Does more cubes equal less boost?

[walker95svt]

Stupid question:
My paxton blower's rated at 8-10lbs of boost with the pulley supplied. If I'm filling more cubes, will it makes less boost? It makes sense to me, more volume equals less psi, but I'm stabbing in the dark here. Case in point being my 331, and a paxton novi 2000 kit soon to go on. Just wondering what people think.

 

[TrueBlue95GT]

Yes, when u make the motor breath better, you have less boost. Same amount of air volume though.

 

[V8SHME8]

Boost is a measure of the air that you are not using so when your motor flows better, then you will see less boost pressure because the motor is able to use more air.

 

[walker95svt]

That's exactly what I figured, I just wanted to see what you guys thought.

 

[Racer X]

Here are some numbers for you.... My stock 302 with heads/cam/blower made 489rwhp 432rwtq at 9lbs of boost.

When I then did the stroker motor.. 347ci same pulley on the charger, same heads and similar cam and basic tune.... 462rwhp 473rwtq at 6-7psi.
With a pulley change and a perfect tuning I'm at 541rwhp 569rwtq at 11-12psi.

 

[Killercanary]

As was said, yes you will see a decrease in boost pressure normally due to the added cubes providing more area for the incomming air to fill. The neat thing is that if you find a way to decrease the restrictions in front of the blower you will normally see an increase in boost pressure because the blower is made more efficient and more air is able to be pulled in per rotation... thus the added benefit of "power pipes."


General rule of thumb is...
Decrease restrictions or increase air flow needs/abilities(ie added cubes, better flowing heads, etc) AFTER the blower and the measured boost will decrease.

Decrease restrictions BEFORE or add restrictions AFTER the blower (like putting the stock heads back on in place of a better flowing aftermarket ones) and measured boost will increase.

This is all because boost is nothing more than a measure of the backpressure in the intake tract and not a measurement of air flow. Intercooled air can also show up an an decrease in boost pressure if the pressure is read AFTER the intercooler if:
1. The intercooler itself is a restriction or
2. The air is more dense (air molecules are closer together) and therefore its not as "expanded" as much when its entering the cylinder.

 

[94GTLaserRC]

:OT:
BUT, Paul, I love your vids at the track, but I think your avatar should still show your car "at the bar"

OR....Photo shop the car "above the bar"

RC

 

[tmoss]

Dang - Paul your avatar is making me dizzy (er)

 

[walker95svt]

I didn't read that 347 response before I made the new thread. Anyway, those mid 400 rwhp numbers are EXACTLY what I was looking for with the new thread. If my car worked out like that at 6-7 psi, I'd be very happy until my long block goes balls to the wall after my next deployment. If anyone's got any combos like that, PLEASE send them to the new one. I think it's going to work out very nicely.