I'm currently putting together a 2x4 set up for my 65 Riv, I have a stock manifold, two new carter afbs, and a kick down bracket. I still need the fuel line, linkage, and the correct distributer. My question is will I see an increase in horse power, or will I just be dumping gas? Do I need to use a different cam? The 401 was rebuilt less than 5k miles ago, so everything is new and runs great, I just want to make sure I do this correctly. Any input is appreciated. Thanks, Dave
There was a recent thread on v8b in which a '66 Skylark GS with a nailhead motor was set up with dual quads, then later with the spreadbore intake and qjet carb. The interesting thing is that, according to the post, the car ran better 1/4 mile ETs with the single qjet! I would assume that mileage was better as well.
As a matter of fact, here is the quote And here is the thread It is the 10th post down (you can't miss it, there's a big pic of Walt's '66 in a display of torque!
I have a stock '64 dual quad setup that I used for several years on my 401 4-speed hardtop. It only uses the back carb until you romp on it. I don't know about the 425, but the 401 uses only 6bbl to effect. The final 2bbl would make more noise during acceleation, but not more power. I never had a rich run condition, and got 18 mpg like clockwork-exactly the same as when I used a single Carter. Dan
Dave, For the linkage, you can buy a generic linkage kit made by Mr Gasket....check Summit or Jegs. Fuel Line I fabbed up using fittings purchased in a auto parts store, and bent steel lines to fit. The cams are only slightly different for the 8bbl motors....Look for the 'Post your Cam Specs' thread (coming soon!)in the Nailhead section. Your stock distributor could be modified to 8 bbl specs. It really helped my cars low rpm performance. Many recommend the HEI distributor offered by DavesSmallBodyHEI.... I really like the driveability of my two 500 cfm setup. But the single Q-jet did give better top-end performance on my modified 425. I'll bet I could get the two fours to perform better with some experimentation with jetting, or maybe using the primaries from a larger 625 carb... Below is an old pic showing the linkage and fuel lines:
Dual quad experimentation In response to Walt's comments about getting better results through experimentation, absolutely!!!! When I switched my stock 66 GS to dual quads, there wasn't a noticable power pickup. Lot's more noise and fuel though. A dyno run at Englishtown changed that. We saw how lean (A/F ratio = 17+) the engine was running with stock jetting (.092's in all the secondaries) with unrestrictive breathers (dual 6 X2 K&N's) Interesting though that with the stock chrome two snorkel breather, it ran at a perfect A/F ratio. Solution: .098 jets in all four secondaries. Plugs ran a nice color after each pass (instead of being white) and mileage wasn't affected because the increased jetting was only in the secondaries. Quarter mile times improved nearly 4 tenths (yes .4 seconds) with the improved jetting. Throttle response is excellent, mileage is poor, thrill factor is high and with the open breathers, you can really see the dual quads. Check it out on this web site http://www.buicks.net/show_and_shine/Kiloton/index.html
