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Old 09-22-2012, 08:42 PM   #1
tnspd

 
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Differences in Pulley swap

Ok, Engine tuners and builders, I need an education.....I read where some people are changing the upper pulley only and some people are changing the lower pulley only. What are the advantages of changing the upper over the lower and the lower over the upper. I would like to understand this difference.
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Old 09-22-2012, 09:09 PM   #2
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Changing the upper only is cheaper and allows you to also change the noisey stock coupler to a quieter solid one.

Changing the lower requires you also change the harmonic balancer so that's the added cost.

The upper does require removing the blower front snout as the pulley is pressed on.

Beyond that, they accomplish the same goal of spinning the blower faster for more boost and some times are done together because going really large on the lower requires moving things around to make room (other pulleys, hydraulic lines) so a combination with a medium lower accomplishes the same boost as a large lower alone.

Hope that helps!
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Old 09-22-2012, 09:28 PM   #3
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Yes, that helps. Is there a difference in the boost that each one will get you? Obviously changing both gets the most but what about the upper versus the lower on boost addition? Which is the best for the motor or that does ot matter?
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Old 09-22-2012, 09:32 PM   #4
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There have been some boost tables posted in other threads. I'll find a link...
Changing cams, exhaust, CAI, and porting will affect boost levels as well (lower) due to freeing up resistance to airflow.
I'm currently running a 9.1 lower / 2.55 upper and the most boost I've seen is 14psi. That with extensive mods to flow air better through the engine.

Keith with KDi who I think you met last night is who I worked with on my build up by the way.

From Blown355 on this thread: http://www.camaro5.com/forums/showthread.php?t=247013

Crank ______SCPulley____Ratio_______Boost
8.0------------2.95--------2.71--------8.6 psi (stock)
8.0------------2.55--------3.14--------13 psi (changeonly SCpulley)
8.6------------2.95--------2.92--------10.5 psi (changecrank pulley)
8.6------------2.55--------3.37--------14 psi (changebothpulleys)
9.1------------2.95--------3.09--------11.5 psi (changecrank pulley)
9.1------------2.55--------3.57--------15.5 psi (changebothpulleys)
9.6------------2.95--------3.25--------13 psi (changecrank pulley)
9.6------------2.55--------3.77--------17 psi (changebothpulleys)
10.0-----------2.95--------3.39--------14 psi (changecrank pulley)
10.0-----------2.55--------3. 92--------18 psi (changebothpulleys)
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Old 09-22-2012, 09:41 PM   #5
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Nice thanks. So changing the upper gives more boost than the the lower unless you go with a large lower pulley.
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Old 09-23-2012, 03:55 PM   #6
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Belt slip would be less likely when increasing the lower pulley compared to downsizing the upper... but what i read is that beltslip isnt an issue on the LSA so thats a mute point
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Old 09-25-2012, 05:35 PM   #7
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I haven't experienced any belt slip yet with about 2000 miles now on my build. I'm guessing the belt might be more likely to slip with age but we'll see...
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Old 09-25-2012, 05:38 PM   #8
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I have 8000 miles on my setup and no belt slip
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Old 09-30-2012, 11:54 AM   #9
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Any boost figures on the 10" lower combined with the 2.38" upper?
I have the 2.38" upper and I'm ordering the 10 inch lower.
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Old 09-30-2012, 02:51 PM   #10
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Quote:
Originally Posted by 2012ZL1 View Post
Any boost figures on the 10" lower combined with the 2.38" upper?
I have the 2.38" upper and I'm ordering the 10 inch lower.
My guess would be 19psi from the above chart. That is probably faster than you should spin the supercharger.
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