Projects 350 Small Block carb options

Hello all I was wondering which is the best choice for my relatively stock chevy 350 crate. Its the 260/350 from GM will have shorty headers a 4 bbl aluminum manifold aftermarket hei and just a pcv system no smog...I currently have a holley 4412 that is less than a year old 500cfm works great on my 326 pontiac I do have an adapter plate for my 2bbl to 4bbl intake but ive been considering the 650 double pumper from holley I'm short on funds so ill be buying a used one then rebuilding at home but I guess my question is how much gain can be had in my daily driver with this set up? Also I'm running a th400 and 2400-2600 rpm stall 2.93-3.03 rear end. Also I know the quadrajet is an option that will be brought up but my intake is strictly square bore unless an adapter is used and I know the holleys and tend to prefer them. Thanks!

 

Also what are the potential downsides to paying half for a used holley and rebuilding it vs 400$ for a brand new unit?

 

I am guessing this is for a 65 Pontiac and with that combo I would be using a vacuum secondary like the 1850 600cfm rather than a double pumper....

 

If you are short on funds , use the 500cfm you have, just adjust your trans so it kicks down a gear when you want to pass someone.

 

The biggest downside to buying used Holley carbs is you just don't know how many fingers have been in them over the years, swapping components, drilling passages, etc.
Unless you know the history, its a crap shoot.

 

If you want some semblance of gas mileage for your daily driver, you shouldn't use a 650 DP or a Holley 2 bbl,
"Ponchoguy"

 

I do not think a DP would make you happy with you engines current configuration , use the 500 cfm untill you can lay your hands on a 600-650 vac. sec. new.

 

I used an old Rochester 4 jet on mine
square bore, and a cheap kit to rebuild
get 10-12 mpg in a school bus

 

I know you like Holleys, but I'd gather up all those Holleys (plus parts) and find someone to trade for or sell to, and go buy a 500 or 600 Edelbrock. You will be much happier.

Trust me, I've been there!

 

Yea, that would work just fine as well.

 

JMO but I would stay away from the Holley street avenger. The ones with the non adjustable floats. They are a little cheaper but not necessarily a bargain.

 

If you have an open plenum intake the adapter for the carb you have makes a lot of sense. it might not work quite as well if the intake has 4 individual runners.
I'd go along with the double pumper not being the right carb for that engine. I've run them but had a pretty good cam and headers to go along with them.
I've run a lot of used Holleys over the years but it is indeed a crap shoot when you buy a used one you don't know the history of. That goes for any used carb though. It's just that on a Holley you never know what jets it has, you don't know what accelerator pump cam has been swapped in or what other changes they made. I ran a 650 for a long time that I had swapped the float bowls for center pivot float bowls and dual feed. That old unit probably messed with the mind of the guy who ended up with the last car it was on. It worked great but if you bought the kit for the carb number you didn't get the right parts.

 

I like Holleys . However a Eddy performer RPM air gap intake and Eddy 500-600 , and a little cam upgrade. You will have a nice mild street sweeper. I ran that set up years ago on a mild 355 SBC, ran great and would still pucker your A$# cheeks.

 

My avatar has one that should work. Lol

 

That would work anytime!!!! LOL.

 

^^^^^^^^Ditto^^^^^^^^^ More than enough CFM's and a good carb for a cruiser.

 

Yeah, Holley all the way.....
I can make those carbs sing any tune you want...

 

Your 400 TH and 24-2600 stall are eating extra hay, if you get and Edelbrock/Carter AFB get a tune kit from one of the suppliers. They all need a little tuning for each engine and are a tad rich-out of the box....

 

^^^^^ TRUE^^^^^

 

I've done alot of Holleys on dirt track stuff in the old days......also Rochester 4bbls., Carter AFBs, and earned a living doing Quadrajet stuff in a GM dealership. Lots of good advice on here......I would try to buy something off a stock running vehicle and then learn the carb overhaul myself unless you just don't have the aptitude.....and not everyone does......and thats OK. Lastly, don't fall for the common crap of thinking just because something is called a "double pumper/thumper/humper./dumper" that it somehow will work for your application........sounds good over a beer, but usually doesn't work out in real life.

 

Good. How about helping the guy with the 327 Chevelle DP Holley?
Hopefully, you can make them sing, over the internet.

 

Jimmy,
I think you're onto something. He could drop on a 65 326 HO AFB, paint the engine Pontiac blue, and be the "Poncho Guy" again.

 

I've got a mechanical secondary 750 double pumper sitting in a box in my garage that I took off of an otherwise stock 69 350/350 about 25 years ago. Replaced it with an 1850 vac secondary 600. Best change I ever made for both mileage and driveability.

 

Don't buy a used carb. As said above, it's a crap shoot. Quick Fuel Technologies makes a Holley copy improved carb. In fact, Holley bought QFT not too long ago and runs it as a separate line. I think they were afraid of the competition. I would suggest QFT SL-600-VS, $300 most anywhere. Heavy car + automatic trans + high rear end ratio = vacuum secondary carb. This QFT carb is 600 cfm and vacuum secondary w/ electric choke. I have one on a 350 about like yours. Great carb right out of the box, but if it needs some tuning the QFT is much more tunable by changing jets in the idle feed restrictors and high and low speed air bleeds. In a Holley these are fixed orifices that must be drilled to be changed.
I also have a QFT SL- 750-VS on another 350. Then I have a QFT HR-850-DP on a 383. All run good. I don't have a nickel in the company, but I ran Holleys for 30 years until I found QFT.

 

DUDE! I stared at your avatar for like 5 minutes, Never saw "one that should work"?

 

Awesome awesome awesome advice thanks for all of the replies its all been great advice and ill be opting to use the 500 cfm with adapter for now on the engine and later upgrade to an edelbrock possibly and what are the advantages of the vac secondaries on the daily driver verses the mechanical? Also is the eddy a square bore or spread bore flange. And how much could the th400 be eating I went with the 400 for their reputation as mostly bulletproof? And the 2400 stall was recommended from the guys who build my trans after I told them the same set up I originally posted....off topic but does anyone believe that it may be too much stall for that car? Thanks for all the tips and tricks I'm happy to be on the forum ✌

 

The QFT sounds like a good choice also ill do some digging into that company and okay what are advantages to the electric choke carbs I've always ran mechanical choke but live in south Texas and cold starts are rare.

 

Thatll work

 

Also anyone with an a body know if ill have hood clearance issues with the 3/4" 4bbl to 2 bbl adapter and my existing 10 inch air cleaner on the 350? I've seen some moroso low profile air cleaners that are a good option. Thanks

 

I read somewhere when it comes to carbs and cams, pick out the one you think you want, and then select one size smaller.