When we last left Modern Mouse, our in-house 5.3 LS dyno mule, we had just run a Zex perimeter plate nitrous system on the now 383-cube stroker. For those who don't remember, the Modern Mouse series was designed to illustrate the many different performance possibilities offered by a 5.3L LM7. Starting with a bone stock, high-mileage unit pulled from a wrecking yard, Modern Mouse was soon subjected to all manner of bolt-ons and boost.
The LM7 stroker has seen numerous head, cam and intake configurations, including ported stock heads from TEA and a set of Trick Flow Specialties 215s. For this test on the new Holley intake manifolds, we made a few changes that included a set of dished pistons from JE to drop the static compression down for future boost, a change to a Crane hydraulic roller cam, and reinstalled the TEA Stage 2 706 (stock) castings.
The new configuration was the perfect test mule to illustrate the differences between the two new Holley intakes designed for cathedral-port cylinder heads. The Hi-Ram was essentially an EFI tunnel ram for LS applications. The designers at Holley saw fit to configure the impressive Hi-Ram to accept either carburetion or fuel injection. Thanks to injector bungs and a removable upper intake section, the lower tunnel ram could be combined with no less than four different induction systems. Induction choices for the Hi-Ram included a single round (102mm) LS throttle body, a pair of four-hole (4150-style) throttle bodies, a pair of 4150 carburetors, or even a pair of Dominator carbs.
The one downside to the Hi-Ram (and all tunnel ram intakes for that matter) is hood clearance. Unfortunately, those same tall intake runners that promote power production will not fit under most stock hoods. The dual-quad, Modular mid-rise intake offered similar induction choices (single LS TB, Multi four-hole TBs and 4160 carbs), but offered them in a more hood-clearance friendly package. Modern Mouse gave us the opportunity to demonstrate (literally) the highs and lows of the two new Holley intake designs. Just for good measure, we also tried the Hi-Ram on our 417-inch Monster Mouse stroker engine.
1|Chose your weapon! Holley now offers hi-Ram and mid-rise intake systems for LS applications. 2| Modern Mouse started out life as a simple 5.3L, but was upgraded to 383 stroker status. 3| Though we started with a set of flat-top pistons, we recently swapped over to a set of 10cc dished pistons from JE. We plan on some more boost in the future, so the dished pistons will give us some safety margin in terms of static compression ratio.
4| Crane supplied the valvetrain components for this installment. The cam offered 0.600 lift, a 232/240-degree duration split, and 115-degree LSA. 5| Though Modern Mouse has seen a variety of different cylinder heads, we went back to a set of CNC-ported factory 706 castings from Total Engine Airflow. 6| Extensive porting unearthed plenty of airflow, to the tune of nearly 320 cfm on the intake and 250 cfm on the exhaust.
7| Holley supplied the intake manifolds for the test. First up was the mid-rise. Thanks to an ingenious multi-piece design, the mid-rise intake offered the ability to accept either dual quads, dual four-hole throttle bodies, or a single LS throttle body. The mid-rise also improved hood clearance by almost two full inches over the Hi-Ram.8| On went the new mid-rise intake in single-throttle body, EFI configuration. The intake relied on O-ring sealing to eliminate vacuum leaks. 9| Holley also supplied the necessary fuel rails to feed the new intake. This test was run with a complete Aeromotive fuel system feeding a set of 36-pound injectors.
10| Tuned with the Holley Dominator EFI system and equipped with the mid-rise intake, Modern Mouse produced peak numbers of 543 hp at 6,400 rpm and 499 lb-ft of torque at 5,000 rpm. 11| Satisfied with the results of the first test, it was time for the Holley Hi-Ram. The Hi-Ram required use of the supplied mounting studs. 12| Run with the impressive Hi-Ram, the 383 stroker produced peak numbers of 563 hp and 505 lb-ft of torque. It should be noted that in addition to providing much-needed hood clearance, the mid-rise designed offered more power up to 4,800 rpm, and kept pace with the larger Hi-Ram up to 5,900 rpm. 13| Thinking that the Hi-Ram was better off on a more powerful application, we had just enough available dyno time to run it on Monster Mouse, our LS3 based, 417-inch stroker. 14| Crane once again stepped up to provide the necessary valvetrain components, including a healthy hydraulic roller cam profile that offered 0.624 lift, a 240/248 duration split and 115-degree LSA. 15| Running a set of Mast cathedral-port heads, the 417 produced 643 hp and 568 lb-ft of torque with the Holley Hi-Ram intake. These Holley intakes are serious power producers.
Holley Mid-Rise vs Hi-Ram
Not surprisingly, the Hi-Ram intake offered more power and torque, with peak numbers of 563 hp and 505 lb-ft of torque. Extra top-end power is always welcome, but what about having to fit it underhood? That is where the mid-rise comes in. In terms of power, the mid-rise was no slouch, offering 543 hp and 499 lb-ft of torque. A review of the graph illustrates that the mid-rise actually offered more power than the Hi-Ram up to 4,800 rpm, and kept pace with its big brother up to 5,900 rpm. Only after 6,000 rpm did the high-Ram pull away, but there is no denying the extra 20 hp offered by the tunnel ram design. Loyal readers will remember we tested the mid-rise previously in carbureted trim back in Modern Mouse, part 5. Regardless of what system you pick, you'll be proud to pop the hood and strut your stuff.