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2013-14 Shelby GT500
Why more torque with lower pulley?
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<blockquote data-quote="19COBRA93" data-source="post: 13691639" data-attributes="member: 10462"><p>I've owned 3 '03 Cobras. One of them had a 10lb lower and a 2.76 upper. I know a thing or two about pulley swaps. </p><p></p><p>First, <strong>it is a myth</strong>. Let's just make sure that's not overlooked. Here's why you gained torque; An 03/04 Cobra Eaton is good to about 500rwh. A 2.76 upper and a port will generally get you there. When you add a lower pulley to a 112 Eaton with a 2.76 upper, you're spinning the blower a lot faster, well over it's intended rating. This doesn't equal HP because it simply can't maintain the airflow and boost in the high RPM (where peak HP is). What it does do, is increase boost in the midrange (peak torque) because that's where that little blower is most efficient. This has nothing to do with the lower pulley, it's simply from increased blower speed, and a lack of airflow in the high RPM. Watch the boost curve of an overspun 112 eaton, it will dive drastically in the upper RPM. </p><p></p><p>Let's do some simple math...</p><p></p><p>The control will be the stock setup: </p><p>Stock GT500 lower (7.1") and stock 3" upper at 4500 RPM (peak torque):</p><p></p><p>7.1/3.00 = 2.36 ratio. 2.36x4500 = 10,620 blower speed at 4500 rpm.</p><p></p><p><span style="color: Red">Lower only:</span></p><p><span style="color: Red">Add 10% lower (8.0") only with same 3" upper at 4500 RPM:</span></p><p><span style="color: Red"></span></p><p><span style="color: Red">8.0/3.00 = <strong>2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.</strong></span></p><p></p><p><span style="color: red">Upper only:</span></p><p><span style="color: red">Now, stock 7.1" lower and a 2.69" upper at the same 4500 RPM. </span></p><p><span style="color: red"></span></p><p><span style="color: red">7.1/2.69 = <strong>2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.</strong></span></p><p><span style="color: red"></span></p><p>What!!? According to this, the lower only <strong>didn't change anything</strong> compared to an equivalent upper.</p><p></p><p>It's a myth, plain and simple.</p></blockquote><p></p>
[QUOTE="19COBRA93, post: 13691639, member: 10462"] I've owned 3 '03 Cobras. One of them had a 10lb lower and a 2.76 upper. I know a thing or two about pulley swaps. First, [B]it is a myth[/B]. Let's just make sure that's not overlooked. Here's why you gained torque; An 03/04 Cobra Eaton is good to about 500rwh. A 2.76 upper and a port will generally get you there. When you add a lower pulley to a 112 Eaton with a 2.76 upper, you're spinning the blower a lot faster, well over it's intended rating. This doesn't equal HP because it simply can't maintain the airflow and boost in the high RPM (where peak HP is). What it does do, is increase boost in the midrange (peak torque) because that's where that little blower is most efficient. This has nothing to do with the lower pulley, it's simply from increased blower speed, and a lack of airflow in the high RPM. Watch the boost curve of an overspun 112 eaton, it will dive drastically in the upper RPM. Let's do some simple math... The control will be the stock setup: Stock GT500 lower (7.1") and stock 3" upper at 4500 RPM (peak torque): 7.1/3.00 = 2.36 ratio. 2.36x4500 = 10,620 blower speed at 4500 rpm. [COLOR="Red"]Lower only: Add 10% lower (8.0") only with same 3" upper at 4500 RPM: 8.0/3.00 = [B]2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.[/B][/COLOR] [COLOR="red"]Upper only: Now, stock 7.1" lower and a 2.69" upper at the same 4500 RPM. 7.1/2.69 = [B]2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.[/B] [/COLOR] What!!? According to this, the lower only [B]didn't change anything[/B] compared to an equivalent upper. It's a myth, plain and simple. [/QUOTE]
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2013-14 Shelby GT500
Why more torque with lower pulley?
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