symptoms of an overspun m90m

M

mmathews

Registered User
So heres what happened.. lol. I welded my stock 94 blower pulley onto the front of my idler pulley. It allowed me to run 1 belt and eliminate the ac and ps. When i calculated it, i got 15,000 rpms at 5500 rpms. It makes 10lbs of boost almost instantly and 5 where it used to gradually run from a vacuum, cept more than half throttle. And it has lost power! It almost seems like it has power til 2000 rms. If i stay slowly on the gas it will get to 14 or 15 psi but at wot it wont pass 10 and it seems to lose boost the longer at wot. The ~~~ is hot too! Did i miscalculate? Or should i try to cool the air more first?
 
Yes, you calculated way wrong. What size blower pulley are you using? Most likely you are trying to run over 40% OD which isn't going to work. You probably have massive belt slip.
 
mmathews said:
So heres what happened.. lol. I welded my stock 94 blower pulley onto the front of my idler pulley. It allowed me to run 1 belt and eliminate the ac and ps. When i calculated it, i got 15,000 rpms at 5500 rpms. It makes 10lbs of boost almost instantly and 5 where it used to gradually run from a vacuum, cept more than half throttle. And it has lost power! It almost seems like it has power til 2000 rms. If i stay slowly on the gas it will get to 14 or 15 psi but at wot it wont pass 10 and it seems to lose boost the longer at wot. The ~~~ is hot too! Did i miscalculate? Or should i try to cool the air more first?
Click to expand...

You welded a 94 blower pulley to the front of the jackshaft pulley ?? If so you are overdriving it to the moon. Accesory drive portion of the crank pulley is already much larger than the supercharger drive portion, and then driving the jackshaft pulley with only a 3" diameter pulley is crazy. I agree with Dave that it's got to be at least 40% OD and I'll bet it's slipping the worst on that supercharger pulley you welded on.

David
 
This is the math I used to calculate final blower RPM.

If the logic is flawed pls chime in so I don't make potentially the same mistake.

Your sizes may be different.

Crank Pulley......... 6.75"
Welded Blower Pulley 3.0 "
Transfer to JS Pulley 4.5"
JS to Blower Pulley 3.0"

Pulley relationship Crank to Welded Pulley 2.25
JS to Blower 1.5

Chosen RPM 5500 x 2.25x1.5 = 18563 rpm at blower.

Paul
 
I rerouted it. I went back to the stock setup on the blower end. For the crank acc pulley, its just like the a/c delete with the reversed top tensioner as seen on here cept i deleted my ps. It used a 53" belt. I had to twist the lower radiator hose to get clearance. I also used a 6 rib belt ran on the outside of the pulleys. It works great. I may add an extension on the lower water pump outlet to get even more clearance. One of these days i'll post pics. I may never be done modifying this thing :)
 
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