I've heard a lot of opinions about underdrive pulleys on this forum - from they're great to they don't do a thing.

Here are the results of my test. Before the pulley kit install I only had a NISMO CAI mod. I installed the pulley kit this weekend, and ran this comparison test with my G-Tech Pro Comp. today.

The black shows my average baseline runs with just the CAI, and the red and green are from today with the pulley kit installed.

 

And here are the HP & TQ numbers.

 

Oh, in case you're looking at the tables and wondering why my car seems so slow in the 0-60 range, it's because for some reason my g-tech, when calculating that value, does not account for the roll out. All of the other numbers are accurate, and if you export the run, the export file shows it correctly.

Anyone else have this problem with their G-Tech Pro Comp.?

 

Nice testing - but were the test conditions the same when you ran the original test as now? Weather (temperature and barometric pressure, etc.) has a significant effect on power, and since the tests apear to be on different days I had to ask, as a nearly 20whp gain from pulleys seems a little optimistic.

 

Given any margin of error, even 10-15rwhp gain isn't unheard of. Whoever said the pulleys don't do anything is talking out their a$$. It's basic physics, and I believe it to be the best $ vs. performance mod available for the Z.

 

FYI, dyno'd 5HP peak

http://www.nissanperformancemag.com/august03/350pulley/

X

 

In the first run, the BP was 30.04 and the temperature was 78 degrees f. On the runs after the pulley install, the BP was 30.80 temperature was 75 degrees f.

So, I suspect that environment could acount for 1 or 2 HP, but that's about it.

Also, last Friday I dyno'd the car just before the pulley install. I'm going to dyno again, first to confirm what the G-Tech is showing, and second to get a new baseline for my next round of mods (Headers, exhaust and TB.)

 

thanks for the info. i've had my test pipes for awhile but have not installed them yet and the pulley will be my next upgrade now.

 

maybe so but why stop there?... then add the additonal pulleys and the flywheel to boot.But really it all depends on how much drivetrain loss ones car is experiencing "as a whole" if you get the gains (10-15) your suggesting - then what that means in basic physics is YOUR losing a ton on YOUR drivetrain and MORE than most! Not exactly a good thing so if someone is getting that much loss they should get the other components as mentioned above that are contributing factors...so it would seem. $ 02

 

Did you know, that when manufacturers post dyno numbers, it is usually the difference between the worst baseline run and the best post modification run?

 

baro going from 30.04 to 30.80 is equivalent to being 760' higher elevation, so that should wipe out any gains from the 3 degree cooler temp.

 

You mean lower elevation right? 30.80 is higher pressure (as if you were at lower elevation), so that added even more power outside of the pulleys. Using the rule of thumb, 3% difference in power for 1000' elevation, this was probably around 4-5hp that we would subtract off just for the baro difference.

 

I had not heard the 3% per 1000' rule of thumb before. See below.

OK, I took all of my values and ran them through the SAE correction factor calculator at

http://www.csgnetwork.com/relhumhpcalc.html

And applied these correction factors to what the G-Tech shows. At the low end of the graph above, I'm seeing a corrected increase of 9.0 HP and at the upper end of that graph, I'm seeing a corrected increase of 12.7 HP.

Next, I exported both of these runs to a spreadsheet, SAE corrected, and averaged the diffence of the runs, I get an average of 11.9 HP and a peak 14.6 HP gain between 3K and 6K rpms.

So, is this a good mod? Well, the pulley kit cost $300 shipped from Coz at Concept Z performance. 300/14.6 = $21/HP = a good mod in my book.

Oh, and your rule of thumb is close according to that calculator. It says 4.5% difference between 0'-1000' but since air pressure does not decrease linearly with altitude, I'd say you're good, especially higher up.

So why the discrepancy between what I see and the dyno discussed above? My guess is that they dyno'd immediately after installing the pulleys. I let the car run for a day before I ran my test. It's peculiar how our ECU will do that - but that's another thread entirely.

I performed an ECU reset, then ran G-Tech tests each day for the next 5 days. For the first two days I saw very noticable performence changes, then the diffences were nominal enough to be factored out by environment. Each day consisted of aproximately 50 miles of mixed driving.

 

I see what your saying, but first of all, the pulleys don't help against drivetrain loss. If i'm not mistaken, the lighter crank pulley helps minimize rotational mass on the crank and thats where you get -most- of the gains. Another 2-3 horses can be gained from minimizing parastic loss by underdriving the alternator and power steering more with their own smaller pullies, but 2-3 hp isn't worth it IMO.

 

The UR accessory pulleys (water pump and alternator) are the exact same size as stock. They are somewhat lighter than stock but are mostly just for show (and they are beautiful!!)

The underdrive comes from the smaller diameter of the crank pulley, which is also much lighter than stock.

 

Yeah I was astonished at the difference in weight. I think I mentioned in another thread that it felt like the difference between a brick vs. a paperback novel

 

Zxsaint,

Looking at your sig. (257rwhp) and calculating for the 17% drive train loss, puts your crank HP at 295. Whatcha gonna mod next to get over the magic 300 mark? You know you gotta do it!

Roark

 

Drivetrain loss is near 13% to 14% per dwnshift...

X

 

I think 17% for manual sounds about right if the advertised 287@crank gets 238rwhp (average of stock dyno number on this board)

But you have to calculate it backwards....

310@crank with 17% loss is 257.3rwhp

Next will be high flow cats or resonated test pipes ... after that, i'll be waiting on the good stuff from Jim Wolf. The rumored agressive cam + ecu bundle from JWT is what i'm hoping for.

 

sounds incorrect im afraid...

to illustrate:

Joe has car that baselines @ 238 RWHP
+ Exhaust and intake @247 RWHP

If he achieved 287 Crank - (17%) =238 RWHP
using same formula w/gains of Exhaust and intake he gets:

298 - (17%) =247

Now if he simply adds a crank pulley or pullies and gets 253 RWHP

you really think pulleys or Flywheels add power @ the crank?

so if that number still is 298 @ Crank but with 253 RWHP the 17% is not the case anymore and cant be computed as such since he still has 298HP.
so now it should look like

298 - ( 15%) =253 RWHP

if thats the case your might have to reduce your 17% to 15 as well. your proabably putting out 302 @ your crank without knowing what your baseline is exactly.As the math would indicate:

302 -(15%) = 257.55 or a little lower.