the crank shaft its harmonic balance?

Huck

If you don't install them I may take them off your hands if the price is right, I just have the normal size stillen crankshaft pulley, I wouldn't mind having an under driven set something to think about.


Sent from my iPizzle using magic and new-fangled science stuff

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DEpointfive0

I said I was gonna lowball him first!!! Lol

luigi90210

from what i read OP is that pulley mods will give you like 2-3whp in 1st gear, 1-2whp in 2nd, and 3rd all gains are negated from the underdrive pulley

honestly it isnt worth the money and the risk, if you want better throttle response, buy a light weight flywheel or have up rev change the throttle tables

the only situation i can see a pulley being worth the money is when you are building an N/A race car and you were given the car for free and given a budget to spend on building the car, then picking up 3whp here and there will add up and might give you the upper hand in the race

DEpointfive0

Again, this is arguably the most polarizing issue here on the forum, and we ain't getting anywhere quickly

Let's leave it to the car owners to install of not install these... If anyone bought a kit and feels it's unsafe, feel free to contact me and I'll lowball you for a quick sale, LOL

I'm not an engineer although I'd really like to think I am... If these REALLY caused premature failure in ANY WAY, SHAPE, OR FORM, there would be overwhelming evidence showing that... We unfortunately are all ASSuming what counterweight this, harmonic that, and pulling quotes from the Internet and other forums, which can be the LEAST reliable sources of information...
I DO believe and will state again that shítty install causes pulley issues...

I have a Stillen 20% under drive, would I ever take it off? No, will I continue to install one on every car I own? Yes
Hell, I already have a kit for the Maxima I am forcing my dad to buy, lol


Some of us (7AT) don't have a flywheel, and it's also about removing rotational mass, so the car feels peppier. I try to explain it as, "Have you ever driven a car with a lightweight flywheel? Well this is like 10% as much as that does"


If it makes díck difference, I'll ask my best friend's dad who IS an engine engineer (for Cummins diesel though) if he has any input

Red__Zed

absolutely. I don't give a crap what you do to your car, but I do think it is important that others making this decision have the requisite information.

Most modifications are not done for reliability, and it is absolutely up to the owner to decide what is worth it for them.

This piece is something I don't agree with. First of, I'm not assuming anything, or basing my stance on what I read on some random internet site. I've got a pretty decent background in frequency response of systems (admittedly not in the mechanical domain, but the math is all the same), and a basic understanding of physics. Most of this stuff is pretty basic physics 101 (OK, maybe 201).

To poke holes in the claim that "if this caused failures, we'd have OVERWHELMING EVIDENCE proving it," let me present the following:

As someone who understands cars, your forehead would probably leave an imprint on your desk/keyboard if someone came on the forum and made such a claim. It's an absolutely ridiculous statement (though it does seem these cars will run for a surprising amount of time with no intake filters, who knew?)

Unfortunately, the general populace is poorly educated on things like frequency response of a system, compared to the intake operation of a combustion image.

To be clear, as I've said before, I'm not sure how dramatic of an effect removing this part will have. But again, neither does anyone else who hasn't modeled the part.

Removing it may shorten the life of the engine by 80%, or 3%. In all likelihood, you'll have the part on for 30-50K max, and no failures will ever be linked back directly to the pulley.

The point here is twofold:

1) Let's make sure we paint the whole story to those who might consider this part. Evidence of operation without failure is great to share, and helpful in establishing just how much the part matters (or doesn't). Pretending like the 3-4 guys that have more than 25K with a pulley unquestionably establish the reliability is silly

2)Don't be a lemming. There's no reason we shouldn't demand more information from pulley manufacturers to show that they've done their homework. It might be enlightening.


that could actually be enlightening. See if you can get him to sign up on the forum.

DEpointfive0

^rep added

DEpointfive0

I agree with most of what Red_Zed has said


Again, if it was a piece that really ruined the engine, we WOULD see at least ONE damn failure or engine blowing up, lol
I have seen a broken pulley due to shite installation...
Just saying that at least if the parts were made bad we'd have more than ONE failure... But I don't think we do... And a lot of us BEAT on our cars, people track with them too


And about the harmonics thing, (again, I'm not an engineer) but lets be real, cast iron isn't a precise science, under heat it can expand and stretch more UNEVENLY than billet aluminum, messing with those harmonics, yeah, 8k RPMs is fast, but I think the amount of play in the pulley will be there with out without that BS rubber band...

Ex: most people think glass is a solid... Watch Mythbusters where they break wine glasses with sound, that bítch bends and wobbles as much as any liquid I have seen (yeah for the record, glass is more a liquid btw) so what makes us think the unrefined MASS produced pulley doesn't wobble that much...


And I also think it's one of those scenarios where the manufacturer tries to make things NICE...
They TRY to make the intake boxes flush, they try (maybe not in our cars) to make them quiet (the exhaust is), they Make the engine mounts and trans mounts rubber... Things like that...
And I bet those intake boxes were "engineered" 15-100 times more than any Stillen, AEM, or Takeda intake, why? To make it quiet or nice looking...

Replace those bushings and intakes and exhausts, the car gets louder, it becomes sharper, you get more power... (they make the car for the 90%, not us forum ássholes 10%, lol)

Red__Zed

Trilitheum

^^ Just to correct an error so people don't get wrong info, Cast Iron has a CTE (Coefficient of thermal expansion) of 5.8 10e-6 in/in deg F, Aluminum 6061 or 7075 has a CTE of ~13.0 10e-6 in/in deg F, (not picking on you DE) the cast iron actually expands less than the billet aluminum by about half as much.

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2011 Nissan 370Z Touring/Sport, 6MT, KAD

DEpointfive0

... Maybe with a nice quality piece of cast iron... That POS the crank pulley is made from... Mehhhhhh... I bet it expands more, or more importantly, unevenly vs aluminum

(That's more what I meant, the uneven expansion in shítty cast iron)

DEpointfive0

I'm going to sleep now at 6AM hopefully.

You guys have fun beating this dead áss horse, and when I wake up I'll jump in again too! YAY!!! Lol

wstar

Well, I'm sure we will see pulley-attributed failure, eventually, if the threads aren't out there already waiting to be found. Some will be installation issues, and some will be choosing the easy target when the real cause of engine failure hasn't been accurately determined and they want a scapegoat. Separating out the true pulley-induced failures over the internet would be difficult in itself.

My engine's at ~34K miles now, with over 2K of that as track miles. I've had Stillen's 20% underdrive pulley on for most of the engine's life, and not had any issues so far as I can tell. I think it's probably reasonable to assume, although certainly not proven, that altering the weight there could at least wear out some bearings faster, as mentioned above. Does it make a 5% difference or more? No idea. If anyone's done the engineering study to figure that out, you'd think it would be the pulley mfgs.

I also question why people never bitch about swapping in lightweight flywheels as much as they bitch about this mod. The flywheel would be at least as important in terms of balance (but maybe not so much damping), and is far more difficult (and critical) to balance correctly when manufactured.

If you're on the fence (not because the data's on the fence, but because nobody here really has conclusive information), my gut feeling is that even if you believe the worst, it's probably even safer on a 7AT car than a 6MT car, as the 7AT has the crankshaft coupled to the Torque Convertor, which probably acts as a huge fluid damper most of the time anyways.

The most-legitimate reason I've seen to fear this mod so far is what GTM documented and others have verified (and makes basic sense): these Al pulleys will often weld themselves to the crankshaft over time. Dissimilar metals and heat and a tight fit and constant rotational torque, etc. If you ever want to take that pulley off again (e.g. to do some engine-internals work... or I think it also has to come off to replace the oil pump) or plan to go FI (which probably ups the harmonics risks and makes it pointless to worry about little things like pulleys), you need to be aware that removing the Al pulley could be very very difficult and require some serious heat and torque.

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7AT Track Car!
Journal thread / Car setup details

7419sundat

A lightweight flywheel does not balance anything. Our cars use a dual mass flywheel to eliminate gear chatter and and make it easier, smoother to get going.

luigi90210

well im just giving OP my opinion on the mod, from what i have read on mustang forums, LS1tech, honda forums, other nissan forums, ect. that underdrive pulleys are generally not worth the money in the same sense that headers are not worth the money and i have read about pulley attributed damage(whether or not it was cause of bad installation is a whole other story) and honestly it doesnt seem like a risk I would be willing to take for just 2-3whp in first gear(again from what i have read whether its Z related or other car related)

if someone likes swapping pulleys on their vehicle, then more power to them, if OP decides to put an underdrive pulley on his car, then more power to them
i personally wouldnt swap pulleys on my car, but thats just my $0.02

SS_Firehawk

Here is the issue regarding arguing my points. There isn't an aftermarket company on the planet that has the R&D of a car manufacturer. Due to the nature of the industry, Most Engineers that design cars are not going to expound in much detail, if at all on why they may have done things a certain way. There is plenty of research on resonance, torsion, N/V/H, and negative harmonics because it's already a known. Most of my findings are from manufacturers, but also reading about the issue at hand. I haven't read a single cited source that has said specifically, the way our pulley was designed, that it is a dampener of potentially destructive harmonics. Every description and engineering paper I read shows a rubber dampener that is encased with the rubber set vertical, or viscous. Ours is horizontal to the motor and only about 5mm thick. It looks like it's preventing all the accessories from vibrating or introducing more N/V/H to the crank as opposed to removing bad harmonics from the engine itself.

Every car company is going to say, leave your engine alone and it will be fine. Every aftermarket company that makes parts for said manufacturer is going to say, "Buy this and it will be even better" Who do you believe? Forums like this is feedback from everyone. I said it before, take everything you read in here with a grain of salt. Yes, even everything I say and argue about, which I admittedly do a lot sometimes. I'm not out to convince the World, but there are always two sides to the story. Obviously, it's difficult to go wrong with a stock crank pulley. I 100% agree. I also believe a well engineered aftermarket crank pulley can be safe to use. Some do not. People ask why, we say what we think, preferably have relevant source material to back our findings. Could I be wrong? Absolutely. Is the Bible indisputable fact? Do you believe every animal floated around Noah's ARK for months and the entire Earth flooded?

I used the word mitigate because regardless of internal or external balancing, spin a motor fast enough and even the best motors can grenade to harmonics. If Nissan plans on spinning the VQ to 9-10,000 rpm or higher, I'm pretty sure we would see a different crank pulley, maybe to a true dampener.

FYI, I never stated my finding's as absolute facts. I listed my arguments to the topic.

Regarding my statement about external balancing not being necessary, it is absolutely true for some smaller displacement motors. I think the VQ fits in this category, but there is room for argument there.

Lastly, and I'm repeating myself, DO YOUR OWN HOMEWORK AND COME UP WITH YOUR OWN CONCLUSION!!! I'm tired of people giving recommendations like it's fact and not letting them decide for themselves by only giving them one side of the argument.

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