Muscle Mustangs & Fast FordsHow To Engine
Testing a Pair of 4.6L Two-Valve Comp Cams on a Stock PI Motor with Nitrous
Would You Like Some Cams With Your Juice?
When it comes to cams and Two-Valve power improved motors, things can be tricky outside of bolting on some sort of power adder. Trying to get more power from a naturally aspirated 4.6L Two-Valve can be tough because of the flow limitations of the factory heads.
Since the PI motors were introduced in 1999, the aftermarket cam companies have worked hard to find profiles and patterns that would agree with the factory heads and give the Two-Valve 4.6L extra punch. Today there are some great grinds out there that work well with stock heads and other bolt-on improvements for these engines. To find out more, we talked to Aaron Mick at Comp Cams. We asked him to fill us in on some of the issues with installing bigger cams for Two-Valve applications.
Mick said, “Duration, lift, and lobe separation all affect piston-to-valve clearance, and these engines are pretty limited on clearance. The mod motor cams will typically be in the 230s to 240s at 0.050-inch duration depending on the setup. But when we use that much duration we can’t tighten the lobe separation up very much, which the mod motors respond to very well. Lift is basically a byproduct of what duration you select. You want it to be good enough to make the head flow, but that’s about it. It’s pretty much the least important spec for both power and clearance. The problem comes in, though, when you increase the duration these engines need to make power, you are limited to lower lift and wider lobe separation angles.”
The factory Two-Valve PI cams spec out at 0.512/0.540 lift, with duration at 0.050 of 200/204, and a very wide lobe separation angle in the 116-118 neighborhood. Compare this to the XE268 cams we chose for our install, which spec out at 0.500/0.500 lift, with duration at 0.050 of 230/236, and lobe separation angle of 114 degrees. Yes, less lift than the factory cam, but at the same time the valves are staying open much longer, allowing for more air/fuel charge to enter the cylinders and more exhaust gases to be removed.
Besides the actual cam profile, the aftermarket cams have other advantages over factory units. Mick explains, “Our cam cores are ground from a solid-billet piece and then gun drilled. This makes the core far more robust, and it will hold up under increased spring pressure and higher rpm usage. Ford doesn’t do it this way simply for cost reasons.”
To see what a cam swap would do, we grabbed a 2004 GT running a stock PI motor out of a P71 Crown Vic, with an Edelbrock single-plane intake installed along with a hundred shot of nitrous. Our baseline at the track was a 12.58 at 109 mph, and on the chassis dyno it produced 269 hp and 272 lb-ft of torque. On a hundred shot of nitrous, it made 377 hp and 411 lb-ft of torque.
01. After the battery was disconnected and the serpentine belt removed, the first big step is pulling the valve covers. We didn’t have to pull the fuel rails to get them off, but we did have to unplug the harness from the injectors. On the driver’s side it was a bear getting the cover off past the master cylinder and hydroboost assembly, so be patient with that one when removing.
02. To get the front timing cover off, the power steering pump has to be unbolted from the front of the motor. Once the pump is out of the way, the balancer can be pulled off the crank, and the front timing cover unbolted and removed.
03. If your motor has a lot of miles on it, this is a great time to swap in a new water pump while it’s easily accessible. We picked up a new one from Summit Racing Equipment, an EMP/Stewart Components high-volume unit (PN EMP-STE50046S). If you have a 2001 Mustang, make sure you verify whether you have an early or late style of water pump before ordering yours.
04. The timing gears have marks on them that align with specially colored links on the timing chain to get everything in time before removing the timing chains. You can see the discoloration on the one link compared to the others. Because the mark on the chain was a bit faded, we went ahead and used a paint marker to highlight the marks to help us see them better.
05. With the power steering pump out of the way, the front timing cover could be unbolted and removed
06. The “gear” is the reluctor wheel for the timing sensor. It simply slips onto the crank snout to be removed.
07. The hydraulic tensioners for the timing chains are marked R for the right (passenger side) of the engine and L for the left (driver side). They use pressurize oil from the block to hold tension against the chains to take up slack from chain wear. You have to use a pair of big vise grips to compress the piston enough to get the chain guide out of the way and take the tension off the chains for removal. Then they unbolt from the block.
08. With the tension off the chains, they can be slipped off the cam gears and the main crank gear.
09. The nylon chain guides/tensioner arms hold pressure against the chain to keep the timing accurate. Ours had over 100,000 miles on them, and to reuse them seemed silly and unsafe considering how hard we were going to be turning the motor. We picked up Trick Flow Specialties tension arm and chain guide kit (PN TFS-51800517) from Summit.
10. Sometimes vise grips won’t do the job getting the hydraulic piston on the tensioner to compress so you can get the chain off. In that case, a good pry bar pressing against the tension arm will do the trick.
11. With the chains removed, the camshaft retaining towers can be unbolted, and then the old cams removed. That allows you to remove the cam followers (pictured) and the hydraulic lash adjusters. The bolts need to be loosened in a cross pattern to relieve the tension on them evenly, otherwise they might bend or distort, which will create problems down the road when installing the new cams.
12. The factory cams have a spacer on them you have to reuse on the new cams. The spacers go behind the cam gears. Be sure not to lose this one, but just in case, Trick Flow sells replacements under PN TFS-51800503.
13. Trying to reuse the original hydraulic tensioners is a royal pain; save yourself time and frustration by getting Trick Flow’s 2V timing set (PN TFS-51800520). It comes with new chains, cam gears, crank gear, chain guides, tensioner arms, and hydraulic tensioners. The tensioners come fully compressed and are held that way by the pin you see in the photo. (Note: Do not pull the pin until you have the tension arms, chain guides, and chains installed. Once everything’s in place, then you can safely pull the pin to set the tensioner.)
14. With the cams out, we could remove the cam followers and the hydraulic lash adjusters.
15. Our lash adjusters were all fine, so we reused them. Before reinstalling them we used a vise to compress them so that installing the followers would be easier.
16. Here’s how things look with our new tensioner, arms, and chain guide installed.
17. Before installing the new cams, we lubed up the cam guides with engine assembly moly paste so they wouldn’t be dry on initial startup.
18. For cams, we went with Comp Cams’ XE268H cams. We wanted to go bigger, but our factory pistons dictated our max lift. The 4.6L Two-Valve PI motors came with four types of pistons from the factory, each with a different dome/compression. The only way to know which pistons you have is to pull the heads, a costly and complicated operation. We knew the max lift of 0.500/0.500 on the 268s would be safe no matter what piston we had. The 268 features a LSA of 114 degrees, duration at 0.050-inch of 230/236, and an optimal powerband of 1,600-5,600 rpm.
19. Because we’re going to be turning our Two-Valve pretty hard with and without nitrous, we didn’t trust the factory powdered metal cam gears to really withstand the abuse. For extra peace of mind and strength, we picked up a set of Trick Flow billet cam gears (PN TFS-51800516).
20. A new item for Two-Valve motors we spotted at the 2014 SEMA Show was this adjustable cam gear set from Comp Cams. By the time this story goes to print they’ll be available through Summit under PN CCA-10254.
21. Our XE268 cams would totally overwhelm the factory valvesprings, so new ones had to be installed. We went with a set of Comp Cams’ beehive modular springs (PN 26125). They run with 120 pounds of pressure closed, at an installed height of 1.640-inch, and open pressure of 275 pounds, with a max lift rating of 0.600-inch. This spring is ideal for street/strip applications, with a rate of 258 that will keep valve float at bay through the entire rpm range. The springs came with new steel retainers from Comp that reuses the factory valve locks.
22. Past experience has shown us reusing old followers (left) on a new cam will usually cause the followers to fail, ultimately wreaking havoc inside the engine. We picked up a set of new Trick Flow cam followers (right; PN TFS-51800510). Trick Flow also has a follower/lash adjuster kit if you need those too (PN TFS-52900515).
23. On the bottom is the factory crank sprocket and on the top our new Trick Flow steel gear. The factory gear is one-piece, while the Trick Flow gear comes in a two-piece configuration, namely the actual gear and the spacer that goes in front of it. Don’t forget to install the spacer prior to installing the timing sensor gear/reluctor.
24. The new crank gear slides onto the crank, then the spacer we showed in the previous photo. Once the chains are in place you can reinstall the timing sensor gear.
25. Even with the chains lined up according to the timing marks on the gears, once you release the tensioners it causes things to move and can throw your timing off by a tooth. We learned this the hard way. What it took was a special tool off the local Snap-On truck to lock the crank in place so it and the chains can’t move when tension is applied.
26. These are the timing marks mentioned earlier. The colored link on the timing chain matches up with the dots on the cam gears, then another pair of colored links matches up with the mark on the crank gear. The cam gears are also unique to the left (driver-side) cam and the right cam. The passenger-side gear has holes in it (pictured), while the driver-side gear is solid.
27. Once the chains are installed and everything is in time, and the crank is locked, the pin can be pulled from the hydraulic tensioners, which allows tension on the chains and locks everything in place. On first startup you might hear a little chain noise, but that will quickly go away once oil pressure feeds into the tensioners.
28. With the cams all set, we reinstalled the timing cover, then the balancer and rest of the front accessories. One of our plastic factory cam covers had a big crack in it, so we decided to ditch the plastic in favor of Trick Flow’s cast aluminum modular Two-Valve cover set for Romeo built engines in black (PN TFS-51811801). This is where some factory goofiness comes into play on Two-Valve motors. Engines built at the Romeo plant used 11 bolt valve/cam covers, while engines built at the Windsor plant used 13 and 14 bolt covers. The Trick Flow part number for those is TFS-51811802. Both applications also come in a silver finish, and the covers can fit engines with either left- or right-side oil fill provisions.