Why more torque with lower pulley?

[1320 Junkie]

This is not a myth if you think it is then you have never had a car that you did a lower swap on. I have a posi ported blower with a 2.76 upper that made about 480 rwhp and 470rwtq. I added one thing a 4lb lower and my numbers went to 490 rwhp and 530rwtq. This works because your peak torque is in the lower rpm's and a larger lower pulley gets it spinning faster in the lower rpm so you have more boost right when you hit it.

Lol..you added boost..ofcourse its going to add tq. Bigger lower = more boost / smaller upper = more boost...we've got that covered. Now take off that 2.76 and put a 3.1 up top...still think you will make more tq because the lower is on there? Aint happening.

The discussion was about the misconception a lower pulley will make more tq when in use compared to a upper pulley while blower rpm and boost is equal....complete Myth.

 

[19COBRA93]

This is not a myth if you think it is then you have never had a car that you did a lower swap on. I have a posi ported blower with a 2.76 upper that made about 480 rwhp and 470rwtq. I added one thing a 4lb lower and my numbers went to 490 rwhp and 530rwtq. This works because your peak torque is in the lower rpm's and a larger lower pulley gets it spinning faster in the lower rpm so you have more boost right when you hit it.

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, it is a myth. 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.

Lower only:
Add 10% lower (8.0") only with same 3" upper at 4500 RPM:

8.0/3.00 = 2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.

Upper only:
Now, stock 7.1" lower and a 2.69" upper at the same 4500 RPM.

7.1/2.69 = 2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.

What!!? According to this, the lower only didn't change anything compared to an equivalent upper.

It's a myth, plain and simple.

 

[1320 Junkie]

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, it is a myth. 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.

Lower only:
Add 10% lower (8.0") only with same 3" upper at 4500 RPM:

8.0/3.00 = 2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.

Upper only:
Now, stock 7.1" lower and a 2.69" upper at the same 4500 RPM.

7.1/2.69 = 2.66 ratio. 2.66x4500 = 11,970 blower speed at 4500 rpm.

What!!? According to this, the lower only didn't change anything compared to an equivalent upper.

It's a myth, plain and simple.

Shazaam....debunked!!!