Tom Wilson
November 12, 2000
01. Horse Sense: The Xtreme Energy line of cams is really based on the premise of opening and closing the valve faster. The rapid valve acceleration helps airflow by having the valve open a greater distance for more time, of course. It also pumps up the critical low-lift period, where the valve is just opening and the airflow is getting started. By applying a more massive airflow signal to the air in the port, the quick opening and closing valves realize a meaningful improvement in power-building airflow. Of course, the trick is whipping the valves around without applying destructive forces to the valvetrain.

When it comes to flexing big horsepower biceps and rippling expanses of torque, setting aside the compact 302 for the fullsize 351W is a major step up in both power production and long-term engine durability. Now, with the recent advent of Ford Racing Performance Parts' $6,295 Windsor-based 392-inch stroker, we've come to enjoy 430 Mustang-friendly horsepower direct from the FRPP catalog. Good for low 11s at the strip or deeply satisfying oomph off the road circuit corners, the 392 crate engine's 351W architecture is an easy-enough bolt-in to late-model Mustangs.

Previous testing has shown Ford's 392 is actually good for a healthy 456 hp and 469 lb-ft of torque on our usual Westech Performance Group's 901 SuperFlow dyno test bench. These figures are considerably higher than FRPP's ratings of 430 hp and 450 lb-ft of torque, a situation we've come to expect with Ford engines, thanks to their relatively conservative power-rating strategy. We should also point out the 392 package is available as a short-block ($2,995) or even just a reciprocating assembly ($1,495) if that better suits your needs. The recipro-cating assembly is designed to work with '93 or later 351 blocks with their one-piece crank seals.

02. Comp Cams offers five mechanical rollers for the 351W in its Xtreme Energy series. We tested the smallest, middle, and largest cams in the lineup, which grow by equally spaced increments of 0.006 inch of lift and 6 degrees of timing with each cam.

Happy as we were after dyno'ing the 392 in its stock form, we started considering what the big-inch, single-plane intake Windsor could show us with a little more cam.

The Cams
Getting together with John Baechtel at Westech, we went through the Comp Cams catalog-Westech has an arrangement with Comp that makes testing Comp gear almost too easy-to see what sort of camming we could try in the FRPP test engine. We wanted a range of cams that were nicely spaced in lift and duration, and that would make good power in the 392.

What we came up with was the Xtreme Energy line of mechanical roller camshafts. The 392 is delivered from Ford with a healthy Comp hydraulic roller, and the Xtreme Energy lineup begins with a mechanical-roller grind that mimics the juice stick. So, as a bonus, we could see if similar hydraulic and mechanical cams offered any power gains relative to each other.

03. Our concerns over piston-to-valve clearance proved unfounded. Even though the lift and duration increased noticeably as we went up the Xtreme Energy cam line, we always had around 0.200-inch p-v clearance. It's the nature of piston and valve timing that as duration increases, the associated valve lift is accompanied by a piston that's farther down the bore.

The chart on p. 42 outlines the stock hydraulic roller and the full five-cam Xtreme Energy lineup. In the interest of time, we ran the small, medium, and large of the Xtreme Energy cams; the two italicized cams were not tested, but extrapolating their performance is easily done.

From the chart it's clear the lower mechanical rollers are definitely streetable units, calling for just 9.0:1 compression and lower-stall converters. The XR280R cam looked to us where any sort of daily-driver status would absolutely require large doses of youthful enthusiasm, and the XR292R is definitely a radical piece. Comp says it features a Pro Street sort of idle and requires a 3,500-rpm stall converter and a good intake and exhaust to show its stuff. We had all of that, minus the compression, so we made a note to give the 292 a bit of leeway when analyzing the results.

More Power, of Course
Aside from having to fish a set of mechanical lifters out of the ether at the last minute (thank you, Ford Performance Solutions!), our test went without incident. We installed the 392 just as it arrived from Ford-our test engine was a demo model that was delivered from Ford wearing a 750 Holley carburetor and FRPP ignition wires-to baseline the stock combination. We were happy to see it register within 1.5 hp of what it baselined a couple of months ago for another test.

04. Moving from a hydraulic-roller cam to a mechanical-roller meant a change in rocker arms as the stock rockers are non-adjustable. Comp offers both styles in a pedestal mount, so we simply substituted its 1.6 adjustable roller rockers when running the three mechanical cams.

We then moved to the three mechanical-roller cams and their lifters, starting with the middle grind, the XR280R. We noted an inch of vacuum at the power peak, and so substituted a larger carburetor to reduce the restric-tion. Westech didn't have an appropriately sized Holley, but did have an 850 Demon, a carburetor we've seen help in the past with better power and lower fuel consumption. Of course, we then had two variables in our test-a cam and a carburetor-so we ran all three of the mechanical rollers with both carburetors. Our procedure was to stabilize the oil and water temperatures at fairly high limits, then make three power pulls. The pulls were then averaged to arrive at the official power and torque figures. The carbs were swapped and the procedure repeated.

We'll let the charts tell the full story, but will point out that the improvements in power are fairly incremental until you get to the largest cam, the 292.

Average Peaks
CamTorque Power
Base 451457
292 449477

05. Our greatest fear during the test was valve float with the larger cams. This was because we could not use these dual springs Comp sent along with the camshafts due to unusually shaped, large-diameter spring seats on the GT-40X heads. Luckily, we never encountered any valve float.

Several factors are at play here.
The 292 cam is listed as needing 11:1 compression to do its best; our engine was likely in the mid-9:1 range. Ford says the 392 has 9.7:1 compression, but gives a whopping +/-0.5 points of compression tolerance range! More compression would definitely help the torque curve, so the torque loss would not be as great as seen here had we installed 12:1 pistons.

To look at it completely differently, this engine is reaching into the smoke zone for street tires. Perhaps less torque and 20 more horsepower is faster with limited traction-it would depend on the chassis. It's also interesting to see the similarly sized mechanical-roller cam made a bit more torque than the stock hydraulic roller, but not much more horsepower.

As for the carburetors, the Demon made more power across the board, but the percent changes cam-to-cam were the same for either torque or horsepower. It's safe to say the cams didn't really care which carburetor was on the engine, but the total package favored the Demon. No jet changes were made during the test, and the electronic ETAS Air/Fuel meter saw both carbs delivering 13.0 to 13.2:1 A/F ratios. The Demon was simply a larger carburetor, and the 392 liked that.

Averages by Carburetor
Cam750 Holley850 Demon
Base 451/457na/na
292 449/477454/483

The conclusions are simple enough. The 392 likes plenty of carburetion, and it does respond to more camming. That said, we'll caution that the 292 grind is rather large and definitely begins freely trading torque for horsepower, unlike the less aggressive cams. At the lower end of this range of cams, we'd opt for the hydraulic roller, exchanging the modest torque gains for quieter, less operation and less maintenance. Once at the 280 cam range, however, the mechanical roller is definitely making a difference. And from a big-picture outlook, the 392 itself seems like a rapid, relatively cost-effective way of hitting real horsepower in a Mustang-friendly package. 5.0

Cam Specs
Cam PNLift Grind No.Valve LiftDuration @ 0.050Lobe Separation AngleNotes
35-522-8XE282HR0.565/0.574232/240112*hyd. roller
35-769-8XR268R0.589/0.602236/2361109.0 comp/2,000 rpm stall
35-770-8XR274R0.602/0.608236/2421102,500 stall, rough idle
35-771-8XR280R0.608/0.614242/24811010.0 comp/3.73 gear
35-772-8XR286R0.614/0.621248/2541103,000 rpm stall
35-773-8XR292R0.621/0.627254/26011011:1 or better comp, 3,500 rpm stall, good int.
Note: Valve lift is computed with a 1.60 rocker.
*Ford lists its 392 cam with 108/116 degrees of lobe separation, which is 112 degrees when the cam is installed 4 degrees retarded. The cam we removed from our 392 test engine was marked as a Comp XE282HR, which specifications we've listed here.

392 Crate Motor Specs
•Bore x Stroke: 4.030x3.850-inch
•Block: Sportsman; two-bolt mains (M-6010-A351)
•Crankshaft: Nodular cast iron; one-piece rear main seal (M-6303-A385)
•Bearings: Federal-Mogul tri-metal
•Pistons: Hypereutectic; floating pin; 1.615-inch compression height
•Piston Rings: 1⁄16 moly top; 1⁄16 cast-iron; 3⁄16 standard-tension oil
•Compression Ratio: 9.7:1
•Camshaft: 0.566/0.576 valve lift (1.6:1 rocker);232/240 degrees duration @ 0.050-inch lift
•Cylinder Heads: GT40X alloy; 64cc chambers; 1.94x1.54-inch valves (M-6049-X303)
•Rocker Arms: Extruded aluminum roller; 1.6:1 (M-6564-B351)
•Distributor: Ford electronic billet
•Intake: Single-Plane Victor Jr. (M-9424-V351)

Xtreme Dyno Results
 Baseline268 Cam*XR 280 Cam*292R cam*

* run with 750 Holley
Ford Racing's 392 crate engine ran stronger than rated in our first tests, and continued to muscle out the power during our camshaft comparo. With no changes to the basic engine short of the cam and rocker arms, the 392 belted out a thumping 483 hp this time around.