Looking at your combination, I can see you have great head flow, but the power numbers can be improved given the flow. Your huge hydraulic cam would want to make power at high rpm, but getting a juice cam to work there can be problematic. I would say a solid-lifter cam would provide a definite advantage in peak power. In terms of the intake manifold, I would go with a single-plane in an application such as yours. Both of the dual-planes you are considering are good intakes, but your engine is more of a high-rpm piece with a set of high-flowing heads. Even though the heads flow 340, the average port flow on the dual-plane intakes are well below that mark, negating some of the flow potential of the heads on the assembled engine. The Offy low-rise is not the answer either. I would use an Edelbrock Victor, with a 950-1,000-cfm 4150-style carb.
High-Performance Dart
I'm currently working on a '73 Dodge Dart Swinger. I have some questions as to which components I should use to get this car to do what I want. This car was originally a 318-powered car with a 904 transmission and a 711/44 rear. I have replaced the 318/904/7.25 with a 360/727/8.75 combo. This car is really for my enjoyment, not for big shows or drag racing. I live by a mountain so I would have to drive over the mountain to take it to work or to my car club's cruise nights.
Here are my current specs. The engine is an '87 360, bored .030-over with a 9.6:1 compression ratio. I have SpeedPro Hypereutectic pistons, and the rotating assembly is internally balanced. The cam is a Mopar Performance 340 resto cam (228/235-duration at .050, 44-degrees overlap, 114-degree lobe separation, .429/.444-inch lift). The heads are retrofitted Magnum units with stock valves fed by a Professional Products Crosswind intake. The air cleaner is a 3-inch K&N with an X-Stream Flow top. The ignition is an MSD 6A. I'm using a 727 transmission with a TransGo TF-2 shift kit with a 3.2:1 kick-down lever and a B&M flexplate. The rear is an 831/44 with a Sure Grip and 3.73 gears and 215/60R15 tires. I'm using a Summit universal aluminum radiator with a separate B&M transmission cooler and am planning on tti headers, 211/42-inch dual exhaust with a crossover pipe, and Flowmaster 50 Delta mufflers. Royal Purple fluids are used throughout.
My questions: which Holley Street Avenger carb should I use, the 670 or 770 cfm? Which stall converter should I use? TCI suggested a 1,600-1,800 stall, but I've been told that's too low. How much horsepower do you feel I could get with this combo using pump gas?
Eric White
Andreas, Pa
That's a nice combination. I see one area in which you can easily get substantially more power, and that is the cam. The old stock 340 cam was good for a production cam when it was designed, but I have tested it against the more modern Comp XE-268 and found significant gains in the small-block, like over 40 hp compared to that 340 stocker. The Comp cam gives a little choppier idle, but very street friendly overall. If you upgrade the cam, I'd go with the larger 770-cfm carburetor, otherwise you can go with the smaller unit. You will make around 350-360 hp with the stock cam, and around 400 with the XE 268.
As far as the converter, I would want to see a 2,600-2,800-rpm, 11-inch unit, similar to the stock 340 or 383 torque converter. The 16-1,800 rpm that was suggested is way too low, much lower in fact than what came as factory equipment in these cars.
Why No A/C?
I just finished reading your article on Mopar crate engines. I'm planning on installing one of the 360 crate motors in my '69 Dodge Dart that is an original a/c car. Every aftermarket source I find states in the details of the engine "NOT FOR USE WITH AIR CONDITIONING." Can you explain why this is?Al GoodwinVia e-mail
I believe this is largely a disclaimer having to do with fitment. With all the variations on factory air-system mounting brackets and such, it would be difficult to assure the customer that the OEM air system will bolt-on. These engines feature the Magnum-style heads, which have differences in the accessory mounting provisions compared to the older LA-series heads. Some custom modifications will be required to the brackets to make it work. Another consideration for owners of '79-and-later Mopars, the thermostat housing style used on the intake manifold will not allow the axial C-171 compressor to clear. The factory used a relocated offset thermostat position in those applications.
Another thing to consider, particularly with some of the higher-output crate engines, is the basic combinations include fairly radical, long-duration camshafts. With long duration comes low vacuum and an unstable, lopey idle. Now, fire that big RV2 A/C compressor at idle, and chances are the engine will just load up and want to stall. For an A/C application, I would recommend steering towards a mild crate or swapping to a cam with 224-degrees of intake duration, max.