also be carefull on your flame arrestor had a h/p one from eddie marine that allowed almost no boost, talked to weiand, told me to try without....picked up 4.5 psi could not believe it !! so watch out there..Rob

How do figure the 8.26#????? That is in the ballpark, but actual boost pressures will vary depending on the flow of heads and if there is an innercooler.
Also, do you mean his belt is slipping???? The pulley can't really slip unless the teeth are bad and that would only happen for minute until its destroys itself.

the 177 blower has rib belt drive not gilmer tooth, usually 6 or 10 rib a weak tensioner spring could be the culprit

I have a formula to calculate theoretical boost. This formula seems quite accurate if all is in order. I know it has been dead nuts on my 3 pulley changes.

Yes, pulley slipping under belt is what I was saying. I know on the smaller blowers when you get down in the 3" pulley range, this can become an issues. Maybe its a tension issue like doggiedave mentioned that shows itself when the contact area of the belt/pulley interface decreases too far.

FWIW, on a driven belt system, if I said the belt was slipping that would have indicated slippage between the belt and the crank pulley (driving member). The belt would have been slipping under the driven pulley. Since I said the pulley was slipping it meant the blower pulley. The belt (driving member) is driving the blower pulley and if the pulley is not moving at the correct surface speed, it means the pulley is slipping. If I said the blower shaft was slipping it would mean the keyed shaft inside the pulley (because the pulley is the driven member) and of course that would not last too long. Its all good Griff....... )

My 177 10 rib belt would start slipping and I replaced it about every season, so I know what you mean. Just making sure I understood what you were saying.

I saw 5 PSI with standard pullies and 8 with smaller ones.I still have a set of smaller ones from my 177's if your interested.Also think i have a lower pulley and some belts.

Hello, I am interested in your smaller pullies and belts. What sizes and how much? Condition of the belts? Will measure mine tomorrow to compare sizes. Thank you....Kevin

I also have 2 of the splined shaft merc type pulleys. They are something along the lines of 2.85" diameter.

Griff, what indicated to you the belts were slipping, low boost?

If I was cruising around 3500rpms and pushed the stick forward quickly, it was sluggish and the boost would only go up to about 4-5lbs when it should have went to 7-8lbs. I got the 10 rib belts at NAPA for about $40 and always just kept a fresh one on the boat. I actually had one completely shred apart during a high speed run.

Sounds like it was slipping all the time most likely, just less when new. What was the diameter and your cid? I'll tell you what your theoretical psi should have been w/ zero slippage.