Secondaries Opening Video *NM*

[Joe C.]

http://smg.photobucket.com/albums/v216/speedo1952/

[Gerard F.]

Re: Secondaries Opening Video

Is that yours, Joe. Amazing what a little $15 gadget will do

Seriously, how did you do that video.

Jerry Fuccillo
#42179

[Clem Z.]

Re: Secondaries Opening Video

it is a lot easier and cheaper to just put a dab of grease on the throttle baseplate on the spot where the WOT stop hits and after the run look at the grease for a mark from the stop

[Joe C.]

Re: Secondaries Opening Video

Hi Jerry,

That's mine alright.

All you need is a loyal,trusty friend with a video camera, and a stout section of rope. Remove hood, lash your "pal" to fender of Corvette. Have him hold the camera tightly, which will occur NATURALLY once you are underway.

Actually, used a laptop computer through a cheap webcam. The webcam is small enough to clamp directly to the vacuum advance signal tube, in the valley between the right side valve cover, and the intake. Not present on your '67, is the choke heat tube. The webcam was directly below that, and set about 2" from the subject.

Looking closely at the vacuum diaphragm link on the secondary shaft, you'll notice a small dab of grease. That was my "backup" in case I lost the camera. Fortunately, I didn't need it.

Yeah, Clem, I know the grease is on the wrong surface of the link..........but I didn't need it anyway.

Best regards,
Joe

[Rob M.]

Re: Secondaries Opening Video

Joe,
Very cool. How about a second web cam on the tachometer so that we can see the opening vs engine rpm. You could superimpose the tach reading on the carb video.

It would be nice to know at what RPM the secondaries open. Maybe different in each gear as the engine load changes??

Rob

[Joe C.]

Re: Secondaries Opening Video

Rob,

Secondaries begin opening at about 3500 @WOT. Actually, they will be free to open at anything past about 3/4 throttle. They are full open, as you can see, within less than a couple seconds. So, as the revs were climbing, I would estimate that they were full open by the time I reached about 5500 RPM. That particular run was made in first gear. I have a longer, 10 minute-long clip, where I took the car on the interstate highway, and accomplished the same thing in second and third gears.

The vacuum for actuation is created by a simple Pitot tap, and is NOT, NOT load dependent. It is simply a function of air velocity through the primary venturis. And, as long as the primaries are open beyond the lockout point (about 3/4 throttle) the actuation will work quite the same, with any torque multiplication factor.

Joe

[Clem Z.]

Re: Secondaries Opening Video

there is also a air bleed into the secondary venturi which allows extra vacuum after the secondary starts to open. this bleed also prevents the secondary from opening too soon as it causes a vacuum loss from the primary side untill the primary side vacuum reaches a certain level.