Holly Carburetor.
12-03-2017, 06:19 PM
#1
Burning Brakes
Thread Starter
Holly Carburetor.
Do ya think that moving up to a 780 Dule feed Holly. From a 650 would make a difference.?Would it be worth it?
Last edited by jhopper408; 12-03-2017 at 06:21 PM.
12-03-2017, 06:25 PM
#2
Big Block, small block? cam? heads? Depends on what specs your engine was built to but not very likely.
Last edited by Dynra Rockets; 12-03-2017 at 06:26 PM.
12-03-2017, 06:36 PM
#3
Burning Brakes
Thread Starter
It's a 383S. But like I've said before. The guy I bought it from, didn't have the spec's. But the engine builder asked him what size Holly he wanted on it. He said for the street,or the strip. I guess that I always ask stupid questions. Laugh!
12-03-2017, 06:51 PM
#4
You wouldn't gain any power and your fuel mileage and throttle response would suffer because venturi velocity at any given mph would be less. Larger-than-needed carburetors give the impression of greater power but only because the amount of air passing through the venturi at 1/4 throttle would be more than 1/4 throttle of a correctly sized carburetor. It's the equivalent of giving it more throttle but once your engine is taking in all the air it can the additional air potential is wasted. And in the case of a vacuum secondary the secondaries would only be able to open maybe 1/4th the way at best if you're running a 350" engine.
Remember, the rule of thumb is to size the carburetor using 1-1/2 cfm per cubic inch of displacement for street engines; meaning no more than 600 cfm for a 350" engine or 750 cfm for a 454" engine.
12-03-2017, 06:54 PM
#5
Le Mans Master
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You wouldn't gain any power and your fuel mileage and throttle response would suffer because venturi velocity at any given mph would be less. Larger-than-needed carburetors give the impression of greater power but only because the amount of air passing through the venturi at 1/4 throttle would be more than 1/4 throttle of a correctly sized carburetor. It's the equivalent of giving it more throttle but once your engine is taking in all the air it can the additional air potential is wasted. And in the case of a vacuum secondary the secondaries would only be able to open maybe 1/4th the way at best if you're running a 350" engine.
Remember, the rule of thumb is to size the carburetor using 1-1/2 cfm per cubic inch of displacement for street engines; meaning no more than 600 cfm for a 350" engine or 750 cfm for a 454" engine.
Remember, the rule of thumb is to size the carburetor using 1-1/2 cfm per cubic inch of displacement for street engines; meaning no more than 600 cfm for a 350" engine or 750 cfm for a 454" engine.
12-03-2017, 07:45 PM
#6
Burning Brakes
Thread Starter
Excellent answer.nevertool.I think you so much. I just wanted a simple answer. Thanks
John.
John.
Last edited by jhopper408; 12-03-2017 at 07:50 PM.
12-03-2017, 07:58 PM
#8
Le Mans Master
The size of the carburetor required depends on a number of factors. Not the least of which is the rpm you will be running. Which of course depends on the cam you are using, etc.
On the other hand, theoretically, at 100% volumetric efficiency, a 383 cubic inch engine at 7,000 rpm, would move 775.75 cfm. While few engines run at 100% VE, the required carburetor really depends on a lot of factors, but a 780 cfm is certainly within the realm of possibilities.
Good luck... GUSTO
On the other hand, theoretically, at 100% volumetric efficiency, a 383 cubic inch engine at 7,000 rpm, would move 775.75 cfm. While few engines run at 100% VE, the required carburetor really depends on a lot of factors, but a 780 cfm is certainly within the realm of possibilities.
Good luck... GUSTO
12-03-2017, 08:36 PM
#11
Le Mans Master
Not necessarily when you typically shift, but when it feels like it is leveling off (stops accelerating?) and it's time to shift.
Dan Dawson is correct, it would require tuning to make the change worthwhile. For that reason, this all might be a topic of discussion you should bring to a local tuner that has access to a dyno. He should be able to look at what you have and how it's set up, and tell you if its worth trying a larger carb. He may even want to put it on the dyno to see what potential you engine has and if it could use more carburetion.
GUSTO
Last edited by GUSTO14; 12-03-2017 at 08:46 PM.
12-03-2017, 08:55 PM
#13
When it comes to selecting carburetors for 85% volumetric efficient street engines bigger isn't always better. It's always best to follow Holley's guidelines: https://www.bing.com/videos/search?q...tail&mid=D29F5
12-03-2017, 08:55 PM
#14
Burning Brakes
Thread Starter
I'm not sure about the rpms. I never look at the tack. I shift by ear. And I will put it on a Dyno in the spring. I've dynoed my last two Zs.
12-03-2017, 09:19 PM
#16
Burning Brakes
Thread Starter
See. I'm just not familiar with carburetors anymore. I'm 62. And believe me I used to be more familiar with them. But I haven't had a carburetor on a car in probably 25 year's. So my questions may seem out of line. I've only had this car for 8 weeks.
12-04-2017, 08:13 AM
#18
Le Mans Master
...and in 1969, the solid-lifter 302-cid V-8 came with an 800-cfm four-barrel carburetor exclusive to the Z28.(Okay depending on who you accept as an authority, anywhere from 780 - 850cfm...)
https://www.camarocentral.com/1968_1..._p/enc-842.htm
http://www.superchevy.com/features/c...69-camaro-z28/
https://musclecars.howstuffworks.com...camaro-z28.htm
GUSTO
Last edited by GUSTO14; 12-04-2017 at 08:39 AM. Reason: clarification
12-04-2017, 09:14 AM
#19
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