Multiple Throttle Plates
 

While I was cleaning/rebuilding the carburetor on my old truck, I thought about how it works as compared to the eTB of my car. I remember from experience and the handy-dandy Haynes manual (best 40$ you can spend IMO), that the secondary throttle plates dont open until the engine looses vacuum. So the old Q-Jet would operate at normal temps and cruising as a small two-barreled carb at WOT, which is what made it so efficient (for a carb). It was only when pedal to the floor that the HUGE secondary's would open to give the engine all 650cfm the carb has.

So my query is this: If a 4-barreled carb operates as a small, unrestricted two-barrel at anything below WOT, would a multiple throttle plate system be of any use to a modern EFI? As in, staged throttles which could provide *unrestricted* flow but still not full power flow. If that makes any sense?

Anyway, that old truck would do 16-18mpg so long as I kept it about 60mph, I thought that was alright for a brick of steel as old as me and no overdrive.

I dont think so. With efi the computer keeps a specific ratio of air:fuel. Having a smaller throttle would limit power but the ratio would.be unchanged. Kind of like the testing done regarding dirty air filters on efi engines.

Yes and no. On carbs, its to keep the velocity up at the throttle plate. On efi this isnt needed since fuel isn't added there.
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Some newer engines don't even have a throttle plate anymore, relying only in the valve timing for that matter.

I know the early water cooled vws had a secondary throttle that opened up at like 75% throttle. With its CIS injection system you can feel and hear it when that secondary opened up. VVVvvvrrrroooooommmmmmmm. :eek:

An uncle of mine had a Brazilian Volkswagen Pointer GTi, basically a rebadged Ford Escort with a Volkswagen EA827 engine, and I don't remember it having a secondary throttle plate. But I do remember some carburettors which featured a dual-stage throttle, such as the Weber 450, locally known as "mini progressivo".

Actually they do have throttle plates, but they're not used in normal operation. They are there for limp-mode and possibly cold start.

http://i1281.photobucket.com/albums/...p/IMG_1825.jpg

http://img194.imageshack.us/img194/3218/throttle1.jpg

The quadrajet that came factory on my Monte Carlo used a similar setup with 2 small primaries that were good for easy cruising and 2 BIG secondaries for when your foot got heavy. Others with better tuned engines than mine have reported getting close to 25mpg highway. Best I ever saw was around 18.

I don't think multi-carb intakes work in the same manner. Usually a dual quad setup has a runner dedicated to each port on the carbs. However, a stock 6-pack intake might use the 2nd and 3rd carbs in progression to keep up with needed power...not sure how exactly the worked though.

I'm thinking that a properly tuned American small block v8 powering a relatively light weight vehicle, such as a small pickup or mid sized RWD car, should be capable of low 30's mpg. Of course there are many many variables that would have to be sorted out, and building one of these vehicles for FE is nearly anathema to the whole point of putting an American v8 into a lightweight car....but I don't really see why we couldn't haul mass while growing grass.