Technical > Matt Shaff's Engine Shop

understanding blower percent driven .. over/under

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noslin:
Ok, i dont have a clue the percentage means and how it relates to boost. i can understand it will be different for each size/type of blower. but lets take 6-71 for discussion purposes.  if you want to get technical then just choose something and state what it is.

for first questions, if there is over and under driven.. what is zero driven.  how many lbs of boost is zero driven or nuetral (however it is refered too).  im guessing over driven will make more boost and visa versa for under driven.  so, what is 10 percent over and under. 

i guess the question would be what is neutral really.  then can go from there i guess.   is neutral atmosphere or one atmosphere? if its one atmosphere then 10% under would be 1.5lbs less.. so 14.7lbs is 1 amto then 10% would be 1.5 less then that?

ty
dean

ricardo1967:
Blower overdrive/underdrive refers to the drive ratio between crankshaft and blower, just that. Manifold boost will be a consequence of that drive ratio (among many other factors).

Not such a thing as 'zero driven' If drive ratio is 1:1, it could be called direct-drive.

dreracecar:
Boost is not increase due to changing drive numbers  the overdrive determines how soon the blower comes up to full boost before it flattens out

noslin:
If a 1:1 ratio, then in a typical blower setup, is the blower itself turning same rpm as motor or is it such like the cam.. 1/2 rpm

Are all blowers rated the same way, industry standard. So to compare same size blowers.

So a person tells me on his setup for 8-71 thats 35% over driven. What does that corelate too?  Just means ramp is faster to peak boost?

Frontenginedragsters:
It means the blower is spinning 35% faster than the crankshaft.
Pressure is higher at a lower engine speed than if it was 1 to 1 ratio.
You also have to know how much is too much.

Matt

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