Looking at your for sale ad I would say you already have an undersized pulley on the 256, I think the Teague superchiller kits for 575 came with 3" or 3.25" depending on the power level of the kit.

yea measured it today...its a 3 inch upper so i'll have to base my lower off of that...hoping to net around 6 lbs would be ideal but anywhere 5-8 I would be happy

so if I have a 7 inch lower and 3 inch upper...from what griff said that will be 2.3333....so would that be 100% overdriven?? how would that equate at 5600 RPM and would that be too much??

https://cimg1.ibsrv.net/gimg/www.off...f4cc32dfb2.jpg

according to this chart from weiand...looking at the 3.05 upper a 7" lower puts me at 130% overdriven...where should I be with the 256?? at what point do these things grenade?? I'm running a chiller as well don't know if I mentioned that

Actually 133% overdriven and most likely it would be close to 10# of boost. I think you will only want to be about 50% overdriven.

TBS 250 pulley/boost chart. http://theblowershop.com/wp-content/...-Catalog-7.pdf

So should I look for a larger upper pulley then?? just looking at the chart I posted even a 6" lower still puts me at 97%

The blower shop chart is based off of a 6.4" lower and seems to correspond with the chart I posted I think??

Also should I factor in my heads/cam and chiller into this equation or just base it off of stock heads and no chiller??

I know its hard to guess boost and overdrive levels I just want to get in the ballpark as these pulleys aint cheap hahaha

Thanks!!

Ok so this is what I came up with...

5.5" lower and my current 3" upper puts me in the 88% overdriven realm...close to anyway....Do you guys think the little ole 256 can handle that?? I haven't been able to find a conversion to put that to a boost number but if you figure I plan to run 5800 rpm on the high side and figure overdrive at 90 to make it easy it puts me at 11,200 blower rpm if I did the math correct....is that ok?? too much??

Mind you I have ported dart heads 8.5:1 comp ratio chiller 454 based engine..I assume the chiller and heads will tame down the boost numbers slightly??

Thanks guys!!

Too much maybe based on the chart
Page 10 http://documents.holley.com/techlibr..._tech_info.pdf

But it looks like Mild Thunder got 7# with those sizes https://www.offshoreonly.com/forums/...ost-chart.html

Something doesn't seem right...the stock lower is 6 1/4" roughly and the 3 inch pulley was part of the whipple chiller kit...I don't understand I guess how that's what it was setup stock(well with the whipple kit) but if I go smaller even on the lower which would lower boost and drive speed it is coming out to spinning it too hard?? I'm just trying to understand...should I just try to match the stock lower?? 6-6 1/2 inch lower???

thanks