Hey guys have a quick question. Would this be to much to install if I already have the 17% pulley installed already ? I bought a ATI in stock form already but seen it was offered with a little more now from when I bought mine or I didn’t notice. Basically asking if this would be safe to run with the 17%. Thanks

 

The one thing with anything that provides more boost is heat. At approximately 19% I think you are either at or past the point where the ECU can effectively manage the fuel mixture. Throw in that after either allot of hard running or some short hard running mixed in with long road drive, heat sink is going to impact performance.

 

And yes I have one but kept my JCW SC stock pulley.

 

Ok thanks. That’s what I was wondering about.

 

In "stock" form, the ATI is already about .8% larger than oem so you are already slightly over 17%. Not sure how percentages translate from the crank pulley to the supercharger, but going with the 2% instead regular ATI will probably get you less than 1% more.

 

Gotcha. I did not know that. Well looks like I’ll just use the one I already have then. Thanks for the info.

 

I see around 14 psi with the 2% overdrive that works out around 2 psi more than the just the JCW 12% pulley. Thinking that Way Motors may have some more information as they had ATI make the special size up.

 

This is interesting. I am interested in who made this measurement and if was done accurately. just saying 0.8% larger is ambiguous. If is the diameter it would translate to 0.4% higher RPM seen by the SC, while radius will translate to 0.8% higher RPM.

 

Way sent me the information once but I may have flushed it when I did some email cleaning.

 

"The stock size ATI damper is actually .8% larger than stock, reason is the design of the damper can't be made any smaller due to the internal weight size. Our WMW 2% oversize ATI is 2% larger than a stock damper. Now just remember that is 2% on the crank, that does NOT equal 2% on the supercharger. With the stock size ATI the most boost increase I've seen is .5lbs. With the 2% I expect the most you'll see is 1.5lbs more."

Posted by WMW here:https://www.northamericanmotoring.co...ml#post3468157



pnwR53S, you're better at calculating these things... do these look right?

On ATI's site the regular ATI is 5.67" OD and the 2% is 5.74" OD. 5.67 x 1.02 = 5.7834 so the regular must be larger than stock?

5.67/1.008 = 5.625 (stock?) x 1.02 = 5.7375 (ATI 2%)

 

Thanks for the source of this info.

LOL. A lot of interferences on the OD's. So these are diameters which in percentage wise is 1/2 the RPM change. The increase in PSI cannot readily calculated and can best be measured empirically, and that is to ignore all the measurement challenges of guarding against measurement error due to ambient temperature change, gradients, heat soak etc etc.

Suffice to say a 0.04 increase in RPM is down in the mud for all practical considerations, and your water pump won't begin to cavitate and the alternator won't cause the precious xenon lights to burn out.

This leave me wonder are the common 15% and 17% reduction pulleys are measured in diameter, as supposed to RPM increase? Just a mental exercise.

 

From what I've seen in past posts when trying to determine what size a JCW pulley is, I believe the SC pulley percentages are also measured by diameter and not boost.

 

I agree that is most reasonable inference.

 

I have an analog boost gauge so my comments above are based on the gauge. Thinking there might be some old posts from the golden age of NAM on what the actual boost values are vs the pulley sizes. Would also think that Jan at RMW has some charts generated during all the testing he has done.

 

So from what I’ve gathered I’m going to just use the stock size I already have now. Will be installing soon just wanted to know pros vs cons of the 2%er. Will my belt work with this crank pulley being it’s a shade smaller ? Also could I send my computer out to be tuned or
Do I need bigger injectors

 

Crank pulleys get larger when with %'s and SC pulleys get smaller. The stock belt should work since the change is minimal, but WMW or another vendor can confirm what size you should go with. In general, a tune or injectors is not needed if you're only changing the crank pulley. It might be a good idea if you're already experiencing some issues, or just want to get the most out of your mods.

 

No issues at all with the car. Just wondering if a tune would tie it all in together. I’ll contact way and see what I should do.

 

Many will say that a tune is required if you install a big head, a cam or change the injectors to over 380's. There are vendors here that will do a tune where you send them the ECU and then there are vendors here that can send you a tune over the internet and buy/rent a special tool to download it.

I went with the second option when I installed both a cam and 450 injectors.

 

Thread Resurrection
Will likely be getting an ATI damper, thinking standard size but curious about the 2% option.
My thought is, I already have a hfs-3 meth kit, so the increased heat of the 2% might not be so much of an issue with my 17% pulley I also have??
So I get the bit more extra boost and can actually use it on top of the 17% pulley because the meth will cool it??
That's my thought.... What y'all think?

 

Remember also, you are not going to be at full boost for very long at any given time. For a second or two, just before you shift.
The ONLY way you would worry about damage is if you are running at El Mirage or Bonneville. That is,100%, full throttle for three or more consecutive miles at a time.

Mike

 

Thanks and I beleive your right. I'm not so concerned about damage as it's should be a safe combo especially with the meth. But will all the supposed power be usable or would I have reached diminishing returns??

I don't track my car, it's a daily, sees some freeway use and plenty of spirited back roads driving.
But I guess if I ever change my mind and decide to track it later I should not go 2% then??

 

Go for it. With the meth can boost all day long

 

Again, how long will the straight be that you will be using ?
Most full NASCAR / Indy car track straights are in the 1/4 or 1/3 mile long area. I doubt full throttle for 1/4 mile will be enough boost heat buildup that the ECM would not notice that and reduce the ignition timing for it's own safety. This reduction change would come from the engines knock sensor. The engine has its own built-in safety system with the ECM in stock or street form.

If I were running my car on the full road course at Fontana Raceway (uses most of the front straight as part of the road course), I would not be afraid to run the larger damper on my car.
Matter if fact, I have one for my JCW. I have a couple of other tasks I need to complete for other people before I can instal my ATI damper. Probably around the beginning of summer.

Again, you won't be at full throttle the whole straight, there will be shifting involved, with the pressure going up and down as you move the gas pedal. I've noticed on my analog gauge, the boost is VERY eager to drop the instant the pedal pressure is lessened, even just a tiny amount.

Mike