Ok, I couldn't resist. Put in a couple of low bids and found myself owning a dual quad Offenhauser Nailhead intake and a pair of identical Carter 4760S (750cfm) "Competition Series" carbs that have just come off a tunnel rammed BBC. Way too much cfm for my 401 but I have put extremely large carbs on small motors (750 Holley on a 4.2 V8) and found that apart from the extra fuel consumption they run just fine. So, I'm thinking that just for fun I'll throw it all on my 401 Electra (I am aware of hood clearance issues and am hoping to source a new hood to cut - I already have a nice scoop). I'm expecting some performance over the fairly strong Q-Jet combo I currently have but am doing this mainly for fun and visual impact. If I was doing it for performance I would look at the cam/heads and would have gone for smaller carbs but like I said - a dual carb sticking out of the hood of '66 Electra is something I have never seen and is right up my style alley - so to speak. What little information I have been able to gather off the internet hasn't helped much. Does anybody know any good sources of information on these carbs? What does the "S" stand for? What diferentiates a "Competition Series" carb from a standard versions? Any advice on setting these carbs up for dual quad operation would be appreciated. I have heard that the Offy manifold doesn't lend itself well to the "Main carb/Secondary carb" approach (due to the way the manifold runners are designed) and will need to run a solid linkage where both carbs open the exact same amount through the entire throttle cycle. These carbs are the "no choke" version according to the seller (I haven't received them yet). Haven't seem much posted about Carters and this might be a good time to have a good 'ol carter discussion. Here's a few pics...
Dual 4760 AFBs Bill: You are correct about the Offenhauser manifold; the runners that would feed some of the front cylinders from the rear carb (in a progressive setup) have a very narrow passage in a couple of areas. The 4760 AFB is an aftermarket Carter from the '70s and early '80s approximately. The "s" is part of Carter's coding that most AFBs had; I don't know the story. Today's equivalent is the Carter 9755. Edelbrock 750s are basically identical, and you can use the Edelbrock jets, metering rods and springs for tuning. They are easy to work on, and are bullet proof once you get them "dialed in". Two 750s is a whole bunch, and low speed performance won't be smooth like the QJet, but she'll go like stink wide open! Happy motoring, Frank Power :beer
Thanks Frank. So, for more information I should research the Carter 9755 or Edelbrock 750s? Any tuning tips on how to make this setup run? The nailhead currently will rev to about 5,000rpm. I wonder if it will be possible to get these carbs to run respectably within that rev range. I like having fun so the low speed response isn't all that important in this application. I expect I will have to pay for such massive amounts of cfm and I'll pay with less low speed response. I'm sure that at some point in the rev range I will have a huge smile on my face. Can't wait to try them out. I just bought a 3.38 rear posi unit which will help (compared to the original 3.07) and I might put some lower tyres on to increase the ratio even more. I currently have 75 profile tyres so I can come down to 60's without too much bother. This will be my first time with dual carbs and I expect I'm going to have a hell of a time tuning them up. I'll need a linkage or will have to fabricate/adapt one. All comments and suggestions are appreciated. I expect that by the time I come to install this setup I will have headers installed and maybe a slightly healthier cam. Any suggestions on a better cam?
Dual AFBs There is a book (manual) published on Carter carburetors, that should be available from the speed shops (Jeg's, Summit, auto literature shops) that has a ton of info on the AFBs as well as the Thermoquad. I have one, but it is "buried" right now. Let me know if you can't find one. The AFBs are easy to work on, and a lot of tuning on the primary circuit can be done with a change of metering rods and their springs, a 10 minute job. To change any of the jets (use a thick bladed screwdriver that fits the slot) you must open the carb. A couple of things to watch ...if you start to change the metering rods, don't remove the little covers...just loosen the screw and rotate the cover. Those little poops like to fall into the carb causing many new words to be shouted! Same with the springs that are under the little pistons that work the metering rods. They (springs) like to stick in the piston until you have them over the carb, then fall out! Those 4760 AFBs are probably jetted pretty rich for your setup, which is really for a radical, "megacube" engine. Edelbrock has a linkage package for the dual carbs, but you'll have to engineer some for your trans. kickdown and the switch pitch torque converter. I can't recommend a camshaft, but would suggest you contact Carmen Faso of Tonawanda NY. I hear good things about him when talking nailheads. Party on dude!!!:beer Frank
Well, this board taught me how to tune a quadrajet so I don't see that learning how to tune a Carter AFB will me much harder, in fact it sounds easier. Thanks for the tip re: Carmen. I know of his reputation and even rang him once (at night) for some timing tips. I'll look for the carter book and will keep you all informed as to how this goes. It might be a while because you can't just go and stick a tunnel ram and 2 750's on a stock motor - can you? I'm going to have fun setting it up. Now, off to find a hood. Speaking of which, does anyone know if a 65 Electra hood will fit my 66? Because, believe it or not I know where one is.
HI Bill, Great score !!:grin: I think the electra hood is much different. Also I have seen several dual 750's on a few Rivs, and have been told Rivs love a lot of gas. Anyone with preferences as to what to put on these nailheads please advise because I have to feed my new dual manifold with something. What should I be lookin' for? Carters or something new outta box? Thanx, Jason-Erik
I too have heard that our motors like a lot of carb. I'm not sure that 1500cfm is necessary but hey, as long it doesn't slow it down I'm happy. I'm really going to need those headers and a cam or maybe I'll put a bid on the big valve nailhead heads that are currently being offered. :Brow: One things for sure, the intake won't be the bottle neck to power any more. :laugh: I would say that for a perfect setup smaller 500cfm carbs would have been a smarter choice but where's the fun in that? Right?
Bill I believe that the original carbs were 600 cfm for the 2x4's so don't even think about downsizing to 500's. A local felllow is running 2-600 Edelbrocks on his 425 which only has a cam change in it and he feels the motor could use more carb. He's had the car since new and knows it well. I'm working on a 30 over 425 with Jim B heads, TA-30 cam, headers etc etc etc and feel a pair of 750 Edelbrocks will be just about right for it to breath through. If I could just find the right blower to set them on top off. Wishful thinking there. :eek2: Love the way you do the pics on your website just highlighting sections of cars. Thats the way I shoot mine too. :TU:
Thanks Doug. I'm glad you like BuickStreet.com. I've had a few favourable comments regarding my 'preview' pics and I get a real kick out of trying to find the best feature of a feature car to present. Sometimes I spend hours on one car so I get real up close and personal to models I'd never get a chance to see in real life. I'm glad that I'm not the only one crazy enough to want to over- carb a nailhead. I've already got a modded 800 cfm Qjet on there and during dyno runs the vacuum always increases at max revs which says to me that the carbs (or the intake) could do with a little more breath. So I'm very keen to just throw it all together for an experiment at least. I'll have complete coverage on BuickStreet and will let you all know how it goes - including a dyno run.
