Headers or Manifolds
I have a ’71 Challenger that originally came with a 383, and now I’m fixing to drop in a hot 440. The 440 has the Stealth heads, a Comp XE285HL cam, JE flat top pistons, and a factory forged crankshaft. It also has a Performer RPM intake manifold, and a Quick Fuel 850 mechanical secondary carb. The ignition is MSD, with a billet distributor and a 6AL.
Even though the engine is built, I have painted the heads and intake stock orange, and I am going to run the stock dual-snorkel air cleaner. I have the stock valve covers off the 383. What I am undecided on is the exhaust. I am trying to decide between using the stock exhaust manifolds, or run a set of Hooker 17⁄8-inch headers. The stock manifolds from the 383 Magnum are the HP type, and I think they are the same used on the 440 engine. I like the idea of manifolds, because of the stock look, and also to avoid the hassle of header leaks. I’ve been told the HP manifolds flow just about as good as headers, and that there wouldn’t really be much power difference. What do you think?
I hate to say it, Jason, but the manifolds are going to be giving up a significant amount of power and torque compared to the headers. Even on a stock 440 Magnum, headers are good for about 30 hp and torque throughout the curve. On a modified engine with much more cam and the other mods you have, the difference can be 50-60 horsepower or maybe more. There is no question that the headers flow significantly better than those stock HP manifolds. However, there is more to the added power from headers than just the flow. The length of the pipes helps scavenge the cylinders, and improve the cylinder fill. This effect is magnified with more cam timing and overlap. That said, if you are intent on the stock look of the manifolds, you engine will still be a strong combination, but be assured that the power will take a big hit compared to the potential with headers.
I have a 440, and am thinking about making the change to a solid-lifter cam. The cam in it now is hydraulic, a Comp XE269H, and I am thinking about swapping to a Mopar 528 solid. When the engine was built, I got new factory-style stamped steel rocker arms. These are supposed to be the heavy-duty version. I think I can change to the Mopar solid cam without having to switch my Comp number 911 valvesprings. I would also like to keep the same rockers. I have an old set of adjustable Mopar pushrods that will fit, but would like to know if you would recommend using them instead of getting new rockers.
Clive, if you are asking if it is possible to run the adjustable pushrods, I would be forced to answer yes, but I definitely would not recommend them for a solid cam. The adjustment is just not precise and positive enough, and the second problem is I have to question the long term durability. I would strongly recommend changing out the rockers and getting a matched set of pushrods.
I just read the April ’13 issue’s Performance Clinic, “To Stroke or Not.” I am putting together a stroker LA 360. I’ve got a 4-inch stroke forged crankshaft, 6.123-inch Eagle I-beam rods, 360 Magnum heads, an Edelbrock 750 carburetor, Air-Gap intake, headers, and a recurved distributor, with 30-degrees of advance that is all in by 1,500-1,800 rpm. What cam would you recommend? This is going in a ’73 Challenger street car with an automatic, and a 3:23 rear.
Mike in Iowa
Mike, it is going to be pretty hard to give you a direct recommendation without knowing a little more about what you want from the camshaft. The first question that needs to be answered is what kind of camshaft you want, hydraulic, or solid flat-tappet, or hydraulic or solid roller. For a true street application, either flat-tappet, or a hydraulic roller will all work quite well, depending upon your objectives and budget. I would stay away from a solid roller for a real street application. A solid flat-tappet will give the most rpm potential of the remaining choices, though with a stroker engine and the relatively small cylinder heads, your engine will want to make peak power at an rpm range below where a solid’s benefits really come into play. This leaves the hydraulics, in either roller or flat tappet configurations. Many builders do prefer the hydraulic roller, and there are advantages in a build like yours, such as the potential for making more power and virtually eliminating the potential for premature cam failure. However, a hydraulic roller is much more costly than a flat tappet. I’m going to have to take a shot here and presume you want to go with a flat tappet.
The next question that needs to be considered is the engine’s specs. Again, this will depend upon what you want out of the engine. If you are looking for a relatively smooth, stock-type idle with plenty of torque, something in the 214 degree intake duration area would do the job. The Crane PowerMax 272 is one that I like for this kind of application. Stepping up from there, a cam in the 224-230-degree duration at .050-inch range makes a good streetable cam. Here the Comp XE268 or the higher-lift offerings from Hughes Engines work well. On the other hand, some guys want a hard-hitting cam with lots of lope. If that’s what you are after, something in the 240-250-degree duration at .050-inch range will make the noise. Of course, the bigger nastier cams will want more converter stall, and deeper gears would be a plus. I’d suggest getting in touch with the cam manufacturer of your choice and going over your end goals in more detail to find a stick to get the job done.