Merc SC800 supercharger pulley/boost ratio?
 

I have a 4.75" ten rib top pulley and a 4.5" ten rib bottom pulley,
blower displaces 420ci
On a 540 tall deck I am guessing this would give me 5-6lbs of boost..
Am I in the ballpark here?

No sir. That's like 6% under drive .stock pulley combo on 800sc was 18% over. You need a larger bottom pulley . that combo you have might make 3psi at best I would think.

You prob wanna start somewhere around 10% over is my guess.

the Holley chart for the blower shows 5" top and 5" (1 to 1)bottom giving 5-6lbs on a 540 tall deck..

Thats what I was using as a starting point..

Forgot about under/over driving.

My bottom pulley is the stock pulley from the SC800,,
top pulley have no idea,,..
Just cant find much aftermarket selection for the ten rib pulleys,,

:)

SC800 was a 577" though..
Thats why I thought I would still make 5lbs on the smaller 540..
Of course i was looking at the wrong numbers..

Thanks for kicking my brain into gear,,
I was only looking at the sizes and not the position,
with a bigger top pulley its underdriven regardless the sizes,,
duhh!!
Feeling stupid now....
:)

I am pretty sure the 800sc bottom pulley is larger than 4.5 inches. The 600SC bottom pulley measures 4.60 diameter. I am betting thats prob what you have. Stock 600sc top pulley, was 4.9 inches. Stock 600sc with that blower was a 502ci, made around 5-6lbs with that pulley combo. The 800sc may have used a 4.75" top pulley, but with a larger bottom to get the 18% overdrive, somewhere around 5.6" in diameter. . Sucks cuz not many pulley options with the merc 10 rib setup.

OP you could try Innovators West they make custom pulleys

I've got a stack of old B&M pulleys that I'm planning on throwing on ebay numerous diameters. I'll see what I've got

Thanks,,let me know..
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