Corona Carbs
- Thread starter Ishiftem
- Start date
My engine guy said I can play all I want. Unfortunately his bench is out of calibration so I’ll only be able see percentages and not an actual cfm number.
Guessing if he bought a new one, he would want you to play as much as wanted but pay by the hour. 
The percentage of change[improvement or not] is what makes the difference anyway.The rest is just window dressing or bragging rights.Since he can accuarately measure that,he'll be able to get a good idea if he's improved things.The Real test will have to be performed on a 1320 ft.long dyno[drag strip],
Screw that!Guessing if he bought a new one, he would want you to play as much as wanted but pay by the hour.
Made my fixture for the flow bench so I can spin the carb and do one barrel at a time. Next is drill and tap for the new inlet and drill and tap the holes where all the old plugs were so I can plug them again. Also got all the goodies to plate all the small parts.
Nice, sure would be nice to wet test it.
The results are in! Thanks to Automotive Engine Specialties in Elk Grove IL for letting me take up space and for being all around helpful. If you are in the area check him out. And yes, he is fully familiar with W engines and owns a 502" 409 himself.
Now for the fun stuff. I did not do a baseline with the choke mechanism in or the secondary air valve since I don't use those anyway. The secondary air valve is a big restriction and the improvement would of been larger if I had compared with and without. Removing just the choke horn showed a
1.43% improvement. Adding the reworked boosters to the former showed a 2.6% improvement. Adding the profiled throttle shafts and knife edged secondary blades to the former showed a 8.5% improvement. Bar none, that is best thing you can do to one of these things airflow wise. Next was blending and smoothing the primary bores. That showed a 2.33% improvement. The total improvement is 15.5%. I am very happy with that! Now you may be adding the individual improvements up and wondering why they don't add up to 15.5%. That is because each improvement affects (or is it effects) the previous improvements but comparing the baseline to the final result shows the sum of all changes is greater than each change individually.
I had time to play with some clay and glad I did. It's going to save me from wasting time and energy by not doing things I would of done without flow testing. First is filling in the well to the top where the weight for the secondary air valves goes next to the secondary booster cluster. That pissed it off and lost flow. Next was adding some clay to duplicate what Dave shows with epoxy in his post. No gain or loss. Next I made a large radius around the top of the air horn. No gain or loss. Next was filling in the well like before but continuing it up to make a smooth transition like I did with my edelbrocks in this picture:
Now you would think that would help. Nope. Nothing. The difference was inconsequential and not worth the effort.
So those are the results. I even did ABA tests to make sure the results were accurate. This was very educational for me. Hope you enjoyed it!
Now for the fun stuff. I did not do a baseline with the choke mechanism in or the secondary air valve since I don't use those anyway. The secondary air valve is a big restriction and the improvement would of been larger if I had compared with and without. Removing just the choke horn showed a
1.43% improvement. Adding the reworked boosters to the former showed a 2.6% improvement. Adding the profiled throttle shafts and knife edged secondary blades to the former showed a 8.5% improvement. Bar none, that is best thing you can do to one of these things airflow wise. Next was blending and smoothing the primary bores. That showed a 2.33% improvement. The total improvement is 15.5%. I am very happy with that! Now you may be adding the individual improvements up and wondering why they don't add up to 15.5%. That is because each improvement affects (or is it effects) the previous improvements but comparing the baseline to the final result shows the sum of all changes is greater than each change individually.
I had time to play with some clay and glad I did. It's going to save me from wasting time and energy by not doing things I would of done without flow testing. First is filling in the well to the top where the weight for the secondary air valves goes next to the secondary booster cluster. That pissed it off and lost flow. Next was adding some clay to duplicate what Dave shows with epoxy in his post. No gain or loss. Next I made a large radius around the top of the air horn. No gain or loss. Next was filling in the well like before but continuing it up to make a smooth transition like I did with my edelbrocks in this picture:
Now you would think that would help. Nope. Nothing. The difference was inconsequential and not worth the effort.
So those are the results. I even did ABA tests to make sure the results were accurate. This was very educational for me. Hope you enjoyed it!
Nice job of testing each step of change Dan. I know you don't run a choke but I thought it might be interesting to some here, when I baseline tested those stock 750 cfm edelbrocks, then simply removed the choke plate and shaft, it gained 30 cfm. Easy gain. I know you have enlarged the passages in the boosters, and thought it might be worth mentioning, I found in the edelbrocks the passage that runs from under the rear main jet over to the booster well was also undersize , the plugs have to be removed to get to these to drill them larger, then to replace the plugs I tapped threads for small set screws.
I know this is not how you stage and launch your car Dan, but thought it might be of interest to some , removing the secondary air valve to gain airflow doesn't always lower your e.t. Depending on how you stage & launch the car. Example would be footbraking an automatic at part throttle, then mashing the throttle at launch might benefit from using , and even slowing the opening of the secondary air valve by adding some weight to the air valve & delaying the accelerators pump shot so its not used up before the throttle is floored. Different driving styles equal different carb setups.
I know this is not how you stage and launch your car Dan, but thought it might be of interest to some , removing the secondary air valve to gain airflow doesn't always lower your e.t. Depending on how you stage & launch the car. Example would be footbraking an automatic at part throttle, then mashing the throttle at launch might benefit from using , and even slowing the opening of the secondary air valve by adding some weight to the air valve & delaying the accelerators pump shot so its not used up before the throttle is floored. Different driving styles equal different carb setups.
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The edelbrocks come with a .107 sec jet and these old Carters come with .092. Kinda tells ya right there how screwed up the edelbrocks are that they had to put a .107 in to get the thing to run right. I never measured the passage in the body of the edelbrock. These Carters are .180. I may not enlarge the tube in the booster on these. They are .107 same as the edelbrock but seeing as these come with a .092 jet, enlarging the tube may not be needed like the edelbrock.
What type of cars have you seen the air valves benefiting? I would think that if you could give the engine the needed pump shot it would be faster. I have never seen where a holley vacuum secondary was faster than the same double pumper. Maybe if the car was really heavy with a low stall and no gears the vacuum holley would be better. These Carters have more pump stroke than the edelbrock and much larger nozzles. Maybe that would help with lighter weights on the air valves for a foot brake car. ???
What type of cars have you seen the air valves benefiting? I would think that if you could give the engine the needed pump shot it would be faster. I have never seen where a holley vacuum secondary was faster than the same double pumper. Maybe if the car was really heavy with a low stall and no gears the vacuum holley would be better. These Carters have more pump stroke than the edelbrock and much larger nozzles. Maybe that would help with lighter weights on the air valves for a foot brake car. ???
These are 750cfm. In practice it likely isn't a direct correlation. A carburetor can flow more or less than it's advertised cfm rating depending on the engine it's attached too.