Holley 600 on a 383

[Paul_G]

I put my 600CFM Holley, #80457-3, on the 383. The 383 is mildly built with a modest cam, long tube headers, Eddy Performer 383 intake, 1" open spacer. I was expecting it to be noticeably lacking in power compared to the Quick Fuel 750 I normally run on the 383. To my surprise it ran ran exceptionally well. Better than I expected with such a small carb.

I think I will try the SA 670 from my 72 360 next. See what that does on the big block.

 

[JakeBorg66]

I think you’re just noticing the better throttle response on a smaller carb, that’s probably too small for a 383. I’ve run different sizes carbs on a 440 in the dyno room and they make max hp with a surprisingly large carb, that 440 really liked an old BG CLAW 950 we had.

 

[krazykuda]

Why fix it if it ain't broke???

I love the Holley 80457, been running it for decades...

We put one on my buddy's, Eddie, 340 in his Dart when we rebuilt the engine... He changed it later to a 650 or 670 and it didn't run as well... We put the 600 Holley 80457 back on and it ran better...

Here it is after we got it fine tuned in....

Bigger isn't always better... (that's not what she said... )

 

[yella71]

My 340 when it had a six pac on it would blow the tires off from a roll in second gear....It would NOT do that after I put a 600 on it.

 

[peabodyracin]

I think you’re just noticing the better throttle response on a smaller carb, that’s probably too small for a 383. I’ve run different sizes carbs on a 440 in the dyno room and they make max hp with a surprisingly large carb, that 440 really liked an old BG CLAW 950 we had.

Absolutely. For street driving, I've consistently found a smaller carburetor to be more responsive overall. Let's face it, we're not into the secondaries hard all that often, and seldom see even 6000 RPM driving around town. It's much like the tendency to pick a cam shaft with a power band well outside of the street driving environment, and then wonder why the engine seem to be a pooch. There's something to be said for the spread bore concept, with smaller primaries.

 

[RJRENTON]

The "secret" is the concept of mixture velocity. The smaller the carb or the spread bore design promotes high mixture velocities resulting in good throttle response and more even cylinder to cylinder fuel distribution due to the high velocities. Over carb-ing and over camming generally results in poor performance in day to day operation especially in low to mid RPM operation.
Operation with a "smaller" carb at HIGH RPMs will result in more pressure loss thru the carb. Most, but not all carbs, air fows are rated at a given pressure drop across the carb, such as 3.0" wg (some manufacturers use mm of mercury, some use 1.5" wg). The carb will flow more air but at a greater pressure, which ultimately result in horsepower being limited due to a reduction in air. This is reason for a spread bore (small primary large secondary) design....the "best of both worlds" so to speak. Just my opinion of course.
BOB RENTON

 

[BSB67]

Most, but not all carbs, air fows are rated at a given pressure drop across the carb, such as 3.0" wg (some manufacturers use mm of mercury, some use 1.5" wg).

What is 3" wg?

What carb companies don't use 1.5 inches of Hg for 4 bbls, and 3.0 inches of Hg for 2 bbls?

 

[RJRENTON]

What is 3" wg?

What carb companies don't use 1.5 inches of Hg for 4 bbls, and 3.0 inches of Hg for 2 bbls?

FYI...
WG is an abbreviation for water guage, where the unit of measure is inches of water. Doesn't Hollry use 3.0 inches or 3" wg ?
Found this info that may explain...
The basis for most cubic feet per minute (C.F.M.) air flow ratings such as those used by Holley and other carburetor manufacturers was established long ago by the Society of Automotive Engineers (S.A.E.).
Standard test vacuum was 1-1/2 inches of mercury for 4 barrel carburetors and 3 inches of mercury “Vacuum” for 1 barrel and 2 barrel carburetors. This was reasonable as it was about what a passenger car would develop. Of course, for the numbers to mean anything, tests would have to be run at a certain temperature and barometric pressure. Or be corrected to standard temperature and pressure. If not otherwise stated, ratings in cubic feet per minute are at standard temperature and pressure.
This system is confusing for racing applications for several reasons. Some racing engines actually develop much more or less vacuum than these ratings, so are difficult to compare. For example, a Nascar 390, 4 barrel equipped car might have 3 times the 1-1/2 inches of mercury standard or a very large 2 barrel equipped car might have only 1-1/2 inches of mercury vacuum.
Even more confusing is the fact that most flow benches in the racing industry measure dry air at low pressure drops, commonly 10 inches of water column (W.C.), one bore or venturi at a time. This result is multiplied by a factor to arrive at what that bore would flow at a higher vacuum (i.e. 1-1/2 or 3 inches of mercury), then that figure is multiplied (by four, in the case of a 4 barrel carburetor) to get the C.F.M. rating. This rating is usually much higher than it actually is.
Sorry if I did not explain it succinctly...there are also conversion tables to allow for comparison between various units of measure
BOB RENTON

 

[Cranky]

Absolutely. For street driving, I've consistently found a smaller carburetor to be more responsive overall. Let's face it, we're not into the secondaries hard all that often, and seldom see even 6000 RPM driving around town. It's much like the tendency to pick a cam shaft with a power band well outside of the street driving environment, and then wonder why the engine seem to be a pooch. There's something to be said for the spread bore concept, with smaller primaries.

I'm usually a bit different in running smaller cams with bigger carbs and turning too much rpm

The "secret" is the concept of mixture velocity. The smaller the carb or the spread bore design promotes high mixture velocities resulting in good throttle response and more even cylinder to cylinder fuel distribution due to the high velocities. Over carb-ing and over camming generally results in poor performance in day to day operation especially in low to mid RPM operation.
Operation with a "smaller" carb at HIGH RPMs will result in more pressure loss thru the carb. Most, but not all carbs, air fows are rated at a given pressure drop across the carb, such as 3.0" wg (some manufacturers use mm of mercury, some use 1.5" wg). The carb will flow more air but at a greater pressure, which ultimately result in horsepower being limited due to a reduction in air. This is reason for a spread bore (small primary large secondary) design....the "best of both worlds" so to speak. Just my opinion of course.
BOB RENTON

Best street carb for me was a TQ on a mild 340. 17 mpg in town was the norm with great throttle response and top end too. They take some 'learnin' but once you get it, they are really decent.

 

[BSB67]

FYI...
WG is an abbreviation for water guage, where the unit of measure is inches of water. Doesn't Hollry use 3.0 inches or 3" wg ?
Found this info that may explain...
The basis for most cubic feet per minute (C.F.M.) air flow ratings such as those used by Holley and other carburetor manufacturers was established long ago by the Society of Automotive Engineers (S.A.E.).
Standard test vacuum was 1-1/2 inches of mercury for 4 barrel carburetors and 3 inches of mercury “Vacuum” for 1 barrel and 2 barrel carburetors. This was reasonable as it was about what a passenger car would develop. Of course, for the numbers to mean anything, tests would have to be run at a certain temperature and barometric pressure. Or be corrected to standard temperature and pressure. If not otherwise stated, ratings in cubic feet per minute are at standard temperature and pressure.
This system is confusing for racing applications for several reasons. Some racing engines actually develop much more or less vacuum than these ratings, so are difficult to compare. For example, a Nascar 390, 4 barrel equipped car might have 3 times the 1-1/2 inches of mercury standard or a very large 2 barrel equipped car might have only 1-1/2 inches of mercury vacuum.
Even more confusing is the fact that most flow benches in the racing industry measure dry air at low pressure drops, commonly 10 inches of water column (W.C.), one bore or venturi at a time. This result is multiplied by a factor to arrive at what that bore would flow at a higher vacuum (i.e. 1-1/2 or 3 inches of mercury), then that figure is multiplied (by four, in the case of a 4 barrel carburetor) to get the C.F.M. rating. This rating is usually much higher than it actually is.
Sorry if I did not explain it succinctly...there are also conversion tables to allow for comparison between various units of measure
BOB RENTON

Didn't really need an explanation. Holley uses inches of Hg. So I think what you're saying is you don't know of anyone using water column.

 

[Frankb]

I ran the 670 SA on my mild 383/auto Charger. Never really liked it. Always ran lean and I could never get rid of the off idle stumble. What bothered me the most though was it surged at cruise. Didn't matter what speed.
Frank