Originally Posted by
Michael
You're right in saying that a properly rebuilt SN should see something in the neighbourhood of 6-8psi of boost, especially with the HO impeller. And from everything you've stated above, your rebuild was done correctly, so I doubt there's any issues with the rebuild itself. Even taking into account the small amount of bleed-off through the throttle shafts, that shouldn't result in a 3-4psi drop (maybe 1 or 1.5psi, depending on how bad the leak really is).
Where are you measuring the boost pressure? At the blower outlet?
If anything is causing your low-boost condition, it's more than likely a combination of the cam you're running and the amount of airflow your heads/intake are capable of flowing. I'm not overly familiar with the Windsor Jr. heads you're running, but if they're flowing good numbers (more than 200cfm), coupled with the cam and high-flow intake then the combination could be a contributing factor to the low boost you're seeing. The SN is good for about 750cfm at just under 40,000rpm. If you're engine is capable of flowing more than that, then the boost you're see will be lower than the expected 6-8psi.
I'm also assuming you're not running a lot of piping or an intercooler between the blower to the carb either. If you are, that will play a role as well. The greater the volume the blower has to fill between it's own outlet and the engine's intake, the lower the boost pressure you'll see.
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