Todd,

What do you mean by a semi PP.

George (down under)

 

Bill,

Sorry, it's a high wing (Bearhawk) that won't be upside down - ever.  I figured the airframe would give me 1.5 psi for a downdraft carb; maybe 2 psi for an updraft?  I always thought I would be totally electronic but I love the setup on my 170: all gravity from both tanks all the time.  The only fuel-related activity I have is making sure there is enough and then regularly sumping tanks and keeping the gascolater screen clean.

 

I am building a semi-pport and will try to run it with a gravity-fed Holley 2300.  At worst, I might have to add a pump or go with a Marvel Schebler MA-4/5 caliber aircraft carb.

 

Todd

 

Todd,
High wing or low wing? The key is if you have a high wing there is at least a minimum pressure available. Anything aerobatic or low wing will need pumps.
Bill Jepson 

 

 

Anyone who knows feel free to explain to me why a Marvel-Schebler updraft can feed 300 hp with gravity but pumps are needed for Webers or Holleys.  I understand the updraft gets another 18” of pressure but am assuming it is simply by design that the response is improved with a few lbs of pressure.  Since we aren’t too worried about throttle response as long as it doesn’t stumble, would a gravity-fed Holley be a waste of time?

 

Todd