I have a mild 350, Performer intake, headers, 2.5 inch dual ex, unknown cam (maybe performer) , T-350 auto, and a Q-jet. The Q-jet is needing replaced. I am looking into the Holly 3310 (750) or the 1850 (600), both vacume secondaries. Do you think the 750 would be too big? Some people have told me to get the 750, but I am woried it may be to big. My Q-jet is not rebuildable, so that is not an option. The car is street only, so I don't want a DP, or 8 MPG. Any help would be great. I want to order a new carb this weekend. Thanks.

If you are trying to get it to be a street bruiser, then buy another Ajet from Edelbrock or somethin.
If you just want a Holley, my VE math tells me 600 w/ Vac Sec.
try this:
350/2= 175
5000/1728= 2.89
175 x 2.89 = 505.75 < this is 100% volumetric efficiency. Most cars are around 80-85% volumetric efficiency.
So mathmatically speaking, your car needs a 500cfm carb. However, the stock jetted 600 holley would work great. You may have to jet it down but I believe it would do great in stock form.
IMHO tho, I would get a Qjet. My experience with them tells me they are the best all-around carb for performance, mileage and consistancy.
Good luck! let us know how it goes.

I would go with a 1850 Holley 600 vac sec...great carb for your combo.

Those Holleys are square bore carburetors, the Q-jet is a spread bore so will you also need an adaptor plate or different intake or is your intake universal mount?

Dan E.
69 SS396 4spd. 4.10 posi. x66 coupe

I just don't go for those formulas that say such and such a carb is the perfect size. I had a mild small block 400 much like yours and two Holleys. One a 750 and the other a 650. Both vacuum secondary. I used to swap them back and forth and the difference was night and day between the two.The car ran much stronger with the bigger carb. I would go with a 750 vacuum secondary on yours.I also ran the same 750 on a 327 using an adapter on a stock spreadbore manifold and it ran extremely well. Both cars were used on the street with the pedal stuck to the mat a lot.One an automatic the other a stick. I hope these examples help in your decision.

Has anyone used the new Summit carb? It looks like a Holly maybe.

I personally think the Summit carb looks more like an old Autolite carb. Be that as it may my recommendation is stick with the Rochester Quadrajet. Buy one professionally rebuilt and set up for your 350 from Jet or any of the other carb shops out there. A properly tuned Quadrajet will make just as much power as a Holley or Edelbrock (Carter AVS) carburetor will but offers better economy if you can keep your foot out of it.

Larger Dave

[QUOTE=Larger Dave;1245715] A properly tuned Quadrajet will make just as much power as a Holley or Edelbrock (Carter AVS) carburetor will but offers better economy

Ditto that^.:thumbsup:

Patrick:

Many years ago I put a 600 Holley on myoriginal 350 and it was a very good match. At the time I used an old aluminum GM intake. With your new Performer intake, I'm sure the 600 would work just fine.

What size you choose ultimately comes down to what you plan in the future. If you see more mods coming, ie heads, cam, converter etc, the 750 might be a better pick. If not, the 600, or as mentioned above, a rebuilt Q-Jet will work fine. Don't underestimate the Q-Jet design - Edelbrock uses them on their 650 hp 555 cubic inch BBC. A rebuild kit will likely be a lot less than a new carb.

Tom

The 750 would run better because it will move ALOT more air. If you plan on hitting 6.5K all the time on the street then go with the 750. If you want a street bruiser use the 600. You will like it.
all IMHO of course.

I agree with the Q-Jet. It gives you the best of both worlds. Great power and great MPG. I suggest you go to a salvage yard and get one from 75-84 non electronic. Rebuild it yourself and save yourself the money. I went the route of buying one of the over priced "professionally rebuilt" units and it was HORRIBLE!!!! They say they are custom for YOUR application, but it is IMPOSSIBLE for a mass production company to build you a custom carb in only 3 weeks. Think of how many other orders they have. How can they tailor build you a carb in 3 weeks while building all the other orders in 3 weeks. It can't be done. Get yourself the best book on Q-Jets. "How To Rebuild and Modify Rochester Quadrajets", by Cliff Ruggles and "Rochester Carburetors", by Doug Roe. Now the 1st book deals specifically with Q-Jets. The 2nd deals with all forms of Rochesters. If you are hell bent on buying a professionally rebuilt Q-Jet, go to Cliff. His carbs takes about 3-4 months, but they are the real deal. If you choose to build it yourself, he also sells everything you will need and is more than willing to discuss any quesions you may have. I got mine from a fellow TC member before I really knew all the workings. I did get the books and since then, have learned gobs about them. They are wonderful carbs, provided they are tuned correctly. Most people who say the Q-Jet is junk DO NOT understand how to make them run correctly. They are a great carb for the street.

every 600 holley iv ran been dogs.imoa,i run a 650dp on the street with no problems at all.i picked up 2/10 of fuel milage going to the dp if i keep my foot out of it.it was like dropping in a new motor it ran so much better

For the street I would go with a Holley #6210. It's the spreadbore replacement that Holley makes for the Qjet. I believe it's a 650cfm.