I am running a 600 cfm Edelbrock AVS carburetor on my 454ci big block Chevy in my Chevy C-10 truck. Is that hurting power any? Would I see a power increase going to a 750 or 800 cfm version?
S.C.
The Edelbrock AVS and now the upgraded Edelbrock AVS2 carburetors are an excellent choice for your 454 truck engine, assuming that this is a mild big block and you’re not trying to make more than about 450 hp which would be one horsepower per cubic inch. Everybody thinks that big engines need a big carburetor but that’s not always the case depending upon the application and how the engine will be used.
If you were to bolt a 750 cfm carburetor on this engine, would it make more peak horsepower? Probably—but the increase would not be dramatic. Without knowing your exact combination of parts, it’s hard to estimate specifically. My guess is that peak power might improve roughly 10 to perhaps 15 hp using a 750 cfm carb as opposed to a 600 cfm version.
Let’s assume your 454 has a mild cam, a good dual plane intake and perhaps even headers. Let’s also assume the engine makes 450 horsepower and perhaps a little more torque at around 470 lb.-ft.
Airflow Restrictions
Most people would offer many reasons why airflow would be the restricting factor. Older 454 truck engines all came with Q-jet carburetors that were rated at 750 cfm. So a larger 750 cfm carburetor would slightly increase the airflow potential. However, there are other factors involved as well. A major issue is the height of the carburetor mounting pad on the intake manifold. Generally speaking, the shorter the carb height, the more restrictive the manifold design because the air and fuel must make a sharp 90 degree turn to transition from vertical to horizontal flow.
This means that while the carburetor may be able to flow 750 cfm, but the intake manifold is so restrictive that this greater volume never makes it to the cylinder heads. Some of the original Corvette big block manifolds around 1973 and 1974 mounted the carburetor nearly on top of the intake ports which makes the transitions to horizontal flow just brutal and restrictive. These were done in order to fit this large engine under the stock hood line.
This only becomes an issue if you searching for more power. If a little more power is a part of your goal, I would first look at optimizing your existing combination. For example, if you experiment with ignition timing and the combination of the initial, mechanical, and vacuum advance curves, it’s possible to improve power and overall drivability without moving to a larger carburetor.
The Edelbrock Carburetor Tuning Manual
Edelbrock offers a tuning manual that comes with every new carburetor that is really good at helping you balance the combination of main jets, primary metering rods, and the power valve spring.
If you don’t have a manual, you can download one from the instructions found for your part number carburetor on SummitRacing.com. Just look for the “instructions” tab and open it up and save it to your computer.
We’ve included a copy of the primary metering tuning chart below.
At first it may look confusing but it’s fairly easy to understand once you study it for a minute. The center of the grid (indicated by the large black numeral 1) is the stock tuning position as the carb comes out of the box. We’re using the grid for a 600 cfm PN 1406 carb. Each carb grid will be a little bit different but the tuning moves are all laid out the same way.
From the center point, if you move above the horizontal main line, this richens the air-fuel ratio. Each number in the upper half will represent a given combination of metering rod and primary jet size. If you want to lean the primary side air-fuel ratio, moving below the main horizontal line will achieve this. Moving left of the main vertical line puts tuning into the cruise side of the tuning equation. So the upper right hand corner of the grind is full power rich while lower left hand side will lean the cruising or part throttle jetting.
By choosing the area you want to tune, you can pick a number in that area and the number will correspond to a combination of main jetting and metering rod. The number 7 position for example, represents a slightly leaner primary jet with a slightly different metering rod that will lean out the cruise portion of the system with only a slightly leaner WOT jetting. This can be compensated for by richening the secondary jetting by one jet size. Again, it sounds complicated but by following the chart you can make minor changes that can and often help both performance and fuel mileage.
The Power Enrichment Spring
Another tuning tool is the power enrichment spring. All Edelbrock AVS and AVS2 carbs use the orange spring but you can play with spring tension supplied in the Edelbrock tuning kit to help with part throttle tuning and just going to a slightly softer spring will allow the engine to run leaner with more throttle opening. Plus, changing both the primary metering rods and/or springs is very easy as you don’t have to remove the top of the carburetor to effect the changes. We recommend trying these tuning mods before spending money on a new carburetor. You might be surprised at how much better your big-block will run with a couple of really simple changes to timing and jetting.
The size of the carburetor depends on the maximum rpm’s the engine will run.
No everyone is trying to achieve maximum RPM unless you’re drag racing. Most street cars I build operate in the low and midrange RPM area. They’re tuned for quick throttle response.
Not everyone is trying to achieve maximum RPM unless you’re drag racing. Most street cars I build operate in the low and midrange RPM area. They’re tuned for quick throttle response.
I’ve got a 1985 All Original except for the motor I have a Vortex 350 motor and I would like to know what is the best carburetor to get the best gas mileage and sound good.?
I run a AVS two it has good throttle response makes good horsepower small block 350 350 and good top end and my 72 Nova Super Sport set the road on fire
I just installed that same motor in my 1995 Chevrolet Silverado pick up. It’s running rich. I ordered the calibration kit. I’m waiting for it to arrive. Do you have any suggestions on the jets and metering rods. I would greatly appreciate the help.
I used a 600 cfm carb on a 454 to keep me from blowing it up. I liked to hear it hum, so I rev-limited it with the carb.
I like Tommy’s approach, combining carburetor,and rev limiter, all in one!! No cumbersome ignition boxes, or wiring needed!!
I have an old charger with a new 500 cu in Hemi, 426 bored and stroked. I have the dual Fitech FI on it, with Edelbrock heads and intake Solid roller cam .620 lift etc. It should be around 700 HP at the flywheel. If I went to dual carbs what would you recommend and how would they come set up to me. The car is street driven, goes to shows and cruise ins, as yet I have not dragged raced it but might just to see what it would do. The RED line is 8000 rpm but would never take it over 6700. What do you recommend?
thank you for the article
I like the way Jeff Smith danced around the question with an answer of “it might”. Then changed the subject completely into a Edelbrock add. Telling about the new version with annular booster, the manual and how to use it, etc.
I’m not a magazine article writer but I am a way above average builder and tuner. The correct answer is that YES, the 750 will make more power, and equal or more torque.
is a 600 cfm Edelbrock to much for a 318 Mopar?it’s a crate motor.
I used a 650 two barrel Holley on my f 350 4×4 ,four door dually, with a 460,1990. I felt like it pulled up loaded to Hwy speeds better. Smooth very torquey feel. Loaded 3 car trailer .