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Old 12-02-2008, 06:49 PM   #1
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jrsc overspin question

hey all,

I was just reading on the FJ and found this post.

I'm quoting.

"The formula is simple and I'll explain it for my PowerWorks blower on my SVT because I know exactly what the specs are. It will translate whatever size pulley you use on a JRSC.

On my SVT the stock crank pulley is 5.2" in diameter. The PowerWorks blower pulley is 2.8" in diameter.

Multiplying diameter by pi gives you circumference.

5.2 x 3.14 = 16.328. The crank moves 16.328 inches of belt per revolution.

2.8 x 3.14 = 8.792. The blower needs 8.792 inches of belt to turn it one revolution.

Now we find out how many revolutions of the blower we will get when we turn the engine one revolution. Simple gear ratio.

16.328 / 8.792 = 1.857142. The ratio is 1:1.86 roughly.

Now we want to find the blower rpm at a given engine rpm. So we multiply the ratio by engine rpm. I'll use 7000 engine RPM.

7000 x 1.857142 = 12999.994

So at 7000 RPM my PW blower spins 13000 RPM with a stock crank pulley and a stock blower pulley.


Class dismissed.


-edit-

I gave you guys the lengthy version. You can also just divide the crank pulley diameter by the blower pulley diameter and multiply by engine RPM. Same answer. But it's intersting to do it my way because them you can determine belt speed. At 7000 rpm, a stock SVT moves 9524 feet of belt length per minute. That's pretty close to two miles.

Before I forget, there is no linear correlation between blower speed and manifold boost pressure. There are WAY too many variables to calculate that with good accuracy."

anyways, the JRSC max rpm is suppossed to be 16000 rpm w/o overspin, so by these calculations, you get.

BBK w/ stock crank pulley. diameter of stock crank pulley is 5.1875 in. and bbk pulley is 2.5 in. so 5.1875/2.5 = 2.075 so at max power for the jrsc, you get 16000/2.075 = ~7711 rpm

BBK w/ 5.7 inch dia. OD crank pulley = 5.7/2.5 = 2.28 so 16000/2.28 = ~7017 rpm.

so is my logic correct here? i may have pulley sizes off but i did some searching and i found those numbers.

so i can safely go w/ a 5.7 OD pulley and be fine?? of course this is w/ a proper tune.


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Old 12-02-2008, 06:52 PM   #2
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o, and this is assuming the IAT temps are safe!!! this is only the idea about overspinning the sc!! i will be using WMI.
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Old 12-02-2008, 07:59 PM   #3
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You wont be able to haul enough WMI to keep it cool.

You can spin the JRSC to stupid rpms but your never really going to make any more power due to its small size, inefficiency and lack of cooling.... basically when you start to overspin the JRSC it just becomes a heat machine.
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Old 12-02-2008, 08:05 PM   #4
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i thought the jrsc started overheating w/ the need for wmi at 16k, not w/ just the bbk.
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Old 12-02-2008, 09:49 PM   #5
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So you think the 2.4" snout pulley w/ the CFM 5.7" crank pulley @7k RPM would be too much for the PWs?
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Old 12-02-2008, 10:00 PM   #6
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Oscar once told me that the SVT JRSC/BBK had a little head room before it would be at max efficency and that the ZX3 JRSC/BBK had no head room and should not be spun any faster. He also touched on his thoughts about WMI and how he thought the water molecules took up volume that does not compress like oxygen. Like Orange said, overspin equals heat machine, equals blown motor.
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Old 12-02-2008, 10:09 PM   #7
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god i wish there was an intercooler for the JRSC!!!! lol
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Old 12-02-2008, 10:16 PM   #8
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I've been researching an intercooler for the (SVT) JRSC on and off for a little while now... nothing concrete yet, though.

As I mentioned on FJ, the Powerworks kit and the SVT JRSC kit both use Eaton M62 blowers, but the JRSC/BBK pulley is 3", and the Powerworks kit is available with a pulley all the way down to 2.4". It seems that even Oscar agrees that there's room to spin his kit, and I think that's proven with the Powerworks. All that's needed is sufficient cooling.
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Old 12-02-2008, 10:18 PM   #9
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ya, but unfortunately, there isn't much in the way for the m45 other than WMI!!
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Old 12-02-2008, 10:34 PM   #10
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Even though the JRSC and Powerworks are M62 blowers, they are not the same. The JRSC is a version 4 and the Powerworks is a version 5. Each version has about 10%-15% improvement over the previous version. I`m hoping that Eaton makes a direct replacement for the M62 with their newest line of blowers.
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