After a long drought, hot-rod parts for the Two-Valve V-8-which powered the legions of Mustang GTs since 1996-are finally coming around. Joining the many bolt-ons are harder-core engine parts, including camshafts.
It's sort of surprising camshafts haven't been more popular with the GT engine so far. To its credit, the 4.6 GT has good cylinder heads. They breathe well and readily handle more airflow from blowers, intakes, headers, and now, camshafts. Furthermore, the cams Ford fits to the GT are relatively mild, so it doesn't take a radical increase in lift or duration to see more horsepower. That means a logically selected cam will raise the power level without turning the engine into a snorting, recalcitrant beast for daily duty.
Compared to all the hardware...
Compared to all the hardware normally associated with a cam change in an overhead valve engine, cam swapping the modular GT requires just two cams and a set of valvesprings. It's also two cams less expensive than working with a Cobra Four-Valve.
The downsides to camming the Two-Valve engines, however, have been-at least perceptually-strong enough to keep people from popping their cam covers. If nothing else, most enthusiasts are unfamiliar with the overhead-cam design of the 4.6 and are wary of tearing into the engine. There is always the fear of throwing a check-engine light or some other driveability or emissions entanglement, and there is always cost.
Well, here we're installing one of the newest options in Two-Valve cams-a set of Comp Cams' Extreme Energy camshafts. The large Comp concern has joined several smaller tuning firms that have offered Two-Valve cams for a while. But given Comp's market exposure, these cams promise to advance the concept of SOHC modular V-8 cam swapping more than any previous effort.
And guess what? The results are good. Without using the hottest cams available, we picked up at least 25 hp and 10 lb-ft of torque at the tires, the check engine light didn't come on, and the driveability remains good. The final benefit was a marvelous lope in the idle that gave our otherwise mild GT a real presence.
There is a left and right...
There is a left and right cam in 4.6 GT engines. They are not marked, but one is slightly longer than the other. Still, you'll save some head-scratching if you take a minute to keep them sorted out.
Gathered under its Extreme Energy banner, three progressively hotter grinds for the GT engines are offered by Comp. Because of dimensional differences between '96-'98 and '99-and-later GT cams, there are a total of six part numbers. And, by the way, these cams fit all modular SOHC V-8s, so if you have a Crown Vic hot rod, the following will work.
All these cams are hydraulic rollers, in that they work with the stock hydraulic lash adjusters and roller-finger followers. Unlike the stock cams, which are built up using hollow shafts and shrunk-on lobes, the Comp cams are traditionally constructed from a solid blank. But this is of no consequence, other than a pound or two of increased weight. Therefore, these cams are direct replacements for the stockers, with no machining of the cylinder head, valvetrain or valve covers required.
One difference in the right...
One difference in the right and left cams is the hex or flats ground in at mid-cam. These accept a wrench to rotate the cam when lining up the sprockets and chains. And no, we don't know why one side is different from the other.
What is required is fitting higher-rate valvesprings. The stock modular valve-spring offers a little more effort than a ballpoint-pen spring, which is fine with the mild, stock lobe profiles, but it won't cut it with the more aggressive Comp grinds. Of course, Comp has what you need in its ovate beehive spring designed specifically to match these camshafts.
To put the three grinds into perspective, Comp describes the XE262 grind as a stock replacement design, yet with "more RV power." That is, this cam will make more torque and horsepower in the stock rpm range. It works nicely with the stock computer and while Comp's higher-rate springs are recommended, they are not absolutely mandatory with this cam. If we had any mileage on our Mustang, we'd opt for the springs. Every other cam listed here requires Comp's higher-rate springs.
The XE268 grind is the one we're testing in this article. Comp says it is good for "mild street performance, 3.23-3.55 gears. Good torque and power. Will work with stock computer. Noticeable idle." By that the company means there is a definite romp, romp, romp in the idle, which we thought sounded way cool. There's no way you'll convince anyone in the pits these are stock cams, however.
Here a stock cam is at the...
Here a stock cam is at the bottom and its Comp replacement is above it. The stock cam uses a hollow shaft with the lobes individually pressed on it. This is easy for Ford-but not the aftermarket-to produce. Therefore, the Comp cam is a billet piece with the lobes machined directly into it. It is noticeably heavier than the stock cam.
Stepping things up is the XE270 grind. According to Comp, it's a "hot street cam, needs 3.55+ gears, 2,000-plus stall. Intake, exhaust, computer and spring upgrade recommended. Noticeable idle."
The XE274 grind is another "hot street cam." Comp says you'll want 3.55-3.73 gears, a 2,000-plus stall converter, and that a "computer upgrade is recommended." Sounds like a chip to us. Its idle is listed as "rough."
Finally, the XE278 grind gets a "street/strip" label from Comp, as it needs 3.73 or steeper gears, a 2,400-rpm stall converter, plus improved intake and exhaust manifolding, a computer chip and valve springs. It gives a "rough idle." A knuckle dragger, we'd say.
Which cam to select is the inevitable but unanswerable question. But for a street car, we're happy with the power gain from the XE268 grind and wouldn't want to get any farther out there on the idle. You may beg to differ, of course.
In the foreground is the stock...
In the foreground is the stock cam showing the detail of its pressed-on lobes. Both cams use hardened steel lobes to work with the roller-finger followers.
At the other end of the spectrum, we wouldn't think going through a cam swap as expensive and involved as this one would be worth it just to install the mildest grind, the XE262. That cam would certainly make sense when dressing a replacement engine while it was on the engine stand, but unless you're looking for something particularly stealthy or really want to avoid changing valve-springs, the XE268 grind seems like the happy spot for a daily driver to us.
Just to give you another reference point, as noted earlier, using a '96 GT with stock headers, an aftermarket after-cat and a cold-air kit, we saw an additional 25 hp and 10 lb-ft at the peaks from an XE268 grind. Comp literature claims a 25hp gain at the peak and a 34hp gain at 5,500 rpm, using the hotter XE274 on a '97 GT with full-length headers and a cold-air kit.
Comp's 4.6 valvespring has...
Comp's 4.6 valvespring has a slightly beehive shape. You have to look closely to see it, as the inward taper is basically confined to the last coil. These springs have 93 pounds on the seat and 198 pounds open at 1.020-inch of valve lift. They're good for all the 4.6 camshafts Comp offers.
The Big Swap
So you like the idea of new cams, but you aren't so sure about installing them. We'll let the photos and captions give the how-to highlights; what we need to address here is the widespread concern about working with the complex and mysterious 4.6 GT engine.
It's true. For the average guy, this is absolutely not a job to tackle at home. There are too many handtools, air tools, specialized tools, and too much workshop room required. There are enough parts involved and clearances are so tight that it will take long after the weekend is a bad memory to get the engine apart and reassembled, given the constraints of a standard garage workshop or-dare we say-the driveway.
That said, there is no rocket science about working on the SOHC 4.6 GT engine that would keep the senior enthusiast from performing this job. Certainly the hobby Mustang that goes down for the winter and emerges the next spring would be an ideal candidate for this swap in a home shop.
Likewise, the enthusiast who's comfortable with his wrenching skills, who's accumulated a well-filled toolchest, and who's modest home shop where the car can come apart for a while, could power through this installation in three to four days without haste. As for a pro install, count on two days to turn your GT around with your local tuner. That can mean more than 10 hours of labor, which gets pricey, so take that into consideration when budgeting this hop-up.
Begin the cam install by clearing...
Begin the cam install by clearing a path to the valve covers and front engine dress. At this point, Westech technician Tom Habrzyk had already removed the cold-air kit, pulled the spark-plug wires, and was inspecting the hardware on the BBK valve covers. The rod rising from just behind the alternator is a long hood prop rod-it's useful in raising the hood to its limits, which increases clearance and lets in plenty of light.
What about timing those camshafts, keeping the timing chains straight, and not fouling the valves with the pistons? These are real concerns, but the answers are easy enough. The key is making your own set of marks on the timing chain and timing chain sprockets. From there, the chains and sprockets are simply reassembled with the marks lined up. They'll only go together one way, so in essence, the job is selfaligning-as long as you make marks during disassembly. You do want to use a durable marker because if the marks rub off, then a longer procedure of lining up the crank and both cams is required. A paint marker, as sold in auto parts stores is ideal for this job-pencils, nail polish, and so on are not because they rub off.
As an overview, the installation involves removing both valve covers and the entire front engine dress so the front timing chain cover can be removed. This involves dismounting the power-steering pump and pulling off the harmonic damper.
The timing chains are then marked and removed, the upper cam bearing halves are removed, and the old cams are lifted out. The rockers are lifted out, and then the valvesprings need to be changed. This requires pressurizing each cylinder in turn with compressed air while a special valvespring compressor is employed. After that little chore, everything goes back together again.
On our '96 subject GT there was no need to break into the cooling system, disconnect the alternator, or open the air-conditioning or power-steering lines. It's clear, however, that you'll have to buy or rent the specialized valvespring compressor, have a puller for the harmonic damper, and be willing to work in tight confines. Changing the valvesprings is also notably tedious as the tiny keepers do their best to go everywhere but between the valve stem and retainer while you bend over the fender and work inside the heavily bulkheaded cylinder heads. It really is a good job for a pro.
Once the cams are in, however, they're no doubt the missing link in unlocking that last 20 or so horsepower or more from every other modification. If you want a GT that runs surprisingly fast, this is a great way to get started. 5.0
|Part||Grind ||Duration at 0.050-in || Operating||Lobe Separation|
|102100||XE262H||224/232||0.500||1,200-5,200 rpm ||114|
|102200||XE268H||230/236||0.500||1,600-5,600 rpm ||114|
|102300||XE274H||236/236||0.500||2,000-6,000 rpm ||114|
|Part||Grind ||Duration at 0.050-in||Operating ||Lobe Separation|
|Comp Cams XE268H |
|1,500|| 62.6||219.8|| 57.8||202.0 |
|1,750|| 76.9||231.5|| 75.9||227.8|
|2,000|| 89.1||234.4|| 90.9||238.1|
| Looking at the charts above and measuring peak-to-peak, the Comp cams gained 25.5 hp over the stockers. That's a tad more than the peak-to-peak numbers generated by the dyno, which reads in much finer detail, detail we don't have the space to reproduce here. Call it 25 hp, and even better-with no meaningful drop in torque or power below 3,300 rpm, where the larger cams really take off. That's a great gain, one that can definitely be felt and seen on the stopwatch.All testing was done at Westech using its SuperFlow chassis dyno. Engine temperature was carefully monitored by noting auxiliary radiator fan onset and shut-off to reduce power variations.|