Very interesting discussions. As usual, when discussing when something
"first appeared" can be hard to nail down. I should have qualified the
questions a little better to leave out racecars or race-only motors. I
know that the early fuelers used eight Strombergs, but that's hardly a
factory car or motor.

Also, does it qualify if it was a turn of the century car that they
only built 50 copies of? Subject to debate. That said, here are the
answers, sort of.

1. The 1920's Duesenberg J engines. Not only OHC, but DOHC and 4 valves
per cylinder to boot. I've read of the 1906 Scott and the 1898
Wilkinson that both had OHC as well, but I've never seen one nor heard
anything in depth about them.
2. The Crosley 4 cylinder engines.
3. The AC Cobra of 1965-1968 with the 427 engine could be ordered the 4
downdraft Webers. The Chevrolet Corvair of 1965 to 1969 with the 140HP
engine came with 4 single barrel Rochester carbs. So, I'm going to call
that a tie.

Feel free to offer corrections if you'd like. This was just for fun and
it's been fun reading the responses.

Here I agree- it was NOT a success. Too many ham-fisted knuckle-draggers
over torqued the bolts when they serviced them and wrecked the carbs by
flexing the phenolic body and making the jet wells pop off. AND it was
the last major new carburetor design before fuel injection, so it was
doomed to a short life in OEM applications anyway. Well, "short" being
about 15 years... But if you set one up and leave it alone, it will work
great for years. And it does a better job of what a carburetor should
do- mix air and fuel very precisely and uniformly over the entire power
and RPM matrix the engine sees, than almost any other carburetor. I get
better mileage with a TQ on my 318 than it did with a 2-barrel, simply
because the TQ primaries with the dual annular boosters are so darned
efficient. To its credit, the QJ is just about as good in that regard.

Granted, today I'd rather have a new-in-the-box Thunder Series (a
re-badged Carter AVS) than an old Thermoquad and that's what I run on my
other daily driver. For my money, THAT is the best carburetor still in
production short of a mega-buck Barry Grant. The AFB is tough as a
brick, but mixes air and fuel about like a brick too. I did like
Edelbrock's Quadrajet re-issue carb, but they had it over priced by
about $200 and it never had a chance to make it in the marketplace.

No argument that the QJ came first. But it was and is a little more
primitive albeit more reliable under abusive treatment. As far as the TQ
being a glorified AVS- can't agree. The TQ doesn't share a single part
with the AVS, is a spread-bore design, 3-piece carburetor to the AVS's
near square-bore, 2-piece all metal design. Someone at Carter started
with a blank page when they designed the TQ. Even the way the metering
rods work is fundamentally different than the AVS, and also different
from the QJ. About the only feature it shares with the AVS (and the QJ)
is the secondary air door, but the TQ's air door is a complex shape that
actually becomes part of the air path when open rather than a flat plate
that just acts as a valve as it does in the AVS and QJ.