe work and exhaust system.. have a few questions they might be daft but this is first time playing with turbos so be gentle

    1: intercooler inlets are 63mm so should i match that size from the turbo to the inlet manifold? or i think the port on the turbo is something like 51mm or 53mm would it strangle the engine running pipes this size and stepping up for the intercooler and inlet..

    2: solid boost pipes be it aluminium or stainless anyone done this? i don't fancy seeing a load of jubilee/hose clamps clips what ever you want to call them used to piece together different sections of hose/pipes

    3: recirc valve.. don't want a dump valve which came with the engine i bought so think the standard cosworth setup was a recirc valve.. what size of pipe/hose would normally been fitted 25mm ID? i take it this gets fed back into the turbo side of the intercooler?

    4: exhaust size.. i have a 2wd down pipe which is meant for a twin pipe system i'd rather a single pipe system. I can chop that then step up in pipe size so what would be best 2.5" or 3" was looking at 2.5" as i might struggle to get 3" up and over the axle.. would it be worth while doing a V band conversion?

    any help/info would be great

    stu

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    Re: cosworth yb boost pipe size/exhaust size

    in theory keeping the intercooler pipes on the small size will make it more responsive, as theres less internal volume for the turbo to fill before you see boost at the inlet manifold, in practice i think it makes very little difference, i would where ever is convenient step up the size from the turbo to the intercooler than just run that bigger size all the way to the inlet manifold.

    no reason not to use solid boost pipes but you still need flexible sections to allow for movement of engine, vibration etc.

    theres no point in feeding a dump valve back in in between the turbo and intercooler it wont do anything, because your trying to bleed boost back into where is come from, dump to atmosphere, the intake side of the turbo or dont bother at all, ive run with and without and couldnt tell the difference, but if you do 25mm pipe sounds about right.

    go with 3 inch exhaust, or consider splitting it ahead of the axle and running twin 2 inch to the back of the car

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  4. #3
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    Re: cosworth yb boost pipe size/exhaust size

    thanks for the reply Graham

    dropping down the boost/intake pipe size would help in the bay to squeeze past the rad.

    yep silicone hoses at the ends to connect to turbo, cooler and inlet manifold

    right so from recirc it should then feed to cold air supply to turbo and not between turbo an intercooler that's cleared that up

    in my head capri's should only have twin tail pipes if they have a v6 or v8 so i'll look into 3" from turbo back

    thanks

    stu

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