Annular boosters on a Tunnel Ram
The reason the main air bleed starts the mains sooner (and that is a result, not necessarily the purpose of the mab) is because at different throttle openings the air moving through the carburetor is not a constant. The pressure drop and the air speed both change at different points in throttle openings and rpm. The extra air introduced into the fuel changes it’s density and that changes it’s flow characteristics.
THANK YOU.
Just because a bleed (or anything else for that matter) exhibits a certain characteristic at some point, doesn’t mean it will behave the same under different conditions.
Thats why I keep saying over and over you have to understand how pressure differentials affect bleed behavior.
In other words, just because the MAB will tilt the fuel curve lean at high air flows doesn’t mean it has to tilt the fuel curve lean at low air flows.
Which is saying that because the main air bleed tilts the fuel curve lean at HIGH air flows doesn’t mean that it will exhibit that same characteristic at low flows and delay the mains.
Like I also said, this stuff is in the Taylor books, but it also includes the math that makes it makes more sense.
Obert covers it, but not as explicitly.
I think that sometimes the tip in stumble guys run into is more a product of the T slot still providing adequate fuel when the booster starts because the MAB is too large.
Look at an early 3310 Holley. I think (my memory isn’t all that good any more) the MAB is .026 and then look at some of the stuff out there today and you’ll find MAB’s in the .032-.034 range.
And that STARTS the mains SOONER. And that overlap of the T slot providing enough fuel and the mains starting causes a rich tip in stumble.
It is so EASY to get lost in all this stuff because it is counterintuitive at times and because of the misinformation out there.
Tuner and Shrinker have left us a really great amount of knowledge for free if we want to find it and read it.
And Tuner is still around. I’m going to call him later today (he sent me a really cool email that included a 2 part attachment of how GM designs, builds and tests cylinder heads using their flow bench) and tell him once again he NEEDS to write a book.
He thinks no one will read it. I say he is wrong.
