I eamiled Brenspeed and today they dropped their price to match the sale Steeda has on the underdrive pulleys, so I ordered them tonight. I requested updated tunes for the XCal to account for the pulleys. Now if I could just get my rig back from the body shop, I'd be giddy.

 

im thinking about doing a really big ordering spree again lol

i want to build an N/A beast before i go forced induction


actually, what would one do to get 400hp n/a?


i would think port and polish head, cams, long tubes, o/r midpipe, catback, intake, tb, pullies and water pump would get you pretty close?

do alumimum driveshafts/flywheels yield more power due to less rotating mass?

 

Yes. ( I e-mailed Brent as well, and he said a new tune isn't required for pullies. )

 

Thanks. Good to know, one less thing to worry about.

 

Got a dumb question. What is the theory behind new pullies..what do they do exactly?

 

They slow down your accessories so the engine can spin faster/make more power. I think that sums it up, anyone with a little more knowledge feel free to correct me.

 

Nope, you nailed it Menace. Nice sum up.

Here's a little different explanation. All of your engine accessories like the water pump, alternator, A/C compressor are driven by the belt coming off of the crank of the engine. So, anytime your engine spins, your accessories spin too. Spinning all of those accessories puts an extra load on your engine so it's not able to spin as fast or send as much horsepower to the transmission as it could without them. Now, since we can't live without our accessories, we have to find another way to take a little load off of the engine while still spinning the accessories. This is where the underdrive pullies come in. By changing the size of the pullies that drive the accessories, you can adjust the speed at which they spin in comparison to the crank. By lowering the speed at which the accessories spin, you are lowering the amount of stress put on the engine by the accessories. This allows the engine to spin a little faster and transfer a little more power to the transmission. More HP, more TQ.

Another step would be to replace the engine driven water pump with an electric model. Then, pumping water isn't taking any horsepower away from the engine, because it's being driven by an electric motor, not be a belt from the crank. [Note: someone will probably argue that the electric water pump still takes horsepower to run because you need more power to the alternator to support the extra electrical load, but that's not really the point here is it?]

All in all, the theory of the underdrive pulley is pretty sound, and they've been around for quite a few years producing a pretty good gain in power in comparison to the cost and ease of installation. However, there are still those who would argue that spinning your accessories at a slower speed decreases their effectiveness and longevity. But, for every argument there is a counter-argument, and many say it doesn't hurt a thing. I am personally planning on installing them on my new 06 and looking forward to the little kick in the pants when I do.

Good luck, hope this helps.

 

You guy's description of the UDPs is great.

However, I AM going to argue a bit about the Electric water pump.

As you stated, the OEM mechanical water pump takes some HP from the crank to run it.

The Electrical pump isn't driven directly off of the crankshaft. HOWEVER, the power to operate it has to come from somewhere. (Remember High School Physics??) The electricty comes from the alternator. And the alternator, in turn, gets it from the crankshaft.

So if you replaced the mechanical water pump with an IDENTICAL electrical pump (same exact flow conditions) it would be a performance DOWNGRADE becasue the electrical pump is providing the same output, but the energy is going through two conversions (mechanical to electrical and then back to mechanical again) in the process. We know from Physics that no conversion of energy is 100% efficient.

However, in the real world electrical water pumps are fixed ouput. That means they don't vary according to RPM.

The net effect is that the Electric water pump COSTS you HP in the low RPM ranges due to its latent inefficiency. However, it has an HP advantage at higher RPM becasue it's output is fixed, whereas the mechanical pump's HP draw gets worse and worse as RPMs climb. Note that this also means that a mechanical pump moves more coolant at higher RPMs too.

 

See, I told you that someone would argue that the electric water pump still takes horsepower.

I'm not arguing with your analysis CrazyAl. Just saying that the whole physics discussion of the electric water pump was not my point in the previous post. It was just an aside to help explain why UDPs (and electric water pumps) increase horsepower.

 

I think some are advertised as like a 10 hp gain, not sure.

Cams, CAI+Tune, Shaker(no HP gain but looks sweet [8D]), udps, off-road X-pipe, T-body, water pump, headers.

That should get you over 440, but just go F/I unless you are gonna get forged internals.