The car revs quicker and defiantly pulls harder from 40 to 120 The factory pulley is said to weight 6.24lbs and KJR 2.08lbs.

The dyno result are disappointing and show no real gain. The HP and TQ curve are basically the same.
This is the second mod to show no definitive HP and/or TQ gain

2003 5AT G35C

Before
Z-tube+Stillen Hi-Flow Airbox, 1/2" MD spacer w/ISO Kit, Invidia G200
250.36 HP _ 229.12 FT-LB

After
Z-tube+Stillen Hi-Flow Airbox, 1/2" MD spacer w/ISO Kit, Invidia G200, KJR LW Pulley
250.49 HP _ 229.73 FT-LB

 

if there was not much gain then how does it accelerate and pull much harder after 40???

 

Some of the mods will not show on dyno. Pulleys and flywheels are the example. They give "equivalent weight saving " gain-same kind you would get from striping your interior for example. Car will be lighter and pull harder, but you will see zero gain on dyno.

 

thats not true. The UR pulleys do show hp and tq increases on the dyno.

 

G35StrongMan, how much was the pulley installed?
If you have file for this run, please post time and speed chart. How is your A/F? Thanks.

 

Finally the truth is out. I'm glad someone FINALLY dynoed the UDP to prove what I've been saying all along.....no gains. I had an UDP on a prior VQ and the motor did rev quicker, but on the track and dyno, absolutely no difference.

Nope. If you reduce rotational inertia (light rims), it will show up on the dyno. Since the pulley is already a lightweight device mounted directly to the crank and it's VERY SMALL in diameter, it's not going to make any measureable difference on the dyno or the track. Period.

 

The KJR is not a UDP. It's OEM sized, just lighter.

 

Dovla,
The shop charged me 2 hours labor ($150 total). It actually took them 2 hours 45 minutes.
3,500 RPM to 6,600 RPM the A/F was 15:1

 

Even so, the VQ underdrive pulleys only underdrive around 8-10%. Hardly worth the effort and all the aftermarket companies claim the gains come from the reduced weight. In theory they're basis is correct, but when you're talking about a smaller diameter component mounted directly to the crank, it's not going to make much difference, especially when you're talking about something with so little weight.

 

Remember... when you dyno you're in 4th or 5th gear going 3000 rpms to redline. That's not where a flywheel or UDP is supposed to shine. You SHOULD NOT see gains from these mods on a dyno, it just doesn't make sense.

Gains from these mods are initial gains. Getting the object in motion easier is the task. Keeping it going is basically no extra work and it's the "keeping it going" that you're measuring on the dyno.

my 2 cents.

 

Where did u get the pulley and how much?

Also, are u throwing and check engine lite with the a/f that lean?

 

http://www.kjrperformance.com/
$170 shipped to my front door.

I haven’t had any CELs with my current setup.

 

If the pulley is just lightened (and not underdrive), it will do virtually nothing in-gear. No surprise here, I've been trying to tell people this for years on forums for my last car. Here's a link I wrote if you're interested in why this is exactly: http://www.stanford.edu/~mpg/lighten...omponents.html

 

What's the stock crank pulley diameter? Assuming 8", I ran the numbers for the KJR crank pulley (scale them by (D/8)^2 if it's not 8"), and the gains are the following percentages in each gear for the 5AT (and the equivalent peak power "gain" assuming 250 whp):

1st: 0.810% (2.02 whp)
2nd: 0.331% (0.830 whp)
3rd: 0.140% (0.350 whp)
4th: 0.0646% (0.161 whp)
5th: 0.0449% (0.112 whp)

Yeah, FEEL THE POWER baby! Screw the possible minuses of excess engine wear or bearing failure, it's worth it for the 2 whp in 1st alone.

Note that these numbers assume the crank pulley's mass distribution is equivalent to that of a flat disc (most accurate of the simple inertial assumptions). However if you assume all of the mass is concentrated in an infinitesimal ring at the outer crank radius, you will get twice these numbers, and a real crank pulley lies somewhere in between. But two times nothing is still nothing. :P