383 Resto to Rad

08. We elected to go to a... 

   

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08. We elected to go to a Mopar Performance single-plane M-1 since we wanted to encourage the short-stroke 383 to rev with subsequent mods. It bolted on with no hassles.

The Demon carb was clearly doing a better job of mixing the air and fuel than the AVS. We knew exactly what was holding the 383 back at higher rpm--that heavy chunk of cast iron sitting under the carb.

Our next mod, naturally, was to swap the stock iron intake for a modern performance piece in an effort to unlock the 383's breathing efficiency. Since we eventually intend to create a high-rpm screamer from our 383, we opted for a single-plane intake. Since Mopar Performance's M-1 has been the best low-deck street/strip single-plane intake we've used to date, it was pressed into service on our 383. With the intake change, the visual character of our 383 was transformed, finally looking like a performance mill. Our next pull showed that the looks were more than skin deep, with the dyno numbers now catapulting to 406 hp at 5,400 rpm, and 433 lb-ft at 4,000 rpm. True to form, we lost a handful of torque down low while going from a dual-plane to a single-plane, but we gained huge up top. The M-1 really unlocked the breathing of the engine, giving us a remarkable 400-plus hp with a stock-cammed, stock-headed 383. Yes, 383s can make power, and make it cheaply. We had a rebuilt stock engine, with headers, carb, and intake, and were churning better than 400 hp.

Our final mod, not surprisingly, was a good old-fashioned cam swap. There was, however, nothing old-fashioned about the grind. Competition Cams has recently introduced a line of Mopar-specific grinds which take advantage of the Mopar engine's .904-inch tappet diameter. Mopars have a tappet diameter of .904 inches, while Fords measure .875 inches, and Chevys .842 inches. Why is this significant? The larger tappet raises the limit on the possible cam velocity in a flat tappet cam. This allows the cam designer to develop more aggressive profiles, giving a faster rate of lift. More lift means more open area at the valve, and typically more power than a lower lift cam of the same duration. Most cam profiles are simply designed to be compatible with .842-inch tappets, since it is the lowest common denominator, and will work with that tappet size or larger.

We were eager to try one of the new Comp grinds, and ordered up an XE285HL-10. This is a fairly serious hydraulic profile, rated at 285/297 degrees gross duration and spec'ing out at 241/247 degrees duration at .050 inches, with .545/.545-inch lift on a 110-degree lobe separation. The cam was degree'd in at four degrees advance and topped with a set of matching Comp lifters. We were still budget-conscious with this engine and elected to retain the stock 383's valvetrain. Unlike some competitive brands of engines, the big-block Mopar hydraulic shaft-mount system is rugged. We upped the valvesprings at the same time to Comp's PN 924 dual-spring assemblies since the high lift cam requires more spring than the stock 383 cam. We used an on-the-head spring compressor from Powerhouse to make quick work of the job.

Back up and running, with the big stick, the 383 had a weightier thump. With the stock heads, the cam would likely not realize its full potential with our present combo, but we still expected a gain and expected to pull higher rpm. With that in mind, the dyno controls were reset to 6,200 rpm, and we opened up the 383 once again. It pulled cleanly through the revs and we now had a 455 hp 383. Peak power was actually 454.9 hp at 6,000 rpm, and 456.6 lb-ft of torque at 4,800 rpm. With the big cam we lost 5-10 hp at the bottom of our test range, but from the mid-range up the big stick just pulled away like a freight train for a gain of nearly 50 hp. The useable rpm range of the engine was extended by better than 500 rpm in the bargain.

We were impressed with the 383. Stock with the exception of the headers, cam, intake, and carb, we were solidly over 450 hp. That's dollar value per horsepower.

Is that the end for this 383? We'll likely revisit it a few issues down the line, looking to increase the head flow capacity and compression ratio. We can handle that in one swap. Maybe a solid lifter cam to up the rpm range, and who knows how far the under appreciated 383 can go.

09. The Demon carb certainly...        read full caption 09. The Demon carb certainly looked more at home on top of the M-1 intake, and proved it was a happy combination, with power now going to 406 hp. Considering that this is a stock rebuild-style long block, with stock heads and a smooth stock cam, 400-plus hp is a remarkable testimony to the 383's power potential. A 400hp small-block would be more expensive to build, requiring aftermarket or ported heads, higher compression, aftermarket valvetrain and cam, and maybe more.	10. Our final mod this time...        read full caption 10. Our final mod this time around was a cam swap. We had already seen good output with the mild stock cam and decided to add somewhat of a thumper. A hydraulic was our choice since it would allow us to retain the stock valvetrain, making it a no-cost change if substituted in the original build. A Competition Cams' XE 285HL was our choice--an aggressive high-lift .904-inch tappet profile delivering .545 inches of lift at the valve. This was one of the first of these sticks to leave Comp.	11. We opened the engine,...        read full caption 11. We opened the engine, liberally coated the cam with the supplied lube, then slipped it into place. This Comp cam is ground on a 110-degree lobe separation angle, and we installed it 4 degrees advanced, putting the intake centerline at 106 degrees.
12. Comp recommends their...        read full caption 12. Comp recommends their dual PN 924 spring with this cam, which we substituted for our stock replacement springs, using this spring removal tool from Powerhouse. The dual springs require valve seat and guide machining to clear on stock heads. We had already performed these two machining operations in the original build in anticipation of this change. Single PN 911 springs would probably cope if the swap were being made to an existing engine lacking the machining required for dual springs.	13. We just bolted the stock...        read full caption 13. We just bolted the stock valvetrain back on with the new cam installed. Although not adjustable, the stock Mopar shaft-mounted stamped steel rockers are rugged.	14. With the new cam, the...        read full caption 14. With the new cam, the engine had a noticeably racier idle and an angry growl up the rev range. We pulled it to 6,200 rpm, and found 455 hp at 6,000 rpm. Not too shabby for a stock 383 with headers, cam, intake, and carb. The 383 had picked up 117 hp with four tried-and-true bolt-ons. What's next? We'll likely shift our attention to building a hot set of heads to turn the wick up even more, and maybe even go to a solid flat tappet cam and watch that 383 scream for mercy.