Technical Carb CFM recommendations

I just got done putting some AFR 180cc heads on my 350 chev. Originally stock top end. It runs quicker, but I am wondering if there is a bit more I can get out of it. This leads me to the carb. Engine is in a '32 Ford, so street. My friend wants me to go Holley, but I just feel Edelbrock is a better fit for this car and the street so looking for good low-end and not so much top-end for sure. Currently an Edelbrock 1405 600 cfm. Can I do a bit more? I know there is an Edelbrock 650 cfm, but would that bit of increase even make a difference?

Engine bored 30-over
Isky cam 232 @50 .485/.485
AFR 180cc heads
Comp ratio about 9.5:1
Holley Contender dual plane
Edelbrock 1405 600 cfm

 

So your planning on driving at WOT 99% of the time instead of 1% of the time and are wanting lower mpg? Is your friend going to buy your gas? We all have our reasons I guess.

 

Properly tuned, the 600 will be just fine. Get the manual out and study it carefully, it’s a bit to get you head around at first. They don’t normally need big changes. Jets, springs, rods. Easy to work on.

Summit has some annular Venturi models out that are getting really good reviews for drivability and gas mileage. Along the lines of the Autolite 2100/4100 the Ford guys like. Worth a look.

There’s nothing wrong with certain factory manifolds and a Quadrajet either on the street and with the right combinations.

 

If this will be a street driven vehicle, then the stock Q-Jet is a MUCH better fit than either of the two you mention. Power, fuel economy, drivability, and reliability will all be better.

If mostly strip, there are those who do not understand the Q-Jet that will argue the Holley will be better.

Jon

 

I agree with Jon 100%. I removed the Edelbrock from Papaw and replaced it with a Quadrajet and he runs so much better. No more fuel percolation/hot start problems, no more lean stumble on acceleration that couldn’t be tuned out. There are many darn good reasons why GM made millions of them.

 

What is your manifold vacuum at WOT....that should tell you if your set-up will take more carb.
2" or under you already have too big a hole....doesn't have anything to do with make

 

I grew up on Holleys not AFB (Edelbrocks) so that's my choice. If you go to a spread bore Quadrapuke you'll probably need a new manifold too.

Truckdoctor Andy doesn't understand - "There are many darn good reasons why GM made millions of them."
In reality they were cheap to make and outlasted the warranty. All things the manufacturer wants. They were built inhouse so no licensing or patent fees and worked to power their street cars. Where did GM turn to when they built performance motors for the Vette, Camaro, etc? Holley.

 

How does it run and how do the plugs look?
Do you think it needs to be faster?

 

a bit more cam would help. factory 4 barrel quadrajet was around 750cfm so ......

 

2 x 4's, everything needs 2 x 4's !

 

Quadrajets , Autolight carbs fuel mileage on a 32 ??? LOL.

The OP has about a $2000 set of heads if there the bottom of there line.
The intakes at his cams lift flow like 250 CFM. thats more than most all out port jobs on any stock factory casting.
His cam is a bit smallish but its a good choice with his Dual plane intake thats going to make peak HP at right at 5500 RPM .

A 600 carb is going to run good pit its not going to give max HP .
There is a damn good reason why any performance orientated 350 SBC is running 650 CFM or bigger carb in engines that are going to go up over 5000 RPM ( Not saying the OP is).

A 650 Edelbrock runs damn good on a mild 350 . I'm a Holley guy but the 650 Edelbrock on my 350 with a similar cam and a Performer intake runs about as good as your going to get .
No bog no hesitation, starts with one pump and the electric choke is perfect.
There is no stumble . Certainly no fuel boiling over and crap like that . Millions of them on the road likely.
Set the fuel pressure to about 4 pounds.

pulls hard to 6000 RPM . Its not remotely to big on my model A with a stock stall converter. I made 375 HP with a 750 Holley when it was Dynoed.

The OPs engine has way way better heads and should be about 400HP plus depending on what RPM it peaks .
Id not be worried putting a 750 cfm carb on it..

J don't know his transmission or gears but he is asking for advice on making it go faster / more power.
If he only has 1.5 ratio rockers he might try 1.6 or so ones , maybe a carb spacer .

A 600 CFM carb can support a 350 at 5000 RPM but its also the quality of the air and velocity fuel atomization .
Zillion dyno tests and quarter mile time slips support a 650CFM or bigger carb.

A properly tuned Holley will run as well as a stock Edelbrock and can be finer tuned on the newer ones with more options. If your not into tuning then get the Edelbrock and likely only need to change a metering rod at the most.

My opinion

 

1biggun- super helpful! Thanks!

 

I’ve always thought that an old Ford hot rod with an exposed engine looks a little undernourished with a single four barrel carburetor. If it was mine, I’d step up to the Edelbrock dual quad intake.

 

A question about carburetors always elicits a number of opinions as to brand.

I mentioned the Rochester Q-Jet in my original post in this thread, NOT because it was a Rochester, but because it is a spread-bore rather than square-bore design. All passenger manufacturers migrated from the square-bore to the spread-bore in the mid/late 1960's because of the higher venturi air velocity at cruise to mid-range RPM. The higher air velocity increased the efficiency of the carburetor. As to how large a carb to use on a 350? I used an 850 TQ (spread-bore) on my 350 Pontiac for years, and it ran like a scalded dog! Difficult to over-carb the engine using the spread-bore, as the air-valve supplies air at higher RPM's upon demand of the engine, not that of the driver.

As to brand, spread-bore carbs were produced, in alpha order, by Autolite (4300), Carter (TQ), Holley (4165), and Rochester (4MV a.k.a. Q-Jet). I mentioned the original Q-Jet, as it would be calibrated for a 350, thus requiring less tinkering. Personally, I would use the TQ, but it would require more tinkering than the Q-Jet (but less than the Holley).

The OP mentioned this was to be street driven, and he wanted more low end; thus the higher venturi velocity of the spread-bore would be desirable.

The biggest disadvantage to the OP in going to a spread-bore would be changing intakes (please don't consider a square ----> spread adapter ).

As to brand, use what you are comfortable with.

And bchbtybob - I totally agree on the 2x4 !

EDIT: I got distracted by the telephone when making this post. 29Sleeper mentioned that GM used Holleys on their performance cars. This, to a certain extent, is true. GM DID use square-bore Holleys on some vehicles they knew had a good possibility of being raced. At the time, Holley, whether justified or not, DID own the performance carburetor market; and virtually every auto parts house in the world handled individual Holley parts (this is not true today, virtually any carburetor part, other than rebuilding kits, must be ordered). But GM also used Q-Jets on a lot of performance "street cars" (Pontiac ram air, Oldsmobile W-series, Corvette, Buicks, etc.). Again, my post is about carburetor style (spread-bore or square-bore), not about brand.

Jon

 

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