I am getting ready to put my 540 9:1 together and i am vasilating on the instalation of the 256 weiand that i have. i found a set of pulleys and a belt and the ratio would be 2.8 TO ONE BELT RATIO. WOULD THIS BE A LITTLE TOOMUCH FOR THIS APPLICATION. I HAVE A .613 .629 CAM AT 236 244 DUR W 112 LSA. AFR HEADS AND A MODDED 850 CARB.

That drive ratio sounds a little high for the weiand 256 blower. What are the pulley diameters? The highest ratio that weiand provided for that blower was 2.13 to 1 or 113% over drive. This was using a 6.5" lower pulley and a 3.05" top pulley. Using the weiand chart the 113% ratio would give you around 10-11 psi boost which is high.

Are you sure that you've got a 256 blower. The one you've had for sale in the classifieds looks like a 177. Also, merc never made an intake for a 256 until it went on the 575sci. I'm noty sure what you've got, but it looks like a 177 to me and thats way too small for a 540. Even the 250 would be too small.

I have measured it and it dose come up to 6.125 tall and 19.5 long. this should be a 256. the upper pulley would be 2.5 and the bottom would be 7 inches. I am vasilating between putting The blower on, or selling it. i wuold have to cut hole in the bonnet or make a new one and put a scoop on it. I already changed direction once and now i have to sned back the pistons and get some for a 4.5 bore w a 4.25 crank. 1st and formost i need this to be trun key dependable. some minor buget concerns but if business continues this way it will all work out. At 14 years old when i built my 1st 11 to 1 pontiac 389 tirpower motor i have alway wanted to build a big inch stroker NA motor. I have fianly reached the point where i can afford it but i do not want to waste money. would this much boost make it too finickey?

When my 540's were built, my 250's would not boost them. I had to go with 10-71's. Just my .02

The 19.5" lenght is correct for the 256 blower if you are measuring from the rear cover to the front cover where the snout bolts on. The case/rotor lenght should be 15.0" long. If you do have a 256 blower I would not run the blower with the pulleys you have. The 256 blower was not designed to run that much overdrive. Like I said earlier, weiand only made a 6.5" lower and 3.05" top pulley in a 16 rib to be the max overdrive. This drive ratio is even a lot for the blower. The 256 Weiand uses only single row bearings in both the front and rear bearing plates. These bearings are not strong enough to support the rotor at that rpm and you will most likely have rotor to rotor contact. If you are looking for something reliable, I would suggest a larger blower which you do not have to spin that hard. Depending on what HP you desired, will depend on what size blower you will need.

the idler pulley on the blower right now is a 10 rib belt. i do not know if this was the one that came on it or not. I believe it was a warranty replacement that this dealer gave to me to sweeten the deal. what boost would be made with this combo and this displacement

Like I said earlier, the 113% ratio will give you 10-11 psi according to the Weiand chart. You have to remember that this is a generic chart based on a stock engine config. The better the heads and cam the less boost you will make but more HP because you are filling the cylinder better. If you are asking how much boost with your pulley combination, that is something I can not answer. That blower was not designed for that much of a drive ratio. You will have belt slip and rotor cavitation, and you will have nothing but hot air. That 2 lobe rotor design is only efficient under 10 psi and works best around 5-7 psi. Instead of looking at how much boost you will make, you need to look at how much boost can you run. Remember you are at 9to 1, do you plan on running pump gas? It also sounds like you want to run a single 850 carb?

Can you post a picture of the blower and pulleys to verify what you have. The 10 rib pulleys were only on the Merc 575 blowers. Weiand never offered a 10 rib for their 256 blower. The Weiand 256 had a keyed shaft for the top pulley that is too long to accept a 10 rib pulley from their 177/142 blowers. Merc 575 blowers had a special splined shaft for their 10 rib pulley which the keyed pulleys will not work with. Weiand also only made a 2.85" 10 rib for their smallest top pulley. If you have a 2.5" top that would be a B&M pulley. It sounds like you have parts that do not go together.

What is your goal, how much boost, HP, what fuel, etc?

I do not have any pulleys, i was looking on ebay and found a set for cheap. i thought they would be reasonable compared to the price of buying new. the blower dose have the splined top shaft and it was originally intended for a 454 or 496. I just made a deal on a block and i am now going to sell it. I know i will probably vacillate a little more before it goes out the door. the first 1100 would take it. Being it will not work well any way. it is not a good idea to spin something fast enough to take the bearings out. And the cavitation thing scares the hell out of me. thanks for the input.

I wouldn't spend too much time trying to mount a 256 on 540. The practical limit is a stock 502. I'd be doing a 8:71 or larger. If do mount the 256, a intercooler will be required. If you don't intercool it, then pull a bunch of timing out and watch your plugs closely.