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Discussion Starter #1
Wondering how everyone sets them up. I have seem many go with 6.87" crank pulley and 3.33" sc pulley how is that compared to 8" crank and 2.85"-3.15" Sc Pulley? Does one setup offer more low end boost? Boost on demand? Love to hear how the setups are.
 

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Oh and underdrive vs non underdrive? Could someone explain? And I understand underdrive runs all equipment, ac, alt, power sterring. Vs non underdrive being the standard belt for the car and then the additional only running the SC?
 

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The 8" lower give you more belt contact to prevent belt slippage as well as the larger upper pulley. Larger the crank pulley the more boost you will have. The smaller the SC pulley the more boost you will have. I am curious to what combo's in pulley sizes match up to make same boost. Example a 6.87" lower pulley with a 2.50" SC pulley make the same boost as an 8" crank pulley with a 3.33" SC pulley. I wish someone would have a chart to reference. Im switching from an S trim to a YSI and would like to have the 8" lower and a large pulley on the SC but currently I'm stuck with the 6.87" with small SC pullies. If they were cheaper it wouldn't be an issue buying a few to see but I'm not rich. LOL
 

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I generally gained around a pound for every pulley size I went down. The 3.12 6.87 is what I rolled with. I tried a 2.85, but gained too much tq and hp for my liking with the stock shortblock.
 

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I have an 8" crank with a 3.33 upper, I see around 15 psi. WIth the 6.87" crank and 3.33 I see 10 psig. The boost comes on earlier and the mid range is alot stronger with the 8" vs 6.87".
 

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I have an 8" crank with a 3.33 upper, I see around 15 psi. WIth the 6.87" crank and 3.33 I see 10 psig. The boost comes on earlier and the mid range is alot stronger with the 8" vs 6.87".
What head unit? I have a YSI with a stock block and I'm trying to figure out what SC pulley i will need to be at 10-15 psi with the 8" lower. Right now i have an S trim with 2.50 and 6.87" hitting around 15.
 

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I have an 8" crank with a 3.33 upper, I see around 15 psi. WIth the 6.87" crank and 3.33 I see 10 psig. The boost comes on earlier and the mid range is alot stronger with the 8" vs 6.87".
great feedback! I have been wondering how the pulley changes affect the curves as well and Vortech support is pretty much useless when i call with these questions, so this helps ALOT! thank you
 

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i have a 8'' 10 rib custom crank pulley also going on my stock cobra with a ysi blower and procharger intercooler setup i am going with 10 rib 3.80 pulley up top
 
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