Stillen Underdrive Pulley - Review/Pics/Dyno/Vid
 

Review & Pics:

My friend and I installed the Stillen Underdrive Pulley this past Friday. The installation wasn't too bad overall. It took a total of about one hour, but that includes the time taken to get the car up on jack stands, remove the undertray, etc. The hardest part of the installation was getting the stock pulley off, because they torque the bolt from the factory really, really tight. My mechanic had to hold the starter in place with a pry bar while I loosened the stock pulley bolt with a torque wrench, and it took a lot of effort/strength to loosen that thing. It would have been easier if the car was on a lift, because I would've been able to use my body weight to pull down on the wrench. Doing it while laying on the ground though, I had to rely on muscle alone.

Here's the Stillen UD Pulley, front and rear:
http://www.the370z.com/members/semte...1-p1000920.jpg

http://www.the370z.com/members/semte...7-p1000918.jpg

Here's the stock pulley, viewed from underneath the car:
http://www.the370z.com/members/semte...2-p1000922.jpg

We used a small gear puller slightly modified with one of the arms shortened (we were following wstar's lead on this, so credit goes to him (see http://www.the370z.com/members-370z-...html#post59072 for more details if so desired)):
http://www.the370z.com/members/semte...9-p1000924.jpg

Stock pulley with the puller attached:
http://www.the370z.com/members/semte...0-p1000925.jpg

Here's how the engine looks after the stock pulley is removed:
http://www.the370z.com/members/semte...3-p1000927.jpg

And here's the new pulley, installed:
http://www.the370z.com/members/semte...8-p1000936.jpg

Driving Impressions:

My butt dyno hasn't noticed any huge gain per se. What is most noticeable to me, however, is that responsiveness has improved, especially off the line. Now, keep in mind that my Z is a 6MT. You know how when you launch off the line there's like a sort of momentary 'dead spot' or 'lag' when you initially engage the throttle and clutch? Well, this is where I notice the most change. That dead spot is virtually gone. My launches feel much more immediate now. The light goes green, I step on the gas and let the clutch out and BAM!! It's on! And I'm not even talking about hard launches. Just with regular around town type of driving, the responsiveness off the line is just more clean and crisp, if that makes any sense.

Also, you know how if you're driving with the AC off and then turn it on, you can actually feel the load the AC is putting on the engine? Like you can feel a bit of power being sucked away. Well, that feeling is noticeably reduced. It's not gone entirely, but it is reduced to a very significant degree.

Dyno:

Okay, enough with the butt dyno. Here's the real thing. I went and put my car back on a DynoJet this morning to see if there are any measurable gains from this thing.

Here's my previous DynoJet dyno:
http://www.the370z.com/members/semte...09balanced.jpg

Here's the updated one:
http://www.the370z.com/members/semte...ced-052009.jpg

So peak HP goes up from 324.61whp to 330.23whp (+5.62). Peak torque also went up slightly, but I'd say that the peak torque increase is negligible. What is more significant, torque-wise, is the positive effect this has had on the curve. Compare the old and new torque curves carefully. It looks like I've gained back some of the low-end torque that I lost when I installed the headers. (This would be consistent with my perception of sharper response off the line.) Also, if you look at the top-end, it looks like the torque isn't dropping off as sharply as before! I'm keeping it up longer!!! ;)

As for horsepower, I don't think a gain of 5.62 is half-bad, considering that I've already got the full intake and exhaust mods (i.e., my returns should be diminishing big time by now). All in all, I'm pleased with the results.

Video

YouTube - Stillen 370Z Underdrive Pulley Dyno Results


Don't forget to rep if you found this informative/useful! ;)

I'm really disappointed you couldn't find a spectacular bedspread to shoot the product photos on.. boo!

I don't think you can fairly compare the low end on those charts, the previous dyno runs were started at higher RPM so you just see the spool up lag.

The high end you can see the distinct change, you picked up 10 ft/lbs at red-line which is impressive. Thanks to the reduced falloff you would probably see a benefit from bumping up the red-line slightly.

semtex journal is back at NUMERO UNO!! haha. congrats on the install.

This is one mod any make of car that nobody dynos individually. Thank you for actually going about and doing it. Its good to see some hardcore proof of gains from an UD pulley.

Thanks man!

I'm only comparing the small bit from 2500-3000 rpm. I think it's fair to compare at those points. But prior to 2500 rpm I agree that it's due to the runs starting at different rpms. Having said that, the delta between the two from 2500 - 3000 rpm isn't much. But I'll take what I can get!

Nice work man. You'll be hearing from my lawyer shortly re: theft of my patented gear puller modification :p

LOL....hey, I've got a stack of gun magazines for a backdrop this time. Gotta change it up every now and then, you know? :p

HA! I'd better get my checkbook ready for the royalty checks I'm gonna have to write, huh?

Yep, fair enough. Now that you have the software figured out you can overlay the old best run with the new best run to really compare.

:icon14: Ditto. Unless Semtex acquiesces and at least throws a cigar magazine into the mix I'll have to stop reading his threads and force him to return my journal.

Thanks for a great writeup. I wonder how the lightweight pulley would compare to the underdrive one in performance. I'm most likely supercharging my Z in the future so an underdrive pulley would be inaptopriate for me.

Skorch, I was wondering the same thing, but have decided I will probably go underdrive for now then swap if the supercharger thing becomes a reality for me. I'm sure the underdrive will be a quick sale to a fellow forum member.

*sigh* Tough crowd. Okay how's this? Surreal enough for you? :wtf2:

http://i618.photobucket.com/albums/t...0/IMG_2299.jpg

You, sir, just won every award there is on this forum. :bowrofl:

One more question: how has the synchro rev-match responded to the pulley assuming that you have the sports package?

Ditto, and the fact I have to change my pants now! :tup:

BTW, great article!

I haven't really noticed much difference. I think a lightweight flywheel would make a more noticeable impact on rev times.

LOL - love the gun, love Jay-Z, and love Thomas! GG you win!

lmao I just spit coke on my keyboard when I saw that picture. Thanks!!

I'll grab my spotlight back soon enough ;)

Hi. Thanks very much for going through the trouble of doing dedicated dyno pulls just for a pulley change. I think this really means a lot to the community and helps us with our upgrade decisions.

On a side note, do you notice any subjective change in noise/vibration/harshness?

Thanks,

-Phim
__________________

Nope. No NVH changes.

Will you be doing the alternator and idler pulley also??

Looks like the UD pulley is 195 and the other two are just another 140.

5 WHP for 200 is definitely worth it, and if the other pulleys can get another 5 or so would be great.

It is on the list for R&D and production, but I know it's behind a couple of other projects, most notably some F/I projects.. :)

Down the road it's a good possibility..

Sorry to bring it back from the dead but this isn't the underdrive pulley but just the lightweight pulley? wow if there are no nvh changes and nothing else is sacrified at all, this could be the mod for people like me who want some ponies unleashed w/out raising db level in the cabin. Would u recommend it to serve that purpose semtex? as in there is literally zero sacrifice from stock? Thanks as always dude.

No, the install in this thread is the underdriven one (which is also light), not the standard diameter lightweight one. AFAICS there's no downside to putting it on, mine's been on for thousands of miles now.

Ah...got it. The underdriven pulley has no effect on the car's ability to produce juice for the accessories? Also, is it safe to assume that if you install just the light pulley as opposed to the underdriven one, the gains will be less pronounced? Thanks for all your help.

tbonesteak, I have an uninstalled regular sized lightened one if you are interested. Never used it, sitting on my desk as a paperweight.

The underdriven pulley is the one that does affect your accessories. The lightweight one (that RCZ is offering you) doesn't. In general, an underdriven pulley is going to slow down your AC, Power Steering, and Alternator at idle / low rpm, which may in turn reduce your available amps of current at idle, etc. Personally I think the effects are no big deal, but esp. if you plan on adding a monster sound system, you might want to consider that...

Haha i guess i didn't word my question properly...but i knew that the underdriven pullies affect the accessories. I was just asking on your personal experience how much you feel it has an effect. What are the differences in the gains between the regular lightweight one and the underdriven one? RCZ, i'll let you know if i want them. Just depends on if the numbers are worth doing the swap for. Thanks.

cant u get both the lightweight pulley and underdriven pulley?

The underdrive pulley is also lightweight. Being that they are cut out of billet aluminum they are significantly lighter than the OEM steel pulley.

It's technically a Lightweight Standard Sized Crank Pulley vs. a Lightweight Underdrive Sized Crank Pulley

ohhhh ok, so they both go in the same spot, their the same thing just for different purposes. therefore you have to get one or the other correct?

Yes.. one or the other.

The standard pulley uses the stock sized belt.. the underdrive pulley uses a slightly smaller belt (because the pulley itself is smaller, and requires a belt that's shorter)

As it's been discussed, the standard sized is for supercharged applications, as underdriving the supercharger would spin it slower and reduce the horsepower gain

^ so this would be ok for a s/c, I just want to make sure cus I plan on buying the stillen s/c

If you're planning on the STILLEN supercharger, you would need to use the Standard Pulley during that time. We have a lot of guys running the underdrive until the supercharger is available, and they will swap then.

^So it's going to be a twin screw s/c ;)

It will be pulley driven.. ;)

i feel kind of worried about underdriving all the belt driven componenets. will it affect the steering considering it will be underdriving the power steering pump?

I've only heard 1 person out of the hundreds that have purchased mentioned the steering at a dead stop seemed to take a little more effort, but that feeling was gone after a couple of days (getting used to it)..

Most others report no change is felt at all.

Very nice! 5whp gain (mind you, on a hotter weather too) from crank pulley is pretty decent!