With the right combination...
With the right combination and tuning, respectable horsepower and torque numbers can be had using factory HP manifolds.
Bolting a set of headers onto your musclecar has to be one of the most popular modifications in the history of hot-rodding. Very few modifications add as much power as quickly and easily as a good set of headers. But given that, there are still a lot of people who for one reason or another don't want to put headers on their car. Maybe a guy wants to maintain an appearance of originality, or he doesn't want to deal with the extra heat and noise that a set of headers can cause. Sometimes there just aren't headers available for certain combinations of engine and body style, and, of course, there are the horror stories of poorly designed headers that don't fit until beaten into place with a sledgehammer and a torch. So for whatever reason you might have to stick with manifolds, we have some tips that will show you how to make big power without headers.
The Situation
Our current project is a '65 Dodge Coronet 500 that we're setting up as a Pro Touring car. This car came from the factory as a 426 wedge, four-speed combination, so we could have just dropped the stroker motor into the factory location. But the motor is positioned fairly far forward on these early B-bodies, and that location isn't the best for weight distribution. So when we swapped out the factory four-speed for a Doug Nash five-speed, we went ahead and moved the motor back about 1.5 inches to improve the weight distribution.
The unique motor location in turn required either severe modifications to standard headers, or a set of custom headers. Neither of those options seemed too desirable to us, so the choice was made to go with a set of factory HP exhaust manifolds.
The Short-Block Combination
First off we have to say that this motor is not a drag race motor, but rather it was designed as a street combination with a big, flat (think Viper) torque curve. So it was important to us that we have a nice stable idle at less than 900 rpm and with 12 or more inches of vacuum. We also wanted to see a lot of torque on tap below 3,500 rpm, since that is where you use it in a street car. Banging through the gears at 6,500 rpm is a lot of fun, but it also tends to attract the type of attention that leads to court appearances and big insurance premiums. Now that we're old enough to join the hair club for men, we focus our attention more towards the lower end of the torque curve.
When it comes to street motors with big torque curves, cubic inches are your friend. Therefore, when we built this motor, we used the popular trick of stuffing an offset ground 440 crankshaft into a 400 block. The RB crankshaft we used came from the scrap pile at a local machine shop since it was undersize and had a couple of spun bearings. We salvaged the crank by grinding the mains down to 2.625 and offset grinding the rod journals down to the Chevy size of 2.200. This small investment in machine work turned our scrap yard refuge into a polished stroker crank.
Offset grinding the rod journals on an RB crank down to the Chevy 2.200 size is a quick way to pick up some cubic inches, but it does create a problem with rod side clearance since Chevy rods are slightly narrower than the Mopar ones. We solved the rod side clearance issue by locating a set of Manley 14279 connecting rods. These rods are Mopar length and width, but use the Chevy 2.200 and 0.990 pin sizes Sad to say, Manley recently stopped production on these connecting rods, and there aren't any other known solutions currently on the market. Maybe if enough people request these rods from Manley, they wiill do another production run.
In order to maximize quench and reduce the chance of detonation, we wanted a flat-top piston with zero deck clearance. But since our stroke of 3.875 inches is rather odd, we had to order a set of custom pistons from JE. Our pistons needed to be rather short (for a Mopar) due to the longer stroke and the 440-rod length, but JE didn't have any trouble coming up with a lightweight design once we provided them with our VISA card number!
Our 466ci low-deck stroker...
Our 466ci low-deck stroker looks rather innocent when dressed up with HP manifolds and a 383 pie tin. You might not be expecting 550 hp from this one.
On the engine dyno, we used...
On the engine dyno, we used 3-inch exhaust tubing off the manifolds and no mufflers. During this particular dyno pull, we had a Holley carb on a M1 manifold.
Here, we are thrashing our...
Here, we are thrashing our way through a cam swap in search of more power. The Edelbrock heads are clearly visible, as is a lightweight Toyota alternator, a Cloyes double-roller timing chain, and the coated HP manifolds.
Our 3-inch head pipes were...
Our 3-inch head pipes were custom-made from mandrel bends in order to minimize the restriction. Notice the bungs for the O2 sensor and the extra thick flanges.
The beehive valvesprings from...
The beehive valvesprings from Competition Cams work well on this motor. With these springs in place, we've spun hydraulic flat tappet cams up past 7,000 rpm with no lifter pump up or valve float. Just make sure to get the proper ones for your application. The stainless steel, 1.60 ratio, rocker arms are from Rocker Arm Specialist in Anderson, California.
The Performer RPM manifold...
The Performer RPM manifold and 800-cfm carb are both from Edelbrock. This combination works great with the Mopar Performance .528 solid cam and the HP manifolds.