Griff

It was not slipping at all until the belt would get worn. I had it for 300hrs and only had the slip happen twice with belts with more than about 75 hrs. I just started replacing them at the beginning of every season and never had another issue. Boost was consistent at just under 8# which was correct for the pulley size I had. The 2.75 top is the 8# pulley for the stock 525SC. I don't remember the exact size of mine. I think it was a 2.81 top and the stock 7" bottom. The engine is long gone anyway.

blue thunder

Here's what mine looks like with the 3.25 blower pulley. 6.09 is the boost PSI, the formating from excel is screwy.

top 3.25 3.5 3.75
bottom 7
11200
constant cfm ratio cid barametric pressure Boost PSI
25.58 177 2.153846154 469 14.7 6.09

blue thunder

Here would be a 454 with a 2.81 top pulley. 10.14 is the theoretical boost pressure. I think your pulley was slipping all the time Griff at elevated rpm. That's why you went through belts. I haven't replaced a belt yet. Just a thought for those that are working these issues now. I know this boat is long gone for you.


top 2.81
bottom 7
12954
constant cfm ratio cid barametric pressure Boost PSI
25.58 177 2.491103203 454 14.7 10.14

Old Navy

Well, you can calculate boost on this all you want and it still might not be real world. Head flow, load, obstructions-ie intercoolers, come in to play. One sure fire way to tell if your belt is slipping is there will be black dust on the tensioner arm. And your boost gage will bounce a little especially at high RPM's. My combo is a 7" lower pulley, 2.85" upper and it makes 6.5 psi @ WOT. On paper it "should" be more but I have good flowing iron heads and an intercooler. Boost is backed up, pressurized, fuel and air waiting to go down the next runner with an open valve. Higher boost does not necessarily equal higher HP.

blue thunder

That is correct, the formuala just gets you in the ballpark and uses a VE of .9 on the unboosted intake tract to account for inefficiencies of the engine airflow. That is actually conservative for a well designed engine package. But I suppose there are engines out there with lower VEs that would indeed produce more boost yet less power. What one would not expect is less boost because the engine can only really flow 100% of its cid, without help. Of course that can be off too. But the formula I use is generally within 5% of actual. If you are off 20% actual vs theoretical it indicates you are not getting the rated cfm out of the blower for whatever reason.

BT

Old Navy

Sounds good, thanks for the clarification.

blue thunder

I'd bet old navy that you could switch to a 3.25 inch pulley and loose very little boost from your 6.5, in fact you may gain if slippage goes down. Spinning these little blowers too fast and creating heat will also be a deterent along with slippage due to small pulley. Just a thought, here is your theoretical assuming 454cid. 6.78psi

top 3.25
bottom 7
11200
constant cfm ratio cid barametric pressure Boost PSI
25.58 177 2.153846154 454 14.7 6.78

Old Navy

No, probably not, thats 6.5 below the chiller.

blue thunder

Ah chiller, gotcha.

kreed

If a 454 with a 177 blower makes 525HP with the 3.25 top pully, what can you expect if you put the 2.85 smaller top pully on? HP gains, speed gains?