the ATI is both overdriven and underdriven

https://my350z.com/forum/5859855-post567.html

I was pretty close with my measurments in that post^

The exact figures for the street pulley (which 99% of us are using) are:

Air Conditioning is 32% underdriven
Power Steering and Alternator are 15% overdriven

They also have race pullies which eliminate the accessories, but I haven't pulled one apart to measure it

 

I have not seen a stock sized fluidampr--just a 6.5" one (od):

http://fluidampr.com/NISSAN.htm

Do you have a part number/link for a stock size fluidampr?

 

Adam do you have the part number for the crank pulley you have? From the ATI site, there are only OD pulley available. I wish there was a stock size or even slightly UD dampened crank pulley by ATI or Fluidampr, but I haven't seen a part number for either. Are you sure you didn't measure the diameter of the inside shell and not the outside. Like others said, chances are you have the street 6.78". The closest to stock size I am seeing is 6.325", which is still OD from the stock size of ~5.7". The smaller size, however, is "race" and I'm not sure what that means in comparison to the larger OD "street" version. Does anyone know?

 

Why not stay with stock pulley? Is there any negative affect by keeping a stock pulley on a built motor? So far I have not had any issues with my stock pulley at 6k miles on the motor.

 

^^That's a possibilty, but the consensus is the stock rubber dampener can degrade over time and does not do as good of a job as the ATI or Fluidampr unit. Some high hp have broke the stock crank pulley as well. But the stocker is definetly better than a completely undampened pulley like a UR. I assume you are F/I if you have a built motor?

 

Yes Sr, Turbo. What kind of power have they broken at if I may ask, by high I assume 700+?

 

^^dunno, first hand, but some searching on threads should reveal.

 

Does anyone know the exact size of the stock crank pulley? I am thinking of asking ATI if they can custom make me one around the size of the stocker.

 

I run an ATI as well same as Rich with the idler deletes.

 

It's 5.75" OEM crank

BTW, I believe you are currently running a normal-sized ATI for the 350z? Do you realize that if you get an OEM sized pulley you will negate any gains you got RPM wise from your supercharger setup? Or are you doing this because you are worried about overspinning the blower?

 

Yes, I am worried about overspinning the blower.

I purchased the stage 5 SC kit and the ATI crank pulley--part number 918588. ATI lists the OD diameter of that part number to be 6.78" (~1" bigger than stock ~5.7"):
http://www.atiracing.com/products/da.../damnissan.htm

From other's measurements, the GTM higher stage 10 psi pulleys are ~85mm (~3.35").
https://my350z.com/forum/8285566-post77.html

From HKS website, the GTS7040 has a 9.444 drive ratio and a max impeller speed of 110,000 rpms.
http://www.hksusa.com/info/?id=3767

I have a revup engine, so my redline is 7,000 rpm.

When I plug these numbers into an impeller speed calculator like the one found here:
http://www.928motorsports.com/servic...ingpulley.html
the impellar speed at 7,000 rpms shows 133,738!

The impellar speed would be passed its max limit around 5800 rpms and would be ~23,700 rpms higher than the max limit by redline. If this is correct, than the blower is overspinning, throwing the flow out of efficiency range, and possibly causing damage to the bearings/shortening the life of the blower?

I was thinking adressing the crank pulley might be good, while leaving the SC pulley as it is. Although I would rather have a true dampened crank pulley on the car, if I put back the stock one (~5.7"), the impeller speed at redline would be ~112,435 at redline. If ATI can make me a custom crank pulley slightly smaller than stock (~5.6"), the impeller speed would be (110,462) at redline (if the calculator/figure are correct).

 

Right...gotcha Hopefully your numbers stay pretty good...

I should have gotten a damper pulley when I built my engine for my Vortech setup...well, I'll have to get that done in the future, and I will be using the Fluidamper because the ATI will overdrive my Vortech in a crazy way as well; the Fluidampr will as well, but not as much, I can cog pulley down to compensate...

 

^^I know I would probably lose a psi or 2, but hopefully the power curve would be more linear to redline and there would be less risk of damage to the bearings/blower.

 

^crazy u just realized that now, havent u been running that HKS kit hard for almost a year now?

 

I'm using the fluidampr pulley and compared it to stock and they are 1:1
so you can use the stock belt sizes

 

yes, unfortunately. Luckily the only times its seen past 5800 rpms was on the dyno and maybe once or twice on the street. Still I need to address the issue now and don't know the best way to go about it.

 

Your part number is 64091. That is listed as having an OD of 6.5". If stoick is 5.7", that's .7" larger than stock size. How can they be the same for you/use the same belts than stock?

 

^I haven't added the accessories but i put the pulley face to face and they seemed the same diameter.

I will try to post pictures once I take out the other motor and show the difference between stock and the fluidampr

 

If you call ATI, they will verify exactly what I have posted and measured. Belt sizes are totally different from stock as a result

 

they will - it will end up costing around $1000 though by the time it's said and done though