Why more torque with lower pulley?

[Grabber07']

I am confused as to how the lower pulley adds more torque then lets say an upper? Less belt slip?

I am debating changing the upper or going with the lower. Looking for advantages and disadvantages. Not ready to do both just yet.

 

[Van@RevanRacing]

I use an analogy that Michael Rauscher from L&M Engines shared with me. The OD Crank pulley is the equivalent of spinning a 2 lb weight over your head with a piece of rope. Your arm is the crank shaft.

The longer the rope the more torque it takes to spin the weight on the rope over your head.

They are essentially similar more length and travel.

 

[RedNightmare06]

I think the increase in torque has allot more to do with the blower speed/air flow.

I like to see a dyno graph where a lower pulley made more torque than a blower pulley swap. Same blower speed between the two , same dyno, same day, same car.

Will a larger flywheel add torque to the motor too?

A larger crank pulley moves the weight futher away from the center of rotation which in theory would take more HP to turn it.

 

[19COBRA93]

The only gain in torque from a lower pulley is because of the increase in boost pressure. That's it. The same gain in torque can be had from just an upper pulley if the boost gain is the same.

 

[Grabber07']

I use an analogy that Michael Rauscher from L&M Engines shared with me. The OD Crank pulley is the equivalent of spinning a 2 lb weight over your head with a piece of rope. Your arm is the crank shaft.

The longer the rope the more torque it takes to spin the weight on the rope over your head.

They are essentially similar more length and travel.

That actually makes sense to me believe it or not.

 

[tomshep]

I use an analogy that Michael Rauscher from L&M Engines shared with me. The OD Crank pulley is the equivalent of spinning a 2 lb weight over your head with a piece of rope. Your arm is the crank shaft.

The longer the rope the more torque it takes to spin the weight on the rope over your head.

They are essentially similar more length and travel.

I could see that if the pulley size and mass increased significantly. But you are talking about a small difference in pulley size and mass.

I would think it would have more to do with when the boost pressure comes in which would be earlier, building more boost hence more torque earlier in the curve.

Tom

 

[19COBRA93]

Which is exactly what an upper pulley does as well.

 

[440sprint]

Which is exactly what an upper pulley does as well.

- without ANY change to the crank pulley!

 

[1320 Junkie]

I think the increase in torque has allot more to do with the blower speed/air flow.

I like to see a dyno graph where a lower pulley made more torque than a blower pulley swap. Same blower speed between the two , same dyno, same day, same car.

Will a larger flywheel add torque to the motor too?

A larger crank pulley moves the weight futher away from the center of rotation which in theory would take more HP to turn it.

The only gain in torque from a lower pulley is because of the increase in boost pressure. That's it. The same gain in torque can be had from just an upper pulley if the boost gain is the same.

^^^^ this

 

[Grabber07']

So you're saying upper is the way to go? hehe

 

[19COBRA93]

So you're saying upper is the way to go? hehe

No, we're saying the myth that a lower pulley adds more torque than an upper pulley is, well, a myth.

It stems from the '03 Cobras and the overspun 112 Eatons. You would add a big lower and only gain torque because they just couldn't make any more HP in the upper RPM.

 

[Crowley]

The way I look at it is the lower pulley helps with Belt Slip. You don't have to go to a smaller upper pulley (or you can go slightly smaller upper and then a different lower to help with Belt slip). This is what I did when I had my 04 cobra w/ a ported blower. I did a 2.93 upper and 4lb lower instead of say a 2.76 Upper.

Crowley

 

[19COBRA93]

I agree, that works well with belt slip.

 

[1320 Junkie]

Lower pulley is needed to achieve max boost on a tvs...otherwise I wouldn't have even done one.

 

[scottGT500]

Lower pulley is needed to achieve max boost on a tvs...otherwise I wouldn't have even done one.

15% right?

I have a TP car so too much trouble to move those lines around...I stuck with the 2.4" upper...right at 17psi.

Scott

 

[majmacv]

please solve for TP car...10% lower + 2.xx mm upper = 18 Lbs? I dont want to grind or re-locate anything

 

[dotmpeg]

please solve for TP car...10% lower + 2.xx mm upper = 18 Lbs? I dont want to grind or re-locate anything

Even a 10% lower requires grinding. So you're screwed either way lol

 

[1320 Junkie]

15% right?

I have a TP car so too much trouble to move those lines around...I stuck with the 2.4" upper...right at 17psi.

Scott

U can go 10% without moving the oil cooler lines :banana:

Yes I have a 15% :beer:

 

[Van@RevanRacing]

please solve for TP car...10% lower + 2.xx mm upper = 18 Lbs? I dont want to grind or re-locate anything

You still have to grind a small portion of the cranks position sensor. No big deal.

 

[Ky GT500]

After seeing my 10% done, the piece ground was no big deal. Had major reservations on the grind but my concern was unfounded. Glad I did it, no regrets.