bump....can anyone comment on using stock pulley sizes?? something doesn't add up to me??

Stock for what?? A 575SCI?? What size are they??
Keep in mind the 575SCI is a 502 ci. The same size pulleys used on a 454 will have 2# or more boost than a 502.

I have the stock 575 lower which is a little over 6..6 1/4ish and the top pulley I know is not stock as its a 3 inch...my question is if they sold this kit for a stock 575 then why couldn't I go with that pulley ratio on my 454?? as far as the blower RPM is concerned?? I understand it would be more boost on a 454 than a 502 I'm just looking at it from a blower speed stand point?? I'm assuming my heads, the chiller, and the boring may put me in the same boost realm as a stock 502...is that safe to say??

thanks

The stock 575sci pulleys for both top and bottom should put your 454 at 6-7# of boost.

Ok that's what I needed to know...do you know the stock size upper?? I need to calculate that drive ratio and shoot for the same on mine then...I cant use the stock lower so I plan to size the lower accordingly to maintain the 3" upper and achieve 6ish lbs of boost

I read this thread multiple times & maybe I'm stupid but I'm lost on what your starting points are.

What do you have for the upper pulley, lower pulley, type of shafts, length, number of splines, 3 belt lower, single belt/serp lower, etc?

Also your running a chiller, if so, it eats up about 2lbs of boost so that need to be calculated in also when your figure your numbers. Plus the charts will be off a few lbs also.

LOL yea I realize this has been a little confusing...it started with me thinking a cog swap of my 256 was going to be easy...jumped the gun on that so its not easy haha

Here's what I have...

256 blower with whipple "kit" I.E. chiller and 3" upper pulley
stock 575 lower pulley which I can't use as I have v-belt accessories so I have to buy a lower pulley to drive the 256
454 based....030 over, dart iron eagle heads ports cleaned not fully ported, cam is similar to stock 525 efi cam with a wider LSA from what the motor shop told me...was half asleep so didn't get all the detail/specs but I will if needed, JE flat tops with head work will net me 8.4ish:1 comp, stock crank, eagle rods
I'd like to see 6ish so 5-8 lbs of boost if possible without killing the small blower

My main question is what size lower can I get to drive the blower with a 3" upper to net roughly in the desired boost range...options that I've found are 5.5,6,6.5,etc up to 8 inch...My thinking is with the stock sized lower that came on the 575(6 1/4" roughly) I should be in the ballpark but maybe not...as griff pointed out the 575 is 502 based and I'm 454 based so my boost numbers will be higher than the 502 based engine...not sure what the 575 was seeing for boost with this kit from whipple on it but if stock is 4 I would have to guess it bumped it some to compensate for the chiller correct?? so if that puts it at 5-6 that should net me 7-8 on my 454 based engine but with my better flowing heads and such will that drop me back down to 5-6 or should I drive it with the 5.5" lower that's available??

I've looked through all the boost and drive ratio charts several times and if I input the pulleys 5.5 lower and 3" upper according to the charts I'm still way higher boost wise than I'd like...however like I said the stock 575 lower is almost an inch bigger than a 5.5 and it was fine?? so will the 454 base make that much of a difference to where a 6" lower will be too much or am I doing something wrong??

I guess the jist of this has turned into lower pulley solutions to drive the 256...my thinking was a 3v standard blower pulley accessory drive and a 16 rib lower blower pulley from whipple that are offered in the above mentioned sizes...I know the 256 is only 10 rib but I figured with a 16 rib lower its wider and I can just run a 10 rib belt and will give me some margin for error as far as blower belt alignment

So that's pretty much where the thread is now hahaha

Sorry for all the confusion!!

how hard would it really be to change out your other pulleys to 575 serpentine stuff? You just need the pulleys

Ok so it sounds like you have a single upper pulley that will work with your 250 blower and it's 3" diameter and you need to buy a 3 v-belt lower pulley which you can get from 5.5 to 8" in 1/2" increments, does this sum it up correctly?

If so,
Drive ratios:
5.5/3 = 1.83
6/3 = 2.0
6.5/3 = 2.17
7/3 = 2.33
7.5/3 = 2.50
8/3 = 2.67

according to the chart:
https://cimg1.ibsrv.net/gimg/www.off...7c4486b054.jpg

Based on your 454 at .030 over I'd estimate your boost would be about 8lbs at 1.63:1 minus your 2 lbs for the chiller reduction so you'd be about 6lbs

https://cimg2.ibsrv.net/gimg/www.off...6f0aaadd6e.jpg

6lbs + 8.5:1 gives you 12.0:1, according to the charts is about pump gas limits.

Base don the books & the numbers I'd shoot for 1.63:1 someone with real world experience might want to chime in and adjust some of this.

So if you're shooting for 1.63:1 it narrows your bottom pulley down to a 5.5" because you can more easily get upper pulleys that put you within adjustment range your shooting for..
5.5/3.5= 1.57
5.5/3.25 = 1.69
5.5/3 = 1.83

If you get a 5.5" lower and my 3.25 upper you'd be at 1.69:1, which is 9.55lbs minus 2 = 7.55lbs at 8.5:1 static, yields you 12.5:1 to 12.75:1



Now if you want to use stock parts off different motors, you need to specify the number of splines on your upper pulley shaft, the length of the shaft & depth of the pulley to make sure there swappable across engine packages. I learned the hard way Merc changed all of this stuff even within the same engine packages over different years and then people mess with them on top of that so be specific on what your set up is unless you like buying parts that won't work on your stuff.

Or why dont you just find a 525sc lower pulley to drive the three V accessories and use the 575 belt on it. There has to be one in the swap shop.