JRider

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.

BBYSTWY

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

BBYSTWY

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??

BBYSTWY

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

Griff

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

BBYSTWY

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??

BBYSTWY

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!!

BBYSTWY

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!!

Griff

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 b&m 250 boost chart

BBYSTWY

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