I have a 1973 roadrunner with a mild 400 (8.7:1 compression) automatic trans with 2,800 stall and 3.55 gears just wandering if I could get an opinion on carb size would a 600 cfm be to small? Should I go with mechanical or vacuum secondaries? I appreciate the help!

holley 3310 vac sec 750 cfm

600 sounds way small for 400ci. My 360 has a 670 Street Avenger and seems like it wants more, so I am going to try a 770 vacuum soon. It is harder to go too big with a vacuum since it will only take as much as the engine can handle when properly tuned (very gross simplification). Some 318's came with thermoquads capable of 750ish cfm, but the vacuum operated air valve made it possible, unlike say a mechanical double pumper.

I'm sure others will chime in, and probably all ask the same question...What is your intended usage? Driver, dragstrip, or street/strip.

That makes three of us. Hard to beat the 3310 for general street/strip use, especially if you equip it with a quick change spring kit,electric choke, and secondary metering block.

street/strip

3310 Simple.

is the 3310 and 4160 similar carbs?

Yep, 3310. Cheap and rocks with just a few easy mods.

""If we are talking a new carb, doesn't the quick change spring kit, choke, and secondary metering block pretty much equal a holley street avenger or quick fuel slayer?


The QF Slayer also has:

""the Slayer™ provides all of the popular options: changeable idle air and high-speed air bleeds, 3-stage emulsion circuits, changeable primary idle feed restrictions and power valve restrictions. A real welcomed feature is the QFT QuickSet adjustment on the vacuum secondary diaphragm that provides a quick external twist adjustment without changing springs. Secondary metering can be altered with changeable main jets and the secondary float is also notched for jet extensions.

Two thoughts here. First, there are not likely to be many Slayers or the like at swap meets for $75-$100 like the 3310s.

Second, if the OP needs help sizing the carb, he is not likely going to be able to take advantage of the added tuneability of the more expensive carbs.

Besides, if he does start learning to tune, he would be better off experimenting with a $75 carb than a $300 carb.

I've tried 4 different carburetors on my 383. a 600, 670, 750 Edelbrock and now the 750 cfm Holley vacuum secondary which is by far the best one. One I've not tried is the 770 Avenger. Another one that seems interesting is the Summit Racing brand 750 carb with annular boasters which are superior on the street. But I also notice that some race carburetors have annular boasters, too. Most carbs have straight leg or down leg boasters.

Edelbrock or Holley
750 cfm
Vacuum secondaries
Electric choke.

Two last points, maybe.

$600 for a rebuild?!?!?!?!??!?!?!?!?! Again, if the Op cannot clean up a carb and throw gaskets in it, he won't be able to tune it.

And the CarterBrocks have mechanical secondaries. Even the secondary air doors are air flow opened, not vacuum.

I just checked the prices in a recent Jegs catalog. Holley 3310=$264.99, quick change kit=$14.99, springs=$11.99. Electric choke = $49.99. I didn't see a secondary metering block, but I would guess about $50.00. Total price for everything $391.96. Price for a Quick Fuel 750 vac. sec.=$526.99, $135.00 more than the 3310 with the options I recommended. As previously noted 3310s can be found used for between $25.00-$100.00. Price for a rebuild kit=$22.00-$25.00 depending on where you buy it. Add in $3.00 for a can of carb cleaner and your still under $30.00 to go through it. FWIW you can buy a Holley jet kit for $50.00 that has a pair of every gasoline jet from 64 to 99 in it so tuning shouldn't be a problem. I am not saying that the 3310 is the right carb for everything, but it is the closest thing there is to a truly universal carb and at a very reasonable price.

No more points, but a few thoughts and a couple more questions.

The OP probably should note that ALMOST everyone in this thread had recommended the 3310.

I am a little lost on the concept of restoring a carb in this thread. The OP wants a recommendation on a style and size of carb. I didn't see any reference to "correct" or OE looking in his question. And why would anyone spend the coin on a used carb, that then needs more money spent on it than a new one would cost?

You should be able to get most 4150 style carb cleaned and gasketed for $100 or so including gaskets. If it needs more than that spent on it, it would probably have been a bad choice to begin with.

For most of us, an electric choke is more trouble than it's worth. Which is why most of these type of carbs are still offered without them.

I'll say again, the CarterBrock style of carbs are MECHANICAL secondaries. Just like a Double Pumper Holley. The difference between those is the type of secondary actuation enrichment. Holley uses accelerator pumps, while the CarterBrocks use the air valve to pull extra fuel from the boosters.

I guess the CarterBrocks are easier to get apart. But when it comes to tuning, have you seen the rod/jet chart in the tuning manual? What a nightmare, and I would like to see someone try to tune one without the chart.

For this application, I do not see the value of the secondary metering block. The primary is where most if not all the street tuning happens. You basically tune the WOT mix with the secondaries and that is usually pretty close to begin with. I rarely need to change much if anything on the secondaries, if the idle mix isn't too far off. And then I can get it close with the primaries anyway.

I do a agree that the Double Pumper would be a poor choice here. But not necessarily because it has mechanical secondaries. But because it is metered for the track, which is way too rich for this kind of street application.

Here's another vote for the 3310 Holley, forget the choke, get a secondary spring assortment, if you buy used make sure the throttle plate isn't warped, and don't overtighten when you bolt it to the intake manifold (100 inch pounds is correct) unless you want a warped/broken throttle plate and a huge vacuum leak.