Hot Rod Forum : Hotrodders Bulletin Board

Hot Rod Forum : Hotrodders Bulletin Board (http://www.hotrodders.com/forum/)
-   Hotrodding Basics (http://www.hotrodders.com/forum/hotrodding-basics/)
-   -   What carb do I need for SBC? (http://www.hotrodders.com/forum/what-carb-do-i-need-sbc-221043.html)

wibas 06-26-2012 09:34 PM

What carb do I need for SBC?
 
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:

Silver Surfer 06-26-2012 10:10 PM

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:

Silver Surfer 06-26-2012 10:10 PM

And I would avoid a double pumper or mechanical secondaries for street driving. Get vacuum secondaries.

my87Z 06-27-2012 09:39 AM

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.

327NUT 06-27-2012 01:17 PM

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.

1971BB427 06-27-2012 02:42 PM

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.

400smb_s10 06-27-2012 05:46 PM

Quick question. Whats the difference of a spreadbore and a square bore? Does one make more power and torque through out the RPM range?

spinn 06-27-2012 05:55 PM

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

400smb_s10 06-27-2012 05:58 PM

ok thanks for the input

wibas 06-27-2012 06:08 PM

If I understand these replies I should use like the avenger 670cfm :welcome: on my dual plane manifold? Thanks

spinn 06-27-2012 06:09 PM

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.

1971BB427 06-28-2012 07:55 PM

Quote:

Originally Posted by spinn (Post 1569147)
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.

spinn 06-28-2012 11:39 PM

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.

my87Z 06-29-2012 08:13 PM

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.

BigChevyFTW 06-29-2012 08:25 PM

Quote:

Originally Posted by wibas (Post 1569152)
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!!!!!!!!


All times are GMT -6. The time now is 09:05 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.