Acceleration problem
Race Director
Joined: Oct 2005
Posts: 12,468
Likes: 1,548
From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
383 CI/1728 X 6000RPM/2= 665 CFM @100%VE. 650-700 CFM would be ideal for this motor.
750 isn't way too large, just not perfectly optimum for street running and fuel economy.
If you want neck snapping performance and fuel economy, the spread bore 6210 Holley (650 CFM) is an excellent choice for a 350-400 CI motor, but you have to put up with the stigma of having a spead bore rather than the macho 750 4779, even if the 4779 wil be slower.
Doug
750 isn't way too large, just not perfectly optimum for street running and fuel economy.
If you want neck snapping performance and fuel economy, the spread bore 6210 Holley (650 CFM) is an excellent choice for a 350-400 CI motor, but you have to put up with the stigma of having a spead bore rather than the macho 750 4779, even if the 4779 wil be slower.
Doug
Last edited by AZDoug; Mar 18, 2009 at 01:59 AM. Reason: spelling
Race Director
Joined: Oct 2005
Posts: 12,468
Likes: 1,548
From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
Pro
Joined: Sep 2008
Posts: 682
Likes: 0
From: Manteo NC
Gents,
Thanks for all of the help. My initial read from two years ago, was that the air gap manifold was the problem. It started once I put it on my LT1 along with an MSD ignition/dist, and a rebuild of my Holley 650. It ran very rough and would bog all of the time. I first thought it was a bad rebuild on the carb. I swapped carbs with no change. The guy that did my engine swap last year is very good. He felt confident that the timing and carb was set correctly and that the fuel air mixture was solid. The only thing that I have not swapped out, is the intake manifold. I'll get another manifold and see if it fixes the problem. Last night I searched the internet and found several sites with threads that discussed the same problem that I am experiencing and all had an air gap manifold. One of the techs at Summit told me that he had the same problem, swapped out his air gap, and the problem was fixed. Too bad their the guys that sold me the air gap anyway. I don't race my car, so I'm not too interested in max power above the 6000 rpm range. What I do want is a smooth ride with plenty of instantaneous low end power and torque. Any thoughts on a manifold?
Bill
Thanks for all of the help. My initial read from two years ago, was that the air gap manifold was the problem. It started once I put it on my LT1 along with an MSD ignition/dist, and a rebuild of my Holley 650. It ran very rough and would bog all of the time. I first thought it was a bad rebuild on the carb. I swapped carbs with no change. The guy that did my engine swap last year is very good. He felt confident that the timing and carb was set correctly and that the fuel air mixture was solid. The only thing that I have not swapped out, is the intake manifold. I'll get another manifold and see if it fixes the problem. Last night I searched the internet and found several sites with threads that discussed the same problem that I am experiencing and all had an air gap manifold. One of the techs at Summit told me that he had the same problem, swapped out his air gap, and the problem was fixed. Too bad their the guys that sold me the air gap anyway. I don't race my car, so I'm not too interested in max power above the 6000 rpm range. What I do want is a smooth ride with plenty of instantaneous low end power and torque. Any thoughts on a manifold?
Bill
I'll swap you both of them for yours, 2 for 1
Last edited by obx2323; Mar 18, 2009 at 06:33 AM.
Le Mans Master
Joined: Jan 2005
Posts: 8,226
Likes: 2
From: Lake Wylie SC
As the summer gets closer and the weather gets warmer I believe that the problems associated with the air gap or crossovers being blocked off is going to disappear and be replaced advantages. Gas is getting worse just about on a daily basis. Even if the perk temperature is staying the same I am seeing vapor lock problems on warm days this spring that I have not seen in the past.
Maybe some fuel experts here might weigh in but it seems to me that fuel is boiling easier and more susceptible to heat soak this year than it was last year. I know they are changing or adding ingredients in different areas of the country and in my area I am not alone with the opinion I just shared
Although heat under the hood is more of a BB problem than it is with a SB there are a lot of happy BB owners that have air gap intakes on them. This last week as I was wrapping my fuel lines with thermo tec and contemplating incorporating a cool can that I have sitting on my shelf I also thought of switching to a air gap....... but I like my Brodix to much.
Bottom line is that the air gap is a great intake and especially so for being a dual plane. It is the only one other than mine (that I know of) that is banned in "stock" classes that require dual plane intakes.
Doug
Maybe some fuel experts here might weigh in but it seems to me that fuel is boiling easier and more susceptible to heat soak this year than it was last year. I know they are changing or adding ingredients in different areas of the country and in my area I am not alone with the opinion I just shared
Although heat under the hood is more of a BB problem than it is with a SB there are a lot of happy BB owners that have air gap intakes on them. This last week as I was wrapping my fuel lines with thermo tec and contemplating incorporating a cool can that I have sitting on my shelf I also thought of switching to a air gap....... but I like my Brodix to much.
Bottom line is that the air gap is a great intake and especially so for being a dual plane. It is the only one other than mine (that I know of) that is banned in "stock" classes that require dual plane intakes.
Doug
Last edited by Shurshot; Mar 18, 2009 at 08:31 AM.
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
As the summer gets closer and the weather gets warmer I believe that the problems associated with the air gap or crossovers being blocked off is going to disappear and be replaced advantages. Gas is getting worse just about on a daily basis. Even if the perk temperature is staying the same I am seeing vapor lock problems on warm days this spring that I have not seen in the past.
Maybe some fuel experts here might weigh in but it seems to me that fuel is boiling easier and more susceptible to heat soak this year than it was last year. I know they are changing or adding ingredients in different areas of the country and in my area I am not alone with the opinion I just shared
Although heat under the hood is more of a BB problem than it is with a SB there are a lot of happy BB owners that have air gap intakes on them. This last week as I was wrapping my fuel lines with thermo tec and contemplating incorporating a cool can that I have sitting on my shelf I also thought of switching to a air gap....... but I like my Brodix to much.
Doug
Maybe some fuel experts here might weigh in but it seems to me that fuel is boiling easier and more susceptible to heat soak this year than it was last year. I know they are changing or adding ingredients in different areas of the country and in my area I am not alone with the opinion I just shared
Although heat under the hood is more of a BB problem than it is with a SB there are a lot of happy BB owners that have air gap intakes on them. This last week as I was wrapping my fuel lines with thermo tec and contemplating incorporating a cool can that I have sitting on my shelf I also thought of switching to a air gap....... but I like my Brodix to much.
Doug
I do not claim to be a fuel expert but i have talked to several of the engineers from Chevron, Shell and Rockett Brand race gas on the subject so yes today's gasoline is quite different from the gasoline of even 10 years ago. the following link is something i did for Kit Car magazine on tuning a carbureted engine for todays gasoline it has a map from Exxon that shows the 14 plus areas of the country that the goverment has mandated different blends of gasoline in a effort to reduce exhaust emmisions but ...........................
i hope this helps henry @ olescarb
