Hot Rod Forum banner
1 - 20 of 27 Posts

·
Registered
Joined
·
79 Posts
Discussion Starter · #1 ·
I have a ZZ4 350 with the GM hot cam, ported oem aluminum heads, 410 gears and 700R4 trans. Guessing 3500 curb weight. Do I run a 750 holley dp or is that too big? :confused:
 

·
More machine than man
Joined
·
846 Posts
A 600 CFM will be more than adequate. Smaller CFM carbs have smaller throats (barrels). This increases air velocity (because it is a smaller diameter) through the venturi's. This gives excellent low and mid range throttle response, power, and torque. When you start getting into higher CFM carbs, they are capable of making more power at higher RPM. But to make that additional power you must sacrifice street manners (aka low RPM power/torque where you spend 99% of street driving). With an automatic on the street you tend to keep the RPM's lower because of the shift points (another good reason to get a smaller CFM carb), with manual trans drivers tend to wind the engines higher between shifts. Everything in engine building is a balance, there is rarely a win-win design. You must find the perfect balance for you driving style and how you plan to drive this car. :thumbup:
 

·
Veteran/Firefighter-Paramedic
Joined
·
1,736 Posts
personally I am not a fan of using a 600cfm carb on a modified 350. they are a perfect replacement for the typical 70's-80's stock 350s that dont like to turn more than 5000rpm. but for a modified 350 that wants to turn 6000rpm i would suggest one of these two carbs.

http://www.summitracing.com/parts/HLY-0-80783C/

or

http://www.summitracing.com/parts/HLY-0-80670/

personally i would go with the 0-80783C, 650 vacuum secondary carb. as for the double pumper idea, unless you plan on doing a good amount of racing then stay with the vacuum secondaires.
 

·
Registered
Joined
·
3,518 Posts
For an all around very good, reasonably priced, easy to find carb....ya just can't beat a Holley 3310 for the street.......unless you want all the trick stuff.
 

·
Registered
Joined
·
2,966 Posts
The 3310 is a great carb, but unfortunately I think it's out of production. The only 3310's available are rebuilt Holleys.

I would go with the 4150 electric choke model if it's a square bore intake, or the 4175 if it's a spreadbore. 650 cfm, and vacuum sec.
 

·
Back Yard Junky :)
Joined
·
368 Posts
Quick question. Whats the difference of a spreadbore and a square bore? Does one make more power and torque through out the RPM range?
 

·
Registered
Joined
·
2,538 Posts
What is with the holleys. How about the AVS/AFB style. They would be my first choice for anything on the street. The Holley is just a jet hole , there isnt much to the metering system except for wide open tuning.

Square has 4 same sized throttle blades. The spread has small primaries to drive on and large secondaries for power.

This is pretty dead on.
-Carburetors are rated by CFM (cubic feet per minute) capacity. 4V carburetors are rated at 1.5 inches (Hg) of pressure drop (manifold vacuum) and 2V carburetors at 3 inches (Hg). Rule: For maximum performance, select a carburetor that is rated higher than the engine CFM requirement. Use 110% to 130% higher on single-plane manifolds. Example: If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 120% to 150% higher
 

·
Registered
Joined
·
79 Posts
Discussion Starter · #10 ·
If I understand these replies I should use like the avenger 670cfm :welcome: on my dual plane manifold? Thanks
 

·
Registered
Joined
·
2,538 Posts
Look at the tech discussion at edelbrock dot com . It is a quick read. Check out the cfm requirement and 5 basic levels of engine build requirements.

It is no lies or superstition.
 

·
Registered
Joined
·
2,966 Posts
What is with the holleys. How about the AVS/AFB style. They would be my first choice for anything on the street.
My first choice for street or strip has and always will be a Holley. No problem if you like Eddys, but I've had nothing but headaches with the couple I've owned.
 

·
Registered
Joined
·
2,538 Posts
Cool, but do you have anything to say that makes them your first choice?

The transition and part throttle calibrations are far superior on the road. Hollies have 3 hole steps in the plates. The smaller volume bowls arent going dry unless you really are up over 5500rpms . Cant leak fuel , unlike the holley where the gaskets seals the fuel. Rod metering and jets are a snap. No crazy power valve that is either 6.5 rating or wrong. All it is are holes. AFB/AVS/Qjet has a rod in the fuel jet hole helps that maintain velocity at all rpms. The spring and balance system keeps the side to side evened out. No powervalve boost indexing needed for superchargers.

Just a few things to think about if you drive your car.

Usually people like the first carb they learned on. Also holleys were rumored to be on all the 80's drag cars so they had to be better,. Superstition. They were replacing qjets with them constantly in the 80's. A Qjet is a fine carb and could never figure that downgrade out.

Bad mood, maybe. Please tell me some ways that holley is better under 5000 rpm. I am sorry to have brought this up, but am curious what others think.
 

·
Veteran/Firefighter-Paramedic
Joined
·
1,736 Posts
I to would choose the holley first, I don't have bunch of technical data to back up why, only my experiences with edelbrocks. I have attempted to use 2 edelbrock carbs, one as a replacement for a Q-jet, and one on my very first engine build while in high school. I had problems with both. I ended up rebuilding the Q-jet and on the other motor I put a 3310 Holley 750 which required very little work to get tuned right. For a street motor I don't have anything wrong with a Q-jet except that once they need to be rebuilt they never seem to be the same anymore. It could just be me. I've rebuilt numerous holley's and never had any problems with them. I will admit that I have never used one of the newer edelbrock carbs.

When it comes right down to it, I'm just not a fan of edelbrock products besides their intakes.
 
G

·
If I understand these replies I should use like the avenger 670cfm :welcome: on my dual plane manifold? Thanks
that is more for a 383ci motor. For a 350, depending on the duration of the cam. id go 600cfm all day unless its a beefy cam. then, a 650 would be the highest i would go! if its a stick car dont worry go 670cfm but silver surfer is right on the money to the TTTTTTTTTTTT!!!!!!!!
 
G

·
its this simple

do you want crisp fast throttle response? or do you want it to hesitate and have slow throttle response?

if you want it crisp a 600CFM carb with vac secondarys is the way to go and youll get better fuel economy.
if you want it to hesitate its a 650-670cfm carb
im running an 850 Mec Sec DB on a 496 thats almost 2 times the size of your motor so you do the math a 600 is the ticket here all day everyday!
 

·
Registered
Joined
·
2,966 Posts
I'm not even gonna try to talk you into a Holley spinn, as I know you can never talk me into a Qjet or a Edelbrock. A Holley is not the first carb I grew to know and love, but it's the one I've learned to like best, and I've had great performance with them on daily drivers, or performance cars.
After many years of using a Holley on my 427 Camaro for both street and strip, I literally wore it out. I decided to give the edelbrock another try, as I hadn't used one in years. I suffered with poor performance in stop and go driving, and even worse when trying to merge on freeway ramps. I bought everything edelbrock reccommended to get it to work right, and eventually got them to replace it. Next one was the same issues. I suffered through several months of trying to get it to perform and finally tossed it and bought another 750 Holley with vacuum secondaries like I had before. Bolted it on and never touched it. That was in 1999, and the '71 is still running great today.
There's nothing you can say that will get me to change from Holleys.
 

·
Veteran/Firefighter-Paramedic
Joined
·
1,736 Posts
its this simple

do you want crisp fast throttle response? or do you want it to hesitate and have slow throttle response?

if you want it crisp a 600CFM carb with vac secondarys is the way to go and youll get better fuel economy.
if you want it to hesitate its a 650-670cfm carb
im running an 850 Mec Sec DB on a 496 thats almost 2 times the size of your motor so you do the math a 600 is the ticket here all day everyday!



if that is the case then why did most all 350's comming from the factory came with a 750CFM Q-jet. Dont get me wrong I agree with you in part, but not all the way. throttle response between a 600 and a 650 will be next to identical, but the 650 will allow you to run a little more RPM without choking out. I've run a 750DP (mildly modified) and a 850DP on my 385 street/strip motor, and I haven't noticed any difference in the down low throttle response, the only real difference i have seen (can't really feel it) is past 6000rpm, the 850DP wants to carry me to 7000rpm where as the 750 dies off around 6500. the 850 gets me another .15-.2 in the 1/4mile. (both are specifically tuned for my motor).

now, would there be a big difference between running a these 600 & 650 carbs when you are talking about the differences between a double pumper and a vacuum secondary carb, absolutley.

I still say a 650CFM vac secondary carb is what you want. a 600 will start to choke out around 5000rpm
 
G

·
if you use a simple math formula. it says to use a 500cfm carb for a street driving application and a "650 for all out racing" the 600 is more suited for a 350 daily drivin street application
considering most came with 500cfm 2 barrels that ran great. the 600 is a better choice for this set up IMO and most engine builders will agree.

and the cars that came with 750's had 4 speed manuals in them or were muscle cars with soild lifter cams
 

·
More machine than man
Joined
·
846 Posts
if that is the case then why did most all 350's comming from the factory came with a 750CFM Q-jet.
Because the Qjet is a spread bore carb. It has the small primaries for street driving and extra large vacuum secondaries for high RPM. Best of both worlds. I don't know why square bore carbs are the norm and preferred.
 
1 - 20 of 27 Posts
Top