72delta88

what carb would be best for a 350 rocket it has an intake and headers soon to be a mild cam

my edelbrock 1406 died im looking at a 500 cfm edelbrock 1403

its my daily and gets 14 mpg in town 23 on the highway ( 72 d88 ht 2dr th400 3.08 gears) with the 600

oldcutlass

I'd stay with a 600-650ish carb.

72delta88

im probably gonna rebuild mine a friend suggested a 500 for better mpg but i can get the same by not playing stop[ light drag

Cutlass Fan

A stock Q-jet should get better mileage because of the smaller primaries, and better performance because of the larger secondaries than an E-brock. Also the smaller primaries give quicker throttle response.

72delta88

i respectfully have to say i'm not a fan of q jets . my edelbrock has been good to me the best i got with the ebrock was 18 in town and that was not leadfooting it

RocketRonnie

There are website designed to do the calculations for you. Run a search in Google for " Carborbotor size formula" or something along those words.. don't take anyone's guess. It's math.

Fun71

The factory original QJet was a 750 cfm carb. It had an air flow actuated secondary air door that tailored the cfm to what the engine needed. Can't get much better than that.

oldcutlass

Don't all vacuum secondary carbs work that way?

Olds64

If you like the Edelbrock carb so much why not just rebuild it? Anything short of a fire or catastrophic collision wouldn't prevent a carb from being rebuilt.

cutlassefi

Quick Fuel Slayer 600. Best carb for the money anywhere imo.

olds 307 and 403

Another option is the 625 cfm Street Demon. If your carb ran well and got good mileage, rebuild it. Most can't accomplish either with the Edelbrock carbs.

Olds64

I had an Edelbrock 1411 for awhile on my 64 98. It was very streetable. The only problem was getting it to run properly with my Slim Jim Rotohydramtic transmission.

redoldsman

I believe Fun71 is talking about the air doors that are above the secondaries on the quadrojet. This is not the same as vacuum secondaries. I became acquainted with these years ago on a 79 Cadillac I had.

jpc647

I have a 1406 edelbrock carb I took off my car. I removed the electric choke, but you could just use the one you have on your car, swap it over and use it.

It's not worth a whole lot to me, and if you're looking to keep the same carb, it could be a relatively cheap option for you.

midnightleadfoot

If you are looking for the best mpg and power you can't do better than a q-jet until you go efi.. and even then you'd have to go multi port .


but if you like your edel rebuild it.. or is that the reason you're not a fan of the q-jet.. you don't know how a carb works , nor how to rebuild one..?
No shame in that, everyone has to learn some how,time.
get a rebuild kit for your edel. and have at it..

ankerclanker

I'm with cutlassefi, I put a quick fuel slayer 600 on my 330, and it really woke it up compared with the e-brock 625. Really happy with the qf slayer.
ted

dream66

https://www.summitracing.com/parts/sum-m08600vs

I run the 750cfm version of this on my 55 gasser with a 427 BBC that spins to 6500RPM, is very streetable and performs flawlessly at the track
Two of my buddies run the 600cfm version on 350 SBC street machines and prefer them over other carbs they've used.

It's an older Holley design that Summit bought and perfected. They operate flawlessly right out of the box and can be tuned with standard Holley Jets and Power Valves etc.

I currently have an Edelbrock on the Cutlass that I don't much care for so I'll eventually get a Sean Murphy Q-Jet for it to keep it original.

I've previously used Holley 4150's, Street Avengers, 3310's etc and none of them compare to the Summit carb

BangScreech4-4-2

I'm mostly a Q-Jet guy, but I had a great experience with a 670 CFM Holley Street Avenger on a 327/350 Chevy. Very crisp, ran great right out of the box, but still very tuneable. A 570 CFM might be good for your application.

72delta88

i went with a street demon 625 and love it after the holley that replaced the edel died

mightyleadfoot

i understand how a carb works i had a q jet on a 305 sbc in my t/a and it was worthless

im getting 19 in town 28 highway with a th400 and 331 gears next step is efi


olds 350 a great engine when you cant find a 455

olds 307 and 403

That is incredible mileage, is that out of box? Glad that carb worked out.

72delta88

i adjusted the secondaries they dont open till around 65 mph and i lean out the fuel mix at idle

oldsmobiledave

Mark


Why the QF 600 & not a QF 750?


At what performance level to you move up to the 750?


thanks

Dave

young olds

Quadrajets aren’t a vacuum secondary carb, technically a mechanical secondary carb. As far as I know a true vacuum secondary carbs second side is either open or closed.

cutlassefi

Hmmm not really. Look at virtually any vacuum secondary carb, they all have a lower throttle plate that has to open before the top ones do.
A true mechanical secondary carb will open the secondaries no matter if there is a vacuum signal or not. A Qjet is NOT a true mechanical secondary carb, sorry.

AZ520

I would just get the new avs 2 edelbrock 600cfm, super easy to tune and now better than ever, those summit carbs get great reviews as well, I have a street demon 625, pretty good as well. Get a AFM and any carb will be good, its all abut the tune. The original question, stick with 500-800 cfm, lol

cutlassefi

I misspoke, I'd do a 750, not a 600.
But as mentioned, don't just bolt one on and go. Use a wideband, you'll be glad you did.

young olds

I’ve never seen a Holley vacuum secondary carb with any type of throttle blade above the ones in the base plate, when the lack vacuum gets to a certain point the vacuum servo opens the throttle blades. On a quadrajet if you open the the primary cycling through to full throttle the secondary’s start opening( idk 3/4 way in) and continue to open to full throttle by the time the primaries do. If that’s not mechanical let secondary idk what is. The “doors” above the secondary’s are basically meters to adjust secondary fuelling based off airflow.

cutlassefi

Edelbrock carbs also have lower and upper secondary plates.
Bottom line, on any vacuum secondary carb, including Qjets, fuel metering doesn't start until the VACUUM operated doors open. On a true mechanical secondary, fuel metering starts the second the mechanically operated plates/secondarys are opened. A Qjet is a vacuum secondary.

olds 307 and 403

The Thermoquad and Street Demon also have that set up.

young olds

I’m not making any claims about when fuel metering starts but quadrajet do not use vacuum to open any part of the secondary throttle. Holleys actually have a vacuum servo to control the opening of the secondary throttle. But none of this helps the op so we can just agree to disagree?

cutlassefi

Sure, not sure what you would call the vacuum operated flaps on top but yeah, sure.

young olds

I’m still waiting for those sensors btw, I keep forgetting to ask about them. OP, sorry about de railing your thread.