So thses are the two carbs I was thinking about going with either the EB Thunder Series AVS 650 cfm part #18054 or the Holley Ultra Street Avenger 670 cfm part #0-86670RD. I was originally gonna use 500's but I spoke with Russell Martin and he said they would be too small. I know nothing about these carbs what would u guys use? Stock 401 nialhead with a automatic tranny 2x4 Eelco intake <!-- / message --><!-- controls -->
I would use the 650 AVS, you can adjust the secondary air door to make them work on the nailhead. Two 500 AFB's would work better I think - especially on a stock motor.
Two carbs on a stock 401? We put two Carter 9400's (400 CFM each) on one and it literally screamed on the street. Really responsive at all RPM's. If a trailer racecar, you might want to go larger, but like gimpy stated above bigger is not always better. Jon.
What about a Preditor carb. They are a ventrie carb they only pull the cfm the motor will take, they have a street version. but they are not cheap. just my .02
Predators are variable venturi carbs (390 to 900 cfm I think) and would work as well. AFB's function similarly on the secondary side with a weighted air valve that takes vacuum to move into the open position. This is why they work well in mild dual quad applications - when you open all 8 throttles, the four primaries do the breathing until the revs come up and there is enough vacuum for the secondary air valves to start opening. In some cases the air valves may not move very much at all, so you get the looks without over-carbureting.
Russ is right, the Nailheads like a lot of carb. I'd go with the Edelbrocks personally, or find a couple of OG Carter's and rebuild them. Yuck... the ugliest carb ever. You must love the 70's. And they don't work that well unless it's a full race application.
Thank you for editing the original post to include the pertinent info. I can't tell if that variation on the vacuum secondary holley has secondary accelerator pumps. Most don't. The carter/edelbrock design is kind of a hybrid between a mechanical secondary and vacuum secondary, and features 4 accelerator pump squirts instead of 2. IMO that extra accelerator pump shot gives them a serious edge in terms of street response. You'd have to own a gas station to even think about mechanical secondary holleys Good luck!
What would you guys use straight linkage or progressive? CarbKing nailhead's came with dual 650's on stock applications
Actually, they were 625's but not splitting hairs, and yes, I was aware of that. And yes, the 400's worked MUCH better on the street than the 625's on a stock engine. On a trailered race car, the 400's would give up maybe 0.10~0.15 in the quarter-mile. The poster suggested this is to be a primarily street driven vehicle. We used solid linkage vs progressive on the original Buick dual quad. Some of the factory dual quad were deliberately too large as NHRA required stock carbs to be used in many classes. With progressive linkage, one could run the overcarbed engine on the street, albeit less satisfactorily than if the carbs were smaller; YET still have plenty of carb to support a "built" engine for racing. I hear much of how a certain engine really liked "more carb". However, consider that even the mighty hemi ran better in the late 1960's with a pair of 625's than with a pair of 750's. Carter built 200 sets of the "Drag Strip" 750's for use on the hemi, and then discontined these units as Chrysler was getting quicker times with the 625's. But back to the point of my post: the original poster stated mostly street, with an occasional run. ANY carburetor is a compromise. One simply has to decide WHAT function to compromise. Jon.
I am not aware of us ever voiding a warranty because someone went into a carburetor and in some cases we may even advise the person to in an effort to make needed changes or tuning. A lot of times we will even warranty stuff out of its original period because we know how projects go and sometimes its awhile before thye even get fired up.
Thank you sir. That's what we like to hear. By the way I've had very good luck with having customers order their carb straight from these guys and it being a lot closer to spot on out of the box. But I still open them up and look.
Holley's like every carb out there, if just a little bit more, need to be tuned to work properly. I find that they are no better or worse performing than what else is out there. They are not the easiest carbs to tune, but also not overly difficult. If you have a "carb guy" in your community see what he prefers, since you might need advice or help when tuning. As a plug for BG, you have a tech RIGHT HERE to talk to. How cool is that?
I'm running a Demon DR (dragrace) 1000 cfm carb on a moderate street/strip 460 ci bigbblock. It's a double pumper with no choke. Honestly way too much carb. However, with a decent knowledge of how these carbs work and some time tuning it, it works ok. I don't think there's an orifice in it that hasn't been modified in some manner. Would a smaller carb work better? Yes, I have no doubt an 800-850 would work better. But I own this one. The primary thing I like about the Demons is that it can be adjusted. Most (if not all ) circuits have replaceable tiny jets. Devin
One of our engine customers did an engine for a guy last year iirc and used a set of our single lines on one. I seem to remember thye were 625's.
I believe Ahotrod's Lime Squeezer had them... I'm sure he'd love to talk about it. And he's got it for sale which makes me sad.
There are many really great carbs out there on the market that would do you really well but I would go with something that would keep it more traditional like a Carter or something along that line . Now if you are going the more modern way I would go with an Edelbrock . RetroJim
The Edelbrock looks fine, and really from a glance doesn't really look any different. Though if you have an air cleaner on there it's really hard to tell at all. Please pardon the MSD box and Optima, I haven't had a chance to make a cover. I've been to busy driving the shit out of it.
I have one of the single line Jr's like pictured on the green car on my Cyclone and reused the factory air cleaner and you really can't tell it is on there either.
I think I am gonna go with Edelbrocks cause they don't need that much adjustment. I would like to run the Holley's cause I would like to have the abililty to be able to step on it if need be. Decsions Decsions
A lot of the issues with guys running dual quads on o the low rise style intakes are the factory desing was for only ONE carb to have idle mixture screws in the idle circuit. By using aftermarket carbs on this style intake you now have added an idle circuit to the front carb causing a harder to tune set-up. The front idle circuit tends to make the front two and on some designs three cylinders to run richer. I have found it much easier to tune the aftermarket carbs like the original set-ups, so I will close the idle circuits off on the secondary carb, in most instances this is the front carb. By doing so you can use the primary carb as was originally desinged. Make sure to not have the throttle blades open on the secondary carb, by this I mean to have the idle speed screw backed out. Do this while you are adjusting your idle speed/circuit. If you have to have the primary carbs idle speed screw in quite a long ways, then you can slightly open the secondary carb with the idle speed screw. Not much will be neccessary if any, then back the primary idle screw down to get the idle speed you desire. There can be some time spent tuning a dual quad set-up on the street, race applications too for that matter, but it can be done very succesfully. The last dual quad nailhead I did was two years ago. The intake was a factory cast iron unit. He used 625cfm carter competition(aftermarket) afb's, these are just like the edelbrocks you are thinking about using. The customer had this set-up on and was done by a reputable garage, but they didn't understand the fact that both carbs having an idle circuit really isn't prime for this intake set-up. I did the above tuning to the idle circuit and set the linkage up progressivly like the original linkage was, and it made a night and day difference, not only performance, but mileage as well. I'm not sure on your intake, but make sure you have enough center-to-center spacing on the carb flanges before you choose a holley. Some of these early style intakes do not have enough spacing between the carb flanges for the holleys to fit on them with the rear fuel bowls, metering plates, etc. The rear bowl on the front carb will hit the front bowl on the rear carb. Just a note incase you were not aware of this point.
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