So, I'm sure I'm not the only one who has an intake manifold with a hole in it, for a wolf whistle, wiper, or trico fan. My question is, how much manifold vacuum does a T make? I never did measure the vacuum on my coupe before I sold it, and frankly, I'm a long way from running the engine in my TT.
I'm also curious as to the "running down the road vacuum". I know this varies dramatically. Can a T drop the vacuum to zero at WOT?
I'm curious about this, not for tuning or the like, but because I just put a Southwind heater in my '49 GMC. I love that thing, I'll bet I could cook hotdogs under it when its on high. Of course, I'm thinking I should maybe put one in my TT, 'cause I like when my windshield is clear, and my toes are warm. But, I frankly don't know if a T engine makes as much vacuum as a "normal" engine. I assume it must make about 18-20", everything else (in my limited experience) does.
Just thought I'd ask, as I bet somebody here knows. Or does only the Shadow know?
Here is a graph of my T at 56 mph, wide open throttle. The blue trace is manifold absolute pressure (vacuum) the red trace is the mag.
As you can see, vacuum never falls below (above?) 0.
I'm glad you provided the proof that it does not drop to zero. If one thinks about it, it is obvious that it would not run at zero because there would nothing to pull the air/fuel moisture into the engine.
Neato, thanks. It seems that a heater would do fine in the TT.
My last daily driver truck had a 216 chev in it, with dual carbs. When you put the petal to the metal, the manifold vacuum would drop to zero, but, I never had it floored for more than 10 seconds or so and truth be told, my vacuum gauge was made in China! Who knows what the real reading was. I suppose the airflow would still produce a low enough pressure in the carb to suck, and atomize the gasoline. So many things I don't have a full understanding of!
My manifold has a hole in it, the engine runs great maybe the hole was drilled for vaccum wipers?