Offshoreonly.com - blower pulley sizing help

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I thought about a serpentine swap however I think I would have to buy more than just pulleys...I think all the brackets are different and I'm running a crossover so I would have to buy the crossover with the pulley on it which is outrageous expensive so that's out lol

I had a 525 sc lower on my motor originally and I sold it with the blower...however it was much longer than the 575 lower so I think I may run into belt alignment issues with that plan

Those are the charts I was referring to and that's what confused me...If you follow the chart for what I have..6 1/4 lower(stock 575) and 3 inch upper...on a 502 that nets around 12 lbs of boost...even with the drop from the chiller that's 10 lbs...does that sound right?? I don't see that chiller kit from whipple adding that much boost??

I'm not saying you're wrong at all just a little confused on these charts and was wanting clarification on it..I agree with what you're saying and I think the 5.5 is the way to go for sure and worst case I can try to find a larger upper

thanks

Since you have the upper 3" already, I'd go with the 5.5 lower and see how it shakes out.
Its about the only option you have to keep the boost as low as possible with the 3" upper pulley.
Charts are charts and they won't be perfect 7 but are often a good reference.
Mild Thunder had real world numbers with the same 5.5" and 3" pulleys and said he saw 7#

For some reason that link to the thread where he talks about that wont work for me anymore...Was he 502 based or 454?? do you recall?

thanks

I would honestly try to use the 671, sell the 575 stuff off and go for it, you would be much happier.

Trust me I’ve been trying....have it listed several places including here with no real hits yet...I’m not gonna give it away tho either

Quote:

Originally Posted by BBYSTWY (Post 4622249)

For some reason that link to the thread where he talks about that wont work for me anymore...Was he 502 based or 454?? do you recall?

thanks

Not sure why the link won't work for you. Here is his post.

Quote:

Originally Posted by MILD THUNDER (Post 3668207)

According to that equation, my engines should have been making 10psi of boost with the 250 blower at the ratio i was turning them. I actually had 7psi.
However, that equation is pretty accurate on my new setup, using the 420 blower. it comes out to 6.6psi, and thats about where i was on the dyno. The 250's had very low hours on the rebuilds, so can't see it being they were tired. Maybe they just were'nt that efficent at 80% over, as the 420's are at 7% under.

All i know is with the 250, I had a 5.5" lower pulley, and 3" upper pulley, gave me 7psi on a 460CI. The 3.25" pulley gave me 5psi. :cartman:

A stock 575SCI had a 4" upper pulley. They ran about 4.5# of boost. I had a 3.25" on mine and had 6#. I had the rotors stripped and gained 1# of boost. I tried a 3" pulley for a while, but had a lot of belt slip.

Yea have been a little concerned about the belt slip..went through that on my ford lightning I used to have....I think I'm gonna try the 5.5 lower and 3" upper and see what happens....worst case i'll have to go up on the upper and lower if belt slip becomes an issue

thanks for all the help everyone!!

BBYSTWY, what ever ended up happening with this?

Long story short lol....

Never ran the 256...sold it and ran an 8-71 on the punched out 454...turned out the heads and cam I bought on here(the dart iron eagles) were junk and the machine shop never caught it. Didn’t hurt the bottom end at all just had other issues. So that being said...had to pull the motor again to put heads and a cam in...through the process of that I ended up with a 540 with engine quest heads(thanks mild thunder for the help!) with a 14-71 and Holley efi on it. Made 960 with 4 lbs of boost at 6k rpm...got it in the boat last fall and ran out of weather. Have to finish some wiring and some in the water tuning and she’ll be on the water early spring fingers crossed!!