I was considering buying the unorthadox pulleys for my car. So i was reading up on them and they claim that it has the possibility to add boost to when added to a car that has a supercharger. Has anyone ever heard of this? I am going to get them and change all the pulleys except the crank because the vortech kit comes with a new crank pulley. Anyone have any ideas about this??

 

only underdrive pulleys will possibly give more boost

 

There are only 2 pulleys which can affect boost on a supercharged engine: the (driving) crank pulley and the (driven) pulley on the supercharger. The ratio of these two diameters is the drive ratio. Multiply that ratio by engine speed and you get compressor shaft speed.

Unless you change one of these 2 pulleys, you won't change boost pressure or air flow or HP. Changing the drive ratio for alternator, water pump, power steering, etc. can only reduce parasitic drag on the crank. Unless the engine couldn't reach redline rpm before, these other pulleys cannot change the compressor's performance.

Compressor shaft speed is the determining factor for compressor performance. Performance curve for centrifugal compressor has air flow on one axis, head (~boost pressure) on the other axis, and different curves for different compressor shaft speeds.

HP is proportional to fuel flow (by energy BTUs/lb of gasoline) which is proportional to air flow (A/F ratio). If you notice on the performance curve, the less head the compressor has to lift, the more air flow you get for any given shaft speed. That's why low backpressure exhaust, ported head, larger TB, etc. all increase airflow and therefore increase HP. Because they lower head load on compressor, moving you to the right on the curve.

 

I think you'll find they are selling two different products and you're getting the proposed benefits confused.

In NA there is some argument that lighter but bigger pulleys for the various accessories results in less parasitic drag and hence more power to the wheels. It's a bit of a ricer argument and might net you a few hp but nothing spectacular.

Of course companies that make these often also make alternative pulleys for the Comptech and Vortech superchargers. A smaller SC pulley results in a higher drive ratio and hence more boost.

Same company, similar product, but two entirely different benefits.

 

I know that a smaller pulley will make more boost, i was just trying to see if anyone had ever heard of the proposed increase in boost due to the pulleys being lighter. I was reading up on the unorthadox pulleys and they said in some cases they had seen a small increase in boost. I dont buy it, thats why i was trying to see if anyone had heard of it.

 

Some folks I've spoken to (non-S2K) have noted faster acceleration due to their light weight pulleys. Is it possible that the slight difference in acceleration is being mistaken for "higher boost"?

 

Less inertia. They have the same effect as a light weight flywheel only to a lesser degree.

 

Well i appreciate the info, i just didnt know if what i was reading was true. I was doubting that lighter pulleys would increase boost, so i guess you guys have helped answer that question.

 

Ok, just keep in mind that the heaviest pulley is the crank pulley.

But it's heavy for a reason. It is a harmonic balancer for the crank and dampens engine destroying vibrations.

Added to that, in a SC application it's what the SC's drive pulley is attached to.

So I'm guessing you're not going to change it in which case the reduction in inertia of all the other pulleys combined wouldn't result in 1hp difference.