I recently had the opportunity to dyno test a variety of carbs on a stock ECZ-B intake. The engine itself is a sixty over 9.2:1 cr 312 that has stock (unported) G heads. The camshaft being used is a Crower Monarch grind with 238° duration at 0.050” and 0.400” lift at the valve. Advertised duration is 280°. While the camshaft is ground on 110° lobe centers, it’s installed in the engine at 2° advance or at 108° intake lobe centerline. Aftermarket 1.4:1 rockers are being used. The exhaust used for this particular test is a set of Reds (might be old Hedmans) headers running into 2” lead pipes ~4 foot long with no mufflers. The test range was 2500-5500 rpms.
The original ½” four hole spacer was used under the carbs in those instances where the carb bores were not too large for the spacer. Where the carburetor bores were too large, the spacer was changed out to either a 1” Moroso or Wilson four hole spacer with matching larger bores. The Moroso spacer had slightly larger bores than the Wilson spacer but both created a lip or shoulder within the bore where the spacer met the intake. Just another variable that must be considered.
The performance of the carbs were looked at from several different perspectives which included peak HP and torque, average HP and torque, and a calculated score. The score is derived by adding the mean (average) HP and torque together, dividing by the cubic inch of the engine, and multiplying by 1000. A score gives a better indication of the overall performance of the carb versus just looking at the individual peak values or averages.
The carburetors tested are listed in descending order from best to worst as based on their dyno test scores.
1. Holley 600+cfm 1572.7pts Model 4150
2. Speed Demon650 1557.8
3. Holley 465 1541.0 Model 4160
4. Holley 635 1534.5 Model 4150
5. Ford 1.08” 1534.2
6. Holley 600 1531.7 Model 4160
7. Holley 520 1528.9 Model 4150
8. Ford 1.12” 1528.0
9. Holley 600 1509.9 Model 4010 (flattop)
10. Holley 410 1502.5 Model 4150
11. Holley 750 1500.3 Model 4010 (flattop)
12. Ford 1.12” 1500.0
13. Holley 830 1487.9 Model 4150
14. Holley 665 1478.9 Model 4150
15. Holley 600 1466.5 Model 4160
16. Carter 400cfm 1466.1
A little clarification is probably in order regarding the cfm sizing for the Ford 1.08” & 1.12” carbs. Although it’s generally accepted that the Ford 1.08” carbs flow 480cfm and the 1.12” carbs flow 600cfm, these numbers have been since discredited by independent flow bench studies performed at Charlie’s Automotive in Apex, N.C.. The newer accepted numbers are 440cfm for the 1.08” carbs and 520cfm for the 1.12” carbs.
Here are the details on each carb. They are listed in the order of their overall performance. All carbs had vacuum secondaries.
#1. Modified L1850 600cfm Holley with Wilson 1” four hole spacer. The choke horn has been removed and a short K&N stub stack is being used. Jetting is 66P-73S. The venturies have been cleaned up but the discharge nozzles remain stock. Estimated flow is 645cfm.
#2. Speed Demon 650cfm with Wilson 1” four hole spacer. Jetting is 67P-76S. This carb was used on my roadster before switching it out for a 750HP Holley.
#3. Holley L1848-1 465cfm vac with ½” four hole small bore spacer. Replacement carb for ’57 T-Bird. Jetting is 57P & -3 secondary plate. Stock carb.
#4. Holley 635cfm vac with Wilson 1” four hole spacer. Jetting is 66P-73S. This carb originally started out life as a L1850 600cfm carb and was upsized by installing drop leg fuel discharge nozzles along with some venturi cleanup.
#5. Ford 1.08” flattop. 440cfm with 47P-57S jetting with ½” small bore four hole spacer. This carb matches the specs for the Ford carb that came factory equipped on the 1957 312 engines. Stock carb.
#6. Holley L80457 600cfm carb with Wilson 1” four hole spacer. Jetting is 65P & #39 rear plate. Stock carb.
#7. Modified L1850 carb with annular discharge nozzles with Wilson 1” four hole spacer. Estimated cfm is 520. Jetting is 64P-67S.
#8. Ford 1.12” flattop with ½” four hole small bore spacer. 520cfm with 49P-60S jetting. Stock carb.
#9. Holley L84010 600 cfm model 4010 flattop with Moroso 1” four hole spacer. Jetting is 67P-75S. Now available with Summit branding. Stock carb.
#10. Holley L1273-1 (ECZ-AD) 410 cfm carb with ½” four hole small bore spacer. This is the original equipment carb for a 1957 312. Jetting is 55P-55S. Stock carb.
#11. Holley L84011 750 cfm model 4010 flattop with Moroso 1” four hole spacer. Jetting is 75P-75S. Now available with Summit branding. Stock carb.
#12. Ford 1.12” flattop with ½” four hole small bore spacer. This carb has had the choke horn removed and is race prepped. Would have originally been a 520cfm but is expected to be flowing more air now. No pwr valve & jetting is 0.065”P & 0.065”S.
#13. Holley 830cfm with Moroso 1” four hole spacer. Has a contoured Proform center section with no air horn. Jetting is 78P-82S.
#14. Holley L3310-2 750cfm carb downsized to 665cfm via installation of annular discharge nozzles. Used with a Wilson 1” four hole spacer & jetting is 69P-73S.
#15. Holley L1850-3 600cfm with Wilson 1” four hole spacer. Jetting is 66P & -9 jet plate. Stock carb.
#16. Carter 400cfm vac secondary with ½” four hole small bore spacer. This carb is also an original equipment carb (ECZ-AA) for the 1957 312 engines. Jetting is 166P-176S.
Click on the picture for a larger version.
Here’s a chart showing the overall summary of each carbs performance. Being the biggest or smallest sized carb is not necessarily the decision maker. The quality of the fuel metering is obviously much more important than the carb size.
|1. Holley 645||313.9||249.9||289.3||217.1||1572.7|
|2. Speed Demon 650||311.7||247.2||286.6||215.0||1557.8|
|3. Holley 465||313.9||238.5||284.3||211.9||1541.0|
|4. Holley 635||305.8||244.8||282.0||212.1||1534.5|
|5. Ford 440||306.9||241.6||282.6||211.4||1534.2|
|6. Holley 600||305.3||242.6||281.8||211.4||1531.7|
|7. Holley 520||305.2||245.4||281.1||211.2||1528.9|
|8. Ford 520||303.2||242.9||281.0||211.0||1528.0|
|9. Holley 600 – 4010||300.3||242.9||277.4||208.8||1509.9|
|10. Holley 410||303.5||239.5||276.3||207.5||1502.5|
|11. Holley 750 – 4010||299.9||239.1||275.8||207.3||1500.3|
|12. Ford 520+||298.8||241.9||275.5||207.5||1500.0|
|13. Holley 830||300.1||241.6||272.9||206.2||1487.9|
|14. Holley 665||303.3||240.3||271.1||205.1||1478.9|
|15. Holley 600||289.6||243.2||268.7||203.5||1466.5|
Next on the list for testing is a better single four intake and an improved exhaust system. This will involve rerunning some of these same carbs and also some other carbs that did not get an opportunity to be run in this round of testing.
Until next time, Ted Eaton.
This article was originally published in Y-Block Magazine, Issue #97, Mar-Apr 2010. Vol 17, No.2