2 Edelbrock 600's on a basically stock 401 Nailhead. Too much carb???

So I found this setup on eGay today for a price I couldn't pass up. It's an Offy dual quad intake with 2 Edelbrock 1406 carbs. Aside from reconditioned heads with stiffer springs, this is a stock 1966 401. Too much? I've seen some of the Nailhead guys here recommend 500s.

 

Zombie
I'm not totally familiar with that model carb, but as I recall, all Edlebrock/Carter type carbs that Edlebrock sells are vacuum secondary, with air doors. If this in fact true, then you should be fine, as the engine will only inhale what it needs.
Jim

 

I run two Carter 600's on a mild sbc, you'll be fine.

 

yes, too much, you migh have problems with it loading up at idle...but it will look kool

 

It's not going to really "hurt" anything. If you run progressive linkage and keep your foot out of it, you will most likely never notice anything. But, at wide open throttle, those two carbs might be a little much.


The only way to know for sure it to hit the chassis dyno for an afternoon. A dyno will have an air/fuel sensor that will tell you everything you need.

Short of that, just drive it...if you have some issues, buy an Edelbrock jet kit and tune her a bit. It is actually VERY easy. The kit comes with detailed instructions and a chart. If you have to tune the carbs at all, you can probably do everything you need just by changeing metering rods. No need to even take the top of the carb off.

I think you will be fine. Good luck, -Abone.

 

Don't listen to the naysayers, they don't know, like Abone said, you'll be fine. Tuning on the dyno is definitely the way to go. And Nailheads like lots of carb. The only issue I have is that the Offy's aren't very good manifolds. And you'll be fine with either progressive or straight linkage.

 

May not be the brand you want, but Holley has a 390 cfm, vacuum secondary with electric choke. I just bought 2 for my 347 build with a 2-4 tunnel ram. One has the quick change vacuum spring top and I plan on putting a balance tube between the 2 secondary diaphrams. With that big engine you might be just right.

 

Take your time tuning the carbs and setting them up , as said the nailheads like alot of carb. Hopefully you can get it to run decent with progressive linkage but if you run it straight it's very quick responding. I can barely drive my sbc progressive but maybe you'll have better luck.

 

I'm running two 600 cfms on 331 inches of sbf and the plugs are light tan and it idles and runs like a stocker. You will be fine with 401 CI. Edelbrocks are tuned out of the box a little on the mild side anyways.

Don

 

I have run 600 eddys in the past on my 400 sb Chevy. Ran good but did load up some at idle. I just used some Vortec heads with a air gap 2X4 intake with 2 500 Eddy's and now much more responsive and a better idle. 600's are easy to come by and like the other guys said, If you fiddle with them they should work out ok.

 

It will work ,Just might have to tune them,They make different stepup springs and jets ,Youll probably be fine ,I had a buddy that tuned his .Im a holley guy ,But there simple enough to play with.

 

Don't know about nailheads but I ran dual quads with the Edelbrock 500's on a BBC. The progressive linkage used the rear carb as a primary which caused the front cylinders to run hot. I switched to straight linkage and it cooled the motor down, however, power was down with the 500's. I bought 600's but never installed them. Edelbrock recommended going to the 600's.

 

Yes I remember reading that the Offy tri power wasn't the way to go and it actually flows less than the stock 4bbl. The dual quad intakes aren't so good either?. I got the whole set up for $599.00. I couldn't pass it up

 

The Offenhauser dual quad intake for the nailhead isn't ideal for progressive carburetion as there is a restrictive passage to a couple of the front cylinders that you can see on inspection. You would be ok with straight linkage. I am running a 500 cfm primary carb (rear) on an otherwise stock 401, and it is too small. Zman and flamedabone are absolutely right... nailheads like big carbs! I am changing to larger carbs for next year. Happy motoring, Buford

 

great thread, I was wondering how a pair of 500 thunder series eddies would be on my 425.

 

Do you remember what intake you were using? I'm building a dual quad 455 Olds & 2 500 Carters in progressive, & that make me worry

 

The air flow frow two carbs will be the halv of wath one carb get, so sometimes you have to get bigger jets with to carbs for the airflow is to low and take to little fuel with air in to the engine, its like a choke, you stop the air and the carb sucks more fuel, with two carbs the air passaes throw the carbs easiely and its sucks little fuel, But you have to carbs so its going to be fine. The best with to carbs is the twice accs pumps you never get a to small carb when you get the pedal to the metal.

Its a roumer thats you get to much fuel with two carbs, you dont get twice the fuel into the engine like many thinks.

 

The dual quad Offy doesn't flow very well either. The stock dual quad manifolds are much better. You can port the Offy or Extrude hone it to make it better. But it's fine for the street.

 

I agree 100%...You'll be fine...especially at $599!!

I've run both carb sizes and both types of linkage, on Offy and stock intakes on 401's and never had problems with any.

I like the dual quads on Nailheads a lot more than a single carb. I'll be switchin my '37 Chev over this winter...don't know why I went with a single in the first place!

 

Here I am so many years later with the dual quads for my '57 still sitting there as I drive around with the single 4. I've just never got to the switching over...

 

On my Offy intake with progressive linkage and the rear carb as main carb the front four plugs were lean. I switched it to straight linkage and it has been great since. I've posted this video before but you can see that it idles fine and has no problem taking the fuel with the straight linkage and 600 cfm carbs, like I said before you will be fine.
http://www.youtube.com/watch?v=aL0xnTbLOtk

.

 

Ok, great info everyone. Thanks. I'm gonna go with it and plan on stopping for gas a whole lot

 

Ive done it before...like I said the only issue you WILL have is it loading up at an idle (not horribly)....just run progressive linkage. Nothin beats the look....run it even if it loads up, just clear its throat everyonce and a while, youll be fine.....nailhead cams had somewhat of an aggressive grind from the factory...they will take alittle extra carb. But if your doing it for power, keep in mind that just because you bolt on another carb wont mean it will have more power...youll probably lose a few HP....as proven by a friend of mine's chassis dyno.

 

Then you need to learn to tune your carbs...

and it doesn't matter if it's progressive or straight. If you tune the carbs correctly the Nailhead will NOT load up at all...

 

I think 2 Fours are too much for it it will load up bad you will be changing out plugs every week! if you keep your RPMs up at launch might get you there but still 1 Big 4 BBL would be good enough!

 

That sounds like a tunnel ram with too much CFM or a badly tuned combo. Those cards he plans on running are not 600 Holleys. They are patterned after Q-jets. Finely tuned, it will not load, nor bog.

 

seriously? If you guys know nothing about Nailheads then just let it go. They came from the factory with two 575cfm Carters and no such problems. Where do you guys come up with this stuff?

 

Nope, they are Carter AFB clones, not Quadrajets..

 

lol, I didnt realize you were the authority on high performance engines and tuning. Sorry for even having a comment on my own personal experience.

 

well being as these engines came from the factory with two carbs suspiciously similar to the ones that he wants to put on, and they had none of these issues you seem to say are unavoidable, and that I have done more than my fair share of Nailheads with this same induction, I wouldn't say I'm the authority, but I have experience with this and none of what you say is going to happen has been an issue with factory setups, or the aftermarket if you have a clue as to how to tune a carb. So maybe go answer a thread you have some idea of what is going on already and leave this one alone.