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Pully question?
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<blockquote data-quote="CobraBob" data-source="post: 3665716" data-attributes="member: 6727"><p>The lower does the same as the upper -- increases boost which increases power and torque. A smaller upper pulley (increases boost) and tend to produce belt slip which causes a loss in power at the upper rpms. A larger lower crank pulley increases boost without increasing (potentially) belt slippage. Which is why a 2.93 upper with a 4 lb. lower is popular. You can use the search feature for additional info.</p><p></p><p>Some also just install a 6 lb. lower and keep the stock upper. Without a ported blower you want to keep your boost to al maximum of 15 lbs. of boost after which inefficiencies enter in with diminishing returns and increased heat. And heat with these motors robs you of power. A 2.93 upper (only) is a popular mod. When you port the blower you can go a couple of additional pounds of boost. So installing a larger lower can be done now, later or not at all. Just remember that it is TOTAL BOOST you're shooting for. Any combination of upper, lower, or upper/lower can get you basically that same goal. Hope this helps. Oh, and one reason why some people prefer only changing the upper is because changing the lower is more difficult and time consuming.</p></blockquote><p></p>
[QUOTE="CobraBob, post: 3665716, member: 6727"] The lower does the same as the upper -- increases boost which increases power and torque. A smaller upper pulley (increases boost) and tend to produce belt slip which causes a loss in power at the upper rpms. A larger lower crank pulley increases boost without increasing (potentially) belt slippage. Which is why a 2.93 upper with a 4 lb. lower is popular. You can use the search feature for additional info. Some also just install a 6 lb. lower and keep the stock upper. Without a ported blower you want to keep your boost to al maximum of 15 lbs. of boost after which inefficiencies enter in with diminishing returns and increased heat. And heat with these motors robs you of power. A 2.93 upper (only) is a popular mod. When you port the blower you can go a couple of additional pounds of boost. So installing a larger lower can be done now, later or not at all. Just remember that it is TOTAL BOOST you're shooting for. Any combination of upper, lower, or upper/lower can get you basically that same goal. Hope this helps. Oh, and one reason why some people prefer only changing the upper is because changing the lower is more difficult and time consuming. [/QUOTE]
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