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All of the powerful original Hemis had multiple carburetors, so it was only natural for Edelbrock to design a dual-quad intake for the modern Hemi.
The dual quad improved power production compared to the single plane up to nearly 6,000 rpm, but the single plane pulled ahead slightly on the big end. For most dual-quad Hemi owners, they will appreciate the look and extra grunt offered by the dual-quad setup much more than any missing horsepower past 6,000 rpm.
Single-Plane vs Edelbrock Dual-Quad for a Modified 5.7L
MP Single-Plane Intake: 479 hp @ 6,900 rpm
Edelbrock Dual-Quad Intake: 463 hp @ 6,600 rpm
Largest Gains: 20 hp @ 6,900 rpm
The dual quad offered improved performance and horsepower production up to 5,900 rpm, but the single-plane MP intake pulled away thereafter. The short-runner single plane was designed to improve power production higher in the rev range, but nothing looks as cool as a dual-quad Hemi!
Single-Plane vs Edelbrock Dual-Quad for a Modified 5.7L
MP Single-Plane Intake: 404 ft-lbs @ 5,300 rpm
Edelbrock Dual-Quad Intake: 420 ft-lbs @ 4,900 rpm
Largest Gains: 24 ft-lbs @ 3,700 rpm
The dual-quad intake from Edelbrock more than looked the part. The design improved torque production by as much as 24 ft-lbs, with substantial gains up to 5,800 rpm. The additional torque offered below 6,000 rpm will be much more useful than the loss in power above that point.
Test 7: Mopar Performance Single-Plane vs Speedmaster Downdraft IR Intake for a Mild 5.7L Hemi
Right off the bat, we should stress that the individual-runner intakes looked so amazing that most Hemi enthusiasts will chose it over any other intake based on looks alone. Nothing screams “look at me” like a downdraft EFI system with eight massive butterflies and full-radiused, polished air horns. These intakes are, however, not for the faint of heart, as tuning them for use as a daily driver can be difficult and time consuming. It’s not impossible. Just be prepared to spend some time getting the thing to idle, take throttle, and drive down the road with civility. The WOT stuff is easy by comparison; there is never a shortage of airflow from one of these systems. Many enthusiasts think that the massive airflow potential of these individual-runner intakes is the reason they make so much power, but the reality (for this test) is runner length produces the power. The single-pane MP intake offered more than enough flow to satisfy the power needs, but just check out the power differences lower in the rev range as airflow is less critical. Power gains that occur through the entire rev range are generally a function of runner length.
This particular test piece was run on a mild 5.7L Hemi equipped with a small Comp 260H-13 cam. The mild Comp cam offered a .522/.525 lift split, a 208/212-degree duration split, and 113-degree LSA. That the 5.7L pulled hard to 6,500 rpm is a testament to the high-RPM nature of the intakes tested. Run with the MP single-plane intake in EFI form with a 4-hole throttle body and FAST injectors, 5.7L produced 430 hp at 6,500 rpm and 391 ft-lbs of torque at 5,200 rpm. The mild cam and high-RPM intake were somewhat mismatched, but the combo produced impressive power given the minimal mods. After installation of the downdraft 8-stack induction system from Speedmaster, the peak power numbers jumped to 462 hp, which was at a slightly lower 6,400 rpm and 418 ft-lbs of torque at 5,300 rpm. Basically, the Speedmaster IR induction improved power everywhere, and would offer even greater gains on a wilder, more powerful combination.
The single-plane intake offered reasonable performance, but there are plenty of better intake systems available for your Hemi.
The individual-runner 8-stack system from Speedmaster looked amazing and offered plenty of performance.
MP Single-Plane vs Speedmaster Downdraft IR Intake for a Mild 5.7L Hemi
MP Single-Plane Intake: 430 hp @ 6,500 rpm
Speedmaster 8-Stack Intake: 462 hp @ 6,400 rpm
Largest Gains: 31 hp @ 6,400 rpm
The individual-runner intake offered impressive power gains through the entire rev range. Thanks to plenty of airflow and optimized runner length, the Speedmaster IR system improved the power output by as much as 31 hp.
MP Single-Plane vs Speedmaster Downdraft IR Intake for a Mild 5.7L Hemi
MP Single-Plane Intake: 391 ft-lbs @ 5,200 rpm
Speedmaster 8-Stack Intake: 418 ft-lbs @ 5,300 rpm
Largest Gains: 25 ft-lbs @ 5,200 rpm
The torque curve was even more telling because the long(er)-runner IR induction system improved torque output from top to bottom. Extra top-end power is always good, but more torque through the rev range will be even more useful.
Test 8: Effect of Runner Length of a Speedmaster Downdraft IR for a Mild 5.7L Hemi
Perhaps the best illustration of the effect of runner length in this chapter comes from this impromptu test on the Speedmaster downdraft system. With no adjustable intake system available from the aftermarket, the author whipped up something to work on the downdraft system offered by Speedmaster. Using a combination of slip-fit aluminum tubing, hose clamps, and duct tape, we were able to quickly adjust the runner lengths to optimize power production at different engine speeds on this 5.7L Hemi. The runner length acts as a tuning
