Picking The 'Stick
When it came time to pick a camshaft for this project, we decided to practice what we preach and seek professional help. In short, we told our man at Isky Racing Cams, Nolan Jamora, that we were looking for a street/strip solid roller cam that would give us a big horsepower number but also provide a broad torque band that would lend itself to drivability. The flow bench figures we provided allowed Jamora to tailor the cam to take advantage of the Patriot heads' qualities while also meeting our powerband goals. He recommended a 108-degree-LSA center as the best compromise between power and drivability. "Less would get us more power," Jamora observed, "but it'd be in a quicker range." After reviewing the flow numbers, he came up with lift figures of 0.640 inch intake and 0.650 inch exhaust. "These heads flow well at the top end, so we want to take advantage of that," Jamora explained. The duration figures, 262 degrees on the intake and 272 on the exhaust, were chosen to keep the powerband in a usable rpm range. It'd be an understatement to say we're thrilled with the results. "The cam's not really that big," Jamora summed up. "We got a flat torque band and a good horsepower number, and it's all in a real-world, usable rpm range. The power comes on and stays on for a while." For our part, we'll just say the time taken to match our cam to these new heads was time well spent.
CAMSHAFT SPECS ...
|CAMSHAFT SPECS |
|Manufacturer ||Isky Racing Cams |
|Part Number ||RR-645 |
|Type ||solid roller |
|Valve Lift ||0.640/0.650 inch, |
| ||intake/exhaust |
| ||(1.75:1 rockers) |
|Duration ||264/272 degrees @ |
| ||0.050, intake/exhaust |
|Lash (hot) ||0.028/0.028 inch, |
| ||intake/exhaust |
|Lobe Center ||108 degrees |
1. Carburetion duties are...
1. Carburetion duties are handled by a Mighty Demon 850 mixer squirting through an 85/93 jet combo; the intake is a tried-and-true Edelbrock Victor Jr. 454-R.
2. Patriot Performance's Freedom Series aluminum big-block heads feature 320cc rectangular intake ports along with 2.25/ 1.88-inch valves. At $1,495 as delivered, they're a steal.3. True to its street/strip mission, this cam/ heads combo yielded 674 hp at 6,300 rpm, but also maintained an exceptionally broad torque band that peaked at 624 lb-ft.
4. Isky Red Zone lifters, one-piece pushrods, and 1.75:1 roller rockers complement the stout solid roller cam. 5. Hooker 2 1/8-inch Super Comp headers deal with the burnt junk.
6. The JMS Racing Engines' short-block runs a 4.350x4.250-inch bore and stroke combo to create 505ci. The two-bolt main block uses ARP studs for strength and comes with forged rods and KB Performance pistons. Compression checks in at 10.5:1.
Whenever JMS Racing Engines...
Whenever JMS Racing Engines installs a camshaft, it breaks out the degree wheel to make sure the new 'stick is correctly phased, and this time was no different. We've covered this job in more detail in the past, so here we'll just point out that for proper installation we used the "square" mark on our crankshaft gear rather than the straight-up position.
When running a roller cam...
When running a roller cam on a block that lacks provision for a thrust plate, a button must be used to limit the cam's lateral movement. If the cam moves too much, ignition timing can be thrown off, hurting performance. The movement is checked by carefully pushing the cam forward in the block against the timing cover. Want a quick way to do it? Install the cover without a gasket, then set the button so it's against the cover. With the gasket in place, the cam will have the proper 0.003-0.005 inch of end play.
Once the cam thrust is set,...
Once the cam thrust is set, the button-in this case one of Isky's slick needle-bearing pieces-is held in place with a lock plate.
The combustion chambers measure...
The combustion chambers measure 119 cc; Patriot's Race Series valves come undercut and swirl-polished. The chambers in these prototype heads were hand-worked to clear a domed piston. The modification will be incorporated into the production castings.