I know this subject has been beaten to death. I'd like to beat it up some more.
I've a fairly decent carb setup right now. Barry Grant Speed Demon 750 (vacuum secondary). It's been modified for adjustable HSAB and LSAB as well as IAB. The PVCR is fixed at .059".
However, I think it's a little too big for my application (more on that later) seeing as Barry Grant rates their carbs at a different test pressure than Holley. So at 750 cfm rating it's actually more than 800 cfm in comparison (at least that's according to BGs literature). The one thing it has going for it is that it has annular boosters which help with the signal gain making it react as a somewhat smaller carb.

My objectives:
Better 1/4 mile ET with emphasis on the 60' time.
Better fuel economy particularly on the highway.

Current performance:
12.64 @ 107.65 w/ 1.87 60'/8.103 @ 85.37 (1/8th) 3650 lbs.
21 Imperial MPG/ 17.5 US MPG Highway.

The previously installed carb was a Holley 670 Street Avenger (VS). With that carb (with basically the same engine and chassis) I had personal best 60' of 1.7 flat. In all fairness that engine was an improved version of the earlier version but still built along the same specs. Small cam and heads. High cranking compression pressures.
Highway MPG was closer to 20 (US).
What that carb didn't have was any adjustability other than the usual stuff. Jetting, secondary timing and idle mixtures (4 corner).

My vehicle specs are in my signature.

I'm leaning towards the QFT 680 VS carbs. Either the Hot Rod or the Super Street series. They both have fully adjustable circuits.

Thoughts?

 

I figured I'd add my vehicle specs:
86 Camaro Coupe
3650 lbs
355 Gen 1 SBC. 9.8:1 SCR. 190 psi cranking pressure.
180 cc iron heads. 250 cfm (+/-) @ .500".
274/280, 224/230 @ .050" w/ .570" lift hydraulic roller. (1.6 rr).
RPM Air Gap.
MSD ignition with fully adjustable mechanical and vacuum advance curve.
Mid length headers. 1 5/8 x 3" with full 3" single exhaust. Flowmaster 40 series muffler in OEM location.
700R4 w/ 10" TCI converter. (Foot brake to 2200 rpm, flash stall to 3500+)
3.73 rear gear.
Stock style suspension w/ OEM spec shocks. Lowered about 2".
26" x 10.5" ET Streets.

What I'm interested in more than anything are other people's experiences with a similar setup. What are your performance results both from the drag strip and the highway?
Thanks in advance.

 

Can I interest you in a nice performance-oriented QJet? Guaranteed better mileage at the same performance level (or better) if it's tuned sharp.

If you want it all, there's still no better street/strip VS carb on the planet.

Other than that, why not go with a modestly sized double pumper? Nothing exotic, but when you want maximum GO, you're not going to beat it at the strip. Mileage on the highway is the same as a VS carb, if you can keep your foot out of the secondaries.

 

I've always liked the primary/secondary layout of the Q-Jet. Those tiny primary bores make for excellent throttle response. And for my application, it would more than serve my needs. There are a couple of characters here that have excellent results too. My problem is that I have a lot invested in the 4150 platform and to do a full turn around now would be a step back. Not to mention the learning curve for me.
As for a double pumper, unless I were to build a dedicated race car and could keep engine rpms above peak engine torque, I wouldn't consider it. There's nothing a VS carb can't do that a mechanical secondary can. The only difference is that the VS carb adds the element of tuning the vacuum portion of the secondary opening and that's not that difficult. It just takes time at the dragstrip. Get it right and you have all the performance of the mechanical carb.
As for mileage, cruising around town with a mechanical secondary crushes your fuel economy when compared to the same size VS carb. Those two accelerator pumps put a lot of fuel into the engine. On the highway...not so much.