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Comparo: How Two Edelbrock Intake Manifolds Perform Under 30 PSI of Boost
If you are any kind of gearhead or have worked with engines for even a little while, then you are likely familiar with the rules of thumb when it comes to intake manifolds and horsepower. The main rules goes like this: Longer intake runners lend themselves to making torque in the low-rpm range, while shorter runners hurt torque on the low end but are much better and making high-rpm horsepower. Another useful rule is that a straight path for the air and fuel to follow from the intake into the port will produce better high-rpm power than a path beset by curves or other obstructions.
Of course, those rules are all about making it easier for an engine to pull air and fuel through the intake manifold and into the combustion chambers. In other words, a naturally aspirated engine. But what happens when we turn that paradigm on its head by adding just a touch of boost? And by “a touch” we mean 30 psi, which is approximately two full atmospheres, from a pair of turbos. Yeah, go big or go home.
When you go from a naturally aspirated to a boosted application, the conventional thinking says that the intake manifold becomes less important. After all, when the intake valve opens, the boost pressure has all the air you could need sitting right there ready to jump into combustion chamber, so the intake manifold configuration doesn’t really matter.
When we found out that the folks at Prestige Motorsports in Concord, North Carolina, were testing a couple different manifolds on their twin-turbo Ford engine package, we thought this would be the perfect time to find out for ourselves. Prestige Motorsports is relatively new on the horsepower scene, but its big-power packages are making this custom engine shop in the heart of NASCAR country pretty popular. The engine Prestige was testing on the dyno is a twin-turbo V-8 designed specifically for Fox-body Mustangs. In fact, the only modification needed for all that turbo and intercooler plumbing is one hole in the inner fender.
The engine package consists of a four-bolt main 302 block that is bored out to 4.125 inches with a 3.400-inch stroke forged Callies crank, creating a total displacement of 362 ci. AFR heads and custom pistons from JE combine for a turbo-friendly 8.5:1 compression ratio. Finally, the valvetrain is controlled by a Comp solid-roller camshaft with a custom grind producing 0.622/0.616 valve lift and 254/248 duration at 0.050 on a 114 lobe separation.
The intercooled turbo system is based around a pair of 62mm turbos. Prestige Motorsports owner Doug Aitken says he purposely kept them small because this is a street package, and the smaller turbos build near-instant power. And, as already mentioned, the blow-off valves are set to limit the boost pressure to a very healthy 30 psi.
For the test, Aitken chose two Edelbrock intakes that are very popular options for Ford engine builders. First, the Victor 5.0 EFI features a layout very similar to older Ford 302 intakes; however, it features several improvements to make it suitable for performance from 4,000 to 7,500 rpm. Edelbrock says it works well on naturally aspirated engines making 400 to 540 hp thanks to an average 11 1/2 -inch runner length. Aitken also added a one-inch phenolic spacer between the upper and lower sections, which adds to the runner length. The Victor 5.0 works with a maximum throttle-body size of 75 mm, so of course that’s what Aitken chose.
The second test subject is Edelbrock’s Super Victor 8.2 intake manifold. This is the conventional single-plane layout with a central mounting pad for a square bore carburetor or throttle-body. The single-plane setup features runners significantly shorter than those on the Victor 5.0, but the 2.0x1.18-inch port dimensions are quite similar to the Victor 5.0, which are 1.96x1.16 inches.
Unlike the Victor 5.0, which forces the incoming air to make a 180-degree turn on the way to the combustion chambers, the Super Victor has straighter runners that are nearly line-of-sight from the carb flange all the way to the top of the valves. Falling right in line with the “shorter runners make better high-rpm power” rule of thumb, Edelbrock says this manifold works best from 5,000 to 9,000 rpm, which is quite a bit higher than the Victor 5.0’s recommended range.
Of course, street engines rarely operate at 9,000 rpm, so Aitken didn’t even bother testing there. In fact, he tested on a fairly narrow rpm range where the turbos would have the greatest effect. Because running an engine with lots of boost on an engine dyno at low rpm ranges can be really hard on a motor, the pulls didn’t begin until 5,300 rpm.
But what we did see is very interesting. The Super Victor was outfitted with a 90-degree elbow before the throttle-body was bolted up just like it would be in a car. And to even things out, a 1-inch spacer was used here, too. Both manifolds were tested with the same 75mm throttle-body from Edelbrock, but because the Super Victor and Wilson elbow could handle a throttle-body as large as 90 mm, Aitken pulled one off his personal engine to test that configuration, too.
It turns out that the manifold configuration does play a large role in engine performance, even when using a power adder to significantly increase the air pressure behind the valves. And remember those rules of thumb we mentioned? Yeah, they still work here, too.
The Victor 5.0 with the 75mm throttle-body made the most torque over the single-plane Super Victor with either the 75mm or 90mm throttle-body. In fact, at peak torque it made more than 65 lb-ft over either. And while the torque falls off pretty quickly, it is passed by the Super Victor with the same throttle-body by 6,000 rpm; it never falls far below the Super Victor for the rest of the pull. As a result, while the Super Victor with the 75mm throttle-body exceeds the Victor 5.0 in horsepower, both make huge numbers (1,130.2 for the Super Victor and 1,128.5 for the Victor 5.0). The difference is practically negligible.
But what the dyno did prove is that the 75mm throttle-body was too small and restrictive for the engine package. When the Super Victor intake manifold was outfitted with the bigger 90mm throttle-body, peak power jumped up 75 to a very healthy 1,204.3 hp. And the bigger throttle-body made more power and torque all the way across the pull. If the Victor 5.0 had been able to accept the 90, we believe it would have made more power, too.
So what did we learn besides the big power numbers? Regardless of how much boost you are running, a proper intake manifold choice is important when it comes to putting together an engine package that performs to your expectations.
It can also be a mistake to think of boost pressure simply as how much power you are going to make. Boost pressure is actually a measure of resistance. Using the same turbo, you can make more boost pressure mated to a cylinder head with smaller ports than one that is appropriately sized. Even though you will see lower boost pressure on the gauge, you’d better believe the properly sized head is going to make more horsepower. The same holds true for the intake manifold.
So even though you can make impressive horsepower with just about any engine package if you use enough boost, it is always best to choose every engine component to work together if you hope to make the absolute most tire-smoking power from the drop of the throttle.
01. Our test subject is a 302-based pushrod small-block that has been stroked and poked to 362 ci and outfitted with a matched pair of 62mm turbos. Burning VP Q16 fuel to be on the safe side, this engine package produces 1,200 hp with ease.
02. Prestige Motorsports owner Doug Aitken explained that this setup wasn’t designed to make the biggest peak power number possible. The turbos may be on the small side for that at 62 mm, but Aitken says they build boost very quickly with minimal lag, which makes for a very fun street performance package.
03. Edelbrock’s excellent Victor 5.0 intake manifold is a popular choice for pushrod 302-based engines, and we can see why. Notice the extremely long runners from the plenum all the way to the cylinder heads. Those long runners enhance an engine’s torque production whether you are running naturally aspirated or boost. In our test this intake produced the most torque by far, even over a single-plane intake equipped with a significantly larger throttle-body.
04. Here’s a look at the Victor 5.0 from another angle. You can see the 1-inch phenolic spacer that helps lengthen the runners even more (but for more practical reasons, was necessary to provide clearance for the throttle-body on the dyno). Also notice the beautiful, gentle curve created as the runners guide the air into the cylinder heads’ intake ports.
05. The second intake in our test is another great option from Edelbrock: The Super Victor single-plane intake. It sits lower than the Victor 5.0, and with all the hoses and wires on the engine it can be difficult to see, so here’s a shot of it on the workbench. On the mounting flange is a 1-inch spacer to match up with the phenolic spacer on the Victor 5.0, and above that is a 90-degree elbow for mounting up the throttle-body.
06. The Edelbrock Super Victor single plane is on the engine and ready to roll.
07. Prestige Motorsports owner Doug Aitken checked over the test engine setup with the Super Victor single-plane before making another pull.
08. We should note that while we only show three dyno pulls on the graph, we actually made dozens of pulls in an attempt to make sure the boost pressure mapped out almost exactly the same for each intake manifold.