Dyno testing is now complete on the 3X2 intake manifolds. The Edelbrock 573 was at the top of the heap with the Offenhauser being at the bottom. There was a 29HP difference between the best and the worst which is a bunch. The dyno test range for each test was 2500-5500 rpms. Besides looking at both the peak and average horspower and torque values, the engine performance with each intake was also ‘scored’ to get a better feel for overall performance using a single value. The score is calculated by adding both the average HP and torque together and dividing that into the cubic inch of the engine and then multiplying that value by 1000. Testing concluded with the first intake being rerun at the tail end as a validation that the engine was holding steady and because there was still some time left at the end of the day, the new Mummert intake was installed with a 600+ vacuum secondary Holley on top of a 2” four hole spacer and also ran.
Here’s how the various 3X2 manifolds ranked in overall performance from the top to the bottom.
1. 1703.7 pts - Edelbrock ‘573’
2. 1674.7 pts - Edmunds ‘DM-425’ large port
3. 1672.4 pts - Edelbrock ‘553’
4. 1667.7 pts - Edmunds ‘DM-424D’ small port
5. 1661.2 pts - Weiand ‘FM436’ large port
6. 1646.9 pts - Edmunds ‘FORD 424’ small port
7. 1561.2 pts - Offenhauser w/no identifying numbers
The test engine is a +060 over 312 with 9.2:1cr, dead stock ‘G’ heads, and Harland Sharp 1.6:1 rockers. The same Stromberg carbs were used on all the manifolds without any jetting changes once manifold testing commenced. The camshaft is a Crower Monarch with 238° @ 0.050”, ground on 110° lobe centers, installed 2° advanced, and 0.434” lift at the valve after valve lash. All testing was performed with four tube headers running through Magnaflow mufflers. This series of 3X2 intake manifold testing is also part of the durability testing being performed on the prototype Harland Sharp rockers which so far appears to be holding up fine.
For those of you that live and breathe horsepower and torque numbers, here are the peak values for the 3X2 intake manifolds but are still being listed in their order of scoring.
1. 336.0 Tq / 279.3 HP - Edelbrock ‘573’
2. 336.1 Tq / 266.5 HP - Edmunds ‘DM-425’ large port
3. 334.1 Tq / 270.1 HP - Edelbrock ‘553’
4. 338.6 Tq / 260.1 HP - Edmunds ‘DM-424D’ small port
5. 332.1 Tq / 266.2 HP - Weiand ‘FM436’ large port
6. 330.4 Tq / 261.9 HP - Edmunds ‘FORD 424’ small port
7. 311.5 Tq / 250.8 HP - Offenhauser w/no identifying numbers
And here’s the order in which the intakes were run on the engine.
1. Edelbrock ‘573’
2. Offenhauser w/no identifying numbers
3. Edelbrock ‘553’
4. Weiand ‘FM436’ large port
5. Edmunds ‘FORD 424’ small port
6. Edmunds ‘DM-424D’ small port
7. Edmunds ‘DM-425’ large port
8. Edelbrock ‘573’ (reinstalled to validate earlier run)
9. Mummert single four intake with 600 Holley (291.9HP / 346.0Tq)
Intake manifold changes were down to 35 minutes each at the end.
Lorena, Texas (South of Waco)