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Bought a used s trim that came with a 2.95 pulley, I am looking for 10-12 psi on a stock 95 cobra. What pulley do i need? Car will have a power pipe also.
 

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Boost is relative to the modification done to the motor so sometimes the pulley size doesn't get the results you want. Here's the thing to remember, the smaller the pulley, the more heat the blower generates and then it's harder to tune. They do make a smaller 2.75 pulley but you don't want to overspin the blower as they become less efficient at their max rpm range. What you really want is the biggest pulley you can put on it to meet your psi goal. The bigger the pulley, the less heat the head unit generates, the easier it is to tune and make safe power. Personally, I think you're pushing the limits on a stock motor with 10-12 psi and I'm not just talking about the block, talking about the stock fuel system, stock injector size, pump gas concerns etc.. There will be plenty of guys on here to tell you to put a smaller pulley on it and go for it, that's your call but not what I would do. Good luck.
 

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PSI on its own is a useless goal, you want the largest airmass that can be supported by that hair dryer.

airmass will be determined by sensible heat content, we call that density

you can have a less dense charge with a higher manifold pressure, ie BOOST, stupid number

put some numbers in this Air density calculator (useful for estimating rho)

and just change the temp, and see what happens to density
 
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