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We learned long ago not to listen to that caveman voice. Instead, we decided to look into how much power we could extract from a set of oval ports. For a testbed, we used our existing cast-cranked Rat motor built back in the Mar. We also included a set of production iron peanut-port heads just to see how they would do as a baseline.

The results of this shootout were more than a little surprising. But be sure to read this entire story, not just glance at the power numbers, because we evaluated these heads in a bunch of interesting ways. Taken as a whole, the oval-port Rat market offers heads that are a lot stronger than you might think. The Mule If you recall, we built a ci Rat in the Mar.

We had to twist that combination up to 6, rpm to achieve that power, which created more than a few Internet blog predictions of imminent engine failure focused on the cast crank and stock rods. Despite those doomsday prognostications, the engine is still very much alive even after this latest thrashing. To remain consistent with a conservative oval-port street concept, we decided to pull back on the cam timing to keep the peak horsepower below 6, rpm. This milder Comp Cams hydraulic roller cam timing is also a better fit with the entire oval-port package, including the Edelbrock RPM Air-Gap dual-plane intake manifold and cfm Barry Grant carburetor.

If peak horsepower had been the goal, we would have chosen any one of many single-plane intakes that would have easily kicked it up over hp. Taken as a whole, this engine package turned out to be extremely successful considering that the engine idles at rpm with 12 to 13 inches of manifold vacuum and offers tire-shredding torque.

Edelbrock Heads The Edelbrock Performer RPM oval ports are an interesting mix within the collection of aftermarket aluminum oval-port heads. They offer the largest intake-port volume of cc with the smallest 2. Among the specs we list for each head is the intake port cross-sectional area.

We measured each of the five heads in the same basic place in the intake port to determine the smallest cross-sectional area. This dimension, in square inches, is intended to give you an idea of which head will generate the highest intake velocity based on size.

A smaller intake-port cross-section will generate a higher intake-flow velocity while larger ports will experience slower velocities. Intake-port velocity up to a point has been shown to have a positive effect on cylinder filling, which results in better power. Another important consideration is that these heads rely on a stock exhaust-port exit position, which helps with header fitment. But add in price and suddenly these heads are players, since they are the least expensive of all the aluminum heads we tested.

Check out our dollar-per-horsepower evaluation and see if you agree that the Edelbrock heads make excellent fiscal sense. Dart Heads These are the newest castings amid the oval-port contenders. Clearly Dart was after serious performance since it fitted these cc intake ports with 2. Only the TFS heads with 2. From a port cross-sectional area standpoint, the Darts are the largest of all the heads we tested, which might have contributed to their overall torque curve performance.

Dart also raised the exhaust-port exit 0. Dart Oval Port 2. TFS Heads If you look at the flow curves, the TFS and Dart intake-flow numbers virtually overlap throughout the entire flow curve on both the intake and exhaust, which is surprising. Despite this, there are a couple of items that differentiate the TFS heads. First, the TFS intake port has the smallest cross-sectional area of all the aftermarket heads at 2. The second point is the raised exhaust port, which creates excellent exhaust flow numbers that would probably benefit from a single-pattern camshaft design.

TFS Oval Port 2. Brodix Heads The Brodix Race-Rite oval-port heads are an interesting approach. When we first flow-tested these heads, we were impressed with their out-of-the-box performance. This change also bumped the compression, which is why this modification is worthy of consideration.

Edelbrock Intake Manifolds W Pre assembled Direct Port Nitrous

Generally, a CNC chamber is also worth some combustion efficiency that is hard to measure unless we did some kind of back-to-back test on the same set of heads. The Brodix has a decent exhaust port, but because it is a stock exit-location port, the exhaust-flow numbers are not as strong as the TFS or Darts.

This may explain why the Race-Rites benefited at the top a little more from the dual pattern cam. Our only complaint with these heads is that the valve-cover rail is low and spills oil on the headers when we remove the valve covers. Overall, this is a great oval-port cylinder head.

Brodix Race-Rite Oval Port 2.

PN RR BB-O. We set up the peanut-port heads with the same good Comp valvesprings, titanium retainers, and roller rocker arms. We also used a set of Comp 0. GM Iron Peanut Port This cast-iron head is called the peanut port because the intake ports are not much larger than their namesake.

Omar Cabrillo at Coast Motor Supply in Canoga Park, California, helped us out by supplying a pair of the heads complete with tiny stock valves, new guides, and a basic valve job. These peanut ports are roughly 30 percent smaller than an aftermarket cc version.

There are larger factory oval-port, cast-iron, open-chamber heads at cc, but the only ones we could find had been modified, which would not be representative of an OE head. If you were looking to build a budget-oriented Rat for towing where power above 4, rpm was not a concern, these heads would be an excellent choice with almost lb-ft of torque at 3, rpm.

If you were to pocket-port these heads and add larger 2. GM Iron Peanut Oval Port 2. The Setup There are a boatload of variables involved in testing five different Rat motor heads.

We quickly discovered that each of them demanded wildly different pushrod lengths based on changes in valve length. For example, both the TFS and Dart heads use 0. After much gnashing of teeth, we ended up with six different pushrod lengths for our five subject heads. Just for fun, many psychology trading binary options profitably the heads also required lash caps on some of the valves to create sufficient clearance between the Comp steel Magnum 1.

The next time you hear a buddy complain about how much money custom engine builders ask for assembling an engine, smack them upside the head and tell them we put a solid 20 hours into setting up these heads so that they would perform and survive as intended.

We also realized that in order to generate a truly fair comparison, all the heads would require the same valvespring pressure. This would eliminate valve float as a variable, which was very important. One item we had no control over was that larger-diameter valves automatically weigh more than smaller valves. To accommodate all the different valve weights, we decided on a Comp Cams PN spring with a common installed height of 1. The measured pounds at 1. Finally, all but one of these heads required its own specific head bolt set as well.

It took a big stack of ARP fasteners to get the job done, and we appreciate all the help that ARP gave us to make this test successful. Pushrod Chart Because these heads were fitted with several different valve lengths, this demanded multiple custom pushrod lengths. The following chart lists the pushrod lengths we established for our hydraulic roller-cammedbut you should still take the time to measure your own required lengths to ensure accuracy.

The chart lists each Comp Hi-Tech stock brokers in columbus ohio length in inches with each part number in parentheses underneath.

These Comp Hi-Tech pushrods can be ordered either individually or in sets of Lightweight Retainers The problem with big-block Chevys has always been big, heavy valves and valvetrain parts. Since valvetrain weight is an issue, we elected to use the Comp dual springs matched with a Comp degree titanium retainer to reduce weight.

The difference in weight between the normal-steel 1. Just as we completed our testing, we learned about new lightweight tool steel retainers from Comp Cams that are only slightly heavier than titanium, yet as strong as steel and, best of all, roughly half the price! How often do you get an improvement in performance while also reducing cost?

Technology is a wonderful thing. Compression Lessons Each of the heads we tested had a slightly different combustion-chamber volume, which means static compression was another unfortunate variable in this test.

The accompanying chart indicates the variation in compression.

Edelbrock Performer Intake Manifold for SB Chevy | JEGS

Both the Edelbrock and the Brodix with its CNC machining had the smallest chambers, so they benefited from the highest compression, while the Dart had the largest chamber and therefore the least compression. The difference is almost a full point of compression, and since one point is worth roughly 2 to 3 percent power, both the Edelbrock and Brodix probably received a decent horsepower bump.

Had we milled the Dart heads to cc, for example, that might have added another 10 hp, which would have made a significant difference throughout the entire power curve, perhaps pushing peak horsepower very close to Test Fit One of the biggest headaches for big-block engines is packaging the exhaust.

When we began this test, it appeared that the raised exhaust ports on the Dart and TFS heads might be a problem when it came to fitting chassis headers in a car, so we decided to put the heads to a simple test. We then bolted on the Edelbrock heads along with a set of Hedman 2-inch chassis headers. The Edelbrock heads fit with no clearance problems, so we then tried a TFS head with the same headers. One tube came very close to the steering column and probably would require a slight dimpling, but that edelbrock stock market the only real consideration.

We did not have the clutch linkage in place, but that did not appear to be an obstruction. One variable that affects any test like this is cam timing. In this case, we chose a dual-pattern camshaft that offers 8 degrees more exhaust duration compared to the intake side. This probably helped the Brodix and Edelbrock heads that had less favorable exhaust flow numbers while perhaps hurting the Dart and TFS heads slightly.

The Dart and TFS heads both have raised exhaust ports and strong exhaust flow numbers that likely would have responded with more power by using a single-pattern camshaft. This is the problem with choosing one camshaft profile for testing multiple cylinder forexte uzun vade. Now you can see why the results of this kind of testing cannot be considered chiseled in stone unless a whole battery of cams go with it.

This just gives you something more to think about. The Test Once we had all the heads assembled and configured, we loaded up the Rat and all the heads and assorted accouterments in the back of our trusty GMC pickup and piled it all up in the dyno cell at Westech.

Steve Brul put on his kidney belt, and we set to work thrashing on the Rat. The procedure for the first test was to bring the engine up to temperature and then go through a series of jetting and timing tests to establish the baseline for the rest of the cylinder heads. It turned out that all the heads used 36 degrees of lead and the same jetting from the Barry Grant Mighty Demon carburetor, which made the thrash a little easier.

Once we had a good tune-up, we made three full pulls on each combination from 3, to 6, rpm, then averaged those runs together to create a power curve for each engine.

Big Block Cylinder Heads - Big-Block Cylinder Head Test - Hot Rod Network

Looking at the numbers, the iron heads performed better than we thought they would, while the aluminum heads were very close in terms of overall power. If you look at the overall torque curve of the four aluminum heads, all four are extremely close from 3, through roughly 4, rpm, where the Edelbrock heads begin to drop off slightly. That also shows up on the horsepower curve. While the power difference appears significant on the horsepower charts, please read the Simulated Dragstrip sidebar.

We tested all five heads in a digital Chevelle down a virtual quarter-mile. Rather than get bogged down by too much detail about the power curves, it may be more important to point out how amazingly close all four heads were in terms of average power.

Stocks in Motion: Information Holdings, Edelbrock - Pg.2 - TheStreet

With an average torque difference of only 8. Especially when you consider that there was a slight difference in compression. Had we evened up the static compression, it would certainly have helped the Dart and TFS heads the most, especially in terms of peak numbers, but it also means that the average differential would probably be a little wider, but still around 2 percent. That could come in the way of a switch to perhaps 1. We plan to bolt a single-plane intake on the Dart head package, and this will certainly push our into the plus horsepower zone.

Either way, this is a killer power package disguised in conservative attire. You just might get away with it-until the word gets out. The Brodix, Dart, and TFS heads all made strong peak power, leaving the Edelbrock slightly behind. Then we divided the price of each pair of heads by their peak horsepower. Here, the Edelbrock is the clear winner in terms of horsepower per dollar.

What this shows is that the Edelbrock heads offer excellent power for the money. So we did the next best thing and loaded each of the five Rat head power curves into a simulated 3,pound street car with a TH trans, 3,rpm-stall speed converter, a 3. Using the Quarter Pro dragstrip simulation program, we ensured that tire spin was eliminated so that we could evaluate each head based on its true potential. We simulated a typical degree day just above sea level, so these numbers are relatively quick.

Even if a normal street car could hook up which is questionablethese e.

Nevertheless, the differential between all the aluminum Rat heads is small-merely 0. Now factor the price again into this equation and you can see that the Edelbrock heads look really good.

The Brodix, Dart, and TFS are so close that reaction time would determine the winner in that race. Also note that even those lame peanut-port heads pushed the test car into the very low 11s. This is bench racing at its finest. As part of our ongoing efforts to make HotRod. As always, thanks for reading HotRod. Hot Rod Roadkill Car Craft Street Rodder Classic Trucks Circle Track Mopar Muscle Engine Masters Hot Rod Deluxe Muscle Car Review.

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